Geology of the 

Sierra Diablo Region 

Texas

GEOLOGICAL SURVEY PROFESSIONAL PAPER 480

Geology of the 

Sierra Diablo Region 

Texas

By PHILIP B. KING

With SPECIAL DETERMINATIVE STUDIES OF PERMIAN FOSSILS

By L. G. HENBEST, E. L. YOCHELSON, P. E. CLOUD, JR., HELEN DUNCAN, R. M. FINKS, 

and I. G. SOHN

GEOLOGICAL SURVEY PROFESSIONAL PAPER 480

Description and interpretation of the varied 

rocks and structures of a mountain range and 

its foothills in the Trans-Pecos Region^ with 

special emphasis on the Lower Permian

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1965
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

Library of Congress catalog-card No. OS 66-227

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402
CONTENTS

Abstract.-_ __-__-__-_-__-__..___-________..__________

Introduction.._____________________________________

Present investigation___--__--___.___--_________

Acknowledgments__ ___________________________

Related investigations.._________________________

Previous investigations._______________________

Annotated bibliography.____________________

Geography ___________________________________

Mountain areas _______________________________

Lowland areas ________________________________

Human geography and history.__________________

Stratigraphy _____________________________________

Precambrian and Precambrian(?) rocks.___________

Carrizo Mountain Formation_________________

Sequence in Carrizo Mountains.__________

Metamorphic features.__________________

Stratigraphic relations.__________________

Igneous rocks intrusive into Carrizo Mountain 

Formation _________________________ _ ...

Metarhyolite. __________________________

Greenstone ___________________________

Veins..________________________________

Allamoore Formation..______________________

Limestone _____________________________

Volcanic rocks..________________________

PhyUite___________________________

Hazel Formation ___________________________

Conglomerate __________________________

Red sandstone.________________________

Van Horn Sandstone____-_-__--______-______

Conglomerate __________________________

Sandstone _____________________________

Ordovician_ __________________________________

Bliss Sandstone___________________________

Main body of formation_________________

Calcareous division.____________________

El Paso Limestone_________________________

Division A____________________________

Division B_____________________________

Division C_____________________________

Beds of Middle(?) Ordovician age___________

Montoya Dolomite.________________________

Cable Canyon(?) Sandstone Member____

Upham Member______________________

Aleman Cherty Member_______________

Silurian_____________________________________

Fusselman Dolomite._______________________

Devonian___________ ___________________________

Beds of Devonian age_______________________

Mississippian____ _ ______________________________

Barnett Shale._____________________________

Pennsylvanian_______________________________

Beds of Pennsylvanian age___-____-_-_-_---__

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Stratigraphy Continued

Permian_______-__-___--_--_____-_-____--_.___.

Presentation of paleontologic data ______

Hueco Limestone____-_-____---_----.----_-_.

Southern part of report area_-________-_.

Baylor Mountains._____________________

Central Sierra Diablo__________________.

Apache Canyon area___________________.

Fossils and correlation__________ _____

Stratigraphic relations.__________________

Bone Spring Limestone___-_-____----_--__-_.

Sierra Diablo escarpment________________

Northern marginal belt_________________

Southern marginal belt____-_-_-_------_.

Baylor Mountains._____________________

Fossils and correlation_________________

Stratigraphic relations.__________________

Victorio Peak Limestone-____----_---_---__-.

Northeastern calcitic facies_____________

Southwestern dolomitic fades.___________

Fossils__________--___._-_--____.

Stratigraphic relations.__________________

Cutoff Shale._._________________.

Brushy Canyon Formation_____ ______

Sandstone tongue of Cherry Canyon Formation. 

Goat Seep Limestone_____________________

Cretaceous______ _______________________________

Pre-Cretaceous surface.__________--__---__--

Yucca Formation_________________________

Bluff Mesa Formation_________________

Campagrande Limestone________________

Sierra Diablo foothills_________________

Western Sierra Diablo_____________ .

Fossils and age____________-__----------

Cox Sandstone_________________________

Southwest of Eagle Flat.________-___.

Sierra Diablo foothills and Cox Mountain. . 

Outlying areas_______________________

Sierra Prieta___________________________

Fossils and age_____--___-___-________

Finlay Limestone___._______.___ __. 

Local features..-___-_._-______- ____.

Fossils and age________________-_-__.

Kiamichi Formation._______________________

Washita Group_________________________

Southwest of Eagle Flat____________

Sierra Prieta___________________________

Fossils_________________________.

Eagle Ford Formation__________________

Igneous rocks____________________________________

I _ Marble Canyon-Mine Canyon intrusive complex . 

Marble Canyon stock__________-_-___---___-

Mine Canyon stock_____________________ _

Outlying igneous rocks___-___---__--__---__-

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in
IV CONTENTS

Igneous rocks Continued Page | 

Marble Canyon-Mine Canyon intrusive complex Con.

Metamorphic rocks_________________________ 92

Interpretation______________________________ 94

Sierra Prieta intrusive-------------------.-------- 94

Igneous rocks_______________-----__-___-_-- 95

Metamorphic rocks_______-_____--__________ 95

Structure-_______________________________ 95

Regional relations__________________________ 96

Intrusive rocks in southern part of report area__.___ 96

Basaltic volcanic rocks__________-___-___________ 96

Unconsolidated deposits of Quaternary age.____________ 96

Landslide deposits____----__-_---_-_-_______---- 97

Deposits of floor of Salt Basin_--__________.______ 97

Fanglomerate __________________________________ 98

Older alluvial deposits__--_______--______-_____ 98

Younger alluvial deposits_______________________- 98

Tectonics-.__-________---_-----__ _______________ 99

Structure of Precambrian and Precambrian(?) rocks_ 100

Streeruwitz thrust fault _____ ___________ 100

Structure of Allamoore and Hazel Formations. _ 101

Faults with strike-slip displacement-__________ 102

Fracture zones in Hazel Formation__________ 103

Structure of Van Horn Sandstone.____________ 103

Structure of the Precambrian surface._________ 103

Structure of pre-Permian Paleozoic rocks __________ 104

Structures of Permian and early Mesozoic age______ 105

Structures of Late Cretacious or early Tertiary age__ 106

Structures of late Tertiary and Quaternary age_____ 107

General features_____-__--_---_--_______---- 107

Faults bordering the mountains.._____________ 107

North Diablo fault zone_____-_______ 107

East Diablo fault_____-_________ 109

North Baylor fault.__.___._____. 109

East Baylor fault______________ 110

Faults on east side of Salt Basin__________ 110

Faults and related structures within the mountains_______ ________ ______ 111

Northern part of Sierra Diablo ___________ 111

Southern part of Sierra Diablo_________ 112

Baylor Mountains.-._____________ 113

Beach Mountain and vicinity ____________ 113

Hillside fault and related structures _______ 114

Joints._-__---___--_-_--_ ____________ ____ 115

Regional interpretations and synthesis________ 117

Economic geology____-_____--________----___________ 118

Copper and silver_______________________________ 119

Tungsten and beryllium.________________________ 120

Talc_______________-_-.-._______ 120

Crushed stone.----.----------------.----------- 120

Marble and brucite-__---_-____-----__-_________ 120

Nitrate and turquoise___-____-_-----_-__________ 121

Ground water________________________________ 121

Oil and gas_______________..________ 122

Descriptions of stratigraphic sections and fossil collections. 123 

Stratigraphic sections and fossil collections of Ordovician, Silurian, and Devonian rocks._____________ 123

Section 1. Sixmile Mountain.__________ T23

Section 2. Yates Ranch___________________ 123

Sections. Dallas mine__________________ 124

Section 4. North side of Beach Mountain____ 124

Section 5. Unconformity locality _____________ 127

Section 6. Southeastern Baylor Mountains___ 128

Section 7. Northeastern Baylor Mountains___ 129

Descriptions of stratigraphic sections, etc. Continued Page 

Stratigraphic sections and fossil collections of Ordovician, Silurian, and Devonian rocks Continued 

Sections. Hawkins Tank___________ 130

Section 9. Point of mountains._______________ 131

Section 10. Apache Spring___________________ 132

Ordovician and Silurian fossils, not collected 

along courses of stratigraphic sections _______ 133

Stratigraphic sections and fossil collections of

Mississippian and Pennsylvanian rocks__________ 133

Section 11. Mine Canyon_______-______ 133

Section 12. Marble Canyon____ __._ 134

Stratigraphic sections and fossil collections of Permian

rocks _____________________________________ 134

Section 13. Wylie Mountains____________ 134

Section 14. Bass Canyon______---__--__.___ 136

Section 15. Threemile Mountain____________ 136

Other fossil collections from Hueco Limestone

in Threemile Mountain area. __--______ 137

Section 16. Beach Mountain________-_______ 137

Section 17. High point of Baylor Mountains. _ 138 

Other fossil collections from Bone Spring Limestone near high point of Baylor Mountains. __ 139 

Section 18. Northeastern Baylor Mountains_ 139 

Section 19. Northwestern Baylor Mountains 141 

Section 20. Eagle Flat_______ _ ______ 141 

Section 21. Streeruwitz Hills__ ____ ____ 142 

Section 22. McAdoo Ranch__________.______ 143

Section 23. West of Old Circle Ranch_____ 144 

Section 24. Old Circle Ranch.___________ 144

Section 25. Hazel mine_____________________ 144

Section 26. Bat Cave________________ 145

Fossil collections from Hueco Limestone near

Sheep Peak.___________________ 146 

Section 27. Second section south of Victorio

Peak.______.__._._-___________ 146

Section 28. First section south of Victorio

Peak________________________ 147 

Collections from Hueco and Bone Spring Limestones on Victorio flexture west of Victorio 

Canyon___________________________ . 148

Section 29. Victorio Peak___ ________ 149 

Section 30. Victorio Canyon________________ 152

Section 31. North of Victorio Canyon._______ 153

Section 32. Marble Canyon_________________ 155

Fossil collections from Hueco Limestone near

Marble Canyon________________________ 156

Section 33. Mine Canyon____________ 157

Section 34. South of Black John Canyon_____ 158

Section 35. Black John Canyon _____________ 159

Section 36. Apache Peak._______________ 160

Fossil collections from Victorio Peak Limestone

in northeastern Sierra Diablo....___________ 160

Fossil collections from Bone Spring Limestone

northwest of portal of Apache Canyon.____ 161 

Section 37. First section in Apache Canyon.._ 162 

Section 38. Second section in Apache Canyon. 163 

Section 39. Third section in Apache Canyon.. 164 

Section 40. Fourth section in Apache Canyon. 165 

Section 41. Apache Tank__.__________. 166

Section 42. Sierra Prieta__________________ 166

Section 43. South Mesa. __ ____________ 167 

Fossil collections from Victorio Peak Limestone 

southeast of South Mesa___________________ 169
CONTENTS

Descriptions of stratigraphic sections, etc. Continued Page 

Stratigraphic sections and fossil collections of Permian 

rocks Continued 

Fossil collections from Goat Seep Limestone

north of South Mesa______________ 169 

Section 44. High point of Delaware Mountains. _ 169 

Stratigraphic sections and fossil collections of Cretaceous rocks_____.________________ 170

Section 45. Eagle Flat_______________ 170 

Section 46. Streeruwitz Hills_____________ 171

Section 47. Dome Peak________________ 171

Section 48. Rock crusher._________________ 172

Section 49. Cox Mountain.______________ 172

Section 50. Black Knobs______________ 173

Descriptions of stratigraphic sections, etc. Continued Page 

Stratigraphic sections and fossil collections of Cretaceous rocks Continued

Section 51. Roberts Mesa___________________ 173

Section 52. Norton Mesa__________________ 173

Collections from Finlay Limestone and Kiamichi 

Formation west of Roberts Mesa and Norton 

Mesa________________________ 174

Section 53. Eastern Sierra Prieta___________ 174

Other fossil collections from Washita Group in

eastern Sierra Prieta_.____________________ 176

Section 54. Western Sierra Prieta_ ___ 176 

References cited___________-___-___________________- 177

Index_____._________________________ 181

ILLUSTRATIONS

(Plates are in separate volume] 

PLATE 1. Geologic map of Sierra Diablo region, Texas.

2. Panoramic views of Beach Mountain.

3. Stratigraphic sections of Ordovician, Silurian, and Devonian rocks of Sierra Diablo region.

4. Profiles showing stratigraphic features of Permian rocks in Sierra Diablo region. 

5-8. Stratigraphic sections of Permian rocks in Sierra Diablo region:

5. Wylie Mountains to Baylor Mountains.

6. Eagle Flat to Victorio Peak.

7. Victorio Peak to Apache Peak.

8. Sierra Prieta to Delaware Mountains.

9. Topographic and index map of Sierra Diablo region.

10. Panoramic views of east-facing escarpment of Sierra Diablo.

11. Panoramic views in Apache Canyon, northern Sierra Diablo.

12. Panoramic views in northern part of Sierra Diablo region.

13. Stratigraphic sections of Cretaceous rocks in Sierra Diablo region and adjacent areas.

14. Geologic map of vicinity of Mine Canyon and Marble Canyon, northeastern Sierra Diablo.

15. Map of Sierra Diablo region showing tectonic features.

16. Geologic structure sections A-A' to J-J' in northern and eastern parts and K-K' to T-T' in southern part of Sierra 

Diablo region, Texas.

Page 

FIGUKB 1. Map of parts of western Texas and southern New Mexico showing area covered by report on Sierra Diablo

region__________________________________________________________________ ________________ 12

2. Map of Sierra Diablo region showing paleogeology of the surface on which the Hueco Limestone was deposited- 44

3. Map of parts of western Texas and southeastern New Mexico showing provinces of Permian time ____ _ 47

4. Map of Sierra Diablo region showing paleotectonics of Hueco Limestone________________________________ 51

5. Detailed sections showing unconformities below and above Hueco Limestone in Baylor Mountains.--________ 53

6. Map of Sierra Diablo region showing paleotectonics of Bone Spring Limestone.___________________________ 62

7. Map of Sierra Diablo region showing paleotectonics of Victorio Peak Limestone.____ ___________________ 75

8. Map of Sierra Diablo region and adjacent areas showing faults and related structural features. ____________ 108

TABLES

Page 

TABLE 1. Rock formations of Sierra Diablo region, Texas____________________________________ ____ __ 18

2. Foraminifera identified from Hueco Limestone in central and northern Sierra Diablo.________ ___________ 56

3. Fossils identified from Hueco Limestone of southern calcitic limestone facies.________________-__--_-_-___- 58

4. Fossils identified from Hueco Limestone, from marl and calcitic limestone in lower part of northeastern Sierra

Diablo (exclusive of Foraminifera)___________________________________-----____-_- ___-_ _ __ 59

5. Fossils identified from Bone Spring Limestone, Baylor Mountains and northeastern Sierra Diablo (Foraminifera)- 67

6. Fossils identified from Bone Spring Limestone, Baylor Mountains and northeastern Sierra Diablo (Porifera,

Coelenterata, Echinodermata, Bryozoa, and Brachiopoda)_________________-_-_-_-----_---_--_-_------ 68

7. Fossils identified from Bone Spring Limestone, Baylor Mountains and northeastern Sierra Diablo (Amphineura,

Coniconchia, Lamellibranchiata, Scaphopoda, Gastropoda, Cephalopoda, Annelida, Arthropoda, and Alga) __ 70
VI CONTENTS

Fagc

TABLE 8. Fossils identified from Victorio Peak Limestone in central and northern Sierra Diablo_..-___________-_----__ 76

9. Fossils identified from Goat Seep Limestone, northern Sierra Diablo ___________________ i'_ _-!_________-____ 80

10. Fossils identified from Finlay Limestone, western part of Sierra Diablo region, Texas.___-_____---._-_-----_- 86

11. Fossils identified from Kiamichi Formation, Cox Mountain, Tex___ ________________________________ 87

12. Fossils identified from beds of Duck Creek age in Washita Group of Sierra Prieta, Tex______-_------_--_-_- 88

13. Fossils identified from beds younger than Duck Creek age in Washita Group of Sierra Prieta, Tex___________ 89

14. Tectonic history of Sierra Diablo region, Texas--___-_-_-________---_____-----_-_------_-_------------- 100
GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

By PHILIP B. KING

ABSTRACT

The Sierra Diablo region covers an area 43 miles long and 33 

miles wide in the western part of the State of Texas. The 

region includes the whole of the Sierra Diablo, a lofty plateaulike range whose summits exceed 6,000 feet in altitude. The 

surface of the range slopes gently westward from its crest, but 

to the east, north, and south it breaks off in abrupt escarpments 

as much as 2,000 feet high. To the southeast and south the 

range is flanked by lower foothills, beyond which are the intermontane desert basins of the Salt Basin and Eagle Flat.

In its broader outlines, the Sierra Diablo resembles block 

mountains elsewhere in the Basin and Range province. In 

detail, its geologic features are complex, as it is made up of 

rocks of many ages and types, which have been deformed during 

several periods.

The oldest rocks of the region, of Precambrian age, are exposed in the foothills south and southeast of the Sierra Diablo. 

They include ancient metasedimentary rocks the Oarrlzo 

Mountain Formation, intruded by igneous rocks, and younger 

unmetamorphosed sedimentary and volcanic rocks the Allamoore and Hazel Formations. The Oarrizo Mountain Formation has been thrust over the younger Precambrian rocks, and 

for some miles north of the trace of the thrust the younger 

rocks have been intensely deformed; farther north they lie 

nearly flat The thickness of the Precambrian rocks cannot be 

determined, but it is probably many thousands of feet.

Deformation of the Precambrian rocks occurred before deposition of the Van Horn Sandstone, which lies on their deeply 

eroded edges. The Van Horn is a coarse red clastic deposit, as 

much as 700 feet thick. As it contains no fossils, its age cannot be proved; but it is probably of late Precambrian age. The 

Van Horn was tilted and eroded before the succeeding Bliss 

Sandstone was laid down over it.

Pre-Permian Paleozoic rocks crop out in the southeastern and 

northeastern parts of the Sierra Diablo region and form a few 

inliers elsewhere; their most conspicuous outcrops are on Beach 

Mountain. They include the Bliss Sandstone, El Paso Limestone, beds of Middle Ordovician age, and Montoya Dolomite, 

all of Ordovician age; the Fusselman Dolomite of Silurian age; 

and chert, limestone, and shale of Devonian age. Total thickness of these units it about 2,000 feet.

In the northeastern part of the Sierra Diablo, these earlier 

Paleozoic rocks are succeeded by the Barnett Shale of Mississippian age and limestone and shale of Pennsylvanian age. 

Because of disconnected exposures, the thickness of the Mississippian and Pennsylvanian rocks cannot be determined; but 

they probably do not exceed a few thousand feet.

The Ordovician, Silurian, Devonian, Mississippian, and 

Pennsylvanian rocks were broadly folded and deeply eroded 

during Late Pennsylvanian time, so that the succeeding Hueco 

Limestone of Early Permian age overlies them with marked 

angular unconformity. In parts of the region the Hueco lies

directly on Precambrian rocks, erosion having removed the intervening formations.

The most extensively exposed rocks in the Sierra Diablo are 

those of Permian age, which consist mostly of the Hueco Limestone of the Wolfcamp Series and the Bone Spring and Victorio 

Peak Limestones of the Leonard Series. These three units, 

which have an aggregate thickness of about 3,000 feet, lie at 

the surface over wide areas on the summits, and are prominently exposed on the bordering escarpments. They are traversed by two prominent monoclinal flexures, the Victorio and 

the Babb, one near the middle and the other at the north end 

of the range. These trend west-northwest and dip north-northeast. South of the Victorio flexure only the Hueco Limestone 

is preserved; to the north the Bone Spring and Victorio Peak 

Limestones overlie it. North of the Babb flexure the Victorio 

Peak Limestone is overlain by the Cutoff Shale, also of Leonard 

age, and by formations of the Guadalupe Series.

At the base of the Hueco, lying unconformably on the older 

rocks, are clastic rocks of the Powwow Member, but the main 

body of the formation is an evenly bedded limestone. The 

Bone Spring is more varied; in the northeastern part of the 

region it is a thin-bedded slope-making black limestone, but 

southwestward, especially near the flexures, this gives place to 

massive limestone reefs and banks. Near the flexures the Bone 

Spring is uncomfortable on the Hueco. The Victorio Peak is 

a gray thick-bedded limestone that forms cliffs above the black 

limestones of the Bone Spring; its lower part intergrades with 

the black limestones, and it is entirely replaced by them in the 

Delaware Mountains, east of the Sierra Diablo.

The formations of the Guadalupe Series north of the Babb 

flexure are the sandstone tongue of the Cherry Canyon Formation and the Goat Seep Limestone. The sandstone tongue lies 

on an eroded surface of the Cutoff Shale and is separated from 

it by a hiatus, as shown by the absence of the Brushy Canyon 

Formation that intervenes between the Cherry Canyon Formation and the rocks of the Leonard Series in the Delaware 

Mountains to the east.

Cretaceous rocks overlie the Permian and older rocks on the 

west slope of the Sierra Diablo and form smaller remnants 

elsewhere. They are separated from the older rocks by a 

marked unconformity. In places in the southwestern part of 

the map area they lie directly on the Precambrian, the intervening Paleozoic strata having been removed by erosion. The 

surface upon which they were deposited was a peneplain, exhumed remnants of which form the summits of other parts of 

the Sierra Diablo, where all trace of the Cretaceous rocks themselves has been removed.

The Cretaceous rocks overlapped northeastward from a geosyncline. Cretaceous rocks that were deposited along the edge 

of the geosyncline extend into the southwest corner of the map 

area, southwest of the Eagle Flat, and include at the base the 

Yucca and Bluff Mesa Formations, a body of sandstone and 

limestone of Early Cretaceous age that is more than 2,000 feet
GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

thick. The Yucca and Bluff Mesa are absent elsewhere in the 

region, except for a thinned equivalent of their topmost beds 

in the Campagrande Limestone.

Elsewhere in the southern half of the Sierra Diablo region, 

the Cretaceous is represented by the Campagrande Limestone, 

100 feet thick; the Cox Sandstone, 400 to 600 feet thick; and 

the Flnlay Limestone, 50 to 100 feet thick. The Campagrande 

is of Trinity age and the Finlay of Fredericksburg age; the 

boundary between the Trinity and Fredericksburg may lie 

within the Cox Sandstone. On Cox Mountain, in the westcentral part of the region, the Finlay is overlain by the Kiamichi Formation, or highest unit of the Fredericksburg Group.

Farther north, the Cox Sandstone apparently replaces both 

the Finlay and Kiamichi, for in Sierra Prieta, in the northwest 

corner of the region, it is overlain directly by the Washita 

Group. Here, as much as 350 feet of the Washita is preserved, 

with beds of Duck Creek age at the base and beds possibly as 

young as of Mainstreet age at the top.

The sedimentary rocks of the Sierra Diablo are intruded by 

igneous rocks of probable Tertiary age. These are most abundant near Mine and Marble Canyons in the northeastern part 

of the mountains, where two stocks and numerous dikes and 

sills lie in the Permian rocks; here, there is a great variety 

of igneous and contact-metamorphosed rocks. Sierra Prieta, 

in the northwestern part of the region, is formed by a thick 

sill-like body of alkalic composition which intrudes Permian 

and Cretaceous rocks. Extrusive basalt is preserved a few 

places in the central part of the region.

The Sierra Diablo was given its present form and outlines 

by disturbances during Cenozoic time. These disturbances 

probably occurred during several phases, extending from the 

early Tertiary into the Quaternary. The rocks near the Devil 

Ridge and Red Hills thrusts in the extreme southwest corner 

of the region were deformed in early Tertiary time, but most 

of the deformation in the Sierra Diabo to the northeast probably 

occurred during late Tertiary time. During this time the Sierra 

Diablo was raised nearly to its present height and was broken 

by faults. The faults belong to two systems: a fairly consistent set trending west-northwest and a less regular set trending generally north. Faults of the latter system follow the 

east base of the Sierra Diablo and Baylor Mountains. During 

Quaternary time faults of this system were displaced again, 

and in some places the alluvial fans were faulted.

The lower areas surrounding the Sierra Diablo are extensively covered by unconsolidated deposits of Cenozoic age, 

formed during erosion of the uplifted mountain blocks. The 

deposits at the surface are all probably of Quaternary age, 

but late Tertiary deposits doubtless underlie them in the deeper 

intermontane basins.

The economic products of the region are varied. In some 

places the rocks are mineralized, and have been extensively 

prospected. One mineralized area is in the exposed Precambrian rocks on the south, where copper and silver have been 

produced from the Hazel and Blackshaft mines and from many 

smaller workings. Another mineralized area is near Mine and 

Marble Canyons in the northeastern part of the Sierra Diablo. 

One of the stocks in that area contains small quantities of tungsten and beryllium. Near these stocks, and near the sill at 

Sierra Prieta, the metamorphosed, originally dolomitic, Hueco 

Limestone has been altered to a mixture of calcite and brucite, 

the latter perhaps a source of metallic magnesium. Since 1952 

the phyllitic beds in the Allamoore Formation have been extensively worked for talc. At a locality 8 miles west of Van 

Horn the metaigneous rocks that intruded the Carrizo Mountain

Formation have been quarried for many years for crushed stone.

The most needed resource in the area is ground water. The 

best and most abundant supplies have been obtained from wells 

in the Salt Basin near Van Horn; elsewhere, the occurrence, 

amount, and quality of ground water vary.

Probably the region contains no important reservoirs of oil 

or gas, as ancient rocks underlie it at relatively shallow depth. 

The region is of interest to petroleum geologists, however, because the rocks here exposed are about the same age and similar in character and structure to those which are deeply buried 

in the oil fields of the west Texas basin east of the mountain 

region.

INTRODUCTION

PRESENT INVESTIGATION

Between 1925 and 1939 the writer, with various colleagues, made a study of the Paleozoic and associated 

rocks exposed in the mountains of Trans-Pecos Texas, 

west and southwest of the west Texas Permian basin. 

This study was begun under the auspices of the Texas 

Bureau of Economic Geology and of Peabody Museum 

of Yale University, but after 1930 it was continued by 

the U.S. Geological Survey. Most of the results of 

this study have been published in official reports of the 

U.S. Geological Survey and the Texas Bureau of Economic Geology (King, P. B., 1931; King, E. E., 1931; 

King, P. B., 1937; King P. B., and Knight, J. B., 1944; 

King, P. B., and Fountain, H. C., 1944; King, P. B., 

King, E. E., and Knight, J. B., 1945; King, P. B., 1948, 

1949; King P. B., and Flawn, P. T., 1953) and in various journal articles (King, P. B., 1934a, b, 1942; and 

others).

The present report presents the remaining results of 

the study that part pertaining to the Sierra Diablo 

region. Field investigations in this region were largely 

completed by 1939, but preparation of a comprehensive 

report was delayed by emergency duties during World 

War II and by new Survey projects which began after 

the war; thus, only summaries of the results of the work 

in the Sierra Diablo region, or reports on special phases 

have appeared hitherto (King, P. B., 1942, p. 556-575, 

613-634; King, P. B., and Knight, J. B., 1944; King 

P. B., and Flawn, P. T., 1953). Because the comprehensive report has been prepared more than 20 years 

after completion of the field investigations, it lacks the 

freshness and novelty it might have possessed earlier. 

Nevertheless, many of the geologic observations that 

were made before 1939 have not been duplicated subsequently, so that a report on the region, based primarily 

on these observations, is still of value to the public.

Field investigations in the Sierra Diablo region were 

made at intervals by the writer and his colleagues between 1928 and 1939, as follows:

1. In the summer of 1928 the writer and E. E. King 

spent 3 weeks in the region, under the auspices of the
INTRODUCTION

Texas Bureau of Economic Geology and Yale Peabody 

Museum. The objective of this visit was a study of the 

Permian rocks; various sections were measured and fossils were collected. Some reconnaissance mapping was 

also done, and a few incidental observations were made 

on formations of other ages.

2. In the summer of 1931 the writer and J. Brookes 

Knight spent 4 weeks in the region for the U.S. Geological Survey. Aguin, chief study was made of the Permian stratigraphy and of fossils in the Permian rocks; 

but on this visit more attention was given to the associated rocks, and a start was made on detailed mapping of 

the region.

3. In the summer of 1936, again with J. Brookes 

Knight, 2 months were spent in the region, continuing 

the study of the Permian and associated rocks and extending the mapping.

4. In the summer of 1938 the writer and J. Brookes 

Knight spent 2^ months on a final review of the region, 

completing the stratigraphic study and most of the mapping. In the autumn of the same year the writer spent 

another month mapping the Precambrian and early 

Paleozoic rocks in the southern part of the region.

In addition, shorter visits and field checks were made 

by the writer during some intervening and subsequent 

years, as in 1933,1935,1939,1949, and 1951.

Mapping during the investigation was done partly 

on enlargements of the excellent topographic map of 

the Van Horn 30-minute quadrangle, whose original 

scale was 1:125,000; but in that part of the region to 

the west and north where only inadequate topographic 

base maps were available, mapping was done by means 

of a net of speedometer and pacing traverses. Kesults 

of these surveys were published in a preliminary map 

in 1944 (King, P. B., and Knight, J. B., 1944). In 1945 

small-scale air photographs of the region became available, in 1948 large-scale air photographs. In 1955 a 

topographic map based on photogrammetry was made 

the Army Map Service. In 1951 and 1955 the writer 

adjusted his earlier field traverses to the air photographs and transferred the results to the new 

topographic base. The resulting geologic map accompanying this report (pi. 1) represents the same features 

as those on the map of 1944, but with some revision and 

with greater precision of form and location.

Stratigraphic studies, measurement of sections, and 

collection of fossils were made largely by the author's 

colleague, the late J. Brookes Knight, at times with the 

assistance of the writer and others. Most of the sections were measured by hand level, and because the 

strata of the region are nearly flat lying, no correction 

for dip was necessary. Many of the fossil collections 

were made along the lines of the measured sections,

although a few in outlying areas could not 'be tied into 

sections.

ACKNOWLEDGMENTS

In the investigation of the Sierra Diablo region the 

writer's greatest debt is to his field associate and collaborator, the late J. Brookes Knight, specialist in 

Paleozoic gastropods and one of the great paleontologists of our time. Much is due him, not only for his 

measurement of sections and collection of fossils, mentioned above, but also for his keen insight into problems 

of stratigraphy, paleontology, and paleoecology, which 

has contributed in no small measure to the merits of this 

report.

During the investigation, geologic features of the 

region were reviewed with many visitors, among whom 

the following are noteworthy.

In 1938, the late Samuel G. Lasky, of the U.S. Geological Survey, reviewed with the writer the mines, 

prospects, and mineral deposits of the region, mainly 

in the Precambrian rocks to the south, but also including those of the Mine Canyon and Marble Canyon area 

farther north. In 1941 Lasky made an independent 

examination of the tungsten deposits of the Mine 

Canyon area.

In 1936 Earl Ingerson, at that time with the Geophysical Laboratory of the Carnegie Institution of 

Washington, reviewed the intrusive rocks of the Marble 

Canyon area with Knight. In 1938 Ingerson reviewed 

with the writer the metamorphic rocks in the southern 

part of the region.

In 1938 the late Josiah Bridge and the late W. H. 

Hass, of the U.S. Geological Survey, reviewed with 

Knight and the writer the stratigraphy and paleontology of the Ordovician and other early Paleozoic 

rocks.

Study and identification of rocks and minerals of the 

region have been made by many petrographers and geochemists of the U.S. Geological Survey. Kock and 

mineral specimens have been identified by C. S. Ross, 

Charles Milton, and Donald E. Lee. Chemical analyses 

have been made by K. J. Murata. In addition, in 1941 

Milton made an extensive study of specimens from the 

Marble Canyon intrusive and its associated contactmetamorphic rocks.

Study and identification of fossils from the various 

formations of the region were made by paleontologists 

of the U.S. Geological Survey. Ordovician fossils 

were identified by Josiah Bridge, P. E. Cloud, Jr., 

Helen Duncan, and Jean Berdan; collections of conodonts from the Devonian rocks, by W. H. Hass; Mississippian and Pennsylvanian fossils, by George H. Girty, 

Mackenzie Gordon, Jr., and E. L. Yochelson; larger 

Permian fossils, by P. E. Cloud, Jr., E. L. Yochelson,
GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

R. M. Finks, Helen Duncan and I. G. Sohn, fusulinids 

and other foraminifers, by L. G. Henbest; and 

Cretaceous fossils, by Ralph W. Imlay.

Before the studies were made by Survey paleontologists, the brachiopods collected from the Permian rocks 

in 1928 had been identified by R. E. King, and the fusulinids collected in 1928 and 1931 had been identified by 

C. O. Dunbar and J. W. Skinner. The memoirs in 

which their results appeared (King, R. E., 1931; Dunbar and Skinner, 1937) are among the earliest of the 

modern studies on the Permian fossils of the West 

Texas Region, and were an invaluable guide in the later 

field investigations in the Sierra Diablo region.

BELATED INVESTIGATIONS

Besides the field investigation in the Sierra Diablo 

region that was made directly by the writer and his associates, other investigations were made in the region 

during the same period by geologists of the U.S. Geological Survey and Texas Bureau of Economic Geology, 

some of the results of which are included in this report. 

The areas covered by some of these investigations are 

shown in figure 1.

Between 1943 and 1946 P. E. Cloud, Jr., and V. E. 

Barnes, of the U.S. Geological Survey and Texas 

Bureau of Economic Geology, made a comprehensive 

investigation of the Ellenburger Group of central 

Texas. As part of this study they measured a detailed 

section of the Lower Ordovician rocks on Beach Mountain and made observations on these rocks elsewhere in 

the Sierra Diablo region (Cloud and Barnes, 1946, 

p. 66-71,352-361).

In 1944 R. D. Sample and E. E. Gould, of the U.S. 

Geological Survey, made a detailed examination of the 

Hazel, Blackshaft, Sancho Panza, and other mines and 

mineral deposits of the southern part of the region. 

Between 1944 and 1946 Elliot Gillerman, of the U.S. 

Geological Survey, studied the fluorspar deposits of the 

Eagle Mountains southwest of the Sierra Diablo and 

mapped the rocks in which they occur (Gillerman, 

1953). His geologic map extends a short distance into 

the south edge of the Sierra Diablo region, and was 

used in compilation of the geologic map which accompanies the present report. In 1948 and 1949 W. T. 

Holser made a detailed survey of the Cave Peak intrusive in the Mine Canyon area for the U.S. Geological 

Survey, as part of a study of the nonpegmatitic beryllium resources of the United States (Warner and 

others, 1959, p. 140-143).

In 1936 and 1937 J. Fred Smith, Jr., mapped the 

Devil Ridge area, part of which extends into the extreme southwest corner of the Sierra Diablo region 

(Smith, 1940). Between 1947 and 1951, under the

auspices of the U.S. Geological Survey, Smith and C. C. 

Albritton, Jr., expanded this and other surveys into a 

comprehensive study of the Sierra Blanca region that 

adjoins the Sierra Diablo region on the west (Albritton 

and Smith, 1965). Geologic features in the southwest 

corner of the map which accompanies the present 

report are based on the surveys by Smith.

Between 1949 and 1951 Peter T. Flawn, of the Texas 

Bureau of Economic Geology, investigated the Precambrian rocks of the Carrizo Mountains and outlying 

areas to the south and also studied the Hazel Mine and 

the talc deposits which occur in the Precambrian rocks 

farther north. He collaborated with the writer in a 

report on the Precambrian rocks of the Van Horn area 

and their mineral deposits (King, P. B., and Flawn, 

P. T., 1953). Mapping and other data in the southern 

part of the present report are are based on this joint 

study.

Other studies of special phases of the geology of the 

region have been made by geologists with other affiliations and have been used in the present report so far 

as their published results are available. F. G. Stehli 

studied the Permian rocks and fossils near Victorio 

Peak for a dissertation at Columbia University (Stehli, 

1954), and C. O. Dunbar investigated the fusulinids of 

the Permian rocks in the same area (Dunbar, 1953). 

H. J. Howe reviewed the stratigraphy of the Montoya 

Dolomite in west Texas and southern New Mexico 

and made significant observations in the Baylor Mountains (Howe, 1959). Hugh Hay-Roe and P. C. Twiss 

studied the Permian and associated rocks in the Wylie 

and Van Horn Mountains, southeast and south of the 

present report area, for dissertations at the University 

of Texas (Hay-Roe, 1957; Twiss, 1959). Some of the 

observations by geologists employed by oil companies 

have appeared in guidebooks of the West Texas Geological Society (Adams and others, 1949; De Ford and 

others, 1951; Haigh and others, 1953).

PREVIOUS INVESTIGATIONS

The Sierra Diablo region was given scant attention 

by the early geological explores and was not visited by 

geologists until the reorganization of the Geological 

Survey of Texas under E. T. Dumble in 1888. Investigation of the geology of the Trans-Pecos Region for 

this survey was assigned to W. H. von Streeruwitz, 

who was in the field with his assistants between the 

years 1888 and 1893 (Geiser, 1957). Although most of 

their work was done in areas farther south and west, 

the mines and prospects in the southern foothills of the 

Sierra Diablo were examined, including the Hazel mine, 

and brief observations were made on the surrounding 

rock formations (Streeruwitz, 1890, 1891, 1892, 1893).
INTRODUCTION

Metamorphic rocks were observed in the Carrizo Mountains and the hills north of Eagle Flat, and their nature 

was interpreted in a petrographic report by Osairn 

(1893, p. 137-138). Eocks farther north were thought 

to consist of a red Diabolo Sandstone, assigned to a 

Devonian age, and an overlying body of limestone, assigned to a Carboniferous age on the authority of C. D. 

Walcott, who examined a few fossil collections. Both 

of these supposed units are now known to consist of 

many formations of diverse ages.

First systematic geologic work in the Sierra Diablo 

region was by G. B. Kichardson, under the joint auspices 

of the U.S. Geological Survey and the University of 

Texas Mineral Survey. In 1903 Kichardson made a 

reconnaissance of the geology and ground-water resources of all the northern Trans-Pecos Eegion in Texas 

(Eichardson, 1904); later he made more detailed surveys of the El Paso and Van Horn quadrangles, which 

were published as geologic folios (Eichardson, 1909, 

1914).

Eichardson's work laid the foundation on which most 

of our modern geologic concepts of the Sierra Diablo 

and adjacent regions have been built. He recognized 

and defined many of the Paleozoic and Mesozoic formations which are still in use and set forth the broader 

outlines of the geomorphology and structure. However, 

as only a small amount of time could be spent on these 

surveys even those for the geologic folios many details have been added later, as may be seen by comparing 

the present map of the Sierra Diablo region with the 

map in the Van Horn folio.

Older Paleozoic formations the Bliss, El Paso, 

Montoya, and Fusselman were defined on the basis of 

the section in the Franklin Mountains north of El Paso 

(Eichardson, 1908, p. 475-^80), still the standard of 

reference. Presence of the El Paso and Montoya was 

also recognized by Eichardson in the Sierra Diablo region, and occurrence of the Bliss and Fusselman has 

been proved there subsequently.

Stratigraphy of the more complex later Paleozoic 

strata was less clarified, although Eichardson benefited 

from the advice of G. H. Girty, who was at that time 

working on his classic memoir on the Guadalupian 

fauna (Girty, 1908), based on collections of Permian 

fossils from the Guadalupe Mountains and adjacent 

regions. Permian formations, the Delaware Mountain, 

Capitan, and higher units, were recognized east of the 

Salt Basin; but the later Paleozoic rocks to the west 

were placed in the Hueco Limestone, supposed to be a 

nearly homogeneous body as much as 5,000 feet thick, 

of Pennsylvanian age. As mapped by Eichardson, the 

Hueco is now known to include, at one place or another, 

formations of Mississippian, Pennsylvanian, and Early

Permian ages. The "Hueco fauna," as understood by 

Girty, however, actually occurs only in one of these 

formations in the Hueco Mountains and elsewhere; the 

name is now restricted to this part of the original 

formation.

In the Sierra Diablo, the Hueco Limestone as mapped 

by Eichardson is now known to consist of several formations of Early Permian age, the lowest of which is 

the restricted Hueco; the angular unconformity recognized by Eichardson below the Hueco has proved to 

be basal Permian, rather than basal Pennsylvanian. 

Mississippian and Pennsylvanian elements, which form 

large parts of the original Hueco in the Hueco and 

Franklin Mountains, are scantily preserved in the Sierra 

Diablo region.

Few geologic observations were made in the Sierra 

Diablo region in the decades immediately following 

the work of Eichardson and Girty. The next period 

in which it was studied began in the midtwenties as 

an outgrowth of petroleum exploration and development in the West Texas basin to the east. This period 

corresponds to that during which the present investigation was made by the writer and his colleagues; work 

done during that time in the Sierra Diablo region by 

other geologists has already been mentioned.

The following annotated bibliography lists chronologically all publications which deal with the geology 

of the Sierra Diablo regions.

ANNOTATED BIBLIOGRAPHY

Perry, C. C., and others, 1857, Geological reports, in Emory, 

W. H., Report on the United States and Mexican boundary 

survey: U.S. 34th Gong., 1st sess., S. Ex. Doc. 108 (H. Ex. 

Doc.l35),v.l,pt.2,174 p.

Reports (p. 4-5) that west of the igneous rocks of the 

Limpia (Davis) Mountains are ridges of stratified limestone, dipping southwest; on the basis of a few fossils 

(Terebratula) James Hall assigns the limestone to the 

Carboniferous (p. 107). Elevated alluvial basins near 

Eagle Spring are shut off from the Rio Grande by a "variable mountain range, composed of Carboniferous limestone 

and variously associated igneous rocks." The Sierra Diablo region to the north is not mentioned in this account.

Jenny, W. P., 1874, Notes on the geology of western Texas near 

the thirty-second parallel: Am. Jour. Sci., 3d ser., v. 7, p. 

25-28.

Discusses the probable Silurian and Carboniferous ages 

of rocks in the mountains of northern Trans-Pecos Texas, 

mostly north and northwest of the Sierra Diablo region.

Cummins, W. F., 1888, Mining districts in El Paso County: 

Geol. and Sci. Bull. (Texas State Geol. and Sci. Assoc., 

Houston, Tex.), v. 1, no. 2.

Includes a paragraph on the "Diabolo district" that is, the 

mineralized area in the southern foothills of the Sierra 

Diablo. Mentions the nature of the copper and silver ores
6 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

and states that these occur in steeply dipping veins in 

massive fine-grained red argillaceous sandstone of unknown 

age (sandstone of Hazel Formation of present terminology), 

which is overlain by Carboniferous limestone.

Streeruwitz, W. H. von, 1889, Mines worked in western Texas: 

Geol. and Sci. Bull. (Texas State Geol. and Sci. Assoc., 

Houston, Tex.), v. 1, no. 12.

Includes brief description of Hazel mine, its ores, and 

mining operations then in progress.

Hill, R. T., 1890, The Eagle Flats formation and the basins of 

the trans-Pecos or mountainous region of Texas [abs.]: 

Am. Assoc. Adv. Sci. Proc., v. 38, p. 42.

Quaternary intermontane deposits of Trans-Pecos Texas 

are interpreted to be of lacustrine origin and are named the 

Eagle Flats Formation, presumably after Eagle Flat in the 

Sierra Diablo region, although this is not so stated.

Streeruwitz, W. H. von, 1890, Geology of trans-Pecos Texas: 

Texas Geol. Survey 1st Ann. Kept. (1889), p. 219-235.

Contains general summary of geology and resources of 

Trans-Pecos Region but includes some notes on geology and 

mineral deposits in Sierra Diablo foothills (p. 221-222, 224).

 1891, Report on the geology and mineral resources of 

trans-Pecos Texas: Texas Geol. Survey 2d Ann. Rept. 

(1890), p. 665-713.

Lengthy description of geology and resources of TransPecos Texas, including notes on geology and mines in Oarrizo Mountains and Sierra Diablo foothills (p. 681-684), 

accompanied by geologic structure sections (pi. 26).

 1892, Trans-Pecos Texas: Texas Geol. Survey 3d Ann. 

Rept. (1891), p. 383-389.

General remarks on Trans-Pecos Region, including notes 

on geology and mineral deposits of Carrizo Mountains and 

Sierra Diablo foothills, and a detailed report on Hazel 

Mine, with plans and sections (pi. 16).

 1893, Trans-Pecos Texas: Texas Geol. Survey 4th Ann. 

Rept. (1892), p. 141-175.

Final summary of the author's 5 yr of observation on the 

geology and resources of Trans-Pecos Texas; includes stratigraphic sections and lists of identified fossils from the 

Paleozoic rocks of the Sierra Diablo (p. 167-175).

Osann, C. A., 1893, Report on the rocks of trans-Pecos Texas: 

Texas Geol. Survey 4th Ann. Rept. (1892), p. 123-141.

Includes petrographic reports on a diabase from the 

Sierra Diablo (p. 125-126) and various metamorphic rocks 

from the Carrizo Mountains (p. 137-138).

 1896, Beitrage zur Geologic und Petrographie der Apache 

(Davis) Mts., Westtexas: Tschermak's mineralog. petrog. 

Mitt., v. 15, p. 394-456.

Includes description of Precambrian metamorphic rocks 

in Carrizo Mountains and adjacent areas.

Hill, R. T., 1900, Physical geography of the Texas region: U.S. 

Geol. Survey Topog. Atlas, Folio 3,12 p.

Includes brief description of topography of Sierra Diablo 

region (p. 5) and several photographs (figs. 24, 35).

Dumble, E. T., 1902, The red sandstone of the Diablo Mountains, 

Texas: Texas Acad. Sci. Trans., v. 4, pt. 2, p. 1-3.

Discussion of stratigraphy of older rocks of Sierra Diablo 

region, based on exposures on west side of Beach Mountain, 

where the red Hazel Sandstone is differentiated from an 

overlying red sandstone (Van Horn Sandstone of present 

usage), believed by the author to be of early Paleozoic age.

Phillips, W. B., 1902, Sulphur, oil, and quicksilver in trans-Pecos 

Texas: Texas Univ. Bull. 9 (Mineral Survey Ser. Bull. 2) 

43 p.

Contains mineral appraisals and brief notes on geology 

of various land-survey blocks in El Paso County (including 

present Culberson and Hudspeth Counties) by B. F* Hill, 

some of which are in Sierra Diablo region (p. 15, 16, 20, 

etc.).

Richardson, G. B., 1904, Report of a reconnaissance in transPecos Texas north of the Texas and Pacific Railway: Texas 

Univ. Bull. 23 (Mineral Survey Ser. Bull. 9), 119 p.

Report on a survey of an extensive region, of which the 

Sierra Diablo region is a part, with special reference to 

ground-water resources but containing the first modern account of the stratigraphy, structure, and geomorphology.

Girty, G. H., 1908, The Guadalupian fauna: U.S. Geol. Survey 

Prof. Paper 58, 651 p.

Comprehensive memoir on Permian fossils, mainly from 

Guadalupe Mountains north of Sierra Diablo region. Includes remarks on some fossils collected from an unknown 

locality in the Sierra Diablo which also appear to be of 

"Guadalupian" character (p. 26); these probably came 

from Bone Spring Limestone.

Richardson, G. B., 1908, Paleozoic formations in trans-Pecos 

Texas: Am. Jour. Sci., 4th ser., v. 25, p. 474-484.

Contains the first definitions of many of the stratigraphic 

units which occur in the Sierra Diablo and other parts of 

northern trans-Pecos Texas and emendations of definitions 

of other units that had been proposed by Richardson in report of 1904.

Van Hise, C. R., and Leith, C. K., 1909, Pre-Cambrian geology 

of North America: U.S. Geol. Survey Bull. 360, 939 p.

Includes summary of observations by Richardson and 

earlier geologists on Precambrian rocks in southern Sierra 

Diablo region (p. 746-749).

Richardson, G. B., 1914, Description of the Van Horn quadrangle : U.S. Geol. Survey Geol. Atlas, Folio 194, 9 p.

Report on the geology of an area which includes the 

eastern half of the Sierra Diablo region, ably presenting 

the larger features, although many details have been added 

by later work.

Beede, J. W., 1920, Notes on the geology and oil possibilities of 

the northern Diablo Plateau in Texas: Texas Univ. Bull. 

1852, 40 p. [1918].

Deals mainly with region northwest of the Sierra Diablo, 

but includes first report of occurrence of strata of "Word" 

(Guadalupe) age at north end of Sierra Diablo (p. 24-26).

Baker, C. L., 1927, Exploratory geology of a part of southwestern trans-Pecos Texas: Texas Univ. Bull. 2745, 70 p.
INTRODUCTION

Reconnaissance survey of an extensive area south and 

southwest of Sierra Diablo region, including notes on Precambrian rocks and Permian (Hueco) limestone in Carrizo 

and Wylie Mountains.

Baker, C. L., 1928, Desert range tectonics of trans-Pecos Texas: 

Pan-Am. Geologist, v. 50, p. 341-373.

Appraisal of evidence for Basin and Range structure in 

Trans-Pecos Texas and New Mexico, with mention of Sierra 

Diablo region (p. 369-371).

Carter, W. T., and others, 1928, Soil survey (reconnaissance) 

of the trans-Pecos area, Texas: U.S. Dept. Agri. ser. 1928, 

no. 35, 66 p.

General account and map of geography and soils of TransPecos Region, with some specific notes on Sierra Diablo 

region.

Baker, C. L., 1929, Overthrusting in trans-Pecos Texas: Pan-Am. 

Geologist, p. 53, p. 23-28.

Discussion of folding and thrust-faulting of Cretaceous 

rocks in southern Hudspeth County, including southwestern 

corner of report area. At northeastern border of disturbed 

belt, thrust sheets moved toward nearly horizontal strata 

of Diablo Plateau, the boundary between them being localized by "shoaling of Cretacic sea" (p. 24).

Blanchard, W. G., Jr., and Davis, M. J., Jr., 1929, Permian 

stratigraphy and structure of parts of southeastern New 

Mexico and southwestern Texas: Am. Assoc. Petroleum 

Geologists Bull., v. 13, p. 957-995.

Deals mainly with Guadalupe Mountain area, but includes 

remarks on Permian rocks of Sierra Diablo and Wylie 

Mountains (p. 960-962).

King, P. B., and King, R. B., 1929, Stratigraphy of outcropping 

Carboniferous and Permian rocks of trans-Pecos Texas: 

Am. Assoc. Petroleum Geologists Bull., v. 13, p. 907-926.

Includes results of first field season of present investigation in Sierra Diablo region on Pennsylvanian and 

Permian rocks (p. 911, 922-923), many of which have been 

superseded by later work.

King, R. B., 1929, Mississippian and Pennsylvanian stratigraphy 

of trans-Pecos, Texas [abs.]: Geol. Soc. America Bull., v. 40, 

p. 190-191.

Mentions occurrence of limestone of Strawn age in the 

Sierra Diablo (the limestone of Pennsylvanian age south of 

Marble Canyon of present report).

Mohr, C. L., 1929, Secondary gypsum in the Delaware Mountain region: Am. Assoc. Petroleum Geologists Bull., v. 13, 

p. 1395.

Presents evidence that the alleged "Dos Alamos gypsum 

member" in the Guadalupe series of the northern Sierra 

Diablo is not an original part of the stratigraphic sequence.

King, P. B., and Leonard, R. J., 1930, Contact metamorphism of 

Hueco limestone in trans-Pecos Texas [abs.]: Pam-Am. 

Geologist, v. 53, p. 316.

Note on contact metamorphism adjacent to the Marble 

Canyon intrusive of northeastern Sierra Diablo.

King, R. B., 1931, Faunal summary and correlation of the 

Permian formations, with description of the Brachiopoda, 

pt 2 of Geology of the Glass Mountains: Texas Univ. Bull. 

3042, 245 p. [1930].

Includes an account of Permian stratigraphy of Sierra 

Diablo region based on first field season of present investigation (p. 14-16) and description of Permian brachiopods, 

in part collected in Sierra Diablo region. Many of stratigraphic interpretations have been superseded by later work.

Girty, G. H., 1931, New Carboniferous invertebrates, pt. 3: 

Washington Acad. Sci. Jour., v. 21, p. 390-397.

Includes description of the brachiopod Schisophoria 

peculiaris Girty from Bone Spring Limestone of Sierra 

Diablo.

Adkins, W. S., 1933, The Mesozic systems in Texas, in Stratigraphy, v. 1 of The geology of Texas: Texas Univ. Bull. 

3232, p.239-518.

Description and interpretation of all Mesozoic formations in Texas, with many incidental notes on Cretaceous 

rocks in and near the Sierra Diablo region.

Arick, M. B., 1932, Occurrence of strata of Bend age in Sierra 

Diablo, Texas: Am. Assoc. Petroleum Geologists Bull., T. 

16, p. 484-486.

Reports discovery of fossiliferous strata of Bend age 

north of Marble Canyon in the Sierra Diablo ("shale of 

Smithwick age" of Plummer and Scott, 1937, "fossiliferous 

shale of Pennsylvianian age" of present report).

Darton, N. H., 1932, Algonkian strata of Arizona and western 

Texas [abs.]: Geol. Soc. America Bull., v. 43, p. 123.

Mentions resemblance of the Millican Formation (Allamoore and Hazel Formations of present usage) to Grand 

Canyon Series and Apache Group of Arizona.

King, P. B., 1932, Possible Silurian and Devonian strata in Van 

Horn region, Texas: Am. Assoc. Peroleum Geologists Bull., 

v. 16, p. 95-97.

Reports discovery of Fusselman Limestone and beds of 

Devonian age in Sierra Diablo region during second field 

season of present investigation.

King, P. B., 1932, Permian limestone reefs in the Van Horn 

region, Texas [abs.]: Washington Acad. Sci. Jour., v. 22, 

p. 288-289; Geol. Soc. America Bull., v. 43, p. 280-281.

Notes on reefs and related deposits in Bone Spring Limestone of Sierra Diablo region, based on observations during 

second field season of present investigation.

Mansfield, G. R., and Boardman, Leona, 1932, Nitrate deposits 

of the United States: U.S. Geol. Survey Bull. 838, 107 p.

Includes description of a nitrate prospect ("Potash 

mine") in Van Horn Sandstone (erroneously ascribed to 

Cretaceous) in Sierra Diablo foothills (p. 66-68).

Sellards, B. H., 1933, Pre-Paleozoic and Paleozoic system in 

Texas, in Stratigraphy, v. 1 of The geology of Texas: 

Texas Univ. Bull. 3232, p. 15-238.

Brief descriptions of all pre-Paleozoic and Paleozoic formations in Texas, including those in Sierra Diablo region.

Darton, N. H., and King, P. B., 1933, Western Texas and Carlsbad Caverns: Internat. Geol. Cong., 16th, United States 

1933, Guidebook 13, 38 p.

Contains a summary of geology of Sierra Diablo region 

(p. 19-27), based on results of first two field seasons of 

present investigation.
8 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Baker, C. L., 1935, Structural features of trans-Pecos Texas, 

Pt. 2 in Structural and economic geology, v. 2 of The geology of Texas: Texas Univ. Bull. 3401, p. 137-214.

Includes brief description of geologic structure of Sierra 

Diablo region and adjacent areas (p. 180-185) and discussion of "Texas lineament" (p. 206-214).

King, P. B., 1934, Permian stratigraphy of trans-Pecos Texas: 

Geol. Soc. America Bull., v. 45, p. 697-798.

Describes Permian stratigraphy of Sierra Diablo region 

on basis of results of first two field seasons of present investigation (p. 745-746, 748-763), some of which have been 

superseded by later work.

King, P. B., 1934, Notes on upper Mississippian rocks in transPecos Texas: Am. Assoc. Petroleum Geologists Bull., v. 18, 

p. 1537-1543.

Includes description of Mississippian and adjacent strata 

in Sierra Diablo region (p. 1541-1543).

Kirk, Edwin, 1934, The Lower Ordovician El Paso limestone of 

Texas and its correlatives: Am Jour. Sci., 5th ser., v. 28, p. 

443-463.

Discusses subdivisions and correlation of El Paso Limestone, with special reference to the Franklin Mountains section but with incidental reference to Sierra Diablo region 

(p. 451). Subsequent work has added many details to these 

results, but has not modified the general conclusions.

Sellards, E. H., and others, 1935, Economic geology of Texas, in 

Structural and economic geology, v. 2 of The geology of 

Texas: Texas Univ. Bull. 3401, p. 215-868.

Contains summaries, compiled by C. L. Baker, of copper 

deposits (p. 410-411), ground water (p. 373-380), and other 

resources of Sierra Diablo region.

Arick, M. B., 1935, Early Paleozoic unconformities in trans-Pecos 

Texas: Texas Univ. Bull. 3501, p. 117-121.

Observations on Sierra Diablo region (p. 118-119) include 

reference to unconformity between Van Horn and Bliss 

Sandstones and to supposed occurrence of Middle Ordovician rocks in the northeastern Sierra Diablo.

Baker, C. L., 1935, Precambrian unconformities in the transPecos region: Texas Univ. Bull. 3501, p. 113-114.

Includes interpretation of Precambrian sequence in Sierra 

Diablo region, based on existing publications by Richardson 

and King.

King, P. B., 1935a, Unconformities in the later Paleozoic of transPecos Texas: Texas Univ. Bull. 3501, p. 131-135.

Includes remarks on unconformity at base of Hueco Limestone in Sierra Diablo region and elsewhere and on supposed absence of an unconformity at top of Hueco (p. 133- 

134).

 1935b, Outline of structural development of trans-Pecos 

Texas: Am. Assoc. Petroleum Geologists Bull., v. 19, p. 221- 

261.

General account of structure of Trans-Pecos Texas, including preliminary results of investigation in Sierra Diablo 

region.

Dunbar, C. O., and Skinner, J. W., 1937, Permian Fusulinidae of 

Texas, in Upper Paleozoic ammonities and fusulinids, v. 3 

of The geology of Texas: Texas Univ. Bull. 3701, p. 519- 

825.

Contains notes on stratigraphy of Sierra Diablo region (p. 

587-590), description of fusulinid species, and lists of fusulinids identified from Sierra Diablo region (p. 722-725).

Plummer, F. B., and Scott, Gayle, 1937, Upper Paleozoic ammonities in Texas, in Upper Paleozoic ammonities and fusulinids, 

v. 3 of The geology of Texas: Texas Univ. Bull. 3701, p. 13- 

516.

Includes identifications of ammonites from shale of Smithwick age north of Marble Canyon in the Sierra Diablo (p. 

25) ("fossiliferous shale of Pennsylvanian age" of present 

report).

King, R. E., Adams, J. E., and Hills, J. M., 1939, Van Horn 

region: West Texas Geol. Soc. Field Trip Guidebook, May 

20-21,1939, 8 p.

Road log in southern part of the Sierra Diablo, describing 

localities in Permian and older rocks, based on field results 

of P. B. King.

Bridge, Josiah, 1940, Correlation of early Paleozoic sections in 

central and western Texas [abs.]: Geol. Soc. America Bull., 

v. 51, p. 1921-1922.

Includes brief comment on correlation of El Paso Limestone and Bliss Sandstone of Sierra Diablo region.

King, P. B., 1940, Older rocks of Van Horn region, Texas: Am. 

Assoc. Petroleum Geologists Bull., v. 24, p. 143-156.

Summary of results of present investigation on Precambrian rocks of Sierra Diablo region, which are given in 

more detail in King and Flawn (1953) and present report.

Miller, A. K., and Furnish, W. M., 1940a, Permian ammonoids 

of the Guadalupe Mountain region and adjacent areas: 

Geol. Soc. America Spec. Paper 26, 242 p.

Includes description of Propinacoceras Jcnighti Miller and 

Furnish from Bone Spring Limestone of Sierra Diablo 

region (p. 42-44).

 1940b, Studies of Carboniferous ammonoids, Pts. 5-7: 

Jour. Paleontology, v. 14, no. 6, p. 521-543.

Includes description of the ammonoids Diaftoloceras varir 

costatum Miller and Furnish and Pseudoparalegoceras 6eZUlineatum Miller and Furnish from "Smithwick horizon of 

Magdalena limestone" in Sierra Diablo (p. 527-532) ("fossiliferous shale of Pennsylvanian age" of present report).

Smith, J. F., Jr., 1940, Stratigraphy and structure of the Devil 

Ridge area, Texas: Geol. Soc. America Bull., v. 51, p. 

597-638.

Geology of deformed Cretaceous rocks in an area southwest of Sierra Diablo region, part of which forms southwest 

corner of present report area.

 1941, Geology of the Eagle Spring area, Eagle Mountains, 

Hudspeth County, Texas: Field and Lab., v. 9, p. 70-79.

Description of a small area just south of southwestern 

part of report area.

King, P. B., 1942, Permian of west Texas and southeastern 

New Mexico: Am. Assoc. Petroleum Geologists Bull., v. 26, 

p. 535-763.

Summarizes final results of present investigation in 

Sierra Diablo region on Permian stratigraphy (p. 556-575) 

and associated structural features (p. 613-634).
INTRODUCTION 9

Wheeler, R. R., 1942, Cambro-Ordovician of southwest [abs.]: 

Geol. Soc. America Bull., v. 53, p. 1812-1813.

Proposes correlations of El Paso Limestone and Bliss 

Sandstone of Franklin Mountains and Sierra Diablo which 

have not been substantiated by any other stratigrapher.

Evans, G. L., 1943, Progress report on copper investigations: 

Texas Univ. Bur. Econ. Geology Mineral Resources Circ. 24, 

6 p.

Brief summary of an extensive investigation of copper 

mines and prospects in Sierra Diablo region and adjacent 

areas.

Adams, J. E., 1944, Highest structural point in Texas: Am. 

Assoc. Petroleum Geologists Bull., v. 28, p. 562-564.

Analyzes criteria for recognition of structurally high 

areas and concludes that "Van Horn dome" in southern part 

of Sierra Diablo region is not the highest structural point 

in Texas.

King, P. B., and Knight, J. B., 1944 [Geologic map of the] Sierra 

Diablo region, Hudspeth and Culberson Counties, Texas: 

U.S. Geol. Survey Oil and Gas Inv. Map 2.

Map of present report area, based on field surveys of 

present investigation, but not adjusted to an accurate topographic base.

King, P. B., King, R. E., and Knight, J. B., 1945, Geology of 

Hueco Mountains, El Paso and Hudspeth Counties, Texas: 

U.S. Geol. Survey Oil and Gas Inv. Prelim. Map 36, 2 sheets.

Includes comment on possible correlation of Pennsylvanian rocks exposed in Sierra Diablo (sheet 2).

Miller, A. K., 1945, Permian nautiloids from the Glass Mountains and the Sierra Diablo of west Texas: Jour. Paleontology, v. 19, p. 282-294.

Includes identification and description of nautiloid 

species from Bone Spring Limestone in the Sierra Diablo.

Sample, R. D., and Gould, E. E., 1945, Geology and ore deposits 

of the Allamoore-Van Horn district, Hudspeth and Culberson Counties, Texas: U.S. Geol. Survey open-file report, 22 p. 

Report on examination of Blackshaft, Hazel, and other 

mines and prospects of southern foothills of the Sierra 

Diablo, and their geological environment. Many of the data 

in this report are reproduced in King, P. B., and Flawn, 

P. T. (1953).

Cloud, P. E., Jr., and Barnes, V. E., 1946, The Ellenburger group 

of central Texas: Texas Univ. Pub. 4621, 473 p. [1948].

Deals mainly with central Texas, but includes discussion 

of subdivisions and correlation of Bliss Sandstone and El 

Paso Limestone in Sierra Diablo region and Franklin 

Mountains (p. 66-74) and detailed section of these formations on Beach Mountain (p. 352-361).

Miller, A. K., and Youngquist, W. L., 1947, American Permian 

nautiloids: Geol. Soc. America Mem. 41, 218 p.

Deals further with nautiloids from Bone Spring Limestone in the Sierra Diablo that were reported on by Miller 

(1945).

Cloud, P. E., Jr., 1948, Brachiopods from the Lower Ordovician 

of Texas: Harvard Coll. Mus. Comp. Zoology Bull., v. 100, 

p. 451-472.

Lists nine species of brachiopods from El Paso Limestone 

of Sierra Diablo region (p. 453) ; descriptions of two of the 

species (Syntrophina magnet Ulrich and Cooper and Diaphelasma oJclahomense Ulrich and Cooper) are based in part 

on specimens collected in Beach Mountain section.

Jackson, A. T., 1948, West Texas caves and shelters, in The 

caves of Texas: Natl. Speleol. Soc. Bull. 10, p. 69-76. .

Includes notes on Bat Cave and Potash Mine shelter in 

Sierra Diablo region (p. 71-72); photographs of Bat Cave 

on p. 113.

King, P. B., 1948, Geology of the southern Guadalupe Mountains, Texas: U.S. Geol. Survey Prof. Paper 215, 183 p. 

D949J

Detailed description of sequence of Permian rocks of 

Leonard and Guadalupe age in Guadalupe Mountains north 

of Sierra Diablo region, with incidental reference to rocks 

of Wolfcamp and Leonard age in Sierra Diablo region 

(p. 12-13). Maps and text also summarize structure and 

geomorphology of Sierra Diablo region (p. 118-120, pis. 

21,23).

Adams, J. E., and others, 1949, The Permian rocks of the transPecos region: West Texas Geol. Soc. Field Trip Guidebook, 

Nov. 6-9,1949, 94 p.

Includes road log in Sierra Diablo region (p. 58-81), 

based partly on publications, but including original observations.

King, P. B., 1949, Regional geologic map of parts of Culberson 

and Hudspeth Counties, Texas: U.S. Geol. Survey Oil and 

Gas Inv. Prelim. Map 90.

Map of a large part of northern Trans-Pecos Texas, including Sierra Diablo region, where it is based on results 

of present investigation.

King, P. B., and others, 1949, Pre-Permian rocks of the transPecos area and southern New Mexico: West Texas GeoL 

Soc. Field Trip Guidebook, Nov. 6-9, 1949, 67 p.

Includes a summary of pre-Permian rocks and road log 

in Sierra Diablo region (p. 18-34), mostly compiled from 

publications.

Smith, J. F., Jr., and Albritton, C. C., Jr., 1949, Conglomerates 

of western trans-Pecos Texas and their relation to a tectonic boundary [abs.]: Geol. Soc. America Bull., v. 60, 

p. 1921.

Discusses relation of conglomerates in Precambrian, 

Permian, and Cretaceous rocks in Sierra Diablo region and 

west of it to an unstable area toward the southwest.

Albritton, C. C., Jr., and Smith, J. F., Jr., 1950, Evidence for 

aridity in west Texas during Early Cretaceous [abs.]: 

Geol. Soc. America Bull., v. 61, p. 1440.

Interprets chalky limestone and limestone conglomerate 

at base of Campagrande Limestone as an ancient soil profile, formed in an arid or semiarid climate.

Broadhurst, W. L., Sundstrom, R. W., and Weaver, D. E., 1951, 

Public water supplies in western Texas: U.S. Geol. Survey 

Water-Supply Paper 1106,168 p.

Gives data on municipal water wells at Van Horn (p. 37).
10 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

DeFord, B. K., and others, 1951, Apache Mountains of transPecos Texas: West Texas Geol. Soc. 1951 Fall Field Trip 

Guidebook, Oct. 26-27,1951, 56 p.

Deals primarily with Apache Mountains east of Sierra 

Diablo region, but includes a note on pre-Permian rocks of 

the Beach and Baylor Mountains (p. 52-53).

Hood, J. "W., and Scalapino, B. A., 1951, Summary of the development of ground water for irrigation in the Lobo Flats 

area, Culberson and Jeff Davis Counties, Texas: Texas 

Board Water Engineers Bull. 5102, 25 p.

Discusses occurrence of ground water in Lobo Flats, a 

southern extension of the Salt Basin just south of the report area.

Flawn, P. T., 1952, The Hazel copper-silver mine, Culberson 

County, Texas: Texas Univ. Bur. Econ. Geology Bept. Inv. 

9, 23 p.

Beport on the Hazel mine preliminary to that given in 

publication of King and Flawn (1953).

Dunbar, C. O., 1953, A zone of Pseudoschwagerina low in the 

Leonard series in the Sierra Diablo, trans-Pecos Texas: Am. 

Jour. Sci., v. 251, p. 798-813.

Describes a new species of fusulinid from lower part of 

Bone Spring Limestone and discusses its occurrence, and 

that of other f usulinids, in the Victorio Peak section in the 

Sierra Diablo.

Gillerman, Elliot, 1953, Fluorspar deposits of the Eagle Mountains, trans-Pecos Texas: U.S. Geol. Survey Bull. 987, 98 p.

Beport on geology and fluorspar deposits of an area southwest of Sierra Diablo region, whose extreme north edge 

extends into present report area.

Haigh, B. B., and others, 1953, Sierra Diablo, Guadalupe, and 

Hueco areas of trans-Pecos Texas: West Texas Geol. Soc. 

1953 Fall Field Trip Guidebook, Nov. 6-7, 1953, 91 p.

Includes road log in Sierra Diablo region (p. 5-37), based 

partly on publications, but including original observations.

King, P. B., and Flawn, P. T., 1953, Geology and mineral deposits of Precambrian rocks of the Van Horn area, Texas: 

Texas Univ. Pub. 5301,215 p.

Comprehensive report on Precambrian rocks and associated formations of Van Horn area, part of which lies within 

present map area. Chapters by Flawn describe Precambrian 

rocks of Wylie and Carrizo Mountains (p. 41-44, 51-69) ; a 

chapter by King describes Precambrian rocks of Sierra 

Diablo foothills (p. 71-121). Also includes descriptions of 

copper, silver, talc, and other mineral deposits in Sierra 

Diablo foothills, Carrizo Mountains, and elsewhere (p. 

150-173).

Follett, C. B., 1954, Becords of water-level measurements in 

Culberson, Hudspeth, and Jeff Davis Counties, Texas: Texas 

Board Water Engineers Bull. 5415,31 p.

Includes data on wells in Lobo Flats and Wildhorse 

Valley districts, just south and east of report area.

Stehli, F. G., 1954, Lower Leonardian Brachiopoda of the Sierra 

Diablo: Am. Mus. Nat. History Bull., v. 105, p. 261-358.

Summarizes stratigraphy of Permian rocks in the Sierra 

Diablo, interprets their conditions of deposition, and treats 

in detail the brachiopods and their ecology in lower part of 

Bone Spring Limestone near Victorio Peak.

Cooper, G. A., and Stehli, F. G., 1955, New genera of Permian 

brachiopods from west Texas: Jour. Paleontology, v. 29, p. 

469-474.

Includes description of Spyridophoroa reticulata (King) 

from Bone Spring Limestone of the Sierra Diablo (p. 472- 

473).

King, P. B., 1955, Orogeny and epeirogeny through time, in 

Poldervaart, Arie, ed., The crust of the earth: Geol. Soc. 

America Spec. Paper 62, p. 723-740.

Mentions the deformational history of Precambrian time 

in the Van Horn region as an example of preservation of 

the record of orogeny (p. 723-726).

Flawn, P. T., 1956, Basement rocks of Texas and southeastern 

New Mexico: Texas Univ. Pub. 5605,261 p.

Includes discussion of Van Horn mobile belt, based mainly 

on outcrops in and near Sierra Diablo region, with speculations as to subsurface extent of the belt (p. 32-36).

Masson, P. B., 1956, Age of igneous rocks at Pump Station Hills, 

Hudspeth County, Texas: Am. Assoc. Petroleum Geologists 

Bull., v. 40, p. 501-518.

Discussion of petrography and structure of Precambrian 

rocks exposed northwest of Sierra Diablo region, with incidental mention of Precambrian rocks in southern Sierra 

Diablo and Carrizo Mountains.

Moody, J. D., and Hill, M. J., 1956, Wrench-fault tectonics: 

Geol. Soc. America Bull., v. 67, p. 1207-1246.

Interprets Hillside fault of southern part of Sierra Diablo region as having large left-lateral strike-slip displacement, and as being a major unit of the "Texas lineament" 

(p. 1223-1224).

Yochelson, E. L., 1956, Euomphalacea, Trochonematacea, Pseudophoracea, Anomphalacea, Craspedostomatacea, and Platyceratacea, pt. 1 of Permian Gastropoda of the southwestern 

United States: Am. Mus. Nat. History Bull., v. 110, p. 

179-276.

Description of gastropods from Permian rocks in many 

parts of Texas, New Mexico, and Arizona, including those 

from 38 collections from Sierra Diablo region, with an 

interpretation of the habitat of the groups considered. 

"Molluscan ledges" of Bone Spring Limestone in Sierra 

Diablo discussed (p. 189-190).

Albritton, C. C., and Smith, J. F., 1957, The Texas lineament: 

Internat. Geol. Gong., 20th, Mexico City 1956, sec. 6, pt. 2, 

p. 501-518.

Summarizes earlier published accounts of the lineament 

and new evidence for an against its validity. Proposes 

that the type locality of the lineament be along Eagle Flat, 

in the southern parts of the Sierra Diablo and Sierra Blanca 

regions, west Texas.

Hay-Boe, Hugh, 1957, Geology of Wylie Mountains and vicinity, 

Culberson and Jeff Davis Counties, Texas: Texas Univ. 

Bur. Econ. Geology Geol. Quad. Map 21.

Geologic map and text dealing with an area mainly east 

and south of Sierra Diablo region, but extending into 

southeast corner of present map area.

Ramlrez, J. C., and Avecedo, C. F., 1957, Notas sobre le geologla 

de Chihuahua: Assoc. Mexicana Geologos Petroleros Bol., 

v. 9, p. 583-770.
GEOGRAPHY 11

An extensive account of the geology of the State of Chihuahua, adjoining Trans-Pecos Texas on the southwest, 

with incidental references to formations and structures in 

the Sierra Diablo region (p. 605-607, 613-614, 620, 630, etc.).

Yochelson, E. L., and Bridge, Josiah, 1957, The Lower Ordovician gastropod Ceratopea: U.S. Geol. Survey Prof. Paper 

294, p. 281-304.

Analysis of a gastropod genus which is abundant in some 

Lower Ordovician sequences, including a summary of its 

occurrence in the El Paso Limestone of the Sierra Diablo 

region and other areas (fig. 103), and a description of 

Ceratopea unguis Yochelson and Bridge, based on specimens from Beach Mountain.

Batten, R. L., 1958, Pleurotomariacea, Portlockiellidae, Pymatopleuridae, and Eotomatiidae, pt. 2 of Permian Gastropoda 

of the southwestern United States: Am. Mus. Nat. History 

Bull., v. 114, p. 159-246.

Includes description of gastropod specimens from Sierra 

Diablo region.

DeFord, R. K., and Brand, J. P., 1958, Cretaceous platform and 

geosyncline, Culberson and Hudspeth Counties, trans-Pecos 

Texas: Soc. Econ. Paleontologists and Mineralogists, Permian Basin Sec., 1958 Field Trip Guidebook, 90 p.

Description of a traverse across the Cretaceous rocks 

just east and south of the report area. Includes two charts 

of plotted stratigraphic sections of Cretaceous rocks in 

Sierra Blanca and Sierra Diablo regions (flg. 11, p. 23; 

fig. 12, p. 25).

Fillman, Louise, chm., 1958, Lexicon of pre-Pennsylvanian 

stratigraphic names of west Texas and southeastern New 

Mexico: Midland, Tex., West Texas Geol. Soc., 153 p.

Short discussions of all pre-Permian formations of west 

Texas-southeastern New Mexico region, including those in 

the Sierra Diablo region. Incidental mention is made of 

occurrences in the Sierra Diablo and other outcrop areas, 

but main emphasis is on subsurface character and distribution in West Texas basin.

Flawn, P. T., 1958, Texas miners boost talc output: Eng. and 

Mining Jour., v. 159, p. 104-105; repr., Texas Bur. Econ. 

Geology Rept. Inv. 35.

Notes on geologic occurrence, mining methods, and production of talc from Precambrian rocks in southern foothills of Sierra Diablo.

Pratt, W. E., 1958, Large-scale polygonal jointing: Am. Assoc. 

Petroleum Geol. Bull., v. 42, p. 2249-2251.

Unconsolidated deposits of the Salt Basin east of Baylor 

Mountains are fractured into polygons about 2,000 ft across, 

as a result of undetermined processes.

Howe, H. J., 1959, Montoya group stratigraphy (Ordovician) 

of trans-Pecos Texas: Am. Assoc. Petroleum Geologists 

Bull., v. 43, p. 2285-2332.

A regional survey and interpretation of Montoya Limestone, including observations on the formation in the Baylor Mountains and a detailed stratigraphic section there 

(flg. 29, p. 2328).

Twiss, P. C., 1959, Geology of Van Horn Mountains, Texas: 

Texas Univ. Bur. Econ. Geology Geol. Quad. Map 23.

Geologic map and descriptive text, covering the area just 

south of the present report area, including data on the 

Carrizo Moutain Formation and Hueco Limestone.

Warner, L. A., Holser, W. T., Wilmarth, V. R., and Cameron, 

E. N., 1959, Occurrence of nonpegmatite beryllium in the 

United States: U.S. Geol. Survey Prof. Paper 318, 198 p. 

Includes description by Holser of Cave Peak intrusive 

complex (Mine Canyon stock of present report) (p. HOWS), notes on Sierra Prieta intrusive (p. 133), and observations on related igneous rocks elsewhere in the TransPecos Region (p. 130-135).

Finks, R. M., 1960, Late Paleozoic sponge faunas of the Texas 

region; the siliceous sponges: Am. Mus. Nat. History Bull., 

v. 120, p. 3-160.

Includes description of specimens of Permian sponges 

from Sierra Diablo region and a discussion of faunal facies 

of the sponges, including those of Leonard age in the Sierra 

Diablo (p. 28-33).

Yochelson, E. L., 1960, Bellerophontacea and Patellacea, pt. 3 of 

Permian Gastropoda of the southwestern United States: 

Am. Mus. Nat. History Bull., v. 119, p. 211-293.

Includes description of gastropod specimens from Sierra 

Diablo region. Bellerophon coquina in lower part of Hueco 

Limestone discussed briefly (p. 216).

Martinez, J. D., Statham, E. H., and Howell, L. G., 1960, A 

review of paleomagnetic studies of some Texas rocks, in 

Aspects of the geology of Texas, a symposium: Texas 

Univ. Pub. 6017, p. 15-47.

Includes paleomagnetic data on red sandstone of Hazel 

Formation (p. 19).

Kepple, H. A., and others, 1962, Leonardian facies of the Sierra 

Diablo region, west Texas: Guidebook 1962 field trip: 

Permian Basin Section, Soc. Econ. Paleontologists and 

Mineralogists, Pub. 62-7,148 p.

Includes road log in Sierra Diablo region, and articles 

on geology by five authors.

Underwood, J. R., Jr., 1962, Geologic map of Eagle Mountains 

and vicinity, Hudspeth County, Texas: Texas Bur. Econ. 

Geol. Quad. Map 24, scale 1:48,000.

Geologic map includes southwestern part of present 

report area and adjacent regions to south and west.

GEOGRAPHY

The Sierra Diablo region lies in the Trans-Pecos 

province of Texas, or the west-projecting part of the 

State between the Pecos River and the Rio Grande 

(fig. 1). Topography, climate, and vegetation of this 

dry mountainous province are more like those of New 

Mexico, Arizona, and Chihuahua than those of the rest 

of Texas. The northern part of the province, in which 

the Sierra Diablo region is situated, has the characteristic topography of the Basin and Range province of the 

States to the west and northwest, with broad, plateaulike mountain masses that rise in steep escarpments 

above intermontane plains or basins. The report area 

is dominated by one of the mountain masses, the Sierra 

Diablo, which rises steeply on the east above one of the
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1. Map of parts of western Texas and southern New Mexico, showing area covered by report on Sierra Diablo region, A., and areas covered b

adjacent areas: B, Boyd, 1958, El Paso Gap quadrangle; 0, Hayes and Koogle, 1958, Carlsbad Caverns West quadrangle; D, Hayes, 1957, Carlsb

King, 1947, southern Guadalupe Mountains; F, Albritton and Smith, 1965, Sierra Blanca area; G} Gillerman, 1953, Eagle Mountains fluorspar 

Horn Mountains; and I, Hay-Roe, 1957, Wylie Mountains.
GEOGRAPHY 13

intermontane plains, the Salt Basin, and slopes gently 

on the west into the less diversified expanse of the 

Diablo Plateau.1

The climate of the report area is arid to semiarid. 

A 20-year record at Van Horn (1939-58) indicates an 

annual rainfall that fluctuated between less than 5 inches 

and more than 27 inches, averaging 9.39 inches. Rainfall increases with altitude, as shown by a greater density of vegetation in the Sierra Diablo and other mountains than in the lower country near Van Horn. An 

arid or semiarid climate has existed in the region since 

the last glacial period and at least intermittently into 

far earlier times. It has thus conditioned not only the 

modern erosional regime and vegetation, but also the 

soils and landforms that require a longer period for 

their creation (Carter and others, 1928, p. 7-11, 25-48).

MOUNTAIN AREAS

The Sierra Diablo, or dominant mountain mass of the 

region, is about 25 miles long, and has extensive summit areas more than 6,000 feet in altitude; its highest 

peak (at North Diablo triangulation station) attains 

6,638 feet (pi. 9). West of the crest the summit areas 

descend 2,000 feet in about 10 miles, and the range 

merges with the lower, less diversified Diablo Plateau. 

The summit areas, formed of Permian limestone, are 

conspicuously even crested. In most places the even 

crests are nearly parallel to the strata beneath, but they 

truncate the abruptly flexed strata near the middle of 

the range and the limestone units that form the crests 

to the north and south belong to different formations. 

The even-crested summit areas were shaped by a peneplain on which Cretaceous rocks were once deposited, 

but from which these have now been stripped. Their 

westward slope carries the peneplain under Cretaceous 

rocks, still preserved in buttes and mesas in the Diablo 

Plateau in the western part of the report area. Rising 

abruptly nearly a thousand feet above the plateau northwest of the Sierra Diablo is the dark jagged, rocky 

Sierra Prieta, formed by a body of igneous rock that 

was intruded into the Permian and Cretaceous strata.

To the east, north, and south the Sierra Diablo ends 

abruptly in steep escarpments that face toward the intermontane plains of the Salt Basin and Eagle Flat. 

Its northeastern part rises directly 3,000 feet above the 

floor of the Salt Basin, without intervening foothills, but 

the lower 500-1,000 feet of the slope is alluvial (sections 

F-F' and G-G'', pi. 16). Farther south the lower Baylor Mountains and Beach Mountain stand between the 

Sierra Diablo and the Salt Basin, and a belt of discontinuous foothills stands between it and Eagle Flat.

1 In some geologic publications the Sierra Diablo has Itself been 

referred to as the Diablo Plateau, but this usage is erroneous and misleading. For the relative extent of the two features, see figure 1.

The escarpments of the Sierra Diablo are outlined by 

faults that have downthrown the rocks on their topographically lower sides on the east by a fault of generaly northerly trend but with bight-and-cusp pattern, 

on the north and south by faults that trend west-northwest. The Bay lor Mountains are likewise a fault block, 

implanted in the southern bight of the fault on the east. 

The summits of the Bay lor Mountains are even crested 

like those of the Sierra Diablo and, like them, were 

probably derived from the pre-Cretaceous peneplain, 

but they stand about a thousand feet lower (sections HH' and /-/', pi. 16). The Baylor Mountain block 

forms an intermediate step between the heights of the 

Sierra Diablo and the depths of the Salt Basin.

The eastern escarpments of the Sierra Diablo and 

Baylor Mountains were shaped directly by faulting, although they were for the most part modified by subsequent erosion. The Baylor Mountains escarpment is 

now much indented at the mouths of valleys issuing 

from the mountains. The upper part of the Sierra 

Diablo escarpment has receded a mile or so from the 

trace of the fault along its base; it is also deeply 

breached by Victorio and Apache Canyons, which extend far headward into the range. These canyons probably originated from major valleys that drained westward before they were diverted to their present courses. 

However, uplift of the Sierra Diablo was so prolonged 

that the lower part of its escarpment in the segment 

north of the Baylor Mountains is newer, and is consequently less eroded. Here, the escarpment ends on an 

even baseline, bordered on the mountainward side by a 

steep rock bench and on the basinward side by a high 

extensive alluvial slope, which is itself broken by a low 

fault scarp at its north end.

The eastern escarpment of the Sierra Diablo is 

divided into three topographically contrasting segments as a result of intersection of the bordering 

fault by two west-northwestward-trending monoclinal 

flexures, each of which has depressed the strata on the 

north so far as to preserve a different sequence of 

formations. In the southeastern Sierra Diablo, south 

of the southern, or Victorio, flexure, the escarpment 

consists of smoothly rounded lower slopes, cut on red 

sandstone of the Precambrian Hazel Formation, and 

an upper sheer cliff of Hueco Limestone, the lowest 

unit of the Permian sequence (left end of upper view, 

pi. 10). In the northeastern Sierra Diablo, north of 

the Victorio flexure, the red sandstone is beneath the 

surface, and the escarpment is formed entirely of 

Permian limestones. Here it is two-storied, with a 

bench of Hueco Limestone below and cliffs of light-gray 

Victorio Peak Limestone at the top, separated by 

smoothly rounded slopes cut on the intervening less
14 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

resistant thin-bedded or shaly Bone Spring Limestone 

(left end of lower view, pi. 10). On the northern, or 

Babb, flexure, at the north end of the Sierra Diablo, 

the Hueco and Bone Spring Limestones in their turn 

pass beneath the surface (upper view, pi. 12). In the 

hills which are a continuation of the Sierra Diablo on 

the north, the top of the Victorio Peak Limestone forms 

a bench at the edge of the Salt Basin which is surmounted by widely spaced mesas, capped by a resistant layer in the Guadalupe Series, the Goat Seep 

Limestone.

By contrast with the escarpment on the east side of 

the Sierra Diablo, that on the south side was produced 

merely by erosion of a terrain that was faulted at a 

remote period. The escarpment is the southernmost 

of several, each formed along faults downthrown to 

the south, by which both the strata and the topographic 

surface step down from the heights of the northern 

part of the range (section P-P'', pi. 16). The escarpments were produced, at least in part, by stripping of 

weak Cretaceous beds off the strong Permian limestone 

beds; Cretaceous beds are still preserved on the downthrown sides of some of the faults toward the west. 

Toward the east the escarpments have been further 

modified by undercutting of weak red sandstone of the 

Precambrian Hazel Formation, so that the capping 

Permian limestone is greatly frayed, and has receded 

irregularly from the original fault traces.

Relief in the southern foothills, between the Sierra 

Diablo and Eagle Flat, is likewise a product of unequal 

erosion of rocks of diverse structures and ages. The 

Streeruwitz, Bean, and Millican Hills to the west are 

low and are separated by broad alluvium-covered rockcut plains, but the Carrizo Mountains and Beach 

Mountain to the east are higher and rise steeply above 

the Salt Basin, probably with an intervening fault. 

Beach Mountain, a rugged mass with an area of about 

15 square miles, projects a thousand feet above the 

lower hills to the west, and is capped by a remnant of 

strong Ordovician limestone (pi. 2). The underlying 

red massive Van Horn Sandstone, exposed west and 

southwest of Beach Mountain in the Red Valley and 

along Hackberry Creek, has been carved into tables, 

battlements, and towers to produce some of the most 

picturesque scenery in the region. Differential erosion 

is further demonstrated along the Hillside fault in the 

Carrizo Mountains to the south. The downthrown 

northern side of the fault is bordered by a steep obsequent faultline scarp of Permian limestone and Cretaceous sandstone, whereas the metamorphic rocks of 

the Precambrian Carrizo Mountain Formation on the 

southern upthrown side have been cut into a valley that

is utilized by the line of the Texas and Pacific Railway 

in its course through the mountains (section T-T', 

pi. 16).

LOWLAND AREAS

Largely because of the long-continued aridity, the 

region has an interior drainage, leading to the Salt 

Basin on the east and the smaller basin of Eagle Flat 

on the southwest, which have no outlets to the sea. 

South of the region, however, this area of interior 

drainage is being attacked by streams that are cutting 

headward from the through-flowing Rio Grande.

The Salt Basin, or dominant lowland of the report 

area, lies east of the mountains and extends far northward, past the Texas-New Mexico State line (fig. 1). 

The Salt Basin is 90 miles long, 5 to 15 miles wide, 

and trends north-northwestward parallel to the grain 

of the mountains and plateaus which border it (King, 

P.B., 1948, pi. 23). Its lowest part, east of the northeastern Sierra Diablo, stands at an altitude a little 

below 3,600 feet. It is a closed depression and the 

focus of a large region of interior drainage. At its 

north and south ends it receives drainage from the high 

relatively well-watered Sacramento and Davis Mountains ; on the west it receives drainage from the Sierra 

Diablo and Diablo Plateau. Along the Guadalupe and 

Delaware Mountains on the east the drainage area is 

smaller, the crests of these mountains being so close 

to the basin that most of their water courses lead eastward to the Pecos River.

Eagle Flat, a less extensive lowland, lies southwest of 

the Sierra Diablo, trending west-northwest across the 

regional grain for about 25 miles. It receives drainage 

from the southern Sierra Diablo and Diablo Plateau, 

and to a lesser extent from the mountains on the south, 

most of whose water courses lead southwestward to the 

Rio Grande. The eastern part of Eagle Flat drains by a 

roundabout course south of the Carrizo Mountains into 

the Salt Basin; but the western part is an independent 

depression whose lowest point is at Grayton Lake, which 

has an altitude of a little more than 4,000 feet.

Both the Salt Basin and Eagle Flat are tectonic depressions, produced mainly by downfaulting of their 

floors relative to the mountains that surround them. 

They have been deeply filled by unconsolidated deposits 

of Quaternary and possibly of late Tertiary age washed 

in from higher lands around them. The unconsolidated 

deposits have been extensively drilled for water in the 

Salt Basin, but in few places deeply enough to determine 

the configuration of their base. A well in the basin 

north of the Sierra Diablo region is reported to have 

been sunk 1,620 feet without reaching the base of the
GEOGRAPHY 15

deposits. Wells at Van Horn are shallower, as are 

those in the irrigation districts of Wildhorse Valley and 

Lobo, to the east and south; but a few of them have penetrated bedrock. Less is known of the depths of the unconsolidated deposits in Eagle Flat, but the Southern 

Pacific railroad well at Hot Wells was drilled into them 

to a depth of more than 1,000 feet (Baker, 1927, p. 37- 

40; Broadhurst and others, 1951, p. 57; Hood and Scalapino, 1951, p. 4-5; Follett, 1954, p. 6-15).

The surface of the southern part of the Salt Basin, as 

far as the north end of the Baylor Mountains, consists 

of alluvial slopes extending from the bordering mountains to the axis of the depression along which Wildhorse Creek drains northward. North of the Baylor 

Mountains the alluvial slopes on each side do not meet, 

and between them is a nearly level floor more than 5 

miles wide, formed probably by deposition on the bottoms of lakes during late Pleistocene time or earlier. 

On the alluvial slopes streams are mostly actively transporting material away from the mountains, although 

near their lower ends on the east side the sandy constituents are now being shifted even more vigorously by the 

wind. Streams are thus prograding material toward 

the basin floor, yet they are not depositing material on 

the floor itself. The floor appears to be virtually stable, 

except for minor leveling or deleveling by the wind. As 

the Salt Basin has interior drainage, theoretically its 

streams should be adjusted to a slowly rising base level; 

but the stability of the floor indicates that this condition 

is not now attained.

The floor of the Salt Basin is diversified by alkali 

flats (locally called salt lakes) and by hills of gypsiferous clay. One set of alkali flats is east of the northern 

part of the Sierra Diablo, another just north of the end 

of the range. They may be final remnants of more extensive lakes of an earlier period, yet today they contain 

water only at long intervals. They are maintained 

principally by the wind, which sweeps material from 

their surfaces down to ground-water level, an effective 

limit to downward erosion. The peculiarly fretted outlines of the alkali flats north of the Sierra Diablo were 

probably shaped by this wind work. The hills of gypsiferous clay were also formed by the wind. Over extensive areas to the north they have no clearly discernible 

pattern, but on the east side of the floor opposite the 

northern part of the Sierra Diablo they form a remarkable set of closely spaced parallel ridges, trending northnorthwest, which curve westward at the south end of the 

floor, just north of the Baylor Mountains. These, and 

others like them farther north, probably mark the 

shores of the shallow lakes of Pleistocene time, along 

which the clays were raised into low dunes. A later

modification by the wind of the clay hills is indicated 

on air photographs by superposition on the gross features of a more delicate grain trending east or eastsoutheast. Between the alkali flats and hills of gypsiferous clay are tracts of level meadowland, underlain 

by brown clay which supports more grass cover than 

that on the gypsif erous clay hills.

The alluvial slopes, formed by coalescence of the fans 

built by streams which issue from the mountains, are 

continuous along the entire western border of the Salt 

Basin at the bases of the Sierra Diablo and other 

ranges, except at the northeast corner of the Baylor 

Mountains where the rock hills have been partly submerged by more distantly derived detritus. The radii 

and gradients of the fans, and the texture of their components, are related to the areas of drainage in the 

mountains of the streams which supply them and to the 

recency of faulting along the mountain bases. Large 

fans of low gradient, composed of relatively fine material, have been built by Hackberry and Sulphur 

Creeks near Van Horn and by Eed Wash, Victorio 

Canyon, and Apache Canyon farther north; lesser fans 

with steeper gradients, composed of coarser material, 

have been built by smaller streams in the intervening 

segments. The steepest coarsest fans are those along 

the segment of the Sierra Diablo north of the Baylor 

Mountains where relatively recent faulting is most 

likely. One of the fans in this segment, 1 mile north 

of Victorio Canyon, has a gradient of 1,000 feet per 

mile, a radius of six-tenths of a mile, and was built 

below a gulch on the escarpment with a drainage area 

of less than half a square mile. On some of the steeper 

fans the courses of recent drainage are marked by trains 

of fresh boulders and gravel, but drainage on fans of 

somewhat larger dimensions is generally incised in the 

fan surface, in places as much as 40 feet, the depth decreasing downslope. Most of the drainage on the 

largest fans is fainter and less incised, but Sulphur 

Creek forms a wide braided gravel-covered channel 

nearly to the lower edge of its fan.

Most of the streams draining eastward from the 

mountains into the Salt Basin have cut downward into 

the rocks of the mountains and have built up alluvial 

fans in front; they have done little leveling of the bedrock by sideward cutting. Chief exceptions are Hackberry Creek, Sulphur Creek, and Red Wash, which 

drain the edges of Beach Mountain and the Baylor 

Mountains and which have cut broad areas of lowland 

in rocks that are mainly not calcareous. Recently 

leveled areas are partly masked by alluvial deposits; 

areas leveled earlier are indicated by terraces a hunded 

feet or more above modern drainage, which are in part
16 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

capped by older alluvial deposits. Cause of the dissection of the earlier terraces is undetermined, but it may 

be related to continued downfaulting of the Salt Basin 

relative to the adjacent mountain areas.

In Eagle Flat, southwest of the Sierra Diablo, erosional and depositional processes appear to be less active 

than in the Salt Basin, partly because of its greater 

tectonic stability in the recent past, partly because of 

the circuitous drainage connection between it and the 

main basin. Alluvial slopes thus extend to the axis of 

Eagle Flat, and extensive rock-cut surfaces have been 

formed on its north and south sides. Within the flat 

itself the fine debris has been raised by the wind into 

low sand dunes in extensive areas, as shown on the 

topographic base map (pis. 1, 9).

On the north, in the southern foothills of the Sierra 

Diablo, these rock-cut surfaces, now largely mantled 

by alluvium, extend between the Streeruwitz, Bean, and 

Millican Hills which were carved from the more resistant conglomerate, limestone, and volcanic units of the 

Hazel and Allarnoore Formations of the Precambrian 

sequence. In the hills a time of earlier planation is 

suggested by accordant levels on their summits.

Toward the east, Sulphur and Hackberry Creeks, 

which drain into the Salt Basin, are dissecting the eastward extensions of the rock-cut surfaces on which the 

streams draining into Eagle Flat are now flowing. The 

bedrock of red sandstone of the Hazel Formation has 

been scored into a network of valleys and ravines, on 

whose crests are gravel deposits that are remnants of a 

surface that once sloped continuously toward Eagle 

Flat. Westward, the alluvium of the valley bottoms 

in the Hackberry and Sulphur Creek drainage areas 

rises and merges with the gravel caps, so that the two 

sets of deposits cannot be differentiated in the drainage 

area of Eagle Flat.

HUMAN GEOGRAPHY AND HISTORY

The valley of the Kio Grande near El Paso, west of 

the Sierra Diablo region, was long a focus of settlement, 

first by agricultural Indians, later by the Spaniards 

and Mexicans. Missions were founded as early as the 

17th century by Franciscan monks, and by the time of 

establishment of United States sovereignty in 1847 there 

were several towns and farming communities. However, the interior of the Trans-Pecos province, including the Sierra Diablo region, remained empty country, 

which was the haunt of roving and marauding bands of 

Indians.

Under the American regime several stage and caravan routes were laid out across the interior of the TransPecos province to connect the settlements on the Rio 

Grande with those farther east. A trail from San 

Antonio to El Paso, which was subsidized as a mail 

route in 1850, passed south of the Sierra Diablo, through 

Bass Canyon and Eagle Spring. The Butterfield Trail, 

which was subsidized as a mail route in 1857, passed 

north of the Sierra Diablo, through Guadalupe Pass 

and Crow Flat. Although American authority over 

the interior of the Trans-Pecos province was virtually 

relinquished during the Civil War period, a road was 

laid out in 1863 by public subscription from the Rio 

Grande settlements to the salt deposits of the Salt Basin, 

which passed near Sierra Prieta in the northwesterni 

part of the report area.

The last Indian battle in Texas was fought in January 1881, when Capt. George W. Baylor, of the Texas 

Rangers, defeated an Apache band under the leadership 

of their chief Victorio, in the heights of the Sierra 

Diablo near the peak which now bears his name. With 

the construction of the Southern Pacific and Texas and 

Pacific railroads a few years later, much of the isolation 

of the region ended, and it was available for occupancy.

The Sierra Diablo region was originally included in 

El Paso County, which at first covered most of the 

northern Trans-Pecos Texas. In 1911 Culberson 

County was established with Van Horn as the county 

seat, and in 1917, Hudspeth County, with Sierra Blanca 

as the county seat. The only town in the report area is 

Van Horn, with about a thousand people, first located 

as a station on the Texas and Pacific Railway because 

of the availability of excellent well water from the 

deposits of the Salt Basin. Its growth has been furthered because of its position on the transcontinental 

highway, at the junction of U.S. Highways 80 and 90. 

Minor settlements are Allamoore on the Texas and 

Pacific Railway and U.S. Highway 80 west of Van 

Horn, and Hot Wells on the Southern Pacific railroad 

to the southwest.

Because of the arid climate and forbidding terrain, 

the Sierra Diablo region has remained sparsely peopled 

until today a region of extensive landholdings used 

for pasturage of cattle, sheep, and goats. During the 

last quarter of a century, modern paved highways have 

been built across it U.S. Highways 80 and 90 on the 

south and U.S. Highway 62 on the north, which have 

brought large numbers of automobile travelers and have 

encouraged the development of businesses catering to 

them. Also, after the Second World War, extensive 

reservoirs of ground water were discovered in the northern and southern parts of the Salt Basin, and these 

have been developed by pumping for irrigation. Agri-
STRATIGRAPHY 17

cultural areas of 10 square miles or more have thus 

come into existence at Dell City, Wildhorse Valley, and 

Lobo, to the north, east, and south of the Sierra Diablo 

region (Scalapino, 1950; Hood and Scalapino, 1951; 

L. A. Wood, written commun., 1959).

Existence of copper and silver in mineralized veins 

in the Precambrian rocks of the southern part of the 

Sierra Diablo region was discovered by some of the 

earliest American visitors. The vein at the Hazel mine 

is reported to have been prospected as early as 1856; 

practically all the veins which have been mined were 

mentioned in the reports of Streeruwitz of 1890 and 

1891 (Streeruwitz, 1891, 1892). The district has produced about 2 million pounds of copper and 4 million 

ounces of silver, but operations have been spasmodic 

and the possibilities of the district have seemingly not 

been great enough to attract large-scale capital. Long 

after discovery of the metallic deposits in 1952, talc was 

found in beds of Precambrian phyllite of the same 

area; the talc is now being mined at various places 

by six companies, who by 1957 had produced about 

120,000 tons.

STRATIGRAPHY

Most of the bedrock that crops out in the Sierra 

Diablo region consists of consolidated sedimentary rocks 

of Precambrian, Paleozoic, and Mesozoic ages (pi. 1). 

Intrusive and extrusive igneous rocks of Precambrian 

and Cenozoic ages occupy smaller areas. Within the 

mountain and foothill areas the bedrock also underlies 

the alluvial deposits at shallow depth, but in the lowland areas of the Salt Basin and Eagle Flat it is probably buried to great depth beneath unconsolidated sedimentary rocks of Cenozoic age.

Precambrian rocks crop out in the foothills south 

and southeast of the Sierra Diablo; they are a varied 

sequence of sedimentary rocks many thousands of feet 

thick, classed as the Carrizo Mountain, Allamoore, and 

Hazel Formations. The Carrizo Mountain Formation 

is variably metamorphosed and is intruded by igneous 

rocks; the Allamoore Formation contains interbedded 

volcanic rocks. The Precambrian formations are overlain by the Van Horn Sandstone, as much as 700 feet 

thick, which is classed as of Precambrian (?) age.

Paleozoic rocks form the greater part of the mass of 

the Sierra Diablo, as well as some of the adjacent smaller 

mountains, and include all the systems except the Cambrian. The Paleozoic rocks are dominantly limestone 

or dolomite, but there are minor beds or units of shale, 

sandstone, conglomerate, and chert. The Ordovician, 

Silurian, and Devonian rocks are about 2,000 feet thick.

Mississippian and Pennsylvanian rocks occur only in 

fragmentary exposures, and their total thickness probably does not exceed 1,000 feet. By contrast, the Permian rocks are extensive and attain a thickness of more 

than 3,000 feet, although only the lower part of the 

system is preserved.

The Mesozoic is represented by the Cretaceous System only. A sequence nearly 5,000 feet thick occurs in 

the southwestern part of the report area and extends 

from the lower part of the Lower Cretaceous into the 

lower part of the Upper Cretaceous. In the Sierra 

Diablo itself, only the Lower Cretaceous is preserved; 

it consists mostly of sandstone with subordinate limestone and marl with a thickness of less than a thousand 

feet.

The Tertiary is represented at the surface only by 

widely separated intrusive igneous rocks and by small 

remnants of extrusive igneous rocks. Poorly consolidated sedimentary rocks of Tertiary age may underlie 

the unconsolidated sedimentary rocks of Quaternary 

age in the lowland areas of the Salt Basin and Eagle 

Flat.

Nearly all the sedimentary rocks younger than the 

Precambrian and Precambrian (?) contain marine invertebrate fossils. They are especially abundant, 

varied, and well preserved in the Permian rocks, from 

which large collections were made during the present 

investigation.

The stratified rocks of the Sierra Diablo region were 

laid down during progressively changing geographic 

conditions, which are partly expressed by contrasts between the successive deposits and faunas and partly by 

the many unconformities in the sequence. Some of the 

unconformities, such as those which occur between most 

of the pre-Permian Paleozoic formations, express 

merely gaps in the record, and are not accompanied 

by appreciable tilting or erosion of the underlying beds. 

Several of the other unconformities indicate deep or 

prolonged erosion, deformation of the underlying beds, 

and even marked orogeny. The Van Horn Sandstone 

thus lies on the eroded edges of the strongly deformed 

and partly metamorphosed earlier Precambrian rocks. 

A lesser angular unconformity separates the Van Horn 

from the Ordovician above. The pre-Permian Paleozoic 

rocks were broadly folded, deeply eroded, and in places 

removed entirely before the Permian was laid down 

over them. Mild deformation occurred again between 

Permian and Cretaceous time, and the Cretaceous was 

deposited over a peneplain which bevels all the earlier 

rocks.

Table 1 summarizes the formations exposed in the 

Sierra Diablo region.
18 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS 

TABLE 1. Rock formations of Sierra Diablo region, Texas

System

Quaternary

Tertiary

Series Formation Remarks

In mountain areas, alluvium, older gravel deposits, and landslide 

deposits; in Salt Basin, bolson deposits, fanglomerate, and 

drifted sand.

Basalt flows and plugs

Intrusive igneous rocks

Approximate thickness (feet)

Unconformity

Cretaceous

.ft MS& 35 t>U o

Lower Cretaceous

«* < 

3 

O

Comanche

Eagle Ford Formation

Washita Group

Kiamichi Formation

Finlay Limestone

Cox Sandstone

Campagrande Limestone

Bluff Mesa Formation

Yucca Formation

Preserved only in southwestern part 

of report area.

Replaced northward by Cox sandstone.

Lies on pre- Cretaceous rocks, except 

in southwestern part of report 

area.

In southwestern part of report area 

only; partly equivalent to Campagrande limestone.

In southwestern part of report area 

only

1,500

350-1, 000

65

60-350

500-1, 000

25-200

1, 000-1, 300

350-1, 500

Major unconformity

Permian

Guadalupe

Goat Seep Limestone

Sandstone tongue of 

Cherry Canyon Formation

Brushy Canyon Formation

Lies on Cutoff shale in Sierra Diablo

In northeastern part of report area 

only

>200

150-200

Unconformity

Leonard

Cutoff Shale

Victor! o Peak Limestone

Bone Spring Limestone

Intergrades with Bone Spring Limestone

Wedges out southwestward by intergradation and overlap

275

900-1, 500

900-1, 300

Unconformity

Wolf camp Hueco Limestone Varies in thickness by overlap at 

base and by pre-Leonard erosion 

at top

300-1, 500
PRECAMBRIAN AND PRECAMBRIAN (?) ROCKS 

TABLE 1. Rock formations of Sierra Diablo region, Texas Continued

19

System Series Formation Remarks

Approximate thickness (feet)

Major unconformity

Carbon- iferous Pennsylvanian

Mississippian

Devonian

Silurian

Ordovician

Upper Devonian

Middle Silurian

Upper Ordovician

Middle (?) 

Ordovician

Lower Ordovician

Beds of Pennsylvanian 

age

Barnett Shale

Beds of Devonian age

Fusselman Dolomite

Montoya Dolomite

Beds of Middle (?) Ordovician age

El Paso Limestone

Bliss Sandstone

Disconnected exposures only

Disconnected exposures only

Undetermined

>135

125

300-450

230-450

60-80

1150

100-160

Unconformity

Precambrian(?) Van Horn Sandstone As much as 

700

Major unconformity

Precambrian

Hazel Formation

Allamoore Formation

Sequence broken

Metarhyolite and greenstone

Carrizo Mountain Formation

Intrusive into Carrizo Mountain 

Formation

5, 000?

2, 500?

As much as 

19, 000

Base concealed

PRECAMBRIAN AND PRECAMBRIAN(?) ROCKS

Rocks older than the Ordovician are extensively exposed in the southern part of the Sierra Diablo region 

and for some miles south of it (pi. 1). Three formations the Carrizo Mountain, Allamoore, and Hazel 

Formations are classed as of Precambrian age; a 

fourth, the Van Horn Sandstone, is classed as of Precambrian (?) age. History of the terminology of these 

units is indicated in the table below. The Precambrian 

and Precambrian (?) rocks of the Sierra Diablo region 

and adjoining areas were described in detail in an 

earlier publication (King, P. B., and Flawn, P. T., 

1953), of which the following account is a summary.

The largest area of exposure of the Precambrian and 

Precambrian (?) rocks is in the foothills of the Sierra 

Diablo, extending northward along the east side nearly

to Victorio Peak and westward along the south side 

beyond Eagle Flat section house. Near the Texas and 

Pacific Railway this area is separated by a downf aulted 

block of Paleozoic and Cretaceous rocks from another 

area of exposure in the Carrizo Mountains. South of 

the Carrizo Mountains and beyond the Sierra Diablo 

region, Precambrian rocks emerge in smaller areas in 

other mountain uplifts on the northeast side of the 

Eagle Mountains, on the west side of the Wylie Mountains, and in two areas in the Van Horn Mountains. 

(See fig. 8.)

CARRIZO MOUNTAIN FORMATION

The Carrizo Mountain Formation, probably the 

oldest Precambrian unit of the Sierra Diablo region, is 

named for exposures in the Carrizo Mountains, south 

of the Texas and Pacific Railway at the south edge of
20 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS 

Development of stratigraphic nomenclature of Precambrian rocks of Sierra Diablo region

Streeruwitz ,1891

Carboniferous

Diabolo Sandstone 

(Devonian?)

(not classified)

Carrizo Schist

Dumble, 1902

Silurian

Potsdam 

Sandstone 

(Cambrian)

Hazel Sandstone

Texan Marble 

(placed above 

Hazel Sandstone)

(not discussed)

Richardson, 1914

Ordovician

Upper 

Cambrian 

(?)

Algonkian

El Paso limestone

Van Horn

Sandstone

Millican 

Formation

Carrizo 

Formation

King, P. B., 1940

Ordovician

Cambrian 

or Precambrian

Precambrian

El Paso Limestone

Bliss Sandstone

Van Horn 

Sandstone

Hazel Sandstone

Allamoore 

Limestone

Carrizo 

Mountain 

Schist

King, P. B., and Flawn, P. T., 

1953

Ordovician

Precambrian(?)

Precambrian

El Paso Limestone

Bliss Sandstone

Van Horn 

Sandstone

Hazel Formation

Allamoore 

Formation

Carrizo 

Mountain 

Group

This report

Ordovician

Precambrian(?)

Precambrian

El Paso Limestone

Bliss Sandstone

Van Horn 

Sandstone

Hazel formation

Allamoore 

Formation

Intrusives in 

Carrizo 

Mountain 

Formation

Carrizo 

Mountain 

Formation

the map area, where it forms the surface in about 25 

square miles (pi. 1). It also crops out at the west base 

of the Wylie Mountains in the southeast corner of the 

map area (Flawn, in King P. B., and Flawn, P. T., 

1953, p. 41-44; Hay-Roe, 1957), as well as in the Eagle 

and Van Horn Mountains farther south beyond the 

map area.

The Carrizo Mountain Formation is a thick body of 

variously metamorphosed sedimentary rocks, which 

have been intruded by large volumes of igneous rocks; 

the latter are separately described under the succeeding heading. On the geologic map (pi. 1) the only 

differentiation made in the sedimentary rock is between arkose and quartzite on the one hand, and various other rocks, mainly schist, slate, and limestone, on 

the other. However, in most areas the formation includes distinctive, varied units that could ranks as formations, were it not for their small areas of exposure. 

In each of the areas these units lie in a stratigraphic 

sequence, partly disrupted by igneous intrusions or 

obscurred by metamorphism, but correlation between 

sequences in the different areas has not been established.

SEQUENCE IN CARRIZO MOUNTAINS

In the Carrizo Mountains the Carrizo Mountain 

Formation, and the igneous rocks which intrude it, 

project in jagged parallel ridges, mostly trending 

northeast, separated by lowlands cut on the less resistant rocks of the formation. The formation dips 

steeply southeastward and strikes mostly northeastward (section T-T', pi. 16). Some of the intrusive 

bodies are irregular but most are sill-like, so that they 

only partly disorder the bedded succession. Where 

sedimentary structures are preserved, mainly in the 

arkose and quartzite units, they indicate that tops of 

the beds are to the southeast, and as the units of the 

formation are not repeated, the whole sequence is probably homoclinal. The sedimentary rocks of the sequence are nearly 19,000 feet thick, although this may 

exceed their original thickness because of contortion 

and injection of minor sills. The sequence has been 

distended another 7,000 or 8,000 feet by much thicker 

sills that are separately mapped.

The sequence consists of the following units, in descending stratigraphic order. The sequence is interrupted by intrusive igneous rocks, but these are indicated only where they break the succession completely. 

Titles of the units are those used by Flawn in his 

original description (in King, P. B., and Flawn, P. T., 

1953, p. 52-58).

Stratigraphic units of Carrizo Mountain Formation in Carrizo 

Mountains

Approximate

thickness

(feet)

11. Limestone: Fine-grained hard brown calcareous rock, exposed on one hill at east edge of 

mountains. Separated by metarhyolite from 

rest of sequence; so relations to other units 

are uncertain; it may overlie them __ (?) 

(Metarhyolite intrusive)

10. Feldspathic metaquartzite and meta-arkose: 

Fine-grained light-gray feldspathic metaquartzite and sericitic meta-arkose, exposed 

in low hills on southeast edge of mountains. 

Foliation is probably parallel to bedding, but 

original bedding planes are not apparent. 

Contains thin interbedded layers of sericite 

schist in lower part, lowest of which is garnetiferous. Basal contact preserved only in 

Bass Canyon, south of map area______ 2,700 

9. Mixed unit: Fine-grained schist and phyllite, 

with some layers of schistose quartzite and a 

thin bed of chert conglomerate. Contains 

numerous small bodies of greenstone, granodiorite, and metarhyolite, and is much contorted_______________________ 4,000 

(Thick sills of metarhyolite and greenstone)
PRECAMBRIAN AND PRECAMBRIAN(?) ROCKS 21

Stratigrayhic units of Carrizo Mountain Formation in Carrizo

Mountains Continued

Approximate

thickness

(feet)

8. Feldspathic metaquartzite and meta-arkose: 

Light-gray sericitic feldspathic metaquartzite toward northeast, where it forms a 

prominent ridge, passing south westward into 

rocks that are more schistose and micaceous. 

Bedding and crossbedding are visible and 

indicate that top of beds are to southeast__

7. Mixed Unit: Fine-grained sericitic quartzite; 

fine-grained biotite-sericite schist, and phylite; some thin beds of limestone and numerous thin sills of greenstone. A few hundred 

feet of similar rocks underlie the metarhyolite sill near its northeast end, and are probably part of the same unit, separated by the 

intrusion_________________________________

(Thick sill of metarhyolite, underlain by a 

thick sill of greenstone)

6. Phyllite: Blue-gray phyllite or slate, in narrow 

lowland between flanking ridges of greenstone 

and meta-arkose. Slaty cleavage may be 

parallel to bedding, but bedding is not visible5. Meta-arkose: Mainly gray fine-grained thin- to 

medium-bedded meta-arkose, containing wellmarked bedding laminae, crossbedding, pebble 

bands, and a few ripple marks. Sedimentary 

structures indicate that tops of beds are to 

southeast. Upper 250 ft is hard red-brown 

meta-arkose in 2-ft beds. Unit forms a prominent ridge on southeast side of Cat Draw, and 

is well exposed in cuts on U.S. Highway 80 

4. Mixed unit: Fine-grained gray or blue quartzite, 

light-gray sericite schist an dark phyllite, 

dark lustrous slate, thin-bedded blue chert, 

and laminated brown and black cherty limestone, all of which are interbedded in thin 

layers. Contains many thin greenstone sills. 

Forms the broad belt of lowland along Cat 

Draw ____________________________________

300

2,000

600

1,700

1,700

3. Meta-arkose and feldspathic metaquartzite: 

Fine-grained thin-bedded light-gray feldspathic metaquartzite and meta-arkose. Contains well-marked bedding and crossbedding 

which indicate that tops of beds are to southeast. Forms prominent line of knobs and 

ridges on northwest side of Cat Draw___ 1,800-2,000 

(Thick greenstone sill, underlain by irregular 

bodies of metarhyolite)

2. Chlorite-mica schist: Fine-grained lustrous 

dark-colored sericite-chlorite-biotite schist, 

thin beds of dark slate, and thick beds of 

coarse pebbly meta-arkose. Forms a low 

hilly area near Mineral Creek in northwestera part of mountains, nearly surrounded by 

intrusive metarhyolite and greenstone, so that 

relations to adjoining units are preserved in 

only a few places________________ 3, 700

Stratigraphic units of Carrizo Mountain Formation in Carrizo

Mountains Continued

Approximate

thickness

(feet)

1. Meta-arkose: Fine-grained light-gray metaarkose, with thin layers of sericite schist and 

phyllite, in small areas in a large greenstone 

intrusive south of Mineral Creek. At one locality the unit dips beneath the chlorite-mica 

schist, indicating that it is the lowest part of 

the sequence_____ ( ?)

Total thickness _____ +18, 700

METAMORPHIC FEATURES

The sedimentary rocks of the Carrizo Mountain Formation in the Carrizo Mountains have been subjected 

to at least two periods of metamorphism and have been 

injected several times by igneous rocks, so that part of 

their stratigraphic character has been destroyed.

The quartzite and arkose units preserve many original sedimentary structures, such as bedding laminae, 

crossbedding, and pebbly seams; but the quartz and 

feldspar are recrystallized, and contain variable 

amounts of chlorite and sericite. The finer grained, 

originally more argillaceous, units mostly contain biotite, which has been partly converted to chlorite. 

These units, and to a lesser extent the quartzite and 

arkose units, contain a foliation that is closely parallel 

to the general homoclinal structure and to the bedding 

where this can be observed. The mica, some of the 

chlorite, and the foliation are products of an early 

regional metamorphism whose grade increases progressively southeastward to a visible climax in exposures 

in the Van Horn Mountains, where some of the rocks 

are garnetiferous.

Alteration of biotite to chlorite (and in some areas 

garnet to chlorite) indicates a later period of retrogressive and cataclastic metamorphism, whose effects 

increase perceptibly northwestward across the exposed 

breadth of the Carrizo Mountains. In many of the 

schist and phyllite units the foliation is distorted by 

crinkles and chevron folds whose axes cross the foliation planes at wide angles. In the Carrizo Mountains 

these structures are most abundant where effects of retrogressive metamorphism are greatest, and especially 

where incompetent units abut the competent metarhyolite intrusions.

The nature of the different rocks of the sequence influenced their response to this complex metamorphic 

history. Preservation of sedimentary features in the 

quartzite and arkose units resulted from alteration by 

mass recrystallization. Greater complexity of the 

structures in the finer grained units, where original sedimentary features are poorly preserved, probably de-
22 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

veloped because these units absorbed much of the applied stress during progressive and retrogressive 

metamorphism.

The earlier progressive regional metamorphism of 

the sedimentary rocks of the Carrizo Mountain Formation preceded their intrusion by metarhyolite and 

greenstone. These were injected in large part as sills 

along the planes of earlier bedding and foliation. The 

intrusive rocks now show strong effects of cataclastic 

and retrogressive metamorphism, evidently related to 

the retrogressive metamorphism of the sedimentary 

rocks.

STRATIGRAPHIC RELATIONS

The sequence of sedimentary rocks of the Carrizo 

Mountain Formation exposed in the Carrizo Mountains 

preserves neither its top nor base, nor can top or base be 

observed in exposures of the formation elsewhere. The 

lower part of the sequence is intruded by metarhyolite 

and greenstone. Northwest of the Carrizo Mountains, 

in the foothills of the Sierra Diablo, these intrusive 

rocks are faulted over other sedimentary rocks of the 

Allamoore Formation along a major discontinuity in 

the Precambrian rocks, the Streeruwitz thrust fault. 

Thus, relations between the Carrizo Mountain and Allamoore Formations cannot be determined directly, although rather tenuous evidence suggests that the 

Carrizo Mountain is the older formation.

IGNEOUS ROCKS INTRUSIVE INTO CARRIZO MOUNTAIN 

FORMATION

Large masses of rhyolite and somewhat smaller 

masses of greenstone intrude the Carrizo Mountain 

Formation. In the Carrizo Mountains they form thin 

to thick sills in the homoclinal sequence of sedimentary 

rocks, as well as a large body at the base of the sequence 

to the northwest (section T-T'', pi. 16). The instrusive 

rocks also crop out discontinuously north of the Texas 

and Pacific Railway, along the south edge of the Sierra 

Diablo foothills next to the alluvial area of Eagle Flat, 

from northeast of Allamoore to northwest of Eagle Flat 

section house (pi. 1). Here, none of the sedimentary 

rocks of the Carrizo Mountain Formation are preserved, 

and the intrusive rocks are faulted over the Allamoore 

Formation along the Streeruwitz thrust fault. A few 

bodies of the igneous rocks in the Millican Hills west of 

the Garren Ranch are entirely surrounded by Allamoore Formation; they are probably klippen of the 

Streeruwitz thrust sheet (section O-O'', pi. 16).

Igneous rocks of the large body in the northwestern 

Carrizo Mountains, referred to above, consisting of 

metarhyolite and minor sills of greenstone, are well 

exposed in low hills southeast of Allamoore and higher 

ridges beyond. They are shown in numerous cuts along

U.S. Highway 80, 2 to 4 miles southeast of Allamoore, 

and in quarry openings of the Holley Plant of GiffordHill Co. northeast of the highway.

METARHYOLITE

The metarhyolite superficially has the appearance of 

an extrusive volcanic rock, as though it were part of the 

stratigraphic sequence of the Carrizo Mountain Formation. Much of it is layered, some of it contains intercalations of sericite schist and phyllite, and the part 

to the southeast is interbedded in thick units with the 

sedimentary rocks. However, the layering and schistose intercalations were produced during metamorphism, 

and the metarhyolite bodies to the southeast are sills, 

which branch or pinch out along the strike and have 

irregular contacts with the enclosing rocks.

The metarhyolite is a hard, blocky or slabby siliceous 

rock of red, pink, brown, buff, or gray color. It is 

formed of feldspar and quartz phenocrysts generally 

less than 2 mm in diameter, now largely broken, set in 

an aphanitic groundmass. Texture and appearance of 

the rock are similar in all exposures, except for variable 

effects produced by metamorphism. Microscopic study, 

however, indicates that the feldspar in the southeastern 

Carrizo Mountains is microcline, whereas that in the 

northwestern Carrizo Mountains and the Sierra Diablo 

foothills is microcline-microperthite and albite; this 

difference may have resulted from albitization of an 

original potassium feldspar in the northwestern areas.

Cataclastic metamorphism has produced a well-developed layering or foliation in much of the metarhyolite, on the surfaces of which phenocrysts and mineral 

aggregates have been crushed, streaked, and drawn out 

to form a pronounced lineation. In the Carrizo Mountains the foliation generally strikes northeast and dips 

southeast, broadly parallel to the foliation of the sedimentary rocks; in the Sierra Diablo foothills the strike 

is east or even southeast, parallel to the trace of the 

Streeruwitz thrust. The lineation extends down the 

dip, mostly southeastward in the Carrizo Mountains, 

but in more varied directions in the Sierra Diable foothills. In places, thin layers of schist or phyllite are 

intercalated in the more massive rhyolite; microscopic 

study indicates that these also are of cataclastic origin, 

as they contain broken remnants of microcline phenocrysts. However, much of the potassium feldspar in 

the schist and phyllite has been crushed and converted 

to sericite as a result of intense shearing. The cataclastic metamorphism is strongest in the northwestern 

bodies of metarhyolite and weakest in the southeastern, 

where layering is not conspicuous and lineation and 

schistose layers are not common.

In the Sierra Diablo foothills, and to a lesser extent 

in the northwestern part of the Carrizo Mountains, part
PEECAMBEIAN AND PEECAMBEIAN ( ? ) KOCKS 23

of the nietarhyolite has been converted to a dense siliceous thinly laminated mylonite, in which the original 

phenocrysts are nearly destroyed. Ordinarily the mylonite is interlayered with less altered rhyolite in beds 

a few feet thick, which are most abundant close to the 

sole of the Streeruwitz thrust fault.

GREENSTONE

Both the metarhyolite and the sedimentary rocks of 

the Carrizo Mountain Formation are intruded by greenstone, mainly as sills which follow the foliation of the 

host rocks. A few of the sills in the southeastern Carrizo Mountains are as much as 1,800 feet thick; but the 

rest are thinner, and many are only a few feet thick. 

However, even the thicker sills contain numerous septa 

of the rhyolitic or sedimentary host rocks. The greenstone occurs throughout the exposures of both the Carrizo Mountain Formation and the metarhyolite, in the 

Carrizo Mountains and the Sierra Diablo foothills, but 

only the thicker sills are large enough to be shown on 

the map (pi. 1).

The greenstone is a fine- to coarse-grained green to 

black rock, now largely an amphibolite but probably 

originally a diorite. The centers of the larger sills are 

hypidiomorphic hornblende diorite, but the walls were 

largely changed to amphibolite during shearing and 

retrogressive metamorphism. Andesine was converted 

to albite or oligoclase, and the epidote and prismatic 

hornblende grains were reduced to felty masses of acicular or fibrous hornblende. The thinner sills are 

thoroughly schistose, with schistosity parallel to that 

of the adjacent metarhyolite and the sedimentary rocks. 

Some of the greenstone also contains a lineation which 

is parallel to that of the enclosing metarhyolite.

VEINS

The Carrizo Mountain Formation, the metarhyolite, 

and the greenstone all contain vein material, generally 

in narrow stringers and irregular blebs a few inches 

thick, but partly in larger bodies. Some veins also 

occur in altered limestone of the Allamoore Formation, 

close to the Streeruwitz thrust, and the overriding 

metarhylite and greenstone.

The veins are largely milky or vitreous quartz, but 

they also contain small amounts of pink feldspar, muscovite, specular hematite, and other minerals. In the 

Carrizo Mountains they contain some tourmaline, as 

well as iron and copper sulfides.

Structural relations of the veins are complex, and 

they probably formed at various times late in the igneous and tectonic history of the enclosing rocks. Many 

veins follow the foliation of the rocks or spread through 

them irregularly; some are slickensided parallel to the 

prevailing lineation. Other veins lie on joints that

cross the foliation, and some cement the brecciated 

metarhyolite. The younger cross joints break and offset 

the veins; they contain no minerals, except scant coatings of specular hematite or chlorite.

Al^LAMOORE FORMATION

The Allamoore Formation crops out mainly well 

south of the Sierra Diablo scarp near Eagle Flat, in a 

belt about 5 miles wide that trends west-northwest 

(pi. 1). It projects in low barren subparallel ridges.

The most prominently exposed parts of the Allamoore are its limestone units, but these are interlayered 

with great masses of volcanic rocks, including flows, 

pyroclastic rocks, and perhaps shallow intrusives. 

Thin units of argillaceous rocks, now altered to phyllite, are also interbedded.

As the Allamoore is exposed mainly to the south 

where deformation of the Precambrian rocks is greatest, the formation is mostly tilted at high angles and is 

complexly folded and faulted (sections K-K', O-O', 

and P-P', pi. 16). Determination of the stratigraphic 

sequence is therefore difficult, and an estimate of its 

total thickness is almost impossible. On Tumbledown 

Mountain (sec. 27, Block 66, Twp. 7), where relations 

are unusually plain, about 1,630 feet of the formation 

is exposed with neither the top nor base preserved; the 

sequence is at least partly duplicated by thrust faults 

(King, P. B., and Flawn, P. T., 1953, table 17, p. 80) 

(upper view, pi. 2). Any traverse across the strike of 

the formation crosses a wide expanse of steeply dipping 

beds that can hardly have been produced by repetition 

of a few thin layers, so that the formation is probably 

as much as several thousand feet thick.

LIMESTONE

Limestone beds of the Allamoore Formation stand in 

jagged ledges and ridges. They are characteristically 

seamed by bands of chert a quarter to half an inch 

thick, parallel to the bedding and spaced at intervals 

of a few inches. Differential weathering of chert and 

limestone imparts a ribbed appearance to the ledges. 

The chert may be a primary or diagenetic feature; at 

least it antedates the Precambrian orogeny because the 

chert seams are sliced and broken where the rocks are 

strongly deformed, whereas the less brittle intervening 

limestone is deformed by flowage.

The limestone itself, where least altered, is mainly 

thin bedded and compact, with some more granular or 

more crystalline layers. Most of the limestone is blue, 

gray, or brown, but some is reddish or purplish. Some 

limestone beds are very thinly and evenly laminated by 

light and dark seams; others as much as 8 feet thick 

are massive and contain no chert. At a few places the
24 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

limestone is interbedded with intraformational limestone-pebble conglomerate.

A specimen of dark gray fine-grained little-altered 

limestone of the Allamoore Formation from Tumbledown Mountain was analyzed by K. J. Murata in the 

chemical laboratory of the U.S. Geological Survey 

(written commun., 1937), and yielded 83.82 percent 

CaC03 and 9.32 percent MgC03 ; it also contained 0.05 

percent of organic insolubles, which are apparently like 

the bituminous material which darkens the Paleozoic 

limestones of the region. Another specimen reported 

by Bichardson (1904, p. 25) is more dolomitic, with a 

higher magnesian content. According to Flawn 

(written commun., 1959), inclusions of carbonate rock 

in the talc-bearing phyllite layers are also dolomitic.

The organic matter in the limestone beds of the Allamoore Formation seems to prove existence of life during 

formation of these ancient rocks, yet searches for fossils 

that have so far been made reveal nothing but possible 

algal remains. Many of the 'chert-banded or laminated 

limestone beds have a crinkled wavy or domelike structure similar to the Cryptozoon or stromatoporiod 

growths in the earlier Paleozoic rocks; in places these 

structures project into the beds above as low mounds 

or reefs. Other beds resemble the mottled limestones 

of the earlier Paleozoic, which were perhaps formed 

by organic growth.

VOLCANIC ROCKS

Volcanic rocks probably make up a quarter to a half 

of the total volume of the Allamoore Formation, but 

they are less conspicuous than the limestone beds and 

are generally worn down to soil-covered slopes, sags, 

and valleys. Their best exposures are in creek banks 

and prospect holes. In a few places more massive parts 

of the volcanic rocks project in rugged black hills. 

The volcanic rocks are interbedded with the limestone 

in units a few feet to hundreds of feet thick, and in 

places they contain thin limestone beds.

Some of the volcanic rocks are very massive and 

weather to brown or black bouldery surfaces; where 

fresh, these surfaces are dark green or red. Diabasic 

structure is prominent in some of the volcanic rocks, 

and in others amygdules are abundant. Most of the 

dark massive volcanic rocks were probably spread out 

as subaerial or subaqueous lava flows, but little remains 

of primary flow structure, except the rather common 

amygdules. Some of the thicker more massive bodies 

may have been shallow sill-like intrusives.

Some of the less massive volcanic rocks are of pyroclastic or sedimentary origin, for they contain detrital 

fragments of igneous rocks and are well stratified. 

Coarser varieties include dark red, brown, or green

sandstone with seams of volcanic pebbles and interbedded layers of volcanic conglomerate. Finer grained 

beds include brown or green siliceous shales, thinly 

laminated pink siliceous rock, and light-green schistose 

laminated rock, all probably derived from different 

sorts of tuffs. Interbedded with the volcanic sediments 

are thin beds of reddish limestone that contain igneous 

fragments.

PHYLLITE

Phyllite is almost as widely distributed as the limestone and volcanic rocks in the Allamoore Formation, 

but it has a smaller volume and generally forms units 

less than a hundred feet thick. These units are grouped 

with the limestone on the geologic map (pi. 1). Like 

the volcanic rocks, the phyllite is poorly resistant to 

erosion and is commonly worn down to low ground between the limestone ledges. In many places the phyllite and volcanic rocks are interbedded, and a single 

interval between limestone units may consist of phyllite 

at one place, of volcanics at another, and of both rocks 

at others. The phyllite beds were originally shale 

units in the Allamoore Formation; their rather intimate 

association with the volcanic units suggests that they 

may in part have had a volcanic source.

The original argillaceous constitutents of the phyllite 

have been thoroughly altered to foliated, sericitic, or 

talcose minerals. Most of the rock is gray to dark 

gray; but parts are black and apparently graphitic, 

and others are calcareous. Bedding is indicated by 

alteration of the gray, black, and calcareous varieties, 

in part in thin laminae, in part in layers several inches 

thick. Bedding is intensely contorted and is crossed 

by strongly marked slaty cleavage nearly parallel to 

the axial planes of the folds. The rock weathers white 

or ashen and splits into flakes, plates, or papery sheets 

parallel to the cleavage.

Since 1952 talc has been mined from the phyllite 

units of the Allamoore Formation at various places in 

the southern Millican Hills, Bean Hills, and Streeruwitz Hills, and these units have been extensively prospected elsewhere (Flawn, 1958). The amount of talc 

in the phyllite beds varies from place to place. The 

mineral may have formed from an original fine-grained 

magnesium-bearing tuff. Carbonate rocks adjacent to 

the phyllite beds contain little magnesium, and are 

mainly limestone rather than dolomite, but dolomite 

forms inclusions in the talc bodies. Large masses of 

pure ceramic-grade foliated to fibrous talc as much as 

150 feet thick occur in places, but in others the talc 

bodies contain layers or irregular masses of chert and 

carbonate rock.
PRECAMBRIAN AND PRECAMBRIAN ( ? ) ROCKS 25

ROCK ALTERATION

Most of the rocks of the Allamoore Formation have 

been more or less changed from their original character, 

perhaps mainly by the deformation to which they have 

been subjected, but probably with the aid of hydrothermal solutions. Alteration is least toward the north, 

as on Tumbledown Mountain, and increases southward 

to a maximum near outcrops of the metarhyolite that 

forms the overriding Streeruwitz thrust sheet.

The limestone beds are variously altered. The most 

striking alteration is by marmorization, which occurs 

in small erratically placed areas, perhaps related to intense flowage, squeezing, or hydrothermal activity. The 

limestone is recrystallized to marble, mostly white, but 

with reddish and bluish streaks that may be inherited 

from original bedding. Where the limestone was originally impure or shaly, it has been made schistose, and 

original bedding laminae are thrown into tight isoclinal 

folds.

In a wide band just north of the trace of the Streeruwitz thrust, the limestone of the Allamoore Formation 

has been extensively silicified to jasperoid. The jasperoid has lost all traces of bedding and other structures of the original limestone and is traversed by many 

quartz veinlets. Its weathered surfaces are brown and 

f elty and are recessed like other carbonate-bearing rocks 

around quartz veins and siliceous knots. Nevertheless, 

the jasperoid probably now contains little carbonate, 

as it breaks with conchoidal fracture into dark-gray 

steel-hard chips.

Where cherty limestone beds have been sheared, the 

chert layers are sliced, offset, and broken along innumerable planes of fracture cleavage, and the intervening 

less brittle limestone has flowed around the chert. 

Where most sheared, the rocks have become a rubble 

of angular chert fragments, set in a carbonate matrix.

The more massive diabasic volcanic rocks may have 

been much changed mineralogically, but this is little 

apparent to the eye and even the amygdules are little 

compressed. By contrast, the fine-grained tuffaceous 

volcanics and the phyllite units are highly contorted 

and are thoroughly schistose.

STRATIGBAPHIC EELATIONS

The base of the Allamoore Formation is not exposed. 

It is in contact on the south with possibly older metarhyolite; but this rock has been emplaced along the 

Streeruwitz thrust fault, so that it now overlies rather 

than underlies the Allamoore. Farther southeast in 

the Carrizo Mountains, the metarhyolite intrudes the 

thick sedimentary sequence of the Carrizo Mountain 

Formation. Relations of these sedimentary rocks to 

those of the Allamoore Formation have not been determined; the Carrizo Mountain may represent a downward continuation of the Allamoore, or the two might 

be far apart in age.

The Allamoore Formation is also in contact with the 

Hazel Formation. From structural relations alone it 

is not possible to determine the original nature of their 

succession, as either formation overlies the other, depending on locality. However, the conglomerate of the 

Hazel consists largely of fragments of limestone and 

volcanic rocks derived from erosion of the Allamoore 

Formation, which indicates clearly that the Hazel is 

younger.

The conglomerate beds show that the Hazel lies unconf ormably on the Allamoore, and the great thickness 

and the coarse and angular fragments of the conglomerates suggest that the Allamoore epoch was closed by 

an orogeny that probably continued into early Hazel 

time. Moreover, some of the limestone fragments in 

the conglomerate beds are marmorized in the same manner as parts of the limestone still in place in the Allamoore.

The nature of the deformation caused by the preHazel orogeny is obscure, as most of the structure now 

visible in the Allamoore is shared by the adjacent Hazel 

and formed during a later, post-Hazel, orogeny. The 

contact between the two formations is strongly discordant in most places; but it is generally sheared and 

faulted along a "surface of movement" (pi. 1), so that 

it is difficult to determine their original angular divergence, or the irregularity of the surface on which the 

conglomerate was deposited.

HAZEL FORMATION

The Hazel Formation crops out in many parts of the 

deformed area in the southern part of the Sierra Diablo 

foothills where its rocks are intimately infolded with 

the Allamoore formation (pi. 1). Unlike the Allamoore, the Hazel is also exposed much farther north in 

areas that were less deformed. It crops out around 

the south and east sides of the scarps of the Sierra 

Diablo where it extends to within a few miles of Victorio Peak (upper view, pi. 10); it also forms a large 

inlier in the interior of the range near Sheep Peak.

The Hazel Formation includes red sandstone which 

characterizes the upper and northern part, and conglomerate, which characterizes the lower and southern 

part. The two rocks are intimately interbedded. 

Adjacent to the Allamoore Formation are thick massive 

layers of conglomerate; but farther from it and higher 

in the sequence conglomerate beds are thinner and more 

sandy and are separated by increasingly thicker beds 

of red sandstone, which finally dominate altogether. 

The conglomerate may wedge out northward in the
26 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

sandstone, away from the uplifted masses of Allamoore 

formation from which it was derived; but this is difficult to prove because of the complex structure.

The Hazel is a very thick formation, but estimates of 

thickness are incomplete. North of the Allamoore formation in the central Streeruwitz Hills is a continuous 

steeply dipping succession which appears to be at least 

5,000 feet thick; of this, more than half is conglomerate. 

On the eastern scarps of the Sierra Diablo near the 

Pecos mine there is more than 2,250 feet of gently dipping sandstone.

CONGLOMERATE

The conglomerate of the Hazel Formation is one of 

the more resistant rock units of the Precambrian succession, and in places forms ridges as high as, or higher 

than, those of the limestone of the Allamoore Formation. In the southern belts of outcrop in the Streeruwitz and Millican Hills, these ridges are covered by 

deep-brown or black-surfaced craggy ledges. Farther 

north the conglomerate is less consolidated and makes 

fewer ledges, although it forms high hills.

The conglomerate is formed almost entirely of fragments derived from the Allamoore Formation and especially of its limestone. All varieties occur in the 

fragments, including chert-seamed, laminated, carbonaceous, and marmorized limestone. There are also 

scattered cobbles of bright red jaspery limestone or 

chert. Fragments of the volcanic rocks are common as 

well, including massive diabasic or amygdaloidal lava 

and coarse to fine pyroclastic rocks. The finer pyroclastic rocks in some of the fragments seem to have been 

rendered schistose before they were incorporated in the 

conglomerate.

In a few places the conglomerate also contains cobbles 

or boulders of red granite and coarse rhyolite porphyry. 

They are especially abundant between Carrizo Spring 

and Tumbledown Mountain in the eastern Millican 

Hills, but a few were observed in the northwestern 

Streeruwitz Hills. The granite and porphyry are unlike 

the igneous rocks that intrude the Carrizo Mountain 

Formation, but they closely resemble those in boulders 

in the succeeding Van Horn Sandstone. Like those in 

the Van Horn, they resemble Precambrian granite and 

porphyry exposed some distance northwest of the Sierra 

Diablo region. The known distribution of boulders in 

the Hazel does not suggest a northwestern source, and 

they may have been derived from other areas, as yet 

unknown, where they are now concealed by younger 

strata.

Fragments in the conglomerate are of all sizes, from 

small pebbles to large blocks, mainly limestone, and 6 

feet or more across. The large blocks are most abundant in the lower part, near the contact with the Allamoore Formation, yet they are surprisingly common at 

hundreds or even thousands of feet above the base. The 

fragments are generally poorly rounded and many are 

angular, thus differing from those in the overlying Van 

Horn Sandstone; their angularity provides a means of 

distinguishing the Hazel fragments from those of the 

Van Horn.

The matrix of the conglomerate varies. In the lower 

and southern conglomerate beds, which are most resistant to erosion, it may originally have been calcareous, but generally it has been silicified and impregnated 

by iron on weathered surfaces. In the higher and more 

northern conglomerate beds the matrix includes more 

sand and arkose, so that the rock is softer and less 

coherent.

Most of the fragments lie helter-skelter in the conglomerate, pieces of all sizes, shapes, and compositions 

being mingled without sorting. Little or no grain gradation is visible from base to top of a single layer and 

in the more massive phases bedding itself is obscure. 

In the higher conglomerate beds are scattered gritty 

seams or lenses and thin interbedded layers of red sandstone. However, rocks transitional from conglomerate 

to sandstone are of small volume. No coarse sandstone 

or pebbly sandstone of any thickness occurs near the 

conglomerate beds, and many of the coarse conglomerate 

beds are inserted abruptly between red sandstone that 

is as fine and silty as that elsewhere in the area.

The thickness of the conglomeratic part of the Hazel 

Formation varies from place to place along the outcrop, but it is uncertain whether the variation results 

from original differences in amount of conglomerate deposited or from structural complication. In the central Streeruwitz Hills, next to the southern outcrops of 

the Allamoore Formation, conglomerate beds are as 

much as 3,000 feet thick, of which the lower half is solid 

conglomerate and the upper half is interbedded conglomerate and sandstone. Conglomerate with a similar structure in the southern Millican Hills is about 

2,000 feet thick.

Near other belts of the Allamoore Formation farther 

north, conglomerate beds of the Hazel Formation are 

more varied and in places much thinner. Here, the 

conglomerate may have been partly removed along the 

"surface of movement" between the two formations, 

but at least a part of the variation is original.

BED SANDSTONE

Red sandstone forms the most conspicuous and extensive outcrops of the Hazel Formation. It crops out 

on smoothly rounded red slopes, only lightly masked by 

vegetation, which extend to considerable heights on the 

scarps south and east of the Sierra Diablo, surmounted
PRECAMBRIAN AND PRECAMBRIAN (?) ROCKS 27

by light-gray cliffs of the Hueco Limestone. At the 

bases of the scarps the slopes flatten into broad pediments, capped in many places by Quaternary gravels 

but mostly carved into an intricate network of hills and 

valleys, such as those between Beach Mountain and the 

Hazel mine. The hills, which are domelike, have 

rounded crests that descend steeply toward the incising 

streams.

The red color of the sandstone is universal, varying 

from brick red in the northern exposures to a darker 

maroon red farther south. Most of the sandstone is 

very fine grained, verging on, or grading into, siltstone. 

It coarsens somewhat southward where it varies more 

in texture from bed to bed; here, some of the coarser 

layers form long strike ridges. Part of the sandstone 

is poorly consolidated, but most is fairly hard and well 

cemented and has a conchoidal fracture.

Bedding of the sandstone is indicated in most places 

by thin closely spaced dark laminae. Much of it is 

crossbedded on a small scale, and in places it is ripple 

marked on bedding surfaces. The sandstone generally 

does not split along bedding planes, as these are 

thoroughly welded together; instead, it breaks into 

angular blocks along innumerable vertical or inclined 

joints, so that in many places the bedding can be determined only by close scrutiny.

The thickness of the red sandstone has not been determined, but it is as much as thousands of feet. On 

the east-facing escarpment of the Sierra Diablo from 

the Pecos mine northward, south-dipping lines of bedding are visible on the red sandstone slopes below the 

cliffs of Hueco Limestone and indicate that more than 

2.250 feet is exposed (section P-P', pi. 16).

ROCK ALTERATION

The Hazel Formation is less altered than the Allamoore Formation, partly because most of it lies farther 

from the belt of strong deformation, and partly because 

its sandstone and conglomerate beds are more competent than the Allamoore.

In the strongly deformed belt toward the south, the 

conglomerate has been sliced in many places along a 

multitude of closely spaced shear or cleavage planes. 

These planes cut through both the matrix and the fragments, but most of the fragments are not flattened.

The sandstone is little altered and pressures were 

evidently dispersed along innumerable clean-cut vertical or inclined joints. The sandstone was not sheared 

or squeezed in the strongly deformed areas, but was 

sliced and offset by many minor thrust faults. The 

thrusts are especially abundant in the outcrop of sandstone in the Millican Hills that extends east from the 

Garren Ranch, where they are marked by slickensided

JT57-108 «S 3

surfaces, many of which are coated with a black highly 

polished substance a few millimeters thick that also 

extends in ramifying stringers through the rock. According to Charles Milton (written commun., 1951), 

the substance is a fine-grained aggregate of crystalline 

tourmaline and hematite dust.

Near some of the large high-angle faults north of 

the Millican Hills the sandstone has been mashed and 

reconstituted, so that it loses its flinty conchoidal aspect, 

and is massive, soft, and earthy.

Near many faults, joints, and fractures in the northern area the sandstone is decolorized. The red rock is 

bleached to buff or yellow for several inches or feet 

away from the fractures. The bleaching is caused by 

reduction or removal of hematite by percolating solutions; it is best developed near prospective or productive veins, and it is considered to be a favorable indication of mineralization by local prospectors. Bleaching 

of the red sandstone was also observed beneath the unconformity at the base of the Hueco Limestone in buttes

3 miles south-southeast of the Old Circle Ranch (sec.

4 Block 67, Twp. 7); this bleaching either occurred 

during pre-Hueco erosion or during later circulation 

of ground water along the unconformity.

STRATIGRAPHIC RELATIONS

The Hazel Formation is overlain by varied strata of 

much younger age, including those of the Permian and 

Cretaceous systems, but the next younger formation 

with which it is in contact is the Van Horn Sandstone. 

Its relations are strongly unconf ormable, even with the 

Van Horn, and the times of formation of the Hazel 

and Van Horn deposits are separated by a major period 

of orogeny by which the Hazel and Allamoore Formations were strongly deformed and by a prolonged 

period of erosion during which they were deeply truncated. Emplacement of the Carrizo Mountain Formation and its intrusive rocks along the Streeruwitz thrust 

fault probably occurred during this orogeny, as the 

conglomerate of the Van Horn is the earliest deposit 

which contains fragments of lineated and mylonitized 

metarhyolite. The Van Horn Sandstone in the Sierra 

Diablo foothills lies on both the Hazel and Allamoore 

Formations; in the eastern Carrizo Mountains it lies 

on the Carrizo Moutain Formation.

VAN HORN SANDSTONE

The Van Horn Sandstone is preserved in relatively 

small areas in the Sierra Diablo region, the wide dispersal and isolation of its outcrops being caused by its 

unconformable relations with various formations that 

overlie it. The most extensive outcrops are in the Red 

Valley, northwest of the town of Van Horn and southwest of Beach Mountain, which Richardson (1904, p.
28 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

28) designated as the type area (pi. 1). It is also exposed on the northwest corner of Beach Mountain south 

of the B-Bar Ranch, at several places in the Baylor 

Mountains, on the southeast corner of the Sierra Diablo 

between the Hazel and Pecos mines, on the south-facing 

scarp of the Sierra Diablo 4 to 7 miles west of the Old 

Circle Ranch, and in the eastern Carrizo Mountains 

south of the Texas and Pacific Railway.

The Van Horn is characteristically a coarse red arkosic sandstone in thick massive beds, mostly friable and 

poorly consolidated, crossbedded in many places, and 

containing scattered pebbles and cobbles. No fossils are 

known. The sandstone is interbedded with, and underlain by, thin to thick beds of conglomerate containing 

rounded pebbles, cobbles, and boulders made up not 

only of the older rocks of the immediate vicinity, but 

also of granite and rhyolite porphyry unlike any exposed in the Sierra Diablo region. The greatest 

thickness of the formation preserved at any one place 

is about 800 feet, but it is generally much thinner.

The red massive clastic rocks of the Van Horn form 

some of the most picturesque outcrops in the region 

(pi. 2). Its sandstone beds project in great rounded 

ledges, largely barren of vegetation, which rise on the 

faces of escarpments into picturesque towers, prows, 

and battlements. Tables, pedestals, and other fantastic 

erosion forms are common. The massive ledge-making beds are separated by others, less resistant to 

erosion and generally more conglomeratic, which form 

intervening shelves. Widely spaced joints, commonly 

set at right angles, are worn into creases or crevices 

that extend across the outcrops and are prominently 

visible from adjacent mountain tops or in air photographs. Stream channels cross the shelves in rounded 

swales, but descend from one ledge to the next in narrow slots that follow the prevailing joints, with many 

swirls and potholes.

CONGLOMERATE

The conglomerate beds of the Van Horn are a few 

feet to several hundred feet thick and are commonly 

thickest and coarsest at the base and thinner and finer 

grained higher up. Its basal conglomerate varies. On 

the Sierra Diablo scarp 4 miles west of the Old Circle 

Eanch, the conglomerate is more than 300 feet thick, 

but it thins both eastward and westward; eastward up 

the dip it apparently thins against a buried hill of the 

Allamoore Formation. In other places, as near the 

Yates Ranch, basal conglomerate is not well defined, 

and conglomerate beds and dispersed pebbles are common throughout the sequence.

Fragments in the conglomerate are pebbles, cobbles, 

and boulders, those in the basal beds 4 miles west of the 

Old Circle Ranch being as much as 3 feet in diameter.

Most are smoothly rounded and some have almost polished surfaces; a few of obvious local derivation are 

somewhat less rounded. Many fragments have been 

shattered, sheared, and offset by deformation, but some 

were afterwards recemented. The fragments are set in 

an arkosic sandy matrix, somewhat less consolidated 

than that of the adjacent sandstone beds; in places the 

fragments are closely packed, but in others they are 

widely dispersed in the matrix. Weathering of the 

poorly consolidated matrix sets free vast quantities of 

the rounded fragments, which strew the outcrops of the 

formation.

The fragments in the conglomerate were derived from 

many older rocks, but the dominant fragments, especially in the northern and northwestern exposures, 

are red granite and red rhyolite porphyry. These differ greatly from any igneous rocks exposed in place in 

the Sierra Diablo region. They are unlike the metarhyolite intruded in the Carrizo Mountain Formation; 

moreover, fragments clearly derived from the metarhyolite also occur in the Van Horn. The porphyry and 

granite fragments resemble most the Precambrian igneous rocks exposed some distance to the northwest, as 

the red rhyolite porphyry of the Pump Station Hills 

(King, P. B.. and Flawn, P. T., 1953, p. 123-124; Masson, 1956) and the coarse red granite at the south end 

of the Hueco Mountains (King, P. B., King, R. E., and 

Knight, J. B., 1945, sheet 1).

Metarhyolite derived from intrusives in the Carrizo 

Mountain Formation is a significant but not a dominant 

constituent. The fragments have the same lineation 

and cataclastic structure as the rocks of the parent 

ledges. The metarhyolite occurs in nearly every outcrop of the formation, but is perhaps most abundant 

toward the south.

Other fragments are fine- to coarse-grained mafic 

igneous rocks, probably derived from the volcanic rocks 

and the greenstone intrusives of the Allamoore and 

Carrizo Mountain Formations; limestone, chert, and 

jasper from the Allamoore Formation; red sandstone 

from the Hazel Formation; and vein quartz.

SANDSTONE

The sandstone beds of the Van Horn are dominantly 

red, but they are generally slightly darker than those of 

the Hazel, being mostly maroon red or purplish red. 

The strong colors die out upward, and the highest beds 

of the formation, where preserved, are orange red or 

red brown. The sandstone which is coarse, has grains 

as much as a millimeter in diameter and scattered larger 

grits and small pebbles; it contrasts with the fine silty 

red sandstone of the Hazel. Quartz and feldspar 

grains occur in about equal proportions; much mica is
PRECAMBRIAN AND PRECAMBRIAN ( ?) ROCKS 29

found at some localities. In most of the rock, beds are 

3-10 feet thick, but some are thicker. Within many 

layers are well-marked crossbeds. Most of these slope 

southward; the others slopes southeastward or southwestward but nowhere northward (King, P. B., and 

Flawn, P. T., 1953, p. 93, fig. 8). These dips are maintained even where the enclosing strata are inclined in an 

opposite direction.

In the higher parts of the formation are some interbedded layers of buff or brown sandstone a foot or two 

thick, which are more cleanly washed than the rest 

and contain more quartz than feldspar. On the southfacing scarp of the Sierra Diablo west of the Old Circle 

Ranch, one of these layers near the middle of the formation extends more than 2 miles. Similar layers are 

common south of Threemile Mountain, east of Hillside 

siding. Near a tank at the summit of the Sierra Diablo 

escarpment 7 miles west of the Old Circle Ranch (sec. 

29, Block 52%), the massive arkosic sandstone is interbedded with 5-foot layers of soft flaggy sandstone and 

greenish clay shale, which are nearly un'consolidated 

and contain possible f ucoidal markings.

SECTIONS OF VAN HORN SANDSTONE

The greatest thickness of Van Horn Sandstone in the 

region is on the south-facing escarpment of the Sierra 

Diablo 4 miles west of the Old Circle Ranch (sec. 2, 

Block 56), where 759 feet was measured, of which the 

lower 335 feet is conglomerate (King, P. B., and Flawn, 

P. T., 1953, p. 94, table 19). Here, the Van Horn lies 

unconformably on the Allamoore Formation and is 

overlain unconformably by the Hueco Limestone, so 

that its original thickness is no longer preserved.

At the northwest corner of Beach Mountain (sec. 19, 

Block 66, Twp. 7) 300 or 400 feet of Van Horn Sandstone is exposed on steep slopes below the cliffs of Bliss 

Sandstone and El Paso Limestone and above red sandstone of the Hazel Formation. The Bliss truncates the 

Van Horn, and 1 mile to the east only 75 feet of the 

latter remains.

On the west side of Beach Mountain three-quarters of 

a mile south of the Yates Ranch (sec. 4, Block 66, Twp. 

8), about 325 feet of Van Horn is exposed between the 

Hazel Formation west of Hackberry Creek and the 

Bliss Sandstone on the face of the mountain to the east. 

Farther south in the Red Valley the formation is probably thicker, as it crops out over wide areas and in 

places dips as steeply as 45°.

STRATIGRAPHIC RELATIONS

In most places the Van Horn Sandstone is overlain 

by the much younger Hueco Limestone of Permian age, 

but in a few places, as on Beach Mountain, it is overlain 

by the Bliss Sandstone of Ordovician age.

The Van Horn and Bliss were not differentiated by 

the earlier geologists (Dumble, 1902; Richardson, 1904, 

p. 28; 1914, p. 4), who interpreted the two units as 

gradational deposits; but they are actually distinct, and 

the contact between them can be located with confidence 

in all exposures. A marked change in sedimentation 

occurred between Van Horn and Bliss time from 

coarse arkosic continental unfossiliferous deposits in 

the Van Horn to fine-grained cleanly washed quartzose 

marine fossiliferous deposits in the Bliss.

The Bliss lies unconformably on the Van Horn and 

in nearly all exposures it truncates the tilted beds of the 

underlying formation at a low angle. The sandstone 

of the Van Horn for a few feet below the base of the 

Bliss is commonly bleached from red to yellow by either 

pre-Bliss weathering or later circulation of ground 

water along the contact.

The unconformity between the Bliss and Van Horn 

is well shown on the north face of Beach Mountain 

east of its northwest corner (sec. 19, Block 66, Twp. 7) 

where the angular divergence between their beds is 

20°, causing more than 200 feet of the Van Horn to be 

removed within a mile along the scarp. The unconformity is also well marked on Tumbledown Mountain 

(sec. 27, Block 66, Twp. 7) where the Van Horn is 

dropped against the Allamoore Formation along two 

faults, the Dallas and Grapevine, on which there was 

movement between Van Horn and Bliss time. The 

faulted terrane is truncated by the Bliss Sandstone, 

which lies on the Van Horn on the downthrown sides 

and on the Allamoore on the upthrown sides in the 

angle between the two faults. The Dallas fault has 

not moved since Bliss time, but the Grapevine fault was 

displaced in the same direction later.

AGE

Dumble (1902, p. 1-3) and Richardson (1914, p. 4) 

interpreted the Van Horn as being of "Potsdam" or 

"Upper Cambrian(?)" age, a conclusion based partly 

on the marked unconformity between it and the underlying Hazel and Allamoore Formations and on the 

occurrence of Scolithus, or worm tubes, in its upper 

part. With the discovery that this upper part was 

equivalent to the Bliss Sandstone and was separated 

by a marked unconformity from the lower part, a Cambrian age for the Van Horn became less plausible. 

Moreover, the Van Horn has little resemblance to rocks 

of known Cambrian age elsewhere. It is therefore nowclassed as of Precambrian (?) age.

Arguments favoring a later age for the Van Horn 

are relatively insubstantial. The sandstone lies with 

marked unconformity on the older formations as a result of a time of orogeny and deep erosion, but these
30 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

events need not necessarily mark the end of Precambrian time. It is poorly consolidated, but so also is the 

still earlier Hazel Formation in regions of slight 

deformation. It is the next formation below the fossiliferous Bliss, but the unconformity between them 

indicates that there was a hiatus of unknown duration 

between Van Horn and Ordovician time.

Arguments favoring an earlier age are stronger. The 

unconformity between the Van Horn and Bliss involved 

tilting, faulting, erosion, and changes in sedimentation. 

The Van Horn is unfossiliferous. It was laid down 

in a continental environment in a region of considerable relief, unlike any nearby Cambrian deposits. Its 

deposits are much more like those of the Hazel than 

those of the Paleozoic, and they seem to imply a repetition of some of the conditions under which the earlier 

formation was deposited, after an intervening period 

of orogeny.

ORDOVICIAN 

BLISS SANDSTONE

The Bliss Sandstone was named for Fort Bliss, 

northeast of El Paso, Tex., its typical exposures being 

in the southern part of the Franklin Mountains immediately adjacent (Kichardson, 1904, p. 27; 1909, p. 3). 

In the Sierra Diablo region the sandstone here termed 

the Bliss was at first grouped with the Van Horn Sandstone (Eichardson, 1904, p. 38; 1914, p. 4) or with the 

El Paso Limestone (Sellards, 1932, p. 153-156), and 

was only differentiated later (King, P. B., 1940, p. 153- 

156). Its designation as Bliss has been queried in 

some reports because of uncertainty of correlation with 

the type Bliss, but present knowledge now permits this 

correlation to be made with greater assurance.

DISTRIBUTION

The Bliss Sandstone crops out only in small areas 

in the Sierra Diablo region (pi. 1); elsewhere, it is concealed beneath younger Paleozoic formations or removed by pre-Hueco erosion. The most extensive exposures are on the north, west, and southwest sides of 

Beach Mountain (pi. 2), where it forms a brown band 

on the escarpment, consisting of slopes and thin ledges 

between the red Van Horn Sandstone below and the 

gray and buff sandstone and limestone ledges of the 

El Paso above. The Bliss reappears in small areas 

in the Baylor Mountains to the north, especially in the 

southern part (geologic section 5), and in hills near 

Hawkins Tank in the northwestern part (geologic 

sections).

THICKNESS

In Beach Mountain the Bliss Sandstone maintains a 

nearly uniform thickness of 105 to 125 feet (geologic

sections 1-4, pi. 3, and p. 123-127 2 ), but it thickens in 

the Baylor Mountains from 145 feet in the south (geologic section 5) to 160 feet in the northwest (geologic 

section 8), most of the thickening being caused by 

wedging in of a calcareous division at the top.

MAIN BODY OF FORMATION

The Bliss is characteristically a white or light-brown 

quartzose sandstone, forming beds a few inches to a 

foot thick. According to Cloud and Barnes (1946, 

p. 67), most of the layers are perceptibly calcareous; 

but in the field this is apparent only in the upper division, the main body of the formation appearing to be 

much more quartzitic than the sandstone beds of the 

overlying El Paso. Most of the sandstone beds in the 

Bliss are laminated, crossbedded, and ripple marked, 

and many of them, especially in the upper part, contain 

vertical worm tubes, or Scolitkus. Some of the bedding surfaces are marked by obscure fucoidal structures. Between the sandstone beds the partings of 

softer, more marly sandstone, which are gray, brown, 

purple or green. According to C. S. Ross (written 

commun., 1940), the green coloration is caused by an 

unidentified iron-bearing clay mineral and not by 

glauconite.

The basal few feet of beds of the Bliss, lying unconformably on the Van Horn Sandstone, is a conglomerate of rounded pebbles less than 1 inch to as much as 

3 inches in diameter, mostly of vein quartz but with 

some of chert, quartzite, and schist. In places, pebbly 

layers are interbedded as high as 60 feet above the base. 

Some of the matrix of the basal sandstone is red, from 

detritus reworked from the Van Horn Sandstone.

CALCAREOUS DIVISION

On the north side of Beach Mountain, Cloud and 

Barnes (1946, p. 67) observed a 10-inch bed of dolomite 

near the middle of the Bliss. Sections measured by 

J. Brookes Knight and the writer in this vicinity and 

farther north indicate that the upper part of the Bliss 

differs somewhat from the main body and consists of 

fine-grained slightly calcareous or dolomitic yellowishgray sandstone in beds a foot or so thick, with partings 

of marl and with ramifying mottlings on the bedding 

surfaces. This upper calcareous division of the Bliss 

is 20-28 feet thick on the north side of Beach Mountain (geologic section 4), but thickens to 43 feet in the 

southern Baylor Mountains (geologic section 5) and to 

52 feet farther northwest (geologic section 8). Its sandstone beds lack Scolithus tubes, and no other fossils are

3 Stratigraphie sections of rocks of Ordovician to Cretaceous age 

which have been measured during the present investigation are described at the end of this report and are illustrated graphically on 

plates 3, 5-9.
ORDOVICIAN 31

recorded. In the southern Baylor Mountains the top 

layer of the division is a crossbedded sandstone.

The sandstone beds of the calcareous division have 

some features like those of the basal sandy part of the 

El Paso Limestone, yet they appear to be distinct and 

to be more closely allied to the main body of the Bliss. 

Occurrence of thin dolomite beds in the typical Bliss on 

the north side of Beach Mountain suggests that the 

calcareous division fades out into the main body of the 

formation southward. Nevertheless, the northward 

thickening of the division, and with it the formation as 

a whole, suggests that in this direction beds younger 

than any on Beach Mountain may wedge in beneath the 

disconformity at the base of the El Paso Limestone.

STRATIGRAPHIC RELATIONS

The Bliss appears to be disconformable beneath the 

El Paso Limestone. On Beach Mountain the contact 

between them is sharply marked, and the poorly calcareous quartzose sandstone beds of the Bliss are succeeded abruptly by the calcareous sandstone and limestone beds of the El Paso. In the Baylor Mountains, 

where the calcareous division of the Bliss intervenes, 

the contrast between the two formations appears to be 

equally striking. Moreover, as observed by Cloud and 

Barnes (1946, p. 68), "commonly as much as 10 inches 

of the basal El Paso is a calcareous reworked sand, and 

locally it contains pebbles and cobbles of quartz and 

sandstone." However, the hiatus between the two formations is slight, as both are of Early Ordovician age; 

the Bliss is approximately equivalent to the Tanyard 

Formation, the basal El Paso to the next younger Gorman Formation of the sequence in the Ellenburger 

Group of central Texas.

FOSSILS AND AGE

The most abundant indication of life in the Bliss is 

the trace fossil Scolithus, probably the tube of a burrowing worm, which occurs in every outcrop of the main 

body of the formation, most abundantly in the upper 

part but at some localities to within a few feet of the 

base. The Scolithus of the Bliss is of the type with 

undulating vertical tubes, termed "Sabettarifex" by R. 

Richter (Cloud and Barnes, 1946, p. 67). Although 

Scolithus was cited by Walcott as evidence for the 

Cambrian (Potsdam) age of the beds containing it 

(Dumble, 1902), the fossil ranges widely through lower 

Paleozoic strata, from Lower Cambrian to Silurian, in 

deposits laid down near the shore, and has ecologic 

analogues in existing shoal water to intertidal sandflat environments (P. E. Cloud, Jr., written commun., 

1954).

Many of the bedding surfaces of the sandstone, especially in the upper part of the main body of the

Bliss, are marked by poorly preserved impressions of 

fossil shells, mainly gastropods and linguloid brachiopods. The most extensive fossil collections have been 

made on the west side of Beach Mountain, up the slope 

from the old Dallas mine (geologic section 3, unit 2). 

Here, 4^8 feet below the top of the formation, several 

collectors have obtained a fragment of the cephalopod 

Clarkoceras, various gastropods including Lytospira, 

OpMleta, and Helicotoma, the trilobite Hystricurus, 

and archaeostracan crustaceans. At a lower level, 27 

feet below the top of the formation, the linguloid 

brachiopod Lingulepis has been collected in beds which 

also contain gastropod cross sections.

The higher fauna is clearly of Early Ordovician age, 

and according to Cloud and Barnes (1946, p. 68), is 

equivalent to that in the Tanyard Formation, or basal 

unit of the Ellenburger Group in central Texas. The 

Lingulepis at a lower level is generally considered to be 

an index fossil of the Upper Cambrian, but, as remarked 

by Cloud and Barnes (idem) 

the abundance of gastropods in the Bliss Sandstone of the Beach 

Mountain sequence, below as well as above Lingulepis, is a feature unusual in Cambrian strata; and in view of the striking 

similarity of the various parts of this sandstone the authors 

are inclined to regard it as a single unit * * * of Lower Ordovician age throughout.

REGIONAL RELATIONS

The Bliss Sandstone forms the base of the Paleozoic 

sequence in the Hueco and Franklin Mountains, west 

of the Sierra Diablo in Trans-Pecos Texas, and throughout southern and southwestern New Mexico. Everywhere in this region the Bliss Sandstone maintains 

much the same character and thickness and is a single 

rock-stratigraphic unit, although, as indicated below, 

its stratigraphy is probably complex in detail.

The type Bliss of the Franklin Mountains was originally designated as Upper Cambrian by Walcott (in 

Richardson, 1909, p. 3) on the basis of Lingulepis and 

other linguloid brachiopods; but in the Sierra Diablo 

similar brachiopods are associated with gastropods of 

Ordovician aspect, and Cloud and Barnes (1946, p. 74) 

conclude that the Bliss of the Franklin Mountains 

should "be considered lowest Ordovician until diagnostic evidence is found." Flower (1958, p. 65) concurs with this conclusion.

However, in New Mexico to the north and west 

Flower (1953, p. 2055; 1958, p. 65-66) has found in the 

Bliss at various levels, from one place to another, fossils of Early Ordovician age and of late and middle 

Late Cambrian (Trempealeau and Franconia) ages, and 

he suggests the probable existence of corresponding 

lithologic subdivisions. Still farther west, in southeastern Arizona, the basal sandy deposit is the Bolsa
32 GEOLOGY OP THE SIERRA DIABLO REGION, TEXAS

Quartzite of Middle Cambrian age. This quartzite is 

followed by the Abrigo Limestone of Middle and Late 

Cambrian age, although the Early Ordovician El Paso 

Limestone is also preserved locally.

The Bliss is thus "part of a homotaxic blanket of 

sediments which began to form in the eastward-expanding Sonoran seaway in southeastern Arizona during 

Middle Cambrian time," and which was not laid down 

farther east, in New Mexico and west Texas, until Late 

Cambrian and Early Ordovician time (Kelley and Silver, 1952, p. 55). This general concept requires modification in detail. The Bolsa and Bliss are probably 

distinct sand wedges (Epis, 1958, p. 2754-2756), and 

the Bliss itself may "represent a period of slow and evidently highly intermittent deposition of sandy material" whose base "may be as old as the middle of the 

Franconia, and its top may extend into the basal Ordovician" (Flower, 1953, p. 2055).

EL PASO LIMESTONE

The El Paso Limestone was named for exposures in 

the southern part of the Franklin Mountains near El 

Paso, Tex. (Richardson, 1904, p. 29), and was later restricted to the rocks of Early Ordovician age in that 

area, the Sierra Diablo, and elsewhere (Richardson, 

1908, p. 476-479). Kirk (1934, p. 450) suggested a 

lithologic and faunal subdivision of the El Paso into 

well-defined lower and upper units, termed the "Piloceras-Calatkium beds" and the "Taffia beds," and a 

rather indefinite intervening unit, characterized mainly 

by Ceratopea. These subdivisions were further refined 

by Cloud and Barnes (1946, p. 67, 74) and were informally designated units A, B, and C. This usage is retained here.

DISTRIBUTION AND THICKNESS

In the Sierra Diablo region the El Paso Limestone is 

most prominently exposed on Beach Mountain, of which 

it forms the main bulk (pi. 2). Farther south and west 

it has been removed by pre-Hueco erosion, but to the 

north it emerges from beneath younger formations in 

small areas around the edges of the Baylor Mountains 

(pi. 1). A few of its uppermost beds may be exposed 

much farther north, at the base of a fault block in the 

salient of the Sierra Diablo northwest of the Figure 

Two Ranch (geologic section 9). The El Paso is also 

exposed in the interior of the Sierra Diablo, where it 

forms an inlier north of Cox Mountain, about 7 miles 

long and 2 miles wide, whose rocks are cut off by the 

Cox Mountain fault on the south and overlapped by 

the Hueco Limestone on the north.

The only complete section of the El Paso Limestone 

in the Sierra Diablo region is on the north side of 

Beach Mountain (geologic section 4, pi. 3 and p. 124-

127), where it lies on Bliss Sandstone, is overlain by 

Montoya Dolomite, and is 1,115 feet thick. Elsewhere in 

the region its sequences are not continuous, and only 

basal, middle, or upper parts are exposed.

DIVISION A

Division A, lying on the Bliss Sandstone, is exposed 

mainly in Beach Mountain, but it appears in some places 

in the Baylor Mountains and forms the base of the sequence in the inlier near Cox Mountain. On the north 

side of Beach Mountain (geological section 4) division 

A is about 250 feet thick. It is separately represented 

on the geologic map (pi. 1) and structure sections (pi.

16>' 

In Beach Mountain and elsewhere division A includes

two or three sandstone units, which crop out in prominent rounded yellowish or buff ledges. Individual 

sandstone layers are 5-30 feet thick. The sandstone is 

medium to fine grained and consists of well-rounded 

quartz grains and some feldspar grains, mainly with a 

dolomitic cement. Many of the layers are crossbedded 

and some are glauconitic.

Between the sandstone layers are units of gray to 

yellow limestone, in part dolomitic, some of which are 

strongly mottled and cherty, between which are partings and layers of marl and siltstone. Many of the 

limestone layers are sandy, some are glauconitic, and 

most of them contain abundant gastropods, cephalopod 

siphuncles, and other fossils.

DIVISION B

Division B of the El Paso Limestone is 813 feet thick 

on the north side of Beach Mountain (geologic section 

4). Throughout most of Beach Mountain and the Baylor Mountains the division is a monotonous sequence 

of gray, brownish-gray, or brown dolomite, in beds a 

few inches to 3 feet thick, which stand in prominent 

ledges and steep cliffs. The dolomite is mostly fine 

grained to microgranular, and contains closely to widely 

spaced chert nodules of various sizes, as well as less 

regular siliceous masses. In the lower 100 feet some 

argillaceous and dolomitic limestone is interbedded. 

Many of the dolomitic layers contain dispersed sand 

grains and on the north side of Beach Mountain 60 or 

70 feet of dolomite near the middle is very sandy. Some 

dolomite beds at about the same level are perceptibly 

petroliferous. Most of the fossils in the division are 

poorly preserved but some are silicified, and large collections have been made in some layers. Especially 

abundant and characteristic of the upper half of the 

division are opercula of the gastropod genus Ceratopea.

At the inlier within the Sierra Diablo north of Cox 

Mountain, most of the El Paso Limestone that is exposed belongs to division B, although the upper sand-
ORDOVICIAN 33

stone beds of division A emerge toward the east. The 

lower 350 to 400 feet of division B, exposed near the 

two county roads 3 miles east-northeast of Cox Mountain (western part of sec. 14 and eastern part of sec. 15, 

Block 45%) is largely limestone rather than dolomite 

as farther southeast. The limestone forms beds a few 

thick, with some 4-foot ledges. Many beds are mottled 

gray and yellow, and contain ropy brown chert; but a 

few beds are gray, aphanitic, and abundantly fossiliferous. A few more dolomitic argillaceous layers are interbedded, some of which contain a green clay mineral, 

and there are several layers of intraformational conglomerate.

Higher beds of division B, exposed farther northwest 

near the Edwards Ranch and beyond, are drab-gray or 

brown finely crystalline dolomite, more like the bulk of 

the division in the Beach Mountain area.

DIVISION c

At the top of the El Paso are the poorly resistant 

strata of division C, which form light-colored slopes 

and thin ledges between the darker cliffs and ledges of 

division B below and the Montoya Dolomite above. 

Division C is largely marly, nodular, gray, yellow, or 

buff limestone and dolomite, with some thin layers of 

more compact dolomite. Some of the beds are slightly 

sandy; a few of the more marly ones are greenish, probably from the presence of an iron-bearing clay mineral. On the north side of Beach Mountain (geologic 

section 4) division C is 50 feet thick. About the same 

thickness of similar strata occurs beneath the beds of 

Middle (?) Ordovician age in the Baylor Mountains to 

the northeast.

STRATIGRAPHIC RELATIONS

In the Beach Mountain section the uppermost beds 

of the El Paso Limestone, or division C, are followed 

by the Montoya Dolomite. Fossil evidence indicates 

that the top of the El Paso is of late Early Ordovician 

age and the base of the Montoya of early Late Ordovician age, or a little older, so that the two formations are 

separated by a disconformity. As indicated below, in 

the southeastern part of the Baylor Mountains the El 

Paso Limestone is overlain by a small thickness of beds 

of Middle (?) Ordovician age. These beds are seemingly conformable with division C of the El Paso Limestone, and the disconformity at the base of the Montoya 

Dolomite must pass above them.

FOSSILS AND AGE

Fossils can be observed in the El Paso Limestone in 

most exposures. In many places they are poorly preserved, especially in the middle part, or division B, 

but identifiable material can ordinarily be obtained in 

a few layers. Extensive collections have been made by

various geologists at numerous levels in the formation 

on the north side of Beach Mountain (geologic section 

4) and in the inlier within the Sierra Diablo northeast 

of Cox Mountain (X-l and X-2). Fossils identified 

from these and other collections, and those which were 

observed in the field, are noted at appropriate places in 

the stratigraphic sections and fossil lists (p. 124-131, 

133).

The sequence of fossils as observed on Beach Mountain and elsewhere is capable of zonation and indicates 

that the El Paso Limestone represents a wide span of 

Early Ordovician time. Cloud and Barnes (1946, p. 

57-71) have compared the zones of the Sierra Diablo 

region with those in formations of the Ellenburger 

Group in central Texas and in formations of the Ozark 

uplift in Missouri, although they indicate that there 

is some uncertainty as to their precise equivalents.

The 250 feet of beds of division A is abundantly fossiliferous, except for the lower 70 feet of the Beach 

Mountain section. The division contains the cephalopods Piloceras, AUopiloceras^ and Kirkocerasl (mostly 

represented only by siphuncles), various gastropods including Opfiileta, Hormotoma, and Lecanospira and the 

brachiopods Diaphelasma, and Syntrophina. These fossils indicate that the division is broadly equivalent to 

the Gorman Formation of central Texas and the Roubidoux Formation of Missouri.

The 800 feet or more of beds of division B contains 

more varied faunas, and has been divided on this basis 

by Cloud and Barnes into subunits B 1 and B 2.

Subunit B 1 (units 10-12, geologic section 4, and all 

the collections of X-l and X-2) is broadly equivalent to 

the Honeycut Formation, or highest unit of the Ellenburger Group of central Texas, and to the Jefferson 

City Formation of Missouri. It is divisible into three 

zones (P. E. Cloud, Jr., written commun., 1954). A 

lower zone is characterized by the gastropods Orospira 

and Barnesella, the brachiopod Xenelasma, and the 

trilobite Jeffersonia. A somewhat higher zone contains 

the brachiopod Archaeorthis and Jeffersonia. A still 

higher zone contains a probable new species of Heliocotomaf. In addition, many beds in subunit B 1 contain the sponge Calathium.

Subunit B2 (units 2-9, geologic section 4) is probably 

younger than either the Honeycut or Jefferson City 

Formations of central Texas and Missouri, but older 

than the Black Rock Formation of Arkansas. It is 

characterized especially by opercula of the gastropod 

Oeratopea (Yochelson and Bridge, 1957, p. 293), which 

permit division into two main zones. The lower zone 

is characterized by a variety of C. tennesseensis Oder 

and by C. keitlii TJlrich. A higher zone contains C. aff. 

ankylosa Cullison and Lopfwnemal.
34 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Division C on the north side of Beach Mountain (unit 

1, geologic section 4) contains a small Maclurites, other 

poorly preserved gastropods, the cephalopod Buttsoceras, and unidentified sponges. Cloud and Barnes 

state (1946, p. 352) 

Small Maclurites is common in high Lower Ordovician strata 

at other localities and Buttsoccras is known only from the Odenville Limestone of Alabama, so it is reasonably probable that 

unit C * * * is approximately equivalent to the Odenville 

Limestone of Alabama and correlative with some part of the 

Black Rock Formation of Arkansas * * *.

REGIONAL RELATIONS

The El Paso Limestone is exposed in the Hueco and 

Franklin Mountains west of the Sierra Diablo in TransPecos Texas and also in many of the ranges of southern 

and southeastern New Mexico. In the Franklin Mountains (Kirk, 1934, p. 447-451; Cloud and Barnes, 1946, 

p. 72-75), where the formation is 1,590 feet thick, the 

same divisions as in the Sierra Diablo region are identiable; but the lower two differ much in lithology from 

their equivalents in the Sierra Diablo. Division A includes more dolomite than limestone, and its standstone 

layers are thinner and less conspicuous. Division B, 

on the contrary, is largely limestone, much of it gray 

and mottled, in contrast to its prevailing dolomite in 

the Beach and Baylor Mountains The northwestward 

transition in the division from dolomite to limestone 

apparently begins within the Sierra Diablo region itself, because limestone dominates the lower part in the 

inlier near Cox Mountain, and in the intervening Hueco 

Mountains the division is limestone like that in the 

Franklin Mountains. The increase in sandstone and 

dolomite in divisions A and B from the Franklin Mountains toward the Sierra Diablo may indicate an approach to a shoreline to the southeast, but the position 

of such a shore cannot be closely identified.

Farther north in the Caballo Mountains of New 

Mexico, the names Sierrite Limestone and Bat Cave 

Formation have been given to subdivisions of the El 

Paso (Kelley and Silver, 1952, p. 40-56). Detailed 

stratigraphic work by Flower (1958, p. 67-69) indicates 

that these subdivisions correspond broadly to divisions 

A and B of the Sierra Diablo and Franklin Mountains; 

but the El Paso is no more than 400 feet thick in the 

Caballo Mountains, and division C is missing at the top. 

Presumably the small thickness of the El Paso, and the 

absence of division C, is mainly due to truncation by 

the succeeding Montoya Dolomite. The Bat Cave, or 

upper unit of the Caballo Mountains, thickens southward toward the Franklin Mountains. The truncation 

has been verified by detailed stratigraphic studies by 

Howe (1959, p. 2289, 2292-2293), which demonstrate 

that the upper 245 feet of the El Paso at its type section in the Franklin Mountains is missing in the Organ 

Mountains 30 miles to the north.

Rocks of Early Ordovician age emerge again about 

350 miles east of the Sierra Diablo, in the Llano uplift of 

central Texas, where they form the Ellenburger Group 

(Cloud and Barnes, 1946, p. 22-42). Drilling in the 

intervening West Texas basin indicates that rocks of 

this age are continuous beneath the surface, or nearly so, 

between central Texas and the Sierra Diablo (Galley, 

1958, p. 401^06; Barnes and others, 1959, p. 25-42). 

As indicated by paleontologic data (see above), division 

A and the lower part of division B are broadly equivalent to the Gonnan and Honeycut Formations of the 

Ellenburger Group. The Bliss Sandstone of the Sierra 

Diablo region is broadly equivalent to the basal formation of the group, the Tanyard, but apparently neither 

the upper part of division B nor division C of the El 

Paso Limestone is represented in central Texas.

BEDS OP MU>D:LE<?) ORDOVICIAN AGE

In one area in the Sierra Diablo region, in the southeastern part of the Baylor Mountains, division C of the 

El Paso Limestone is overlain, apparently conformably, 

by strata of probable Middle Ordovician age. These 

strata were observed by the writer during his fieldwork, 

but are sketched only approximately on the geologic 

map (pi. 1); they have been studied further by C. C. 

Branson (written commun., 1950) and H. J. Howe 

(1959, p. 2289-2291), who have termed them the "Simpson (?) Formation.

The strata of Middle (?) Ordovician age extend along 

the southeast-facing escarpment of the Baylor Mountains for about 5 miles, between the El Paso and Montoya Formations. Howe ascribes them, a thickness of 

116 feet, but at least the lower 40 or '50 feet of the interval is equivalent to division C of the El Paso Limestone 

of the Beach Mountain area, so that they are probably 

nowhere more than 60 or 80 feet thick (geologic sections 

6, 7, pi. 3 and p. 128-130).

The strata include two layers of medium-grained 

brown calcereous sandstone, between which are beds of 

shaly or silty limestone and marl, some of which are 

green. Sedimentary analyses of the sandstone indicate 

a textural resemblance to the St. Peter Sandstone of the 

northern interior region (Howe, 1959, p. 2289-2291) 

and a textural difference from the sandstone of the 

Cable Canyon Member of the Montoya, which also apparently occurs in parts of the Sierra Diablo region.

Few fossils have been observed in these strata, but a 

brachiopod was collected in the lower of the two sandstone beds by C. C. Branson, which was identified by 

G. A. Cooper (written commun. to Branson, 1949) as a 

probable Desmortkis, a genus which occurs high in the
ORDOVICIAN 35

Pogonip Group of Nevada and in the Joins and Oil 

Creek Formations of the Simpson Group of Oklahoma.

The strata of Middle (?) Ordovician age in the southeastern part of Beach Mountain are evidently the western featheredge of a unit which is much thicker and 

more extensive farther east, and which is missing farther west. In the West Texas basin drilling indicates 

the presence between the El Paso and Montoya Formations of as much as 2,000 feet of limestone, shale, and 

sandstone, which is of Middle Ordovician age and is 

equivalent to the Simpson Group of Oklahoma (Fillman and others, 1958, p. 122-124; Galley, 1958, p. 

406-407). Middle Ordovician strata, 235 and 930 feet 

thick, have been reported in two deep wells in the Delaware and Apache Mountains, less than 20 miles east of 

the nearest outcrops of Ordovician rocks in the Sierra 

Diablo region (Maley, 1945, p. 280-281; M. E. Upson, 

in DeFord and others, 1951, p. 50-52) (Gulf Oil Corp., 

1 M. A. Grisham, sec. 18, Block 99; Humble Oil & Refining Co., B-l Reynolds Cattle Co., sec. 33, Block 62).

It is appropriate here to mention another reported 

occurrence of beds between the El Paso and Montoya 

in the Sierra Diablo region (King, P. B., 1934a, p. 1541- 

1542; Arick, 1935, p. 118-119). On the salient of the 

Sierra Diablo iy2 miles northwest of the Figure Two 

Ranch (center of southern part of sec. 9, Block 66, 

Twp. 5), the sandstone at the base of the Montoya Dolomite of geologic section 9 is bordered up to the dip to 

the northeast by a descending sequence of dark shale, 

cherty limestone, and finally by light-gray dolomite at 

the edge of the alluvium. Relations are obscured by 

slumping of blocks of the Montoya over strata farther 

down the slope. The questionable beds to the northeast, however, are like no Ordovician strata in the region; they are like the Mississippian, Devonian, and 

Silurian strata exposed not far away and are here interpreted and mapped as a downf aulted block of these 

strata (pi. 1). In a few ravines marly limestone is exposed in sequence below the Montoya on the upthrown 

side of the fault (unit 1, geologic section 9); although 

its age is undetermined, it is tentatively correlated with 

division C of the El Paso Limestone.

MONTOYA DOLOMITE

The type area of the Montoya Dolomite is in the 

Franklin Mountains north of El Paso, Tex., and the 

formation is named for Montoya station on the Santa 

Fe railroad west of the mountains (Richardson, 1908, 

p. 478-479; 1909, p. 4). A more specific type section of 

the formation has more recently been designated and 

measured, and the top redefined (Pray, 1958; Howe, 

1959, p. 2321, fig. 24). At the time of the original work, 

the Montoya was also recognized in the Sierra Diablo

757-10S--&5 4

region (Richardson, 1914, p. 4-5), with much the same 

character and extent as indicated by later investigations.

The Montoya has long been known to contain wellmarked subdivisions in all its areas of exposure, and in 

the Caballo Mountains of New Mexico these subdivisions have been termed the Cable Canyon Sandstone, Upham Dolomite, Aleman Formation, and Cutter Formation (Kelley and Silver, 1952, p. 56-66). 

The Upham forms the lower cliff-making part of the 

Montoya, and the Aleman, the upper slope-making 

cherty part; the Cable Canyon is a basal sandy deposit, gradational into the Upham and not everywhere 

developed; and the Cutter is a unit transferred from 

the Fusselman Dolomite, of which it was formerly 

considered to be a lower member (Darton, 1928, p. 14). 

In the Sierra Diablo region the Upham and Aleman are 

certainly represented in the Montoya and also possibly 

the Cable Canyon, but the Cutter is apparently missing 

(Howe, 1958, p. 2328, fig. 29).

In many recent reports the Montoya has been classed 

as a group and its subdivisions as formations, but this 

is mainly a matter of personal preference. In the present report the subdivisions are classed as members of 

the Montoya Dolomite.

On Beach Mountain the Montoya Dolomite caps the 

El Paso Limestone in parts of the summit areas, and 

is also downf aulted along the eastern side (pi. 1 and 

upper view, pi. 2). It crops out at many places along 

the edges of the Baylor Mountains, generally forming 

the first ledges beneath the Hueco Limestone, although 

the Fusselman Dolomite intervenes in places. In the 

Sierra Diablo farther northwest it forms a small inlier 

in Victorio Canyon west of Yictorio Peak, and is exposed in many of the fault blocks in the salient of the 

Sierra Diablo between the Figure Two Ranch and 

Apache Canyon.

The Montoya Dolomite is generally a cliff-making 

unit. Its lower beds form a wall-like escarpment rising above the weaker beds of the upper part of the 

El Paso, and surmounted by receding ledges of the higher beds. From a distance the formation appears darker 

colored than the underlying and overlying El Paso and 

Fusselman Formations, and its basal sandstone beds, 

where present, form a brown band on the mountain 

sides.

The Montoya Dolomite is 250 to 325 feet thick in the 

eastern Baylor Mountains (geologic sections 6, 7, pi. 3 

and p. 128-130) and is somewhat thinner in the northeastern salient of the Sierra Diablo (geologic sections 9, 

10). On Beach Mountain (geologic section 4) 416 feet 

of beds has been assigned to the Montoya, but the upper 

110 feet might be part of the Fusselman Dolomite.
36 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

CABLE CANYON(?) SANDSTONE MEMBER

In parts of the Sierra Diablo region, sandstone beds 

are prominent at the base of the Montoya, but their 

stratigraphic relations are complex. Most of the sandstone beds in the southeastern part of the Bay lor Mountains are probably below the Montoya and are of 

Middle(?) Ordovician age, whereas those on Beach 

Mountain are gradational with the dolomite of the 

Upham Member and are more certainly part of the 

Montoya. Affinities of the sandstone beds in other 

parts of the region are less clear, and deserve further 

appraisal.

On the north side of Beach Mountain (geologic section 4), a single massive bed lies between division C of 

the El Paso Limestone and the dolomite of the Upham 

Member. It is a ledge-making pinkish sugary sandstone 35 feet thick, dolomitic throughout, and contains 

a few poorly preserved horn corals a,nd brachiopods. 

Farther south on the mountain only the lower 10 feet 

is sandstone; the remainder is sandy dolomite. These 

beds resemble the Cable Canyon Sandstone as described 

in the Caballo Mountains, and like it, appear to be gradational with the Upham above, but precise correlation 

of such basal sandy deposits between distant areas is not 

assured.

In the Baylor Mountains, where several sandstone 

layers occur in the beds of Middle (?) Ordovician age, 

sandstone at the base of the Montoya itself is poorly 

developed, being no more than 10 feet thick in most 

places, and in some, missing altogether. On the salient 

of the Sierra Diablo V/2 miles northwest of the Figure 

Two Ranch (geologic section 9), the Upham Member is 

underlain by 55 feet of sandstone, of which only the 

lower half forms a strong ledge, the upper half being 

thinner bedded and with interbedded marly layers.

UPHAM MEMBER

The Upham Member is a prominent cliff-making unit, 

which is about 100 feet thick toward the south (geologic 

sections 4, 6) but somewhat thinner farther north 

(geologic section 9). For the most part it is a homogeneous light-gray or pinkish-gray fine-grained dolomite, forming massive beds as much as 5 feet thick 

that weather to dark-gray jagged surfaces. Some of 

the beds contain spherical chert nodules, and in the 

southeastern Baylor Mountains there is a very cherty 

layer 30 feet below the top. Few fossils are preserved 

in the dolomite, although silicified brachiopods and 

corals occur in places.

Parts of the member in the northeastern Baylor Mountains (geologic 'section 7) are of a different facies a 

gray limestone mottled by anastomosing yellow dolomite 

and containing fairly abundant fossils. This facies

forms the greater part of the member in the Hueco and 

Franklin Mountains farther west. Probably the homogeneous fine-grained dolomite facies of the member 

developed from the mottled limestone facies by dolomitization and recrystallization (Howe, 1959, p. 2298, 

2299).

ALEMAN CHERTY MEMBER

The Aleman Cherty Member forms a succession of 

cherty ledges above the cliff-making Upham Member, 

and is 150 to 240 feet thick in the south (geologic sections 4, 6, 7) but about 110 feet in the north (geologic 

sections 9,10). The Aleman Member is gray dolomite, 

in beds a few feet thick with interspersed thicker beds. 

Nearly all the beds are cherty, and chert makes up 30 

or 40 percent of the volume of some of the beds. The 

silica content of the member is greater than that of any 

other unit in the Paleozoic sequence in the Sierra Diablo 

region, with the possible exception of the beds of Devonian age.

In some beds chert forms closely spaced layers a few 

inches thick that taper as long lenses; other beds are 

crowded with spherical chert nodules and irregularly 

knotted lenses. Brachiopods, corals, and other fossils 

in the dolomite are also commonly silicified, and project 

on weathered surfaces. Much of the silica in the Aleman 

was probably an original sedimentary constituent, perhaps derived from distant areas of volcanism (Howe, 

1959, p. 2306), although the chert itself has been greatly 

rearranged during diagenesis of the original sediment, 

and later.

On the north side of Beach Mountain (geologic section 4) the 286 feet of strata preserved above the Upham 

Member is notably less cherty than in other sections. 

Two very cherty units, 40 and 25 feet thick, occur in 

the lower part, but the upper 110 feet is a massive cliffmaking dolomite without chert. No fossils were observed in this unit, and although it is tentatively mapped 

with the Montoya and does not resemble the Fusselman 

of nearby areas, it is perhaps an unusual facies of the 

latter, or a remnant of the Cutter Member that is otherwise missing in the region.

At the inlier in Victorio Canyon in the central Sierra 

Diablo, about 100 feet of Montoya is exposed which 

consists of thin to thick beds of gray dolomite, the thinner beds crowded with chert layers and lenses. Both 

the lithologic features and the rather abundant fossils 

indicate that all these beds are part of the Aleman 

Member.

STRATIGRAPHIC RELATIONS

In the Sierra Diablo region the Aleman Cherty Member of the Montoya Dolomite is overlain by the Fusselman Dolomite. Where the Fusselman is of massive 

dolomite facies, the contact is abrupt; but in the few
ORDOVICIAN 37

places where the Fusselman is of limestone facies, the 

contact is more obscure. Although paleontological data 

regarding the age of the Fusselman are rather meager, 

fossils of Silurian aspect have been observed here and 

there, in places not far above its base.

Farther northwest in Texas and in southern New 

Mexico, the Aleman Member is separated from the Fusselman Dolomite by the Cutter Member, about 165 feet 

thick, which contains a fauna of late Late Ordovician 

age (Kelley and Silver, 1952, p. 62-64; Howe, 1959, p. 

2315-2326). Observations by the writer and by Howe 

(1959, p. 2319) indicate that this unit must be missing 

in the Sierra Diablo region. Here, the Aleman Member 

of the Montoya Dolomite is apparently separated from 

the Fusselman Dolomite by a disconformity, whose 

hiatus includes the time during which the Cutter Member was deposited farther northwest.

FOSSILS AND AGE

Fossils are rather plentiful in the Montoya Dolomite 

of the Sierra Diablo region, especially in the Aleman 

Cherty Member, although most are silicified and poorly 

preserved. Collections made during the present investigation are meager, but more extensive ones, which indicate a zonation of the sequence, were made by Howe 

(1959, p. 2328, fig. 29) in the Baylor Mountains.

In the Upham Member streptelasmid and halysitid 

corals and the brachiopod Lepidocyclus (formerly 

Rhynchotrema) were observed at various places in the 

homogeneous fine-grained dolomite facies. More abundant fossils occur in the mottled limestone facies in the 

northeastern Baylor Mountains (geologic section 7), 

where the sponge Receptaculites, halysitid and f avositid 

corals, the brachiopod Lepidocyckis, the gastropod 

Maclurites, and large orthoceratid cephalopods were 

observed.

Near the top of the Upham Member and in the lower 

part of the Aleman Member (geologic section 6) Howe 

(1959, p. 2301, 2310-2314) has obtained an extensive 

brachiopod fauna which includes the genera Lepidocyclus, Onniella, Thaerodonta, Plaesiomys, Rhynchotr&ma, Austinella, and Glyptorthis. Higher in the Aleman he has observed a distinctive zone characterized 

by the coral Paleoptiyllum thomi (Hall).

From various localities in the Aleman Member the 

writer and his colleagues have collected the following, 

which were identified by P. E. Cloud, Jr., Helen Duncan, and Jean Berdan: streptelasmatid corals of the 

Streptelasma foerstei and S. prolongatum groups, Foerstephytluml, PcHeophyllum thomi (Hall), trepostomatous bryozoans, Dinorthis (Plaesiomys], "Rafinesquina" 

Platystroptiia, Lepidocyclus, and HypsiptycKwl

Opinions have varied among paleontologists as to the 

age of the Montoya and related units in the Western

States. According to the original determinations by 

Ulrich (in "Richardson, 1909, p. 4), the Montoya contains faunas of two ages, one of Trenton (Galena) age 

in the Upham Member and the other of Richmond 

(Fernvale) age in the Aleman Member. On the other 

hand, Kirk (in Richardson, 1914, p. 4; Kirk, 1930, p. 

464, 465) judged that the whole formation was of Late 

Ordovician age, although perhaps pre-Richmond. More 

recently available evidence has been reviewed by Howe 

(1959, p.2301,2302,2315).

Perhaps the fauna in the Montoya that is most significant for correlation with the eastern Ordovician 

sequences is the assemblage of brachiopods which occurs 

in the upper part of the Upham Member and lower part 

of the Aleman Member. This faunal assemblage has 

close affinities with that of the Elgin Limestone Member 

of the lower part of the Maquoketa Shale of Iowa and 

may be correlative (Howe, 1959, p. 2301). Correlation 

of the Maquoketa with the type Cincinnatian (Upper 

Ordovician) of Ohio is subject to alternative interpretations ; it may be entirely of Richmond age, or it may 

include equivalents of the Eden, Maysville, and Richmond. If the former interpretation is correct, both 

the Upham and Aleman Members of the Montoya are of 

Late Ordovician age; if the latter, the Upham Member 

includes beds of late Middle Ordovician (Trenton) age.

According to Howe, the fauna of the lower part of 

the Upham Member, including Receptaculites and 

Maclurites, "finds its closest relation with the Red 

River formation of southern Manitoba and its widespread correlatives" (1959, p. 2301), but the age of the 

Red River in terms of the eastern sequences has not been 

established. The higher brachiopod faunas of the 

Aleman member "possess a strong upper Maquoketa 

aspect" (1959, p. 2315). The fauna of the Cutter Member, which overlies the Aleman west of the Sierra 

Diablo, is of Late Ordovician and probably Richmond 

age (1959, p. 2326).

For purposes of the present report, it seems best to 

classify all the Montoya Dolomite as of Late Ordovician 

age, but with recognition that at least part of the Upham Member may be somewhat older.

REGIONAL RELATIONS

The Montoya Dolomite is exposed in the Hueco and 

Franklin Mountains northwest of the Sierra Diablo in 

Texas and in the mountains of southern New Mexico at 

least as far north as the Caballo Mountains and as far 

west as Silver City. Throughout this area the formation and its members are remarkably constant, except 

for minor regional variations and for the more drastic 

disappearance of the Cutter Member eastward in the 

Sierra Diablo. The regional aspects of the Montoya in 

west Texas and New Mexico have been reviewed by
38 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Kelley and Silver (1952, p. 64-66) and have been 

studied in more detail by Howe (1959).

The Montoya Dolomite extends eastward beneath the 

surface from its outcrops in the Sierra Diablo and underlies that part of the West Texas basin southwest of a 

line between Lubbock and Edwards Counties, Tex. 

(Fillman and others, 1958, p. 90-93; Galley, 1958, p. 

407-410). Except for a single small remnant (Barnes, 

Cloud, and Duncan, 1953), no rocks of Late Ordovician 

age are preserved in the outcrops of older Paleozoic 

rocks farther east, in the Llano uplift of central Texas.

SILTJEIAN 

FTJSSHLMAN DOLOMITE

The Fusselman Dolomite was named for exposures 

near Fusselman Canyon in the Franklin Mountains 

north of El Paso, Tex. (Richardson, 1908, p. 479-480; 

1909, p. 4). Later, a type section of the Fusselman was 

designated farther north in the Franklin Mountains, 

and the base of the formation was redefined (Pray, 

1958). Existence of the Fusselman Dolomite in the 

Sierra Diablo region was not reported during the earlier 

investigations (Richardson, 1914) and was only discovered later (King, P. B., 1932).

DISTEIBUTION

In the Sierra Diablo region the Fusselman Dolomite 

crops out in more restricted areas than the earlier 

Paleozoic formations, as it has been more extensively removed by pre-Hueco erosion. It is exposed discontinuously beneath the Hueco along the eastern escarpment of the Bay lor Mountains for several miles north 

and south of the eastern portal of Red Tank Canyon; 

it also occurs in many of the fault blocks in the salient 

of the Sierra Diablo between the Figure Two Ranch and 

Apache Canyon (pi. 1).

THICKNESS

The full thickness of the Fusselman Dolomite between the Montoya Dolomite below and the beds of 

Devonian age above is preserved in few of its exposures. 

In most places the eroded top of the Fusselman is overlain by Hueco Limestone, and where beds of Devonian 

age overlie the Fusselman, its base is concealed. One 

of the most prominent exposures of the Fusselman in 

the region is on the point of the mountains 1% miles 

northwest of the Figure Two Ranch (geologic section 

9, pi. 3 and p. 131-132), where it forms a wall-like ridge, 

bordered on the northeast by Montoya Dolomite and on 

the southwest by beds of Devonian and Mississippian 

age; however, the structure is obscure and the rocks 

dip steeply, so that their thickness is uncertain.

In the northeastern B,aylor Mountains (geologic section 7) where the structure is plainer, the thickness of

the Fusselman between the Montoya and beds of Devonian age is about 300 feet. At Apache Spring in the 

northern Sierra Diablo (geologic section 10), 420 feet 

of Fusselman occurs between the Montoya and the 

Hueco, but the beds of Devonian age and an unknown 

thickness of the upper part of the Fusselman have been 

removed by pre-Hueco erosion. The two sections indicate a northward thickening of the Fusselman, which 

is the reverse of relations in the Montoya.

LITHOLOGY

Throughout much of its extent the Fusselman is a 

monotonous body of massive white or light-gray 

crystalline dolomite, without chert. Dolomitization 

during diagenesis has destroyed or obscured much of 

its original structure. The greater part of the dolomite is now finely crystalline or sugary, with ghosts of 

fossils here and there, and with patches, vugs, and veinlets of coarsely crystalline calcite. Indistinct bedding 

planes divide it into layers a few feet to more than 5 

feet thick, with some partings of thin-bedded hackly 

dolomite. The dolomite crops out in light-gray ragged 

bouldery surfaces, which contrast with the darker gray 

well-bedded ledges of the Montoya and Hueco Formations below and above.

At a few places the massive dolomite grades into 

another facies of darker gray well-bedded limestone 

and dolomitic limestone, containing chert and silicified 

fossils in many layers. This facies occurs in the Baylor 

Mountains near the eastern portal of Red Tank Canyon 

(sec. 4, Block 122) and at Apache Spring (northeastern 

part of sec. 7, Block 66, Twp. 5). Near Apache Spring 

the facies contains irregularly bedded reefy limestone 

bodies as much as 30 feet thick, formed largely of 

corals. The well-bedded limestone and dolomitic limestone beds somewhat resemble the upper beds of the 

Montoya Dolomite on which they lie, and when first 

observed during the present investigation, they were 

mapped with that formation. They are distinguishable from the Montoya because they overlie the full 

thickness of its Aleman Member, and because of their 

gradational relations with the dolomitic facies of the 

Fusselman. Both in the Baylor Mountains and at 

Apache Spring some thin to thick layers of light-gray 

dolomite are interbedded with the limestone; these layers thicken toward the areas of dolomite, so that one 

facies is replaced entirely by the other within less than a 

mile.

The dolomite and limestone facies of the Fusselman 

are probably reef and interreef deposits which were laid 

down contemporaneously on adjacent parts of the sea 

floor. Within the limits of exposure, gradation from 

one to the other takes place in varied directions, and
DEVONIAN 39

the exposures are not extensive enough to indicate any 

general pattern. Similar gradations on a smaller scale 

have been observed in the Franklin Mountains (Pray, 

1958, p. 36); they also resemble the gradations which 

have been reported between the Silurian Lone Mountain 

and Roberts Mountains Formations in Nevada (Winterer and Murphy, 1960).

STRATIGRAPHIC RELATIONS

The Fusselman Dolomite is overlain abruptly by 

chert, siliceous shale, and thin-bedded limestone of 

Devonian age. No indications of erosion were observed 

at the contact, but the two formations are probably disconformable and are separated by a hiatus that represents considerable parts of Silurian and Devonian time.

FOSSILS AND AGE

Fossils in the dolomitic f acies of the Fusselman are 

mostly poorly preserved and difficult to identify, because 

of the prevailing recrystallization; better preserved 

fossils occur in the limestone facies, some of which are 

silicified.

At most localities in both the dolomite and the limestone, the common fossils are colonial corals of favositid 

and halysitid types, and various horn corals, but more 

varied assemblages were observed or collected in places. 

In dolomite in the upper part of the formation north of 

the mouth of Black John Canyon (center of western 

part of sec. 9, Block 66, Twp. 5), Josiah Bridge and 

J. Brookes Knight observed stromatoporoids, f avositid 

corals, crinoid stems, pentamerid brachiopods, and 

trilobite fragments. On the ridge north of Apache 

Spring (northeastern part of sec. 7, Block 66, Twp. 5) 

in the limestone facies, the same geologists collected the 

trilobite Dalmanites from near the middle of the formation and stromatoporiods, f avositid and halysitid corals, 

and brachiopods from higher and lower beds.

Information obtained during the present investigation is insufficient to determine closely the age of the 

Fusselman Dolomite in the Sierra Diablo region, and 

the fossil collections which were made are not now available for further study. The various corals could not be 

differentiated in the field from those in the Montoya 

Dolomite and would require more detailed study than 

has been given to them if they were to yield diagnostic 

evidence. However, the occurrence in the Fusselman 

of pentamerid brachiopods and Dalmanites suggests 

that the formation is partly or wholly of Silurian age.

REGIONAL RELATIONS

Like the underlying Paleozoic formations, the Fusselman Dolomite extends farther west in Trans-Pecos 

Texas and also occurs in many of the ranges of southern 

and southwestern New Mexico. It attains a maximum

thickness of about 770 feet in its type area in the Franklin Mountains, and in New Mexico is a few hundred 

feet thick or less.

The Fusselman has been assigned a Middle Silurian, 

or Niagaran age (Richardson, 1909, p. 4; Darton, 1928, 

p. 14), but recent observations in New Mexico indicate 

that the formation as originally defined contains strata 

of more varied ages. In New Mexico two members in 

the Fusselman have long been recognized, but the lower, 

or Cutter Member, is now known to contain fossils of 

Late Ordovician age, and has been transferred to the 

Montoya (see above). In the restricted Fusselman fossils representing different ages of Middle Silurian and 

possibly Early Silurian time have been obtained, so that 

the formation may include two or more original depositional units, whose identity has been obscured by 

dolomitization (Flower, 1958, p. 72).

Rocks of Silurian age have been penetrated by drilling in the western part of the West Texas basin east of 

the Sierra Diablo, and part of them has been designated 

as Fusselman; but this part, however, interfingers with 

other units, and the stratigraphy of the whole is as yet 

uncertain (Fillman and others, 1958, p. 53-57).

DEVONIAN 

BEDS OF DEVONIAN AGE

Overlying the Fusselman Dolomite in a few places in 

the Sierra Diablo region is a thin unit of chert, thinbedded limestone, and shale of Devonian age. As theunit is scantily preserved in the Sierra Diablo, it is inappropriate to give it a new stratigraphic name based 

on that region; moreover, stratigraphic terminology of 

better preserved comparable beds in the Hueco and 

Franklin Mountains farther west has not been satisfactorily resolved. In this report the unit will therefore 

be referred to by the informal title of "beds of Devonian.

ajre.

DISTRIBUTION AND THICKNESS

Beds of Devonian age are preserved in two areas inthe Sierra Diablo region (pi. 1). Their main occurrence 

is near Black John Canyon in the salient of the Sierra 

Diablo northwest of the Figure Two Ranch (sees. 9 and 

12, Block 66, Twp. 5), where they form parts of many 

of the fault blocks in an area of several square miles. 

Relations are complex, not only because of the faulting 

during Cenozoic time, but also because of pre-Hueco> 

deformation and the unconformity at the base of the 

Hueco, so that complete sections of the unit are preserved 

in few places. In the outermost fault block in the salient 

of the Sierra Diablo (northeast of base of geologic section 9), the full thickness of this unit between the Fusselman Dolomite on the northeast and the Barnett Shale 

on the southeast appears to be about 125 feet. Beds of
40 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Devonian age are also preserved in a much, smaller area 

in the Baylor Mountains to the south, on the southeastern spur of the high point of the mountains (unit 14, 

geologic section 7, pi. 3, sec. 11, Block 122), where 30-50 

feet of the lower part of the unit intervenes between the 

underlying Fusselman and the overlying Hueco Limestone.

LITHOLOGY

Beds of Devonian age are characteristically siliceous. 

In large part they are bedded chert, mainly buff or 

brown, but partly white, gray, black, or dull green, in 

layers less than an inch to several inches thick; near the 

middle there are also some more massive beds of buff 

vitreous chert a foot or more thick. Some of the chert, 

especially in the lower part, is interbedded with dolomitic or argillaceous thin-bedded limestone, which itself 

contains many irregular chert nodules and lenses. In 

the upper part the chert is interbedded with, and grades 

into, siliceous shale, which is platy, black or brown, and 

bituminous. Conodonts, spicules, and spores are visible 

under a hand lens in many of the shales. These upper 

shaly beds are preserved only in the salient of the Sierra 

Diablo; the remnant in the Baylor Mountains (geologic 

section 7) consists only of the lower chert and limestone 

beds.

STRATIGRAPHIC RELATIONS

In most places the beds of Devonian age are overlain 

with angular unconformity by the Hueco Limestone, but 

the next higher unit of the normal sequence, the late 

Mississippian Barnett Shale, is preserved in the southeastern part of the salient of the Sierra Diablo. Exposures there are insufficient to determine its relations 

to the beds of Devonian age, but the known ages of the 

two units suggest that they are disconf ormable and are 

separated by a large hiatus.

FOSSILS AND AGE

Collections were made by W. H. Hass and others in 

1938 from the beds of Devonian age in the lower course 

of Black John Canyon (southeastern part of sec. 9, 

Block 66, Twp. 5). The material collected is gray and 

brown shale and siltstone, presumably from the upper 

part of the unit. In this material W. H. Hass (written 

commun., 1959) has identified the following conodonts:

Ancyrodella sp.

Ancyrognathus euglyphea Stauffer

Bryantodus sp.

Hibbardella sp.

Hindeodella sp.

Icriodus sp.

Ligonodina sp.

Neoprioniodus alatus Hinde

Paltnatolepis cf. P. subrecta Miller and Youngquist

Paltnatolepis sp.

Polygnathus sp.

According to Hass 

Conodonts in this collection indicate that the rocks from 

which they came are early Late Devonian. This age determination is based chiefly on the presence of Ancyrognathus 

euglyphea and Neoprioniodus alatus. In the western New York 

section Ancyrognathus euglyphea had been found by me in the 

Pipe Creek member of the Hanover shale, and in Chadwick's 

type Letchworth shale, which Pepper, DeWitt, and Colton place 

in their West Falls formation. All of these formations fall into 

G. A. Cooper's Chemung stage of the Upper Devonian. I have 

also collected A. euglyphea from the basal beds of the Dunkirk 

shale near Hornell, New York. This formation is the basal 

member of Pepper and DeWitt's Perrysburg formation. 

Neoprioniodus alatus has a somewhat longer range. It appears 

to range from very high in the Middle Devonian into the highest 

beds of the Upper Devonian Hanover shale. The species is most 

common in authentic Upper Devonian rocks. The specimens 

identified as Palmatolepis cf. P. subrecta occur in the collection 

as molds. P. subrecta is commonly found associated with 

Ancyrognathus euglyphea in New York and elsewhere throughout the Interior States. Supporting evidence for a Devonian 

age is indicated by other specimens, which belong to the following genera: Ancyrodella whose known range is high Middle 

Devonian-Upper Devonian; Icriodus, Devonian; and Palmatolepis, Upper Devonian.

REGIONAL RELATIONS

Beds of Devonian age crop out in the Hueco and 

Franklin Mountains farther west in Trans-Pecos Texas 

and also in many of the ranges of southern and southwestern New Mexico.

The beds in New Mexico have long been termed the 

Percha Shale (Barton, 1928, p. 15-16), but later they 

were subdivided into various formations of Middle to 

Late Devonian age (Stevenson, 1945, p. 220). Other 

geologists (Kelley and Silver, 1952, p. 72-78) have 

judged that these formations are faunal zones and not 

mappable; hence, they have retained the name Percha 

for the whole unit.

In the Franklin Mountains north of El Paso, Tex., 

beds of Devonian age, lying between the Fusselman 

Dolomite and beds of Mississippian age, are about 175 

feet thick, they have been termed the Canutillo Formation (Nelson, 1940, p. 1964; Cooper and others, 1942, 

p. 1749; King, P. B., King, E. E., and Knight, J. B., 

1945, section A, sheet 2; Laudon and Bowsher, 1949, p. 

46). Part of these beds may be equivalent to those 

in New Mexico; but they are not entirely comparable, 

and despite their small thickness their stratigraphy 

may be complex. The Canutillo of the Franklin 

Mountains includes an upper shale, a medial fossiliferous limestone, sandstone, and siltstone, and a lower 

chert. The upper shale has been correlated with, the 

restricted Percha of New Mexico and the medial unit 

with the Onate Formation of New Mexico (idem); 

hence, these parts are of late Middle and early Late 

Devonian age. The lower chert has yielded few or no
MISSISSIPPIAN 41

fossils and its age is undetermined, except that it is 

older than the beds of Middle Devonian age and is 

younger than the Silurian Fusselman. A similar, but 

less fossiliferous, sequence occurs in the Hueco Mountains (King, P. B., King, R. E., and Knight, J. B., 1945, 

sections B to F, sheet 2; Loudon and Bowsher, 1949, 

p. 32-34).

In the Sierra Diablo the conodont-bearing beds are 

probably in the upper part of the unit here discussed. 

According to Hass, these beds are of early late Devonian age, hence probably equivalent to the middle or 

upper part of the Canutillo. They may also be equivalent to part of the Woodford Chert of Late Devonian 

and Early Mississippian age, which has been identified 

in the West Texas basin to the east (Fillman and others, 1958, p. 144-145) and in a drill hole between the 

Sierra Diablo and Hueco Mountains to the northwest 

(Lloyd, 1949, p. 50). However, the dominantly cherty 

beds which form the greater part of the unit in the 

Sierra Diablo are probably correlative with the lower 

chert of the Canutillo Formation in the Franklin 

Mountains and, like it, belong to some undetermined 

earlier part of the Devonian.

Correlation of the lower cherty beds in the Sierra 

Diablo and Franklin Mountains with the Caballos 

Nbvaculite of the Marathon region farther southeast 

has been suggested (King, P. B., and King, R. E., 

1929, p. 912; King, P. B., 1932, p. 96); but this correlation has little precise meaning, as the Caballos is probably a composite unit, formed during a relatively long 

span of Devonian and possibly early Mississippian time 

(Berry and Neilsen, 1958, p. 2258-2259).

MISSISSIPPIA1T 

BARNETT SHAIKH

Beds of Mississippian age in the Sierra Diablo region 

were previously designated the Helms Formation 

(King, P. B., 1934a, p. 1542-1543; King, P. B., and 

Knight, J. B., 1944), for a unit whose type area is in 

the Hueco Mountains farther northwest in TransPecos Texas. The beds in the Sierra Diablo are of the 

same general age as the typical Helms, but, as explained 

below, are of different facies and are more like the 

Barnett Formation, whose type area is in the Llano 

uplift of central Texas (Plummer and Moore, 1921, p. 

24); the name Barnett is therefore used in this report.

DISTBIBUTION

In the Sierra Diablo region the Barnett Shale is exposed only on the southeast side of the salient of the 

Sierra Diablo northwest of the Figure Two Ranch 

(mainly in sec. 12, Block 66, Twp. 5; pi. 1). Its main

occurrence is on the southwestern or upthrown side of 

the complex of fault blocks in the salient, but a small 

remnant is also preserved in the northeasternmost fault 

block of the salient (south-central part of sec. 9, Block 

66, Twp. 5). Through most of its extent the Barnett 

is overlain by the Hueco Limestone, and much of its 

surface is covered by landslides, talus, and wash derived from that formation. It is thus exposed only 

intermittently, where ravines have cut through these 

surficial deposits.

LITHOLOGY AND THICKNESS

The Barnett is black, purplish, or dark-gray, carbonaceous shale, which contains small phosphatic and pyritic nodules and lenses and beds of earthy limestone. 

Most of the shale is barren of larger fossils, but limestone lenses contain cephalopods, fish teeth, and a few 

pelecypods and brachiopods. Fossils in the limestone 

lenses weather free and strew the surface of the 

outcrops.

The Barnett Shale is visible only in small outcrops, 

so that its full thickness cannot be determined. In the 

northeasternmost fault block of the salient about 75 

feet is exposed, lying on beds of Devonian age and cut 

off by a fault above. About a mile to the southwest a 

large ravine exposes 135 feet of beds beneath the Hueco 

Limestone. (See geologic section 11, p. 133-134.)

STRATIGRAPHIC RELATIONS

Although the Barnett Shale is overlain unconformably by the Hueco Limestone in most places, it is bordered on the south by limestone and shale of Pennsylvanian age. The contact of the two units is not exposed, 

although small outcrops of each lie closely adjacent; 

presumably, however, the beds of Pennsylvanian age 

succeed the Barnett in normal stratigraphic order. As 

the Barnett is of Late Mississippian age and the limestone and shale are of Early Pennsylvania age at their 

base, the two stratigraphic units are probably conformable or are separated at most by only a small hiatus.

FOSSILS AND AGE

The principal occurrence of larger fossils in the 

Barnett Shale of the Sierra Diablo region is in the exposures described under geologic section 11. In 1931 

J. Brookes Knight collected fossils from units 2,3, and 4 

of geologic section 11 (USGS 7019), and in 1936 obtained additional material, probably from the same locality (USGS 14945). From these collections, the following forms have been identified by Mackenzie Gordon, 

Jr., and E. L. Yochelson, who supplemented earlier
42 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

identifications by G. H. Girty (written comimm.; 1954, 

1955):

Coelenterata:

zaphrentoid coral, gen. undet______________

Brachiopoda:

Composita sp_________________________

Leiorhynchus sp___-___________________.

Ambocoelia sp__ _ _______________________

Cleiothyridinat sp_ ____________________

Lamellibranchiata:

Edmondia? sp__________________________

Posidoniella sp_________________________

Nuculana sp___________________________

Cypricardella sp________________________

Gastropoda:

Indeterminate specimen ______________

Cephalopoda:

Bactrites sp____________________________

orthoceratoid nautiloid- _________ __________

Girtyoceras sp____________________________

Neoglyphioceras cloudi (Miller and Youngquist)_________-_______-___-_---___.

Neoglyphioceras sp_____________________

Goniatites choctawensis Shumard__________

Goniatites crenistria Phillips______________

Pisces:

Fish teeth and plates____________________.

USGS Collection No.

7019 14945

X

X 

X

X

X 

X 

X

X 

X 

X

X

X 

X

X

X 

X

X 

X

X 

X

X 

X 

X

X

From another collection from the same locality 

Miller and Furnish have identified the cephalopods 

Goniatites sp., Girtyoveras sp. cf. G. mesleranum 

(Girty), and Lyrogoniatites sp. cf. L. newsomi (Smith) 

(W. M. Furnish, written commun., 1959).

According to Gordon 

These collections are Mississippian in age (Meramec-Chester). 

Goniatites choctawensis and NeoglypJiioceras cloudi are also 

known from the Barnett shale of north-central Texas and represent a zone that elsewhere crosses the Meramec-Chester 

boundary. A wide form of G. crenistria first described from 

British rocks is found in the upper part of the Moorefield Formation of Arkansas. G. choctawensis appears higher, in the 

Ruddell Shale and Batesville Sandstone. The two species of 

Goniatites are not generally found together, G, crenistria being 

an earlier form.

According to Furnish 

The lirate goniatitids are one of the indices for P2 or upper 

Visean, world-wide. This now means upper Bollandian of 

northern England and lower Ohesterian of the Midcontinent.

\

REGIONAL RELATIONS

From its type area in central Texas the Barnett 

Shale extends westward beneath the West Texas Basin, 

where it has been penetrated by drilling (Galley, 1958,

p. 414-417). Throughout its extent it is a deposit of 

black shale f acies, generally of middle to late Mississippian age, containing brachiopods (LeiorJiynchus) , 

various cephalopods, and other fossils characteristic of 

that facies. In its type area the Barnett is mainly of 

Meramec age and probably does not extend into the 

Chester (Cloud and Barnes, 1946, p. 59), but in the 

West Texas basin Fillman and others (1958, p. 16-17) 

state that similar shale 

varies in age from place to place in the subsurface so that its 

age is Kinderhook, Osage, Meramec, and Chester in the southern part of the Midland and Delaware basins and Central Basin 

platform. Northward the Barnett Shale grades laterally into 

limestone which comes into the section from the bottom, so that 

its age is progressively younger and younger until in northern 

Gaines County it is restricted to the Chester.

Presumably the shale exposed in the Sierra Diablo lies 

near the western edge of this broad sheet of deposit. 

Farther northwest in Trans-Pecos Texas, in the 

Hueco Mountains and beyond, equivalent beds of middle to late Mississippian age are of different facies, and 

constitute the Helms Formation (Beede, 1920, p. 7-8; 

King, P. B., King, K. E. and Knight, J. B., 1945, sheet 

2). The Helms consists of 300 to 500 feet of slabby 

limestone, gray and cherty below, changing to brown 

and sandy above, where much green shale is interbedded. It contains brachiopods, bryozoans, and crinoidal fragments of several faunas, the lower of which 

are of Meramec age and the higher of Chester age. 

Some geologists have restricted the name Helms to the 

Chester part of the sequence and have named the Meramec part the Eancheria Formation (Laudon and 

Bowsher, 1949, p. 17-30, 34), but it is doubtful whether 

these subdivisions represent more than faunal zones. 

The Helms is probably an equivalent on the outcrop of 

the limestones which interfinger northward with the 

Barnett in the West Texas basin, as described above. 

Presumably a similar interfingering between the Barnett and Helms facies occurs between the Sierra Diablo 

and Hueco Mountains, beneath the surface of the Diablo 

Plateau.

PENNSYLVANIA^ 

BEDS OF PENNSYLVANTAN AGE

Beds of Pennsylvanian age in the Sierra Diablo were 

previously termed Bend Formation and Magdalena 

Limestone (King, P. B., and Knight, J. B., 1944), the 

first name being derived from central Texas and the 

second from New Mexico. For the present, however, 

it seems best not to give them formal names. The beds 

which are exposed in the Sierra Diablo are only fragments of a larger sequence, and although they may be 

equivalent to parts of the Bend and Magdalena in their 

typical areas, the latter have much broader strati-
PENNSYLVANIAN 43

graphic range. Moreover, relations between the socalled Bend and Magdalena within the Sierra Diablo 

itself, are in doubt as indicated below.

DISTRIBUTION

Beds of Pennsylvanian age are exposed along the 

lower part of the Sierra Diablo escarpment west and 

southwest of the Figure Two Kanch for a distance of 

about 3 miles, or from north of Mine Canyon to south 

of Marble Canyon (pis. 1, 14). However, its outcrops 

are interrupted for more than a mile in the middle, 

between Mine and Marble Canyons, where Hueco Limestone and Tertiary intrusive rocks extend to the base 

of the escarpment. Moreover, the Pennsylvanian rocks 

north of Mine Canyon, like the adjacent Barnett Shale, 

are extensively concealed by landslides and wash from 

the Hueco Limestone higher on the slope.

LOCAL FEATURES

The strata north of Mine Canyon (western part of 

sec. 16, Block 66, Twp. 5) are those previously called 

Bend Formation. Both sequence and structure are obscure because of poor exposures, but there is apparently 

a lower limestone and an upper shale, which dip generally southward and are truncated northward by the 

unconformity at the base of the Hueco Limestone.

The lower limestone is well exposed in several ravines 

near the foot of the escarpment on the downthrown side 

of a fault in the northwestern part of sec. 16, where 

about 35 feet of beds is visible. The limestone is fine 

grained to aphanitic, dark gray to black, and weathers 

variously buff, yellow brown, or blue gray. The beds 

are a foot or two to less than an inch thick, and some 

are separated by layers of platy, shaly limestone. The 

limestone is interbedded with units as much as 4 feet 

thick of brown or black bedded chert. It is only 

sparsely fossiliferous, but small collections have been 

obtained.

The upper shale is mainly exposed farther south, in 

the southwestern part of sec. 16, near some f elsite intrusives that project as low knobs at the foot of the escarpment. The shale is best revealed just north of the 

portal of Mine Canyon, but because it is much decomposed at the surface, no more than 10 feet of beds is 

exposed at any one place. The shale is poorly consolidated, gray to black, carbonaceous, and richly fossiliferous. Large areas of its surface are strewn with fossils 

that were originally pyritized, but which have now 

weathered to limonite and have been separated from 

their matrix.

The beds of Pennsylvanian age south of Marble Canyon (east edge of sec. 21, Block 66, Twp. 5), like those 

north of Mine Canyon, form the basal part of the Sierra 

Diablo escarpment and are overlain unconformably by 

the Hueco Limestone. However, as this part is formed

of thicker bedded strata than those farther north, it is 

much better exposed. Its tilted ledges beneath the flatlying Hueco are plainly visibly from Texas Highway 

54, nearly 2 miles distant to the east (upper view, 

pi. 10).

The Pennsylvanian rocks in this area are gray granular thick-bedded limestone that stands in prominent 

rounded ledges as much as 25 feet thick separated by 

thinner bedded limestone of much the same nature. 

Some of the layers contain moderately abundant fossils, 

but none of the limestone is cherty. The beds dip about 

10° southward, each bed being truncated northward by 

the unconformity at the base of the Hueco, so that, 

although less than 100 feet is exposed at any one place, 

more than 170 feet of beds occurs in a distance of about 

half a mile along the scarp. (See geologic section 12.)

STRATIGRAPHIC RELATIONS

The Pennsylvanian rocks, like the other pre-Permian 

formations of the Sierra Diablo region, lie with angular 

unconformity beneath the Hueco Limestone. The 

strata are the youngest which are preserved beneath 

this unconformity at any exposure in the region, and 

probably lie in the trough of a syncline that was produced during the pre-Hueco deformation (fig. 2). As 

indicated below, the part of the Pennsylvanian sequence 

that is preserved in the Sierra Diablo is no younger than 

Middle Pennsylvanian age, and strata of later Pennsylvanian age are missing. These beds and the Hueco are 

thus separated by a considerable hiatus.

FOSSILS AND AGE

The Pennsylvanian rocks of the Sierra Diablo region 

are sparingly to abundantly fossiliferous, the most prolific part being the upper shale beds north of Mine Canyon, whose fossils have previously been discussed by 

Arick (1932, p. 485-486), Plummer and Scott (1937, p. 

25), and Miller and Furnish (1940b). The fossil collections from these beds that are here reported on were 

identified by Mackenzie Gordon, Jr., and E. L. Yochelson, supplementing earlier identifications by G. H. 

Girty (written commun., 1954,1955).

A few fossils were collected by J. Brookes Knight in 

1931 from the lower limestone north of Mine Canyon, 

from exposures in the northwestern part of sec. 16, 

Block 66, Twp. 5 (USGS 7023). These consist of 

Chonetes sp., Cleiothyridina sp., and G-astrioceras 

octidentale (Miller and Faber). In addition, gastropods were observed in the limestone in the field, but they 

are not now represented in the collections. These 

fossils are too meager to indicate the stratigraphic position of the beds containing them, but the Gastrioceras 

also occurs in the upper shale beds, exposed nearby to 

the south.
44 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

EXPLANATION

MODERN OUTCROP AREAS

Rocks older than Permian

Limestone and shale of 

Pennsylvanian age

M 

Mississippian

Barnett Shale

DS

Devonian and Silurian

Beds of Devonian age and

Fusselman Dolomite

Oum

Upper and Middle (?) Ordovician

Montoya Dolomite and beds of

Middle(?) Ordovician age

01

Lower Ordovician 

El Paso Limestone and Bliss Sandstone

p v 

Precambrian(?)

Van Horn Sandstone

p 

Precambrian

Hazel, Allamoore, and Carrizo Mountain 

Formations, and associated igneous rucks

Modern geologic contact

Known or inferred 

paleogeologic contact

Faults which are known or inferred to

have been displaced in pre-Permian time

Dotted where concealed by younger

pre-Permian deposits

FIGUEB 2. Map of Sierra Diablo region showing paleogeology of the surface on which the Hueco Limestone (basal Permian) was deposited.
PENNSYLVANIAN 45

The upper shale beds north of Mine Canyon have 

yielded the following fossils.

Coelenterata: 

Chaetetes sp ____ _____ ___ __ _ _

Zaphrentoid coral, gen. undet _______

Bryozoa: 

Stenoporoid bryozoan. _____ _____ _

Brachiopoda: 

Composita sp_____________ ________

Productoid brachiopod indet _ _____ _

Lamellibranchiata : 

Nuculana arata (Hall) .__ ___________

Nuculana n. sp_____ ___ ___ _____ _

Nucula cf N. (Nuculopsis) girtyi Schenk. 

Conocardium n. sp_._____ ___________

Gastropoda: 

Euphemites sp. indet_._ _ ___ _____

Knightites (Retispira) bellireticulata

Cindidonema cf. C. texanum Knight- __

Platyzona sp______ _____ ___________

Slraparollus aff. S. savagei Knight- __ _

Spirioscala sp ___ _ ________ ___

Gastropod n. gen _ __ ___ _ _____

Gastropods indet ___ _____________ _

Cephalopoda: 

Bactrites sp __ _ _____ ___ ___ ____

Dolorthoceras 3 spp __ ______ ___ _ _

Cydoceras sp___ __________________

Adnatoceras sp _ _____ __ ___ _____

Lirocerast sp _______________________

Stenopronorites ?p__ _________________

Boesites scotti Miller and Faber___ ___

Gastrioceras occidentale (Miller and 

Faber) _______ _ __________

Diaboloceras varicostatum Miller and 

Furnish___ __ ____ _____________

Pseudoparalegoceras lenticulare (Plummer and Scott)________._ _ ______

Glaphrites raymondi Plummer and 

Scott __________ ___________

Proshumardites primus (Plummer and 

Scott _ _ _____________________

Pisces: 

Fish teeth __ ____________________ _

USGS Collection No.

7018

X

X

X

X 

X

X

X

X

X

X

X

X

X

X

X

X 

v

X

X

X

X 

X 

X 

X

X

14944

X

X

X

X

X 

X 

X 

X

X

X 

X 

X

X

X

X

X 

X 

X 

X 

X

8105

X 

X 

X 

X 

X

X 

X

X

X

X

X 

X 

X 

X

8106

X

X

X 

X

X 

X

----

X

X 

X 

X 

X

7018 (field loc. 12). Shale hills north of portal of Mine Canyon and west of felsite 

intrusive, in southwestern part of sec. 16, Block 66, Twp. 5. Collected by J. 

Brookes Knight, July 1931.

14944 (field label Pbs-1). Approximately the same locality as that of 7018. Collected 

J. Brookes Knight, 1936.

8105. Approximately the same locality as that of 7018. Collected by M. B. Arick 

for Humble Oil Co., February 1931.

8106. About a quarter of a mile north of the locality of the preceding collections, 

north of felsite intrusive. Collected by M.B. Arick for Humble Oil Co., February 

1931.

In addition to the cephalopods listed above, Miller 

and Furnish (1940b) have described the species Pseudoparalegoceras "bellUineatum.

The cephalopods of this fauna indicate that it is of 

Atoka age. These were correlated by Plummer and 

Scott (1937, p. 25) with those of their Gastrwceras 

listeri zone, which occurs a little below the top of the 

Smithwick Shale of the Llano uplift in central Texas, 

or in strata now considered to be late Atoka in age. 

However, Gordon (written commun., 1954) states: 

"This fauna is correlated with that in the lower part of 

the Atoka Formation in eastern Oklahoma and western 

Arkansas, particularly because of the occurrence of 

Diaboloceras varicostatum Miller and Furnish in both."

A small collection of fossils was made by J. Brookes 

Knight and the writer in 1931 from the limestone beds 

south of Marble Canyon, probably mainly from units 5 

and 6 of geologic section 12 (USGS 7010A; field loc. 12). 

According to Gordon and Yochelson (written commun., 

1954) 

The Pennsylvanian age of the rocks is borne out by the fauna. 

Included are such forms as the corals Caninia and Chaetetes ; 

the brachiopods Chonetes, Dictyoclostus, Marginiferal spp., 

Echinoconchus, Rhipidomella, Girtyettal, Dielasma, Spirifer cf. 

S. rockymontanus Marcou, Punctospirifer, Phricodothyris perplexa (McOhesney), Crurithyris, Cleiothyridina, and Composita 

subtilita (Hall) ; and several pelecypods and gastropods.

Besides these fossils, Garner L. Wilde reports the occurrence in the rocks south of Marble Canyon of Fusulina^ Wedekindellina, and Fusulinella, which indicate an 

early Des Moines age (Kepple and others, 1962, p. 20).

The corals and brachiopods of this fauna are not diagnostic of any particular zone in the Pennsylvanian, but 

some of them are more characteristic of the lower part 

than the upper part of the Pennsylvanian in nearby regions. Chaetetes and Spirifer rockymontanus are thus 

common in the lower division of the Pennsylvanian 

in the Hueco Mountains farther northwest in TransPecos Texas (King, P. B., King, R. E., and Knight, 

J. B., 1945, sheet 2, sections G, H). The fusulinids reported by Wilde confirm this correlation.

REGIONAL RELATIONS

Pennsylvanian rocks are exposed in many mountain 

ranges northwest of the Sierra Diablo region in TransPecos Texas and in New Mexico; they have also been 

penetrated by numerous wells in the West Texas basin 

to the northeast and east (Galley, 1958, p. 419-423). In 

most places the Pennsylvanian sequence is thicker and 

more complete than in the Sierra Diablo, and much is 

known of its stratigraphy (see, for example, Thompson, 

1942, p. 27; Lloyd, 1949, p. 34H.O). Because of the 

fragmentary representation of the Pennsylvanian rocks 

in the Sierra Diablo, it is inappropriate to summarize
46 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

the regional stratigraphy of the Pennsylvanian in this 

report, but it is appropriate to speculate regarding the 

relation of this fragmentary sequence to the more complete sequences known elsewhere.

In the Sierra Diablo the sequence and relations of the 

different parts of the Pennsylvanian strata are uncertain, not only because of disconnected exposures, 

but because the rocks and fossils of the parts north 

of Mine Canyon and south of Marble Canyon are 

so different that few comparisons between them are 

possible. However, the strata in all exposures dip to 

the south, and those north of Mine Canyon are adjacent 

to exposures of the Mississippian Barnett Shale, so 

that they would seem to form the base of the unit and 

to lie beneath the strata south of Marble Canyon.

Comparison with the more complete section of the 

Magdalena Group in the Hueco Mountains farther 

northwest in Trans-Pecos Texas suggests another possible interpretation (King, P. B., King, K. E., and 

Knight, J. B., 1945, sheet 2). In that area the Magdalena Group, which is about 1,300 feet thick, forms 

three lithologic divisions which can be correlated on the 

basis of fusulinids and other contained fossils with 

the subdivisions of the standard Pennsylvanian section 

of the midcontinent region. The lower division, 500 

feet thick, is thick-bedded coralline limestone and 

is approximately of Morrow and early Atoka age. The 

middle division, 300 feet thick, is marl, marly limestone, 

and shale and is approximately of late Atoka and early 

Des Moines age. The upper division, of variable thickness because of the unconformity at the top, is limestone and interbedded marl and is approximately of 

late Des Moines, Missouri, and early Virgil ages.

Lithologically, the lower limestone of the Magdalena 

Group in the Hueco Mountains closely resembles the 

beds south of Marble Canyon in the Sierra Diablo, and 

like them contains Chaetetes and Spirifer rockymontanus. This lower limestone lies directly on the Mississippian Helms Formation, with no intervening shale 

or thin-bedded cherty limestone like the beds north 

of Mine Canyon in the Sierra Diablo. The first 

shale in the Hueco Mountains section is that in the 

lower part of the middle division. Like the shale north 

of Mine Canyon in the Sierra Diablo, this is of Atoka 

age. The two shales might be equivalent, although that 

in the Hueco Mountains lacks the prolific cephalopods 

of the Sierra Diablo, and contains mainly a brachiopod 

fauna. If the two are equivalent, the true sequence of 

the Pennsylvanian limestone strata in the Sierra Diablo is the reverse of the sequence indicated by the 

field relations.

A possible alternative is that the thick-bedded coralline limestones and the cephalopod- or brachiopodbearing shales of the lower part of the Pennsylvanian 

System in the west Texas-New Mexico region do not 

form persistent time-stratigraphic units of wide extent, 

but are f acies that occur in different stratigraphic order 

from one mountain area to another.

PERMIAN

Rocks of the Permian System occupy the largest surface area of any in the Sierra Diablo region. They are 

prominently exposed on the escarpments on the east, 

north, and south sides of the Sierra Diablo and form 

many square miles of its summits. They also occur in 

the adjacent Baylor Mountains, Beach Mountain, and 

the Carrizo Mountains, as well as in the Delaware and 

Wylie Mountains, across the Salt Basin in the northeast 

and southeast corners of the report area (pi. 1).

Because of the variability of the subdivisions of the 

Permian System in the Sierra Diablo region, it is difficult to ascribe a total thickness to the part preserved 

there. Several thousand feet is exposed nearly everywhere along the escarpments in the northeastern Sierra 

Diablo (pis. 4-8), the maximum being 2,128 feet on 

Victorio Peak. At the north end of the range near 

South Mesa, 2,140 feet is exposed, which includes strata 

higher than those on Victorio Peak. Smaller thicknesses of the lower part of the Permian are preserved in 

the southern Sierra Diablo, the Baylor Mountains, 

Beach Mountain, and the Carrizo Mountains. In the 

Wylie Mountains to the southeast the Permian sequence 

is 4,473 feet thick, but most of it is exposed only east of 

the report area. Permian strata exposed in the Delaware Mountains within the report area are 1,783 feet 

thick, but they are only part of the much thicker sequence of the Delaware and Guadalupe Mountains.

The Permian rocks of the Sierra Diablo region are 

largely limestone, dolomitic limestone, and dolomite but 

there are subordinate layers of shale, sandstone, and 

conglomerate. Their stratigraphy is the most complex 

of the rocks of any system in the region. They vary 

greatly, not only in thickness, but also in lithology and 

faunas. In some areas the whole Permian is a monotonous sequence of poorly fossiliferous dolomitic limestone, yet only a few miles away it may be interbedded 

richly fossiliferous massive limestone, thin-bedded limestone, and shale (pi. 4). Many of these variations are 

visible in three dimensions because the rocks are exposed not only on the escarpment faces, but in canyons 

behind the escarpments and in outlying mountains in 

front of them.

The complex variable stratigraphy of the Permian 

rocks was created by unequally subsiding tectonic units 

in the depositional area the Delaware basin on the 

northeast and the Diablo platform on the southwest 

(fig. 3). Because of unequal subsidence, the basin gen-
107' 106 =

105'

PERMIAN

104° 103' 102' 101'

47

100°

29

EXPLANATION

Outcrops of Wolf camp, Leonard, Guadalupe, and Ochoa 

Series (Permian), and their 

equivalents

Boundaries of provinces of Basin areas 

Permian time

Deformed pre-Wolfcamp 

Paleozoic rocks of Marathon folded belt

Area covered by 

this report

FIGURE 3. Map of parts of western Texas and southeastern New Mexico stowing provinces of Permian time.
48 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

erally stood at greater depth than the platform; thus, 

the basin received mainly shaly and sandy deposits, 

the platform mainly stratified carbonate deposits; on 

the intervening basin margin grew extensive limestone 

reefs and banks which were the home of varied marine 

life. Because of unequal subsidence, many of the units 

on the platform are also separated by unconformities, 

along which the underlying strata have been eroded, 

and the overlying strata wedge out by overlap.

The Permian rocks of the Sierra Diablo region belong 

largely to the Wolfcamp and Leonard Series, the succeeding Guadalupe Series being represented merely by 

small remnants at the north end of the range. This 

situation contrasts with that in the Guadalupe Mountains, across the Salt Basin to the north, where only the 

upper part of the Leonard Series emerges from beneath 

a thick sequence of the Guadalupe Series, the latter being followed by part of the Ochoa Series (King, P. B., 

1948, p. 7-100). The Permian section in the Sierra 

Diablo thus usefully supplements the more famous

Permian section in the Guadalupe Mountains and extends the sequence to the base of the system.

Stratigraphic terminology of the Permian rocks in 

the Sierra Diablo region has varied with the work of 

successive geologists and has evolved with increasing 

knowledge. Because of the long span of the present 

investigation, the Stratigraphic terminology used by the 

author and his colleagues is not the same in their successive publications. The following table compares 

the classification used in the present report with that 

in earlier reports.

The Permian rocks were investigated primarily by 

means of description and measurement of Stratigraphic 

sections, mostly the work of J. Brookes Knight. The 

greater part of the fossils collected were on the lines of 

these Stratigraphic sections. Details of the nature of 

the Permian rocks may be found in the descriptions of 

the sections at the end of the report. The sections are 

also illustrated on plates 5-8. Variations in the Permian rocks between the sections were observed during

Stratigraphic classification of Permian rocks in Sierra Diablo region

Richardson, 1914

Not 

observed

Hueco 

Limestone

Beede, 1920

Word

Leonard

Manzano

King, P. B., and King, E. E., 

1929; King, B. E., 1931

Delaware Mountain 

Formation

Formation Leonard Victorio Peak 

Member

Bone Canyon 

Member

Hess 

Formation

Upper 

Wolfcamp 

Formation

Formation Gym 

King, P. B., 1934b

Delaware Mountain 

Formation

Limestone Bone Spring 

Victorio Peak

Massive 

Member 

(zone D)

(zone C)

(zone B)

(zone A)

Basal beds

King, P. B., 1942; King, P. B., 

and Knight, J. B., 1944

Goat Seep 

Limestone

Sandstone tongue 

of Cherry Canyon 

Formation

Spring Limestone Bone 

Limestone Hueco 

Cutoff 

Shaly 

Member

Victorio Peak 

Gray Member

Black

limestone, 

etc.

Limestone

Basal clastic 

member

This report

Goat Seep 

Limestone

Sandstone tongue 

of Cherry Canyon 

Formation

Cutoff Shale

Victorio Peak 

Limestone

Bone Spring 

Limestone

rt Main body 

-2 of formation

d)

Fi

i-3 

g Powwow 

g Member

HH 

HH
PERMIAN 49

field mapping, as shown on the geologic map (pi. 1) 

and in views of the escarpment faces and canyon walls, 

which are illustrated in the panoramas (pis. 10,11, and 

upper 12) and in geologic sections V-V to Z-Z' (pi. 4). 

The text which follows is a summary of these data.

PRESENTATION OF PAUBONTOLOGIC DATA

Fossils were collected from the Permian rocks of the 

Sierra Diablo region during successive field seasons of 

the present investigation, and have been identified at 

different times by various paleontologists. Brachiopods of the earlier collections were identified by E. E. 

King (1931, p. 14-15), and fusulinids by C. O. Dunbar 

and J. W. Skinner (1937, p. 587-590). Later collections were identified by P. E. Cloud, Jr., E. L. Yochelson, and L. G. Henbest (written commun., 1954,1955); 

additional identifications were made by E. M. Finks, 

A. E. Palmer, and I. G. Sohn. Fossils collected by 

other geologists from the Permian rocks of the region 

have been identified and described by G. H. Girty 

(1931), A. K. Miller and W. M. Furnish (Miller and 

Furnish, 1940a; Miller, 1945), C. O. Dunbar (1953), 

F. G. Stehli and G. A. Cooper (Stehli, 1954; Cooper 

and Stehli, 1955), E. L. Yodielson (1956, 1960), and 

others.

Identifications of Permian fossils collected during 

both earlier and later phases of the investigation are 

listed on pages 134-170, in the texts of the stratigraphic 

sections, or in appropriate geographic order where not 

collected in measured sections. Stratigraphic position 

of most of the collections is indicated on the plotted 

stratigraphic sections (pis. 5-8) and their geographic 

position on the index map of the region (pi. 9).

Because many revisions of the fossil terminology and 

taxonomy have been made between the times of the 

earlier and later investigations, the names used for the 

same fossils are likely to vary from one collection to 

another. Although it has not been feasible to revise the 

earlier identifications to agree with the later, the earlier 

identifications are of historical interest; some of the 

earlier collections, for example, contain type specimens 

of genera or species. All collections marked "KEK" 

and "D & S" on pages 134-170 are therefore listed in the 

form in which they were originally presented, with 

the understanding that they would require review to 

harmonize them with the collections marked "USGS" 

or "F."

To provide a sampling of the whole fauna of the different Permian formations in the Sierra Diablo region, 

based on a single taxonomic standard, the later fossil 

identifications have also been assembled in a set of tables 

(tables 3-9).

The fossils listed in these tables represent only part 

of those which have been collected and identified during the present investigation and do not include those 

yielded from other investigations. In each table the 

fossils are shown according to the formations in which 

they occur, and in the order in which they are given in 

the stratigraphic sections and fossil lists (p. 134-170). 

It has not proved feasible to introduce any further refinements in zonation. However, the fossils of the 

Hueco Limestone occur in several well-marked f acies, 

shown separately in tables 3-5 the calcitic limestone of 

the southern and southwestern part of the Sierra Diablo 

region, the marl and calcitic limestone of the northeastern part, and the main body of the formation of the 

northeastern part, containing only foraminifers. The 

fauna of the Bone Spring Limestone, although not divisible into zones or facies, is so extensive that it has 

been subdivided according to taxonomic groups into 

tables 5-7. The faunas of the Victorio Peak and Goat 

Seep Limestones are shown in tables 8 and 9, respectively.

HUECO LIMESTONE

The lowest Permian formation of the Sierra Diablo 

region is the Hueco Limestone, whose type area is in the 

Hueco Mountains farther northwest in Trans-Pecos 

Texas. As indicated above, the Hueco as now defined 

includes only part of the beds originally so named by 

Eichardson (1904, p. 32-38; 1908, p. 480-482), or the 

part which contains the Hueco fauna as understood by 

Girty. This part is a carbonate facies of the Wolf camp 

Series, which is extensive in northwestern Trans-Pecos 

Texas and adjacent areas. In both the Hueco Mountains and the Sierra Diablo, the Hueco lies unconformably on Pennsylvanian and earlier rocks. In the 

Hueco Mountains its top is poorly defined, because of 

uncertainty as to what strata, if any, are preserved above 

it; in the Sierra Diablo the Hueco is overlain by the 

Bone Spring Limestone of the Leonard Series, at least 

in part unconformably.

OUTCBOP

The Hueco Limestone is extensively exposed in the 

southern half of the report area (pi. 1). It forms most 

of the surface of the Sierra Diablo south of the Victorio 

flexure and stands in ledges or cliffs at the edges of the 

bordering escarpments. It also forms much of the bulk 

of the Baylor and Wylie Mountains to the east and 

southeast, and is preserved in smaller outliers in Beach 

Mountain, the Carrizo Mountains, and the Streeruwitz 

Hills. North of the Victorio flexure in the Sierra 

Diablo, the Hueco stands at a lower level than farther 

south, and is extensively covered by younger Permian 

formations. Here it projects as a bench on the lower 

part of the escarpment between Victorio Peak and 

Apache Canyon; within the range it emerges only in
50 GEOLOGY OF THE SIEKRA DIABLO REGION, TEXAS

Victorio and Apache Canyons and in the uplift on the 

south side of the Sierra Prieta intrusive. The Hueco 

Limestone doubtless extends northwestward beneath 

the surface from the Sierra Diablo and joins the type 

Hueco in the Hueco Mountains.

THICKNESS

The thickness of the Hueco Limestone varies remarkably. The gross pattern of the variations is not 

entirely clear, as in many places the full thickness of 

the formation is not preserved; where preserved, it appears to be greatest in the platform area to the south 

and southwest and thinnest near the edge of the 

basin area to the northeast.

The Hueco is about 1,400 feet thick in the Wylie 

Mountains (geologic section 13) and 1,100 feet or more 

thick in the head of Apache Canyon (geologic sections 

37-40). At the lower end of Apache Canyon it thins 

to a few hundred feet (geologic sections 36, 37). Along 

the Sierra Diablo escarpment between Apache Canyon 

and Victorio Peak, the thickness averages 500 feet, but 

it is thicker than 900 feet in places and thinner than 

400 feet in others (geologic sections 27-34). At several 

places in the northern Bay lor Mountains it wedges out 

entirely, so that the succeeding Bone Spring Limestone 

directly overlies the earlier rocks.

Many of the variations in thickness of the Hueco are 

caused by overlap of the formation against its unconformable basal surface and by truncation of its top before the Bone Spring was deposited over it. These 

relations, or combinations of both, are well displayed 

in Apache Canyon and parts of the Baylor Mountains. 

There is also a possibility, difficult to assess, that different thicknesses of Hueco Limestone were deposited 

from place to place.

LITHOLOGY AND SUBDIVISIONS

In the Sierra Diablo region the Hueco Limestone includes a thick main body of bedded calcitic and dolomitic limestone and thinner basal beds, the Powwow 

Member.

The type Powwow Member is in the Hueco Mountains, where it forms a basal lens of conglomerate and 

red beds a few miles long (King, P. B., and King, R. E., 

1929, p. 911; King, P. B., King, E. E., and Knight, 

J. B., 1945). The beds termed Powwow Member in the 

Sierra Diablo region (King, P. B., and Flawn, P. T., 

1953, p. 34-36; 98-99; Hay-Roe, 1957; Twiss, 1959) 3 

are more extensive and varied. They everywhere underlie the main body of the formation except at a few places 

on the higher parts of the pre-Hueco surface where they

8 Hay-Roe and Twiss class the Powwow as a formation separate from 

the Hueco Limestone, which they restrict to the main body of the 

formation of present terminology.

wedge out by overlap. The Powwow Member of the 

Sierra Diablo region is formed of varicolored coarse to 

fine clastic rocks, which become coarser downward and 

southward, and pass upward and northward into marl 

and thin beds of limestone that are conformable with 

the main body of the formation. All the Powwow 

strata are poorly resistant to erosion and form slopes 

between the ledges above and below, on which exposures 

are likely to occur only in ravines; in places the Powwow has been mapped principally by its topographic 

expression. As in other transgressive deposits, fossils 

occur only in the more marly or limy beds above the 

base; these fossils are like those in the main body of 

the formation which succeeds it, and their facies vary 

in the same manner as those of the fossils of the overlying strata.

The main body of the Hueco Limestone is not divisible into units except in local areas, but its lithology and 

faunas vary significantly from place to place (fig. 4). 

Toward the south and southwest it is a thin- to thickbedded gray calcitic limestone with a well-defined but 

rather restricted invertebrate assemblage. Farther 

northeast, as in the Baylor Mountains and the central 

and northern Sierra Diablo, much of the main body is a 

thin-beded dolomitic limestone, containing few fossils 

other than fusulinids. However, in the same area the 

basal Powwow member contains invertebrate fossils 

much more varied than those farther southwest. This 

fossil assemblage extends in places into the main body 

and occupies all of it near Victorio Peak; here it occurs 

in thin- to thick-bedded calcitic limestone, unlike the 

prevailing dolomitic limestone of the vicinity.

The calcitic southern and southwestern facies was 

deposited on the platform of Hueco time. The other 

two facies to the northeast were deposited nearer the 

basin of Hueco time. However, the facies of the Hueco 

seem to be little related to the Victorio flexure, which 

markedly influenced the distribution of facies in the 

succeeding Bone Spring deposits.

SOUTHERN PAET OF REPORT AREA

In the southern part of the report area the Powwow 

Member is thick and coarsely clastic at most places; the 

main body of the formation is of the calcitic southern 

and southwestern facies. The full sequence of the 

Hueco is exposed in the Wylie Mountains (geologic section 13, pi. '5), but only partial sections of the lower part 

are preserved farther west where, in places, the eroded 

top of the formation is overlain by Cretaceous strata. 

Among the better exposed sections to the west are those 

on Threemile Mountain northwest of Van Horn (geologic sec. 15, pi. 5) and on the butte northwest of Eagle 

Flat section house at the south end of the Streeruwitz 

Hills (geologic section 20, pi. 6).
PERMIAN 51

EXPLANATION

OUTCROP AREAS

Rocks older and younger 

than Permian

OTHER SYMBOLS

Thickness of Hueco Limestone 

in feet, where determined

Edge of hills or escarpments which 

were partly or wholly overlapped 

by Hueco Limestone

Trend of linear features in 

Hueco Limestone

Alined fusulinid tests or 

echinmd spines

Boundary between calcitic limestone 

on southwest and thin-bedded 

fusulinid-bearing dolomitic lime95 stone on northeast

Approximate western limit of marl 

and calcitic limestone in lower 

part of formation which contains 

varied fossils

FIGURE 4. Map of Sierra Diablo region showing paleotectonics of Hueco Limestone.
52 GEOLOGY OF THE SIEKKA DIABLO REGION, TEXAS

In the southern part of the report area the Powwow 

Member lies mainly on various Precambrian and Precambrian(?) formations, although on Beach Mountain 

it extends onto Ordovician rocks. Its basal surface was 

moderately irregular, as shown by large variations in 

thickness of the member within short distances and by 

variations in the character and volume of the coarser 

clastic constituents. In the Wylie and Carrizo Mountains these variations indicate a basal topography with 

a relief of several hundred feet (Flawn, in King, P. B., 

and Flawn, P. T., 1953, p. 34-35, 43; Hay-Roe, 195T; 

Twiss, 1959). In the Carrizo Mountains, Powwow 

deposits were laid against a north-facing scarp along 

the Hillside fault. North of the fault the Powwow is 

as much as 250 feet thick and overlies the Van Horn 

Sandstone, but it contains abundant angular fragments 

of the metarhyolite that intrudes the Carrizo Mountain 

Formation south of the fault. These fragments decrease in abundance and coarseness northward, where 

they are intermingled with fragments from other 

sources (King, in King, P. B., and Flawn, P. T., 1953, 

p. 99). The Ordovician carbonate rocks of Beach 

Mountain must have projected as an erosion remnant on 

the pre-Hueco surface. At Threemile Mountain the 

basal 70 feet of the Powwow is a lenticular mass of 

limestone pebbles and cobbles of the El Paso Limestone, 

evidently derived from talus of an ancestral Beach 

Mountain, not far to the north.

Aside from the breccia and conglomerate derived 

from earlier rocks, much of the Powwow in the southern 

area is bedded coarse sandstone, partly arkosic, of vermilion-red, purple, brown, or yellow hues. Some of this 

sandstone was assigned to the Van Horn by earlier 

geologists (Richardson, 1914, p. 4; Baker, 1927, p. 9), 

but its true age is indicated not only by its more varied 

nature, but by its unconformable relations below and 

conformable relations above.

The coarsely clastic and varicolored parts of the 

Powwow are succeeded at most places by more calcareous strata, mainly gray or yellow calcareous shale 

or marl, but they include thin intercalated limestone 

beds. These strata are fossiliferous the fossils 

weathering free on the surface in places and they have 

yielded large collections at Threemile Mountain and in 

the Streeruwitz Hills.

The overlying main body of the formation is stratified limestone in thin to thick beds, mainly gray and 

calcitic, but with some more dolomitic layers, and with 

many poorly resistant marly partings; a few of the beds 

contain small chert concretions. The main body characteristically forms ledges and slopes. The limestone 

beds contain an abundant but restricted invertebrate 

fauna that includes minute staffellid foramiiiifers,

echinoid spines and plates, and a few brachiopods. The 

marly layers contain mollusks, particularly poorly preserved bellerophontoid gastropods. Fusulinids are 

lacking in most places, although a few stray forms have 

been discovered. They are abundant about 500 feet 

above the base in the Wylie Mountains, at a level higher 

than any strata preserved farther west, as at Threemile 

Mountain and Eagle Flat.

Farther north this calcitic limestone changes into 

more dolomitic fusulinid-bearing limestone. In exposures on the east side of Beach Mountain (geologic 

section 16), both the main body of the Hueco and the 

Powwow Member are dolomitic, but the same fossil 

assemblage occurs as farther south, here nearly destroyed by dolomitization. Along the south-facing 

escarpment of the Sierra Diablo, dolomitic layers come 

in gradually eastward, by interbedding and intertonguing, and fusulinids increase correspondingly. On 

the escarpment above the Hazel mine (geologic section 

25, pi. 6) the main body of the Hueco is largely thinbedded dolomitic limestone, which is different from the 

limestone farther south and west and contains many 

fusulinids. The boundary between the calcitic and dolomitic facies of the main body of the Hueco is traceable 

northwestward from the Old Circle Ranch (geologic 

section 24, pi. 6) across low exposures in the southern 

part of the Sierra Diablo.

BAYLOR MOUNTAINS

In the Baylor Mountains the Hueco Limestone lies 

with angular and erosional unconformity on older 

Paleozoic rocks, mainly the El Paso, Montoya, and 

Fusselman Formations, and is separated from the Bone 

Spring Limestone above by a less evident unconformity 

(fig. 5). The Hueco varies greatly in thickness in 

different parts of the mountains, by overlap along the 

unconformity at the base and by truncation along the 

unconformity at the top.

Striking features of the basal unconformity are hills 

of older Paleozoic rocks, against and over which the 

Hueco was deposited (fig. 4). The pre-Hueco hills 

seem to be most extensive in the northern part of the 

mountains, near the Victorio flexure, but the west edge 

of another hill is well exposed at the "unconformity 

locality" in the southern part (sec. 3, Block 65, Twp. 

7) (fig. 5A) . The edges of some of the hills were steep 

scarps as much as 200 feet high, near which the basal 

Hueco contains breccia lenses formed of coarse fragments of the adjacent older rocks. The Hueco was 

draped over the hills of older rocks, and its strata slope 

away from them with initial dips, some as steep as 15°.

Draping of the Hueco over the hills of older rocks 

may account for some of the truncation of its upper 

surface. At the beginning of Bone Spring time the
PERMIAN 53

WEST EAST

Ei Paso Limestone

^prTT.\» .:..*I».*."-r: v»; ' : ' - * ; Van Horn Sandstone % « - «Y;l'V'»'*V.^r

NORTH

Bone Spring Limestone

SOUTH

B

EAST Bone Spring Limestone 

3

WEST

500

APPROXIMATE SCALE 

1000 1500 2000 FEET

FIGURE 5. Detailed sections showing unconformities below and above Hueco Limestone in Baylor Mountains. A, South end of mountains 

("unconformity locality," northwestern part of sec. 23, Block 65, Twp. 7) showing unconformity at base of Hueco and one between Van 

Horn sandstone (Precambrian?) and Bliss Sandstone (Ordovieian). B, Northwestern part of mountains (southwestern part of sec. 43. 

Block 65, Twp. 6) showing unconformities below and above Hueco. 0, Outlying hill northwest of mountains, west of Texas Highway 54 

(center of sec. 9, Block 66, Twp. 6) showing unconformity at top of Hueco.

higher standing parts of the Hueco, over the buried 

hills, were eroded more than the lower. The most 

prominent exposure of an angular unconformity between the Hueco and Bone Spring is on a hill in the 

northwestern Baylor Mountains west of Texas Highway 54 (summit 4410, sec. 9, Block 66, Twp. 6) (fig. 

50) , where the Bone Spring overlies Hueco strata that 

dip 1° west or southwest; inclination of the Hueco was 

probably a primary slope off a hill of El Paso Limestone that is exposed east of the highway.

The Powwow Member is thin in the Baylor Mountains and is missing entirely near the buried hills in 

the northern part. It is thickest to the southeast, but

even here does not exceed 100 feet. Where the Powwow occurs, it is red, bun3, and yellow marl and shale 

interbedded with conglomerate layers containing 

pebbles of the older Paleozoic carbonate rocks.

The main body of the Hueco Limestone in the Baylor 

Mountains is largely thin-bedded aphanitic dolomitic 

limestone, containing few fossils other than molds of 

small fusulinids. Although few of the limestone beds 

are thick or massive, the whole unit stands in steep 

slopes or cliffs. The main body is as much as 700 feet 

thick along Red Tank Canyon and elsewhere in the 

southern part of the mountains, but farther north both 

it and the underlying Powwow thin out. In the north-
54 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

ern part of the mountains the Hueco is a dolomitic limestone no more than a few hundred feet thick (geologic 

sections 18 and 19, pi. 5), and at a few places it is 

missing entirely on tops of the hills of the underlying 

rocks (fig. 5B ; section Z-Z', pi. 4).

CENTRAL SIERRA DIABLO

On the east-facing escarpment of the Sierra Diablo, 

the Hueco forms a bench or line of cliffs which is at the 

top to the south of the Victorio flexure, but which descends to the base to the north (pi. 10). The Hueco is 

also exposed behind the escarpment in Victorio Canyon.

In the central Sierra Diablo the uncomf orable base 

of the Hueco emerges only toward the south and north. 

South of the Victorio flexure the Hueco lies on red 

sandstone of the Precambrian Hazel Formation, but 

it overlies a hill of steeply dipping Montoya Dolomite 

in Victorio Canyon (section X-X', pi. 4). Where the 

base is exposed again from Marble Canyon northward, 

the Hueco lies on higher Paleozoic formations, including rocks of Peimsylvanian age.

The Powwow Member at the base is generally somewhat more than a hundred feet thick, but it is as much 

as 250 feet thick at a locality south of Victorio Peak 

(geologic section 27, pi. 6) and another three-quarters 

of a mile south of Marble Canyon, both probably in 

local valleys on the pre-Hueco surface. At the east 

foot of Victorio Peak (geologic section 29, pis. 6, 7), 

134 feet is exposed, but the base is not visible. The 

lower part of the Powwow is clastic, varicolored, and 

conglomeratic. Conglomerate fragments were derived 

from the Hazel Formation, the Van Horn Sandstone, 

and various older Paleozoic formations. The associated 

sandstone and shale beds are arkosic and red, yellow, 

or gray. The upper part is yellow or gray marl and 

shale interbedded with thin layers of limestone, and in 

places is abundantly f ossilif erous. Large collections of 

invertebrate fossils have been obtained from this part 

of the Powwow Member near the portals of Victorio, 

Marble, and Mine Canyons.

The overlying main body of the Hueco is more than 

600 feet thick at Bat Cave south of the Victorio flexure 

(geologic section 26, pi. 6), where the top is not preserved, and about 800 feet thick south of Black John 

Canyon (geologic section 34, pi. 7), but it is much thinner at nearby localities. At Marble Canyon (geologic 

section 32, pi. 7) it is 357 feet thick, and at the east base 

of Victorio Peak (geologic section 29, pis. 6, 7), about 

200 feet.

Most of the main body, and especially its upper part, 

is thin-bedded dark-gray aphanitic dolomitic limestone 

containing few fossils other than fusulinids, most of 

which are preserved as molds. Near Marble and Mine

Canyons (geologic sections 32 and 33, pi. 7), however, 

the lower 120-150 feet is thick-bedded blue-gray calcitic 

limestone, with some intervening thinner beds, which 

contain fusulinids and other fossils similar to those in 

the Powwow Member beneath. At the east base of Victorio Peak (geologic section 29, pis. 6, 7), where the 

main body is exceptionally thin, it is fossiliferous 

throughout and is all calcitic limestone in thin to thick 

beds. The thin beds are dark gray to black, with wavy 

bedding surfaces, irregular chert nodules, and partings 

of marl. The thick beds are light gray and cherty and 

are lenticular or moundlike; some are brecciated. At 

the top is an especially thick lens or reef body (the 

"KHz lens" of Dunbar, 1953, p. 802), a quarter of a mile 

across and 115 feet thick at the apex. It is mostly massive gray limestone containing sponges, corals, massive 

bryozoans, and a few other fossils, but it is brecciated 

at its edges. The succeeding Bone Spring beds overlap 

the lens.

APACHE CANYON AREA

At the lower end of Apache Canyon the Powwow 

Member is thin or missing, and the overlying main body 

of the formation is less than 200 feet thick (geologic 

section 36, pi. 8). The Hueco dips south westward at an 

angle of a few degrees up the canyon, but its top, overlain unconformably by Bone Spring Limestone, rises 

a thousand feet in the same direction (pi. 11; section 

V-U1', pi. 4). The Hueco thus forms as much as the 

lower half of the walls and the canyon in its middle 

and upper course, but the beds exposed are younger and 

higher than those at the lower end. The whole of the 

formation is not exposed-in the upper part of the canyon, but matching of units in different sections suggests 

that it is more than 1,100 feet thick.

Three subdivisions of the Hueco Limestone are recognizable in the canyon, designated as divisions A, B, and 

C in geologic sections 37,38,39, and 40 (pi. 8). Division 

A at the base is about 400 feet thick; it is thick-bedded 

dolomitic limestone, weathering brown and craggy, and 

contains some interbedded thinner layers. Division B, 

about 250 feet thick, is light-gray to dark-gray calcitic 

limestone, resembling the southwestern f acies of the formation, which forms ledges that are lighter gray and 

less massive than those of the divisions below and above. 

Division C is preserved only in the headwaters of the 

canyon, where it is about 400 feet thick; it is thickbedded dolomitic limestone like division A. In places it 

contains thin interbedded layers of porcelaneous dolomite that weather white and splintery. All the divisions contain abundant fusulinids, but other fossils are 

scarce. The three subdivisions are local units that have 

no counterparts elsewhere in the Sierra Diablo region; 

they have probably been produced by intertonguing of
PERMIAN 55

the northeastern and southwestern facies of the formation.

Northwest of the head of Apache Canyon the Hueco 

is exposed in an uplift on the south side of the Sierra 

Prieta, over an area of a few square miles. About 550 

feet of beds emerge, whose base is cut off by the igneous 

rock (geologic section 42, pi. 8). Most of the limestone 

is dolomitic and resembles the upper part of the Hueco 

in the head of Apache Canyon.

FOSSILS AND CORRELATION

Smaller foraminifers occur in nearly all parts of the 

Hueco Limestone, but the larger f oraminifers, the f usulinids, are vastly more abundant in the northeastern 

part of the region (table 2). In the marl and calcitic 

limestone of the lower part in the northeastern sections, 

fusulinids are associated with varied fossil of other 

phyla, but in the dolomitic limestone of the upper part 

they crowd the layers, almost to the exclusion of other 

fossils. In the calcitic limestone of the southern and 

southwestern area, fusulinids are strangely rare, except 

for a zone about 500 feet above the base in the Wylie 

Mountains and small staffellids which are common in 

many layers.

The fusulinid fauna of the Hueco Limestone in the 

Sierra Diablo region is notable for the abundance of 

small species (Dunbar and Skinner, 1937, p. 589), especially Parafusulma linearis (Dunbar and Skinner), 

Pseudofusulina emaciata (Beede), P. powwowensis 

(Dunbar and Skinner), Schubertella kingi Dunbar and 

Skinner, and Schwagerina beUula Dunbar and Skinner. 

This assemblage furnishes a ready field criterion for 

distinguishing the Hueco from the overlying Bone 

Spring, with its perceptibly larger forms of fusulinids. 

In some layers of the Hueco the small species are associated with species of the larger, more robust genus 

Pseudoschwagerina. The characteristic fusulinids of 

the Hueco seem to range throughout the formation and 

have been observed low in some sections, high in others 

(table 2); no zonation within the formation is apparent from the available data.

The remaining fossil groups, as noted in the stratigraphic descriptions, are markedly differentiated into 

southwestern and northeastern f acies that correspond 

to lithologic differences between the strata in the two 

areas.

The fauna of the southwestern facies is well-defined 

but little varied, and is remarkably alike at all localities 

(table 3). The most abundant brachiopods are the 

productoids Dictyoclostus wolfcampensis (King), D. 

(n. subgen.) cf. D. hessensis (King), and the nonproductid Composita, particularly C. subtUita (Hall). 

Hustedia was observed at many places in the field,

but it is scantily represented in the collections. Dielasma is abundant at a few localities, but rare elsewhere. 

Mollusca, especially gastropods and pelecypods, are 

numerically as abundant as the brachiopods, but are 

equally restricted as to kind. The most widely distributed gastropods are bellerophontaceans, mainly preserved as steinkerns (Yochelson, 1960, p. 216). Less 

abundant are species of Omplmlotrochus^ Straparollus 

(Euomphalus) , and Meekospira. The pelecypods include species of AUorisma, Aviculipinna, and Septimyalina. Fragments of the scaphopod Plagioglypta occur at many localities. Of the remaining fossil groups 

perhaps the most abundant are echinoids, but these are 

preserved only as detached spines and plates that are 

probably specifically indeterminate by modern standards. The only other fossils of interest are dasycladacean algae, which occur at a locality on the southfacing escarpment of the Sierra Diablo southwest of 

the former McAdoo Ranch (geologic section 22, pi. 6) ; 

these probably lived in an environment of very shallow 

tropical to subtropical waters (P. E. Cloud, written 

commun., 1954).

Fossils in the marl and calcitic limestone of the lower 

part of the Hueco in the northeastern part of the region 

show a much greater diversity, especially among the 

brachiopods (table 4). Dictyoclostus wolfcampensis 

(King) and species of Composita occur here as farther 

southwest, but they are overshadowed by other genera 

and species, including Dictyoclostus (Ghaoiella) aff. D. 

boliviensis (d'Orbigny), Buxtonia (Kochiproductus] 

victorioensis King, species of Linoproductus, "Marginifera" (Kozlowskia) capaci (d'Orbigny), "Marginifera" 

aff. uM.n lasallensi-s (Worthen), "Marginifera" (Kozlowskia) cf. "M" wabasliensis (Norwood and Pratten), 

and a fine-spined species of Waagenoconcha. Mollusks 

are numerically and taxonomically less abundant, and 

include much the same assemblage as in the southwestern area, with the addition of a few orthoceratid 

cephalopods. Corals occur at many localities, and 

bryozoans are abundant at a few, especially in the Powwow Member near the mouths of Marble and Mine 

Canyons.

REGIONAL RELATIONS OF FAUNA

All the fusulinid species of the Hueco Limestone occur in beds of Wolf camp age throughout a wide region 

in the Southwestern States. However, according to L. 

G. Henbest (written commun., 1955), most of them 

characterize more particularly bed 14 and higher parts 

of the Wolf camp at its type section in the Glass Mountains, and he suggests that the highest fusulinid-bearing layers in the Hueco Limestone of the Sierra Diablo
56 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

TABLE 2. Foraminifera identified from Hueco 

[Identifications by L. G. Henbest. Explanation of symbols: X, genus or species present; var, variety of species present; cfr, specimen

Distribution of fossils in stratigraphic section,

Foraminifera:

Millerellidsp.. __ .. .._ . .- 

sp .- -_ . .-_ . . __ . . .

Staffetta lacunosa Dunbar and Skinner. ... _____________

Tetrataxis sp . _______________________________

Textulariidae __________ . __ . _ __ . __________

Trepeilopsis sp _______________________________

Tritidtes subventricosus Dunbar and Skinner _____________

spp . .. 

26 Bat Cave

1« 

fe

1

X

X

X

fe

var

1

1

1

 *t

s

fe

X

var

1

1

fe

1

X

X

TO 

1 (M

fr

X

X

aff

Sheep Peak area

<N

S

fe

cfr

1

fe

X

1

X

X

fe

X

X

1

X

X

X

fe

1

1

aff

Second 27section ofsouth Victorio Peak

S3

§ 

fe

X

1

X

aff

1

1

X

X

Victorio flexure

o

§ fe

X

X 

X

X

X

X

1

X

X

X

a

fe

1

1

aff

X

X

X

X

i

E=H

X

X

1

X

1

1

X

00

s 

fe

X

1

aff

X

1

X 

X

pq

X

cfr

X

1

X

X

1 Osagia is a consortium or an alternative association of incrusting algae and tubiform, sedentary foraminifers of the subfamily Cornuspirinae.

region may be younger than any beds preserved in 

the type Wolf camp.

Differentiation of the Hueco faunas into a northeastern and southwestern facies may represent a transition 

from a fauna like that of the type Wolfcamp into one 

like that of the type Hueco, although available collections from the Sierra Diablo region are not so varied 

as those from either of these units in their type areas. 

Presumably the differentiation expresses a change from 

a depositional environment of shale, marl, and limestone 

in the basin area to one of dominant limestone in the 

platform area. However, the differences are mainly in 

relative abundance of species and groups rather than 

in the gross assemblages. Thus, E. E. King (1931, p.

14) has noted the identity of many brachiopod species 

of the northeastern facies to those in the type Wolfcamp, but some of the brachiopods of this facies, such 

as Buxtonia (Kochiproductus) victorioensis King and 

Dictyoclostus (Ghaoiella) aff. D. boliviensis (d'Orbigny), also occur in the lower part of the Hueco near 

Powwow Canyon in the Hueco Mountains.

Many of the brachiopods and gastropods of the Hueco 

fauna are very similar to, or specifically identical with, 

those in the upper part of the Cisco Group and in the 

Wichita Group of central Texas. Brachiopods in the 

Camp Creek Shale Member of the Pueblo Formation 

are like those in the Hueco, and Dictyoclostus (OJiaoiella) aff. D. boliviensis (d'Orbigny) is abundant there.
PERMIAN 57

Limestone in central and northern Sierra Diablo

compared with the species Usted; afl, specimen related to species but probably different; ?, specunen doubtfully assigned to genus or species]

locality, and collection number indicated

29b Victorio Peak

I

^

X

to

X

EH

X

X

X

?

1O

S

fc

X

En

X

X

to

var

X

1

h

X

X

30 

Victorio 

Canyon

fr

X

var

X

?

?

r~

£

h

X 

X

?

f

31 North of 

Victorio Canyon

fr

X

?

PC*

X

var

?

?

?

off

fe

X

X

<N

fe

X

?

X

Marble 32 Canyon

BF 2718 

XXXX

?

X

Xvar 

X

X 

X

X

X

?

X

37 First section 

in Apache 

Canyon

fe

X

X

?

38 Second section in 

Apache Canyon

ta 

fc

X

?

X

X

?

X

o

fc

X

X

X

var

?

fe

X

var

?

?

X

X

X

F9832

var

X

?

?

X

39 Third 

section in 

Apache 

Canyon

fe

X

X

X 

X

X

fc

X 

X

X

X

cfr

?

X

Apache Tank 41 

ta 

o

§ 

fe

afl

?

?

?

Sierra Priet 42 

fr

X

X

afl

X

On the other hand, the Hueco gastropods resemble those 

at somewhat higher levels in the central Texas section. 

The Hueco species of Straparollus (Euomphalus) and 

Naticopsis occur in the Grape Creek Limestone Member 

of the Clyde Formation, and those of Omphalotrochus 

extend as high as the Lueders Limestone.

Faunas like those in the Hueco also extend well to 

the west of Texas; for example, Williams (in Gilluly 

and others, 1954, p. 39-41) has compared the Hueco 

fauna with that of the Colina Limestone of the Naco 

Group in southern Arizona.

STEATIGRAPHIC RELATIONS

As indicated above, the Hueco Limestone lies unconformably on all the earlier rocks of the sequence

throughout the Sierra Diablo region (fig. 2). During 

the latter part of Pennsylvanian tune these rocks were 

broadly folded, locally faulted, and greatly eroded. 

Erosion penetrated deepest in the more uplifted area 

to the south and southwest, where the Hueco was deposited on the Precambrian and Precambrian (?) formations. Earlier Paleozoic formations (the El Paso, 

Montoya, and Fusselman Formations) were preserved 

from pre-Hueco erosion in synclinal areas in Beach 

Mountain and the Baylor Mountains. Later Paleozoic 

formations (the Barnett Shale and Pennsylvanian 

rocks) were similarly preserved in a deeper synclinal 

area in the northeastern Sierra Diablo. In many places 

erosion progressed so far that the Hueco was deposited 

on a nearly level surface, but in others it was laid
58 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

TABLE 3. Fossils identified from Hueco Limestone of southern calcitic limestone fades

[Identifications by P. E. Cloud, Jr., Helen Duncan, R. M. Finks, L. G. Henbest, and E. L. Yochelson. Explanation of symbols. Under Foraminifera: X, species or genus 

present; ?, specimen doubtfully assigned to genus or species. Under other biological groups: A, abundant; C, common; X, present; R, rare]

Distribution of fossils in stratigraphic section, locality, and collection number indicator

Foraminifera:

Porifera:

Coelenterata:

Echinodermata:

Bryozoa:

FtZTlGStcUd SD

Bryozoans indet., encrusting, massive, and fenestrate

Brachiopoda:

Lamellibranchiata:

Gastropoda:

sp .

Sublitidindet. -I '__ . ____ .' ____ .'. ......

Scaphopoda:

Cephalopoda: 

Nautiloid indet- _____________________

Arthropoda:

Plants:

13 Wylie 

Mountains

7005

R

R

X 

A

X

C

X

7005x

X

X

X

15 Threemile 

Mountain

14430

X

X

A 

X

A

X

C

X

6937 

14437 

F 2718c 

F9812

X

X

X 

X

X

X

c

X 

X 

R

R

A

C

A 

X 

A 

C

X

X 

X 

X 

X

X 

X

R 

C 

X

X 

R

X 

C

X 

A 

X

C

X

Near Threemile 

Mountain

14438 

F9813

X

X 

X

R

R

C 

X

C

R

X 

C 

X

14426

X

X

R

X

20 Eagle Flat

7028

R

R 

X

X

A

A 

X 

R

X

R

R 

X

R

X

A

X

A

C

7008

R

X

X

X

X

X

X

20 Streerawitz Hills

7003 

7003a 

14431 

F9808

?

X 

X

X

c

R

X

C 

R

R

C

X

X

X

A

X

X

X

X

7003b

?

R

A

X 

X

X 

R

C 

A

R

A

R

X

X 

R

X

R 

X

R

A

C 

X

14432 

F9809

? 

X

X 

X

A

R

A

C

X

A

22 McAdoo 

Ranch

7013 

7013a 

7013b

X

X

X 

X

Near 

Sheep 

Peak

14424

R

C

A

C 

X

R

R 

C 

A

R
PERMIAN 59

TABLE 4. Fossils identified from Hueco Limestone, from marl and calcitic limestone m lower part, in northeastern Sierra

Diablo (exclusive of Foraminifera)

[Identifications by P. E. Cloud, Jr., Helen Duncan, R. M. Finks, and E. L. Yochelson. Explanation of symbols: A, abundant; C, common; X, present; R, rare]

Distribution of fossils in stratigraphie section, locality, and collection number indicated

Number

Porifera:

Coelenterata:

Echinodermata:

Bryozoa:

Brachiopoda:

Dtetyoclo&tus (ChaoieUa) aft. D. bolioiensis

"Marginifera" (Kozlowskia) capad (d'Orbigny).

cf. "M." wabashensis (Norwood and Pratten).......................................

Lamellibranchiata:

Myalinid indet ________________ ..

Sevtimualinat so.. . - ...

27 

Second 

section 

south 

of 

Victorio 

Peak

14452

X

X

R

X 

R

X

X

X

X

X

Victorio 

flexure

14429

X

C

R 

X

C

X

R

X

29 Victorio Peak

8553

X

X

R

C

X

8554

X

8555

R

X

X

X

A 

C

R

C

A 

A

C

X

A

A 

X 

R

A

C 

X

A

X 

X 

X

8556

C

C

X

C

X 

R 

X

X

30 

Victorio Canyon

8557

R

X 

X 

C

A

X 

X 

X

c

A

X

X

R 

R 

X

X 

X 

X 

X

31 

North 

of 

Victorio Canyon

8558

R

X

A

R

X

32 Marble 

Canyon

8551

X

C

8550 

7050

X

X 

X

R 

X

X

R 

R 

A 

C

C 

C 

C

R

X 

X

R

X

X

X

33 Mine Canyon

7001a 

7004 

8552

X

C

R

A 

C

X

R 

X 

C

C 

C

A 

A

X

C

C 

R 

X 

R

X

C

X

C

C

X

R 

R 

X

C

X

7004a

X

X

c

R

C 

C

C

C

R 

R

X

R

X 

C 

g

X

X

A

R

C

X

7001

X

X

R 

R

X

X 

X

34 

South 

of 

Black 

John Canyon

7056

X

X 

X

757-108 65 5
60 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

TABLE 4. Fossils indentified from Hucco Limestone, from marl and caldtic limestone in lower part, in northeastern Sierra

Diablo (exclusive of Foraminifera) Continued 

pdentiflcations by P. E. Cloud, Jr., Helen Duncan, R. M. Finks, and E. L. Yochelson. Explanation of symbols: A, abundant; C, common; X, present; R, rare]

Distribution of fossils in stratigraphic section, locality, and collection number indicated

Number

Gastropoda:

OT\

Cephalopoda:

Annelida:

Arthropoda: 

Trilobite indet.. _________________

27 

Second 

section 

south 

of 

Victorio 

Peak

14452

C

Victorio 

flexure

14429

R 

R

X

X

X

29 Victorio Peak

8553 8554

X

8555 8556

X

X

30 

Victorio Canyon

8557

X 

X 

X

X 

X

X 

X

31 

North 

of 

Victorio Canyon

8558

32 Marble 

Canyon

8551

8550 

7050

R

R

X 

X

X

X

X

33 Mine Canyon

7001a 

7004 

8552

X

X 

X

X

7004a

X

7001

34 

South 

of 

Black 

John Canyon

7056

over hills and valleys with a relief of several hundred 

feet.

Similar pre-Permian deformation and erosion occurred in the Hueco Mountains farther northwest 

(King, P. B.5 King, K. E., and Knight, J. B., 1945), 

and it may correspond approximately to the climax of 

deformation in the Ouachita fold belt of the Marathon 

area to the southeast (King, P. B., 1937, p. 134-136). 

However, in many of the ranges of southern New Mexico the sequence is nearly complete from the Pennsylvanian into the Permian, and any unconformity between them is slight or local. Conformable relations 

between Pennsylvanian and Permian strata are also indicated by drilling in the West Texas basin to the east. 

In the part of Texas and New Mexico northwest of the 

Ouachita fold belt, pre-Permian deformation and erosion was probably greatest in the positive areas and was 

slight or lacking in the negative areas.

The top of the Hueco, where preserved, is likewise an 

unconformity. In the southwestern part of the Sierra 

Diablo region, the Hueco is overlain by Cretaceous 

rocks, and has been variably truncated by pre-Cretaceous erosion. Farther north the Bone Spring Limestone 

is preserved, and also lies unconfonnably on the 

Hueco certainly in many places, and perhaps everywhere. The unconformity is most evident along the 

edges of the basin of Bone Spring time, in Apache Canyon, on the Victorio flexure south of Victorio Peak, and 

in the northern Baylor Mountains, where Hueco strata

are angularly truncated. Here also, as described below, 

the Bone Spring overlaps the Hueco surface and passes 

into marginal reefs, banks, and pebble beds, the latter 

containing fusulinids reworked from the Hueco. Field 

evidence is less conclusive for an unconformity between 

the Hueco and Bone Spring elsewhere, as in the segment of the Sierra Diablo scarp between Victorio Peak 

and Apache Canyon; but the large variations in thickness of the Hueco in this segment may have been caused 

partly by erosion of its top. Very likely the unconformity at the top of the Hueco fades out into the basin 

area, like the one at the base, but its disappearance may 

be northeast of any outcrops in the Sierra Diablo 

region.

BONE SPRING LIMESTONE

The second formation of the Permian System in the 

Sierra Diablo region is the Bone Spring Limestone, 

named for exposures in Bone Canyon below Bone 

Spring, in the Guadalupe Mountains north of the 

Sierra Diablo (Blanchard and Da vis, 1929, p. 961).

The type Bone Spring, and that farther south in the 

Guadalupe and Delaware Mountains, is "black limestone" (the "basal black limestone" of Girty, 1908, p. 

10), but in previous reports the term Bone Spring has 

been applied also to rocks of other sorts, laid down in 

different environments, the gray Victorio Peak Limestone (King, P. B., and King, K. E., 1929, p. 922) and 

the Cutoff Shale (King, P. B., 1942, p. 569-570); it has
PERMIAN 61

thus been used for all strata of Leonard age in the 

northern Trans-Pecos Region.

However, the term Leonard Series is adequate to express time-stratigraphic relations in northern TransPecos Texas. Moreover, the Victorio Peak Limestone 

and Cutoff Shale are thick persistent units with their 

own special characters in the shelf and platform areas. 

It is therefore appropriate to restrict the Bone Spring 

to deposits primarily of basin facies like those at the 

type locality and to class the Victorio Peak Limestone 

and Cutoff Shale as other formations of the Leonard 

Series. In the Delaware basin area, represented by 

exposures in the Delaware Mountains in the northeast 

corner of the report area, the Bone Spring occupies the 

whole of the Leonard interval; but in the Sierra Diablo 

it occupies only the lower part and is succeeded by the 

Victorio Peak and Cutoff, of later Leonard age. The 

Bone Spring Limestone of the Sierra Diablo region has 

its own assemblage of marginal deposits, different from 

those of the units above.

OUTCROP

The Bone Spring Limestone, as thus restricted, crops 

out at midheight on the east-facing escarpment of the 

Sierra Diablo from near Victorio Peak northward past 

Apache Canyon, where it is a little less than a thousand 

feet thick (pi. 1). Most of it is black limestone that 

characteristically forms a smoothly rounded slope between the bench of Hueco Limestone below and the cliff 

of Victorio Peak Limestone above, but the slope is interrupted by ledges in the lower part (pi. 10). Similar 

rocks are preserved hi a large outlier in the northern 

Baylor Mountains, and form the lower part of the westfacing escarpment of the Delaware Mountains, as in the 

northeast corner of the report area. Marginal deposits 

of the Bone Spring, mainly thinner and including ledgemaking limestone reefs and banks, are exposed on the 

Sierra Diablo escarpment near Mine and Marble 

Canyons and south of Victorio Peak, as well as in the 

central Baylor Mountains, but they are best shown in 

cross section on the walls of Apache and Victorio 

Canyons behind the escarpment.

LITHOLOGY AND FACIES

The dominant rock of the Bone Spring is "black limestone" which, in the type area in the Guadalupe Mountains, is a fine-grained impure limestone in beds a few 

inches thick, colored dark gray or black by bituminous 

material (King, P. B., 1948, p. 14-15). Elsewhere in 

the Delaware Mountains, the Sierra Diablo, and the 

Baylor Mountains the facies called black limestone is 

more varied, as it includes both thinner and thicker 

black limestone beds and thinly fissile black or brown 

siliceous shale. Layers of the black limestone dip irregularly, especially near the marginal areas. Irregularly dipping layers are extensive and well exposed in 

the Guadalupe Mountains (King, P. B., 1948, p. 15-16; 

Newell and others, 1953, p. 86-88), and occur also in 

the Sierra Diablo region.

In the Delaware Mountains in the northeastern part 

of the report area, well out in the basin of Bone Spring 

time, the exposed part of the formation is all black limestone; but the lower part of the black limestone in the 

Sierra Diablo is interbedded with various lighter gray, 

more clastic or more dolomitic layers, which are mainly 

tongues of the marginal deposits.

In the Sierra Diablo region black limestone deposits 

of the basin area are bordered by marginal deposits toward the southwest, whose position coincides with the 

Babb and Victorio flexures that cross the northern and 

central parts of the range (fig. 6). Both flexures are 

downbent northeastward toward the basin and were 

probably in process of growth during Bone Spring 

deposition, although they were much accentuated later. 

One marginal belt extends east-southeastward across 

Apache Canyon to the front of the mountains near Mine 

and Marble Canyons and parallels the upper end of the 

Babb flexure. Along it, the black limestone deposits 

pass abruptly into limestone reefs which overlap and 

wedge out against the sloping surface of the Hueco 

limestone. At the southeast end of the belt the reefs 

either terminate or bend southwestward beneath a cover 

of Victorio Peak Limestone to join the marginal deposits along the Victorio flexure. The marginal belt 

along the Victorio flexure is exposed across the central 

Sierra Diablo, east-southeastward to the front of the 

mountains south of Victorio Peak, and reappears in the 

northern Baylor Mountains. Along it, black limestone 

interfmgers up the dip with thickening limestone banks, 

which are truncated by erosion at their upper ends and 

do not wedge out against the older rocks of the flexure.

On the platform at the upper end of the northern 

marginal belt, at the head of Apache Canyon, the Victorio Peak Limestone is separated from the Hueco Limestone by only a thin wedge of strata, and the area received no deposits during most of Bone Spring time. 

On the platform at the upper end of the southern 

marginal belt, in the southern Sierra Diablo and the 

central Baylor Mountains, Bone Spring Limestone extends over the Hueco a mile or so south of the Victorio 

flexure. The Bone Spring must have wedged out 

eventually farther south, because in the Wylie Mountains the Victorio Peak Limestone lies directly on the 

Hueco.

SIERRA DIABLO ESCARPMENT

Bone Spring Limestone is exposed along the northeastern segment of the Sierra Diablo escarpment from
62 GEOLOGY OF THE SIEERA DIABLO REGION, TEXAS

EXPLANATION

OUTCROP AREAS

Bone Spring Limestone

Light shading indicates black limestone

and associated deposits; dark shading

indicates marginal deposits, principally

massive limestone reefs and banks

Older and younger Permian rocks

Rocks older and younger 

than Permian

OTHER SYMBOLS

1270

Thickness of Bone Spring Limestone, 

in feet, where determined

Trend of linear features in 

Bone Spring Limestone

Alined fusulitrid tests

Gradational boundary between black 

limestone on northeast and marginal deposits on southeast

Inferred southwestern margin of 

Bone Spring Limestone

Formation absent farther southwest b\f 

overlap on Hueco Limestone and by 

intergradation with Victoria Peak 

Limestone

10 MILE?

FIGURE 6. Map of Sierra Diablo region showing paleotectonics of Bone Spring Limestone.
PERMIAN 63

south of Victorio Peak nearly to Babb Canyon, where 

it passes beneath the surface. In this segment the Bone 

Spring is mainly black limestone, except for the marginal deposits on the Victorio flexure at the south end and 

for an interruption of several miles by the reef body 

near Mine and Marble Canyons. Stehli (1954, p. 273) 

proposed that the black limestone north of the reef body 

was deposited in an open basin and that to the south in a 

deep lagoon behind the reef, but the rocks of the two 

areas are identical lithologically and faunally and are 

not likely to have been deposited in different environments.

Most of the Bone Spring in this segment is darkgray or black dense thin-bedded limestone, which 

weathers platy, light gray, buff, or brown, and is carved 

into rounded slopes. Much of it is siliceous or argillaceous; analysis of one specimen indicates 23.65 percent organic insoluble material (King, P. B., 1948, p. 

14, specimen 3). Most of the beds are a few inches 

thick, but some are thicker, others paper thin; parts are 

featureless within the beds, others very thinly laminated. Some beds contain chert in long thin layers 

or lenses. Interbedded with the limestone, in places 

in thick units, is brown platy or papery siliceous shale, 

which grades locally into stony shale or bedded chert. 

These limestone and shale beds are nearly unfossiliferous, but some contain spicules, brachiopod shells, and 

more obscure organic markings. Further details of the 

nature of the black limestone have been given by Stehli 

(1954, p. 278).

In many places bedding in the black limestone dips 

irregularly, at a steeper angle than that of the formations above or below. Irregular bedding on a small 

scale in the lower part was observed in ravines between 

Victorio and Marble Canyons, where channels in limestones are filled by limestone of slightly different character, and where some beds are contorted, broken by 

minor thrusts, and truncated by beds above. Irregular 

bedding on a larger scale occurs near the marginal belts. 

In Apache Canyon (geologic sections, 36, 37, and 38, 

pi. 8) black limestone beds dip away from marginal 

reefs at angles of 12° to 25° northeastward; at the head 

of Marble Canyon (geologic section 32, pi. 7) they dip 

at a lower angle southward. Exposures are generally 

insufficient to determine the gross pattern or origin of 

these structures. In part at least they resulted from 

primary deposition on the slopes of the higher-standing reefs and other marginal deposits; some were probably acentuated by slumping or sliding of the newly 

deposited sediments.

Interbedded with the black limestone, especially in 

the lower part of the Bone Spring, are layers of lighter 

gray thicker bedded limestone, which project as ledges.

Many are tongues of the reefs and banks of the marginal belts, and increase toward them in number and 

thickness. At Victorio Peak and Marble Canyon 

(geologic sections 29 and 32, pi. 7) they extend as high 

as 400 feet above the base of the Bone Spring; but 

farther away from the marginal belts, as near Victorio 

Canyon (geologic sections 36 ancf 37, pi. 8), they occupy a smaller interval. In places a hundred feet or 

so of ledge-making beds succeeds the ledge-making 

Hueco Limestone, with few partings of black limestone, 

so that the boundary between the Bone Spring and 

Hueco is topographically indistinct. However, the 

rocks above and below the boundary differ in both texture and fossils.

Individual ledge-making beds are a few feet to more 

than 150 feet thick. Some are well bedded and persist 

for miles along the outcrop, others pinch or swell 

within short distances, changing from bedded to massive, and a few are lenses of small extent. The ledgemaking beds are partly calcitic but mostly dolomitic, are 

fine to coarse grained, and in places brecciated. Many 

beds are crowded with brachiopod and mollusk shells, 

some of which are silicified, but others contain little 

else than fusulinids and crinoid columns.

Most of the ledge-making beds are bioclastic and are 

formed of fossil shells and fragments. Part of the 

organic material accumulated in place, in patcli reefs 

or more extensive layers; in these Stehli (1954, p. 278) 

has observed shells still in position of growth. Part 

was redeposited from growth areas elsewhere, mainly in 

shallower water, and was spread over the black limestone deposits in broad sheets, or as local banks or windrows. Two special kinds of bioclastic deposits deserve 

notice.

A little above the base of the Bone Spring in Black 

John Canyon (section 35; USGS 6938, 7055), northwest of the portal of Apache Canyon (USGS 14439), 

and in the Baylor Mountains as described below, are 

"molluscan ledges," which are very local lenses packed 

with molluscan shells. Gastropods dominate, but there 

are also pelecypods and cephalopods, as well as a few 

scaphopods, pteropods, and chitons. P. E. Cloud, Jr., 

and E. L. Yochelson (written commun., 1954) state 

Fossils from these beds were silicified and have been prepared 

for study by etching with hydrochloric acid. The residues contain great quantities of shell fragments compared to the complete specimens recovered. The rock resembles the present-day 

coquinas in concentration of shell fragments.

These shells are not in position of growth, and were 

probably removed from their growth areas by waves 

and currents, which redeposited them in banks on the 

sea floor (compare Yochelson, 1956, p. 190).
64 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Fusulinids collected at many localities within a hundred feet of the base of the Bone Spring are either Wolfcamp (Hueco) species, or a mixture of Wolfcamp with 

Leonard (Bone Spring) species, whereas the associated 

larger fossils are of Leonard affinity. Collections of this 

kind were made at Victorio Peak (geologic section 29b, 

F 2716), Victorio Canyon (geologic section 30, F 2723), 

and northwest of the portal of Apache Canyon (F 9815, 

9816, 9817). (See p. 151-153,161-162.) Petrographic 

study of specimens from these and other localities by 

Henbest demonstrates that the anomalous association of 

Wolfcamp and Leonard fusulinids results from redeposition of the Wolfcamp f usulinids in younger sediments. 

Typical is the following report on specimens from about 

70 feet above the base of the Bone Spring on Victorio 

Peak (geologic section 29b, unit 16, F 2716) by L. G. 

Henbest (written commun., 1955).

These specimens include two kinds of f usulinid-bearing limestone, which will for convenience be termed types 1 and 2.

Type 1 is a calcarenite that consists of well-sorted subspherical grains 0.15 to 0.45 mm in diameter. The grains are highly 

rounded fragments of lithified fusulinids, echinoderm ossicles, 

and very fine grained limestone. Each grain is coated with a 

layer of clear calcite 15 to 20 microns thick. This clear coating 

has no oolitic structure, and contrasts with the well-graded 

matrix, which consists of calcareous fine silt. In the sample 

the grains are as closely packed as they can lie.

Most of the grains are fusulinid fossils. The high degree of 

rounding indicates that these were either: (a) filled with sediment and lithified before they were eroded, rounded, and redeposited, or (b) impregnated and lithified during abrasion. The 

latter is indicated because the chamber filling is silt and detritus, 

whereas before breakage the interior volutions of fusulinid shells 

are ordinarily inaccessible to silt and are generally filled with 

crystalline calcite. Further support to this alternative is given 

by the weathered, corroded conditions of the shells, and the presence of a coating of chemically precipitated or nonoolitic type.

The fusulinid detritus consists of species of Schwagerina, 

Pseudofusulina, and perhaps other genera of Schwagerininae. 

These appear to be Hueco fusulinids. No Bone Spring species 

were recognized, but the preservation is so fragmentary that 

certain Bone Spring species could occur without recognizing 

them as such.

Type 2 consists of unsorted partly silicified angular to rounded 

detritus, containing an extraordinary variety of well-preserved 

shells of fusulinids and other foraminifers. Indistinct particles 

of limestone of a different facies are also present, as well as a 

few coated sand grains like those of type 1 lithology.

In this f aunal aggregate part of the species are typical of the 

upper part of the Hueco Limestone in the Sierra Diablo, and 

to some extent of the uppermost beds of the type section at 

Wolfcamp, notably: Pseudoschwagerina gerontica, P. teatana 

var. or Pseudofusulina huecoensis var., Parafusulina linearis, 

Bchubertella kingl, and part of the smaller foraminifers. On 

the contrary, Parafusulina schucherti, P. diabloensis, other 

parafusulinid species, and Schwagerina gumbeli are characteristic of the Bone Spring. The exact range of none of these 

forms can be stated with finality, but the evidence is clear 

lithologically and biologically that this fauna is a depositional 

aggregate, in which Hueco fossils have been redeposited with 

early Bone Spring fossils.

NORTHERN MARGINAL BELT

The northern marginal belt of the Bone Spring Limestone emerges from younger Permian rocks on the west 

wall of Apache Canyon, and is exposed thence eastsoutheastward for 5 miles to the front of the Sierra 

Diablo near Mine Canyon. Marginal deposits of the 

belt were laid on an eroded surface of the Hueco Limestone, which is low and flat along the mountain front, 

but which rises southwestward nearly a thousand feet 

in Apache Canyon.

The marginal belt is well exposed in cross section on 

the northwest wall of Apache Canyon (pi. 11; section 

F-F', pi. 4). Here the Bone Spring Limestone thins 

southwestward from 880 feet (geologic sections 37 and 

38, pi. 8) to a few hundred feet (geologic sections 40, 

41, pi. 8), mainly by overlap on the rising surface of 

the Hueco but partly by intergradation of the upper 

beds with the Victorio Peak Limestone. The thick body 

of Bone Spring in the northeastern part of the canyon 

is mainly black limestone, but it passes southwestward 

into marginal deposits. No more than a few hundred 

feet of marginal deposits occur at any locality, although 

they have a vertical range as great as the slope of the 

underlying Hueco.

At about midpoint in the canyon (geologic section 

39, pi. 8) the Bone Spring includes a massive unit of 

saccharoidal dolomitic limestone that stands in massive dark ledges and a thinner underlying unit of cherty 

and marly limestone. The massive unit contains little 

else than fusulinids, but fossils are more varied in the 

unit below and many are silicified. Tongues of the 

massive unit extend with primary dip into the lower 

part of the black limestone farther northeast. The 

black limestone itself has steep primary dips, and includes many lenses or lumps of massive gray limestone, 

some of which are crowded with sponges, bryozoans, 

and other fossils. Probably these lenses were patch 

reefs that grew along the edge of the overlapping Bone 

Spring deposits. In this part of the canyon the unconformable basal surface is generally overlain by 25 feet 

or so of ledge-making dolomitic limestone, which is not 

obviously conglomeratic but which may have been reworked in part from the Hueco beneath. In places it 

contains not only indigenous fusulinids but f usulinids 

of Wolfcamp type that were redeposited from the 

Hueco.

In the southwestern part of the canyon, where the top 

of the Hueco stands high, it is separated from the Victorio Peak Limestone by thin-bedded slope-making 

dolomitic limestone, generally a few hundred feet thick 

but thinning to less than 50 feet in the westernmost 

exposure (sec. 15, Block 32). This unit is mapped as 

Bone Spring, although it is equivalent to only a little 

of the upper part of the formation in the northeastern
PERMIAN 65

sections. At Apache Tank (geologic section 41, pi. 8) 

the limestone of the unit, which is interbedded with 

pink and yellow marl, overlies a conglomerate of limestone pebbles and cobbles that was probably derived 

from the Hueco.

Southeast of Apache Canyon the marginal deposits 

form an escarpment nearly a thousand feet high, from 

which the strata in front have mostly been eroded (section F-F', pi. 4). The rocks of the escarpment are a 

reef of dolomitic limestone, parts of which are very 

massive, parts thick bedded with a primary dip to the 

northeast. Within the reef, much of the original organic structure has been destroyed by dolomitization 

and recrystallization, but in places obscure traces of 

crinoid columns, bryozoans, sponges, and algae are 

visible, as well as better layered streaks or lenses of 

bioclastic debris.

The intertonguing of the reef mass with the black 

limestone is preserved at a few places, as on the spur 

that extends north to Apache Peak. Here, outer ends 

of the reef tongues and isolated patch reefs embedded 

in the black limestone are not so dolomitized as the 

main reef and preserve better their original nature. 

Many contain a profusion of sponges, massive bryozoans, crinoid columns, thick-shelled productids and 

other brachiopods, as well as cobbles and pebbles that 

are at least partly of algal origin.

Near Mine Canyon the reef extends to the edge of the 

Sierra Diablo escarpment, and any further extension 

to the southeast has been downfaulted. Probably it 

did not continue much farther in this direction, because 

dips in the reef and associated black limestone change 

from northeast near Black John Canyon, to east near 

Cave Peak, to south at the head of Marble Canyon 

(section W-W, pi. 4). By coincidence, this change in 

dip is near the large igneous stocks at Cave Peak and 

Marble Canyon, but the stocks disturbed the strata very 

little during their intrusion. The dips were not produced by the intrusions, but are primary features of the 

reef. On the escarpment face at the head of Marble 

Canyon, intertonguing of the reef front southward with 

black limestone is well exposed, and presumably the 

reef continued thence southwestward under a cover of 

younger Victorio Peak Limestone (fig. 6).

SOUTHERN MARGINAL BELT

The southern marginal belt of the Bone Spring Limestone extends east-southeastward like the northern and 

is exposed for 8 miles along the Victorio flexure, emerging from alluvium on the west and projecting to the 

Sierra Diablo escarpment on the east. Best exposures 

are on the escarpment south of Victorio Peak and in 

Victorio Canyon (upper view, pi. 10; sections X-X'

and T-T'j pi. 4); exposures farther west are less informative as the relief is lower.

In the southern marginal belt, as in the northern, both 

the surface of the Hueco Limestone and the strata of 

the Bone Spring slope northeastward, the former descending more than a thousand feet and the latter dipping 5° to 20°. Part of this slope is primary, as in the 

northern belt, but the slope was much accentuated by 

later movements on the Victorio flexure. The surface 

of the Hueco Limestone was much eroded before the 

Bone Spring was laid over it, as indicated by variations 

in thickness of the formation, by angular discordance 

between it and the Bone Spring, and by pebble beds in 

the Bone Spring; Bone Spring strata, however, do not 

overlap the Hueco as they do in Apache Canyon.

The Bone Spring Limestone on Victorio Peak (geologic section 29a, pi. 6) north of the flexure is 970 feet 

thick, but at midpoint on the flexure (geologic section 

28, pi. 6) it has thickened to 1,050 feet, despite loss of 

much of its upper part by intergradation with the Victorio Peak Limestone. At the top of the flexure (geologic section 27, pi. 6) 850 feet of the formation is 

preserved, although the Victorio Peak is missing. 

Southward thickening of the Bone Spring is caused by 

swelling of each layer as it changes into marginal f acies, 

so that the thick sequence in the south is equivalent only 

to the lower part of the thinner sequence in the north.

These relations are well shown in cross section south 

of Victorio Peak and in Victorio Canyon (sections 

X-X' and F-F', pi. 4). On the east slope of Victorio Peak and in the lower course of Victorio Canyon, 

a 100-foot bed of gray limestone forms a prominent 

ledge about 300 feet above the base of the formation. 

This bed is traceable to the upper end of the flexure, 

where its thickness and its distance above the base of 

the Bone Spring have doubled. To the north, beds 

below and above the ledge are mainly black limestone, 

but to the south, thick units of cliff-making dolomitic 

limestone wedge in. These have been interpreted as 

reefs (King, P. B., 1962, p. 630), but "although the deposits are largely made up of organic debris, there is 

little evidence for more than occasional wave-resistant 

structures" (Stehli, 1954, p. 274). Between the wedges 

the black limestone changes into green clay shale and 

yellow nodular limestone, both containing many fossils, 

some of which weather free. Some beds are formed of 

closely packed fusulinid shells, which in places include 

both indigenous species and species reworked from the 

Hueco.

In the southernmost exposures many beds between the 

lower wedges are conglomerate, derived in part from 

erosion of the Hueco Limestone farther south. The 

conglomerate is formed of well-rounded limestone peb-
66 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

bles of various colors and textures, % inch to 1 inch in 

diameter, which lie in a matrix of dolomitic or marly 

limestone. Both matrix and pebbles contain fusulinids 

and other fossils.

One wedge of massive dolomitic limestone directly 

overlies the Hueco and thickens southward like the rest, 

extending a mile or two beyond succeeding parts of the 

Bone Spring and the upper end of the Victorio flexure 

to form remnants on the crest of the Sierra Diablo. 

This basal dolomitic limestone is more massive than the 

Hueco Limestone on which it rests, and it weathers more 

jagged. Unlike the Hueco, it contains large fusulinids 

and other fossil shells in places, some of which are 

silicified.

BAYLOR MOUNTAINS

The Bone Spring Limestone forms most of the northern part of the Baylor Mountains and resembles that in 

the Sierra Diablo. The downfaulted eastern extension 

of the Victorio flexure crosses the northeast corner of the 

mountains, where Bone Spring strata dip 10° to 30° 

north-northeastward with the Victorio Peak Limestone 

at the top, but both flexure and earlier structures are 

obscured by closely spaced northwest-trending faults of 

Cenozoic age (section Z-Z', pi. 4). The full sequence 

of the Bone Spring is exposed only toward the northeast, where it is probably about a thousand feet thick, 

but only the lower part could be measured (geologic 

section 18, pi. 5).

Most of the formation in the northeastern part of the 

mountains is black limestone, which includes the usual 

thin-bedded dark-gray or black limestone and platy 

siliceous shale. However, the uppermost 500 feet forms 

beds as much as several feet thick and contains many 

chert nodules. Southward, as on the Victorio flexure 

in the Sierra Diablo, part of the black limestone gives 

place to shale, calcareous marl, and earthy limestone. 

These rocks contain abundant fossils, many of which 

weather free.

The black limestone contains layers of lighter gray 

thick-bedded or massive limestone, but most of them are 

very lenticular. One group of lenticular layers 300 or 

400 feet above the base of the Bone Spring is more persistent than the rest, although the layers wedge out and 

nearly disappear in places, and in others coalesce into 

a prominent ledge several hundred feet thick. Not far 

above these layers at one locality (geologic section 18 ; 

USGS 6983,14475) is a "molluscan ledge" like those in 

the northeastern Sierra Diablo.

Southward in the Baylor Mountains, as farther west 

on the Victorio flexure, a massive dolomitic limestone 

wedges in at the base of the Bone Spring and caps the 

Hueco over much of the central part of the mountains 

(section Z-Z*', pi. 4). Higher wedges are preserved

near the high point of the mountains (BM 5568), which 

slope northward with primary dip into the black limestone. Some of them are dolomitic, others calcitic; 

some are fine grained, others coarse and bioclastic with 

abundant silicified fossils.

FOSSILS AND CORRELATION

Fossils are preserved in varying abundance in the 

different kinds of rocks of the Bone Spring Limestone, 

but all its fossils make a varied assemblage (tables 5-7). 

Fossils are scarce in most of the black limestone, probably because of an original poverty of life; they are 

poorly preserved in the reefs and banks, because of subsequent dolomitization and recrystallization. They are 

most abundant and best preserved in the ledge-making 

beds and lenses of gray limestone that are interbedded 

in the lower part of the black limestone. Fusulinids 

and other f oraminif ers occur here in varied associations. 

On the other hand, the kinds of larger invertebrates 

vary greatly in proportion from bed to bed and place 

to place, owing to either environmental differences in 

the growth areas or sorting of the shells during transportation and redeposition. Variations from these 

causes overshadow any faunal zonation within the formation, if such exists.

FATJNAL ASSEMBLAGES

Fusulinids of the Bone Spring Limestone include 

such characteristic species as Parafusulina diabloensis 

Dunbar and Skinner, P. imlayi Dunbar, and P. schucherti Dunbar and Skinner. Earlier collections from 

the Sierra Diablo did not yield Scfiwagerina hessensis 

Dunbar and Skinner, S. gumbeli Dunbar and Skinner, 

or S. crassitectoria Dunbar and Skinner, which are 

characteristic of the lower part of the Leonard Series 

of the Glass Mountains, and it was thought that the 

lower Leonard might be missing here (Dunbar and 

Skinner, 1937, p. 589). However, all these species have 

been discovered later in the Sierra Diablo (Dunbar, 

1953, p. 804-809; L. G. Henbest, written commun., 

19.55), and the supposed hiatus must not exist. Similarly, Parafusulina fountaini Dunbar and Skinner and 

Pseudofusulina setum (Dunbar and Skinner), which 

were supposed to characterize the younger Victorio 

Peak Limestone, are now known to occur more sparingly in the Bone Spring.

At many places, mostly within a hundred feet of the 

base of the Bone Spring Limestone, fusulinids of Wolfcamp (Hueco) type are mingled with those of Leonard 

(Bone Spring) type but, as stated above, studies by 

Henbest (written commun., 1955) indicate that the 

Wolf camp fusulinids have been redeposited from earlier 

strata. All the specimens of PseudoscJiwagerina which 

have been identified from the lower part of the Bone
PERMIAN 67

TABLE 5. Fossils identified, from Bone Spring Limestone, Baylor Mountains and northeastern Sierra Diablo (Foraminifera)

[identifications by L. G. Henbest. Explanation of symbols: X, genus or species present; var, variety of species present; aff, specimen related to species but probably different; 1, specimen doubtfully assigned to genus or species]

Distribution of fossils in stratigraphic section, locality, and collection number indicated

Foraminifera: 

Indigenous and probably indigenous 

genera and species:

ParafusiMna attenuata Dunbar and

? Parafusulina diabloensis Dunbar

Parafusulina fountaini Dunbar and

schucherti Dnnbar and Skinner. .

Pseudofusulina setum (Dunbar and

Schwagerina^ franklinensis Dunbar

Schwagerina gumbeli Dunbar and

ISchwagerina gumbeli Dunbar and

pseudoregularis Dunbar and

Genera and species redeposited from 

Hueco limestone: 

IParafusvMna gracUUatis (Dunbar

Parafusvlina linearist (Dunbar and

Pseudofusulina, powwowensis (DunPseudoschwagerina gerontica Dunbar

Pseudosehwagerinat laxixsima (DunPseudoschwagerina texana Dunbar

Schubertdla kingi Dunbar and

Schwagerina beUula Dunbar and

19 

Northwestern 

Baylor 

Mts.

PH

X

X

var

X 

?

X

X

X

27 Second 

section 

south of 

Victorio 

Peak

si 00 ^1 Ei

X

X

?

X 

X

?

X

51" 

[z, Jt

X

?

? 

X

X

X 

X 

X

X

Victorio 

flexure

<M?T 

ll

X

X

X 

X

X

2§f 

§5*

f**>L

X

X 

X

X

var

X

29b Victorio 

Peak

toll !?f^-~^

aft

X

X

X

X

X 

X

X

X 

X

X

X var

var

?

X

23s!

aff

?

?

......

30 

Victorio 

Canyon

£1

X

?

X

X

?

X

X

X

?

X

aff

31 

North 

of 

Victorio 

Canyon

si

£!

var

? 

X

var

Northwest of 

Apache Canyon

«>5 

Zl

X 

X 

X

?

X

X

Xvar

X

?

var

fe

X

X

X

to 3! 

|3 

II (Z)^--

X

X

?

?

X

X

aff

37 

First 

section 

in 

Apache 

Canyon

sl So2 %i

X

aff 

X 

X

X 

X

38 Second 

section in 

Apache Canyon

§ 

^

X

X

IsSZA

X

X

X

X

X

?

X

X

?

' 10

h

X

39 

Third 

section 

in 

Apache 

Canyon

^

1

?

var

Spring are probably of this origin, except the oddly 

shaped Pseudoschwagerina stanislavi Dunbar, which is 

indigenous to the Bone Spring and is seemingly a late 

variant of the genus (Dunbar, 1953, p. 809-812).

The remaining groups of invertebrates of the Bone 

Spring Limestone form two contrasting assemblages, 

with few forms in common. The most widely distributed assemblage is dominated by brachiopods, the other 

occurs in the "molluscan ledges."

A typical collection dominated by brachiopods, from

757-108 05 6

the lower part of the Bone Spring in the Victorio Peak 

area, is summarized as follows by Stehli (1954, p. 280):

An interesting feature of this and other collecting localities is 

the complete imbalance of the organic assemblage. There are 

ten times as many brachiopod individuals as all others combined. Second in importance are the bryozoans, which occur 

in large numbers and include both stony forms and delicate 

fenestellids. Pelecypods are next in variety but are very low 

in numbers of individuals. Crinoid debris is abundant. Corals 

are present in moderate numbers. Gastropods are of limited 

variety, but there are moderate numbers of individuals. Cephal-
TABLE 6. Fossils identified from Bone Spring Limestone, Baylor Mountains, and northeastern Sierra Diablo (Porifera, Coelentera

and Brachiopoda)

[Identifications by P. E. Cloud, Jr., Helen Duncan, and R. M. Finks. Explanation of symbols: X, present; C, common; A, abundant; R, ra

Distribution of fossils in stratigraphic section, locality, and collection number indicated

Porifera: 

Qirtyocoelia dunbari R. H. King- _ _ __

Coelenterata:

Echinodermata:

Bryozoa:

StTiatovora sp. . 

17 

High 

point of 

Baylor 

Mountains

7048

X

X

C

X

Near High point 

of Baylor 

Mountains

7053

X

R

7009

X

X

18 Northeastern Baylor 

Mountains

7000a 7000

A

6983- 

14475 Molluscan 

ledge

X

R

C

R

X 

C 

R 

R 

R 

X 

C 

X

19 Northwestern Baylor 

Mountains

7002a

X 

X 

X

X

7002b

X

C

X

X

R

X

27 Second section 

south 

of 

Victorio 

Peak

14454

X

X 

X

Victorio flexure

8544 8543

X 

X

X

X

C

X

R

8542

R

X

X

29b Victorio 

Peak

8562

X

X

c

X

R

C 

R 

R

C

X

X

8561

X

X 

X

X

c 

c

R

X

3

Vic

Can

85

A

A

X
PERMIAN 69

X

X

X

XX

X

G 

CQ

X

'.I 

1

BuxtonialKochiproductus) King victorioensis 

o

0 0

>

c

j

i1

1*-

o

ox

o

XX

sppCompositasp.. .................................

<M

O

X 0

o

1

tf

X

X

X

-

o

X

X

X

o

X

p*

W 1*^ X

o

Derbyiasp ...................................... (Chaoiella) guadalupensis (Girty) Dictyodostus 

«

o

>

c

I

1

K 

l c 

1 

1 '*

1

g

V.

1 -j

t

C

£>i^

i

! £

X

X

X

X

X

tf

P5X

X

. I1V.

1

X

' 

_

i

g

'!

£

x

x

X

X

XX

X

X

Leptodussip ____ -. (Cancrinella) Linoproductus spp.. ____ .__"M." affcapaci "Marginifera" (Kozlowskia) 

M'Orhifmv* _.

t

c

£

1s

1 

/

~(Kozlowskia] aff "M/'wabashensis (Nor-

-

>t

c

a

'4 11

>s

««.

c

O

o

X

X

X

X

<{ P4

X

X

XO

Xtf

X

X

p»

X

XXX

XX

X

X Xo

O

XX

 »

»

i 

>>

\

; c

) y

g

1 

1

1 

c

1

! i

o

0 0

o

X

>

*

J"»

o

X

\/

X

X

indet Orthotetacean 

Productids indet.. . 

X

X

'c

i3

4

I

J'1

o

X

P5

P5

X

'5

1

g

1 1

1

c 

a

^g

i

/

o

P5

iSgjiarnMiari<rsp. and Sguamularial sp...... ..

v/

«X

>/

X

X

1-^

I 

>a

3

t g

g

« 

?

j 

1

P5

«

«

X

o

1 ^

1

,h
TABLE 7. Fossils identified from Bone Spring Limestone, Baylor Mountains and northeastern Sierra Diablo (Amphineura Co

Scaphopoda, Gastropoda, Cephalopoda, Annelida, Arthropoda and Alga)

[Identifications by W. M. Furnish, A. K. Miller, I. G. Sohn, and E. L. Yochelson. Explanation of symbols: A, abundant; C, common; X, present; 

Distribution of fossils in stratigraphic section, locality, and collection number indicated

Amphineura:

Coniconchia(?): 

Hyoltthessp. .............. ______ ____

Lamellibranchiata:

Myalinid indet _____ __ _________

Nuculana spp_ __________________ .

Pectenoid indet. _______________

Permophorus sp... _______________ ..

Pterial sp. _____ __ _____ _ _______

Schizodussp. ........ ...........................

Streblopteriasp. ..... . __ ___________

Pelecypods indet. ______________

Seaphopoda:

" Laevidentalium" sp ___ _ _ _ _ _.. __ _

Gastropoda:

Apachetta sp __ __ _____ _______

Bellerophontid indet. _______________

Cinclidonema sp. _ -.._ . ... _______

Discotropis girtyi Yochelson _________ _

Donaldinat sp. _ ________ . . __ - _____

Euconospira pulchra Batten. .--_-. ... ______

Euphemites cf. E. imperator Yochelson ___ _

cf. E. kingi Yochelson. __ _. ._ __ _

SP_____ - 

Glabrocingulumsp.-.-. ..... _______ _____

Glyptospira sp ____________ _ __ .. _

Knightttes (Retispira) sp. _ _ - _ -- - _ _ __

iMmellospira conica Batten. _.--_---.- _______

cf. Lozonemasj)... .................... ________

Murchisonid indet- _________ _____

Naticopsis sp _______________

Orthonema sp _______________ __ ___

Peruvispira sp. _ _ __________ ___________

Pharkidonotus sp__ ____ _________ _ ..

Platyceras sp .. _. _______________

Pleurotomarian indet--- _______ -_ _ _

Pseudozygopleuran indet _____ ._. _____

17 

High 

point of 

Baylor 

Mountains

7048

X

X

X 

X

X 

X 

X

X

Near high 

point of 

Baylor 

Mountains

7053

X

C

7009

X

X

X

X 

X

X

18 Northeastern 

Baylor Mountains

700a

R

7000

X 

X

6983- 

14475 Molluscan 

ledge

R

X

A 

X

C 

R 

C

X 

X

c

X 

X

c 

c

X

c

R 

X

X 

X

X

c

X

X 

X

X

19 Northwestern 

Baylor 

Mountains

7002a

X 

X

X

X

X

X

7002b

X

X

X

X

X

X

X

27 Second 

section 

south 

of 

Victorio 

Peak

14454

X

Victorio flexure

8544

X

X

X

X

8543

X

8542

29b Victorio 

Peak

8562

X

X

8561

X

X

X

X

X

30 

Victo

Cany

853

X

X
Straparottus (Euomphalus) glabribasis YochelSublitid indet __________________

Cephalopoda:

spp

Annelida:

Arthropoda:

Alga:

X

X

X

X

R

R

R
72 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

opods are very rare. Sponges and arthropods are represented 

by rare fragmentary material. Fusulinids are abundant.

Distinctive brachiopods of the assemblage are Dictyoclostus (Chaoiella) guadalupensis (Girty), Buxtonia (Kochiproductus) victorioensis King, Chonetes 

(Chonetinella) victoria/mis Girty, species of Enteletes, 

Wellerella, and Stenocisma, and a small species of 

Avonia. Many layers also contain Meekella, Leptodus, 

and ProrwJithofenia,) adapted to life on a firm substratum, probably in a reef environment. Collections 

from some beds contain many productids, whereas 

others are dominated by Enteletes and other nonproductids; but these differences are not stratigraphically significant. Many of the brachiopod species of 

the assemblage have been described by R. E. King 

(1931), some by Stehli (1954, p. 289-357).

Bryozoans are varied, but most of the genera at any 

locality are represented by only a few specimens, except 

for fistuliporoids, which form abundant large masses in 

some layers. Sponges are abundant in places, most of 

the identifiable ones being Heliospongia or Defordialike forms. Spicules have been recovered in many insoluable residues and indicate a greater abundance of 

sponges than would be inferred from the larger specimens that have been collected. Horn corals of lonsdaleoid type and colonial corals occur here and there.

In the brachiopod-dominated assemblage mollusks are 

notable mainly for their paucity of number and variety, 

in contrast to the assemblage in the "molluscan ledges."

The assemblage in the "molluscan ledges" is dominated by mollusks, almost to the exclusion of other 

phyla. Brachiopods are represented by only a few 

specimens; sponges, corals, bryozoans, and crinoid 

debris are uncommon. The mollusks are mainly gastropods and pelecypods, the first dominating the ledge 

northwest of Apache Canyon (USGS 14439), the second, the ledge at Black John Canyon (USGS 7055, 

6938); cephalopods, scaphopods and chitons are less 

abundant. According to Yochelson (1956, p. 189) 

Pelecypods are abundant, comprising well over half of the 

fossils recovered at the locality [at Black John Canyon]. Of 

these, Nucula, Nuculana, and Astartella are the commonest 

types, and parallelodontids are fourth in abundance. Most of 

the other pelecypod genera are represented by only a few 

specimens.

Gastropods are varied, being represented by nearly 20 genera. 

High-spired forms of several unrelated genera are somewhat 

more common than gastropods of other shapes; however, there 

is no striking difference in numbers of individuals among the 

several genera. No large gastropods occur, and few of medium 

size are present.

Cephalopods from the ledge northwest of Apache 

Canyon include the ammonite Propinacoceras knighti 

Miller and Furnish, four genera of coiled nautiloids,

and the straight-shelled genus Pseudorthoceras (Miller 

and Furnish, 1940a, p. 42-44; Miller, 1945).

The fauna of the "molluscan ledge" in the northeastera part of the Baylor Mountains (USGS 6983,14475) 

is transitional between the molluscan and brachiopod 

assemblages. Although it includes abundant pelecypods, these are associated with Meekella, Enteletes, ProricJithofenia, and other brachiopods, as well as massive 

bryozoans. A collection from near the high point of 

the Baylor Mountains (USGS 7009) is of similar transitional character, as it contains nearly equal numbers 

of brachiopods and mollusks.

CORBELATION

Bone Spring faunas differ from those of the underlying Hueco, and have many affinities with the higher 

faunas of the Guadalupe Series. They include 

the earliest of the large fusulinids which characterize 

the zone of Parafusulina, as well as the peculiarly 

adapted brachiopods Leptodus and Prorichthofenia. 

These and other distinctive features of the Bone Spring 

fauna characterize the Leonard Series in the West 

Texas Region.

From the stratigraphic position of the Bone Spring 

Limestone in the Sierra Diablo, between the Hueco 

Limestone and Victorio Peak Limestone, it would seem 

to be equivalent to the lower part of the type Leonard 

Series of the Glass Mountains, and there is some confirmation of this in the fossils. Thus, a group of 

schwagerinid species by which Dunbar and Skinner 

(1937, p. 586) characterized the lower part of the type 

Leonard occurs also in the Bone Spring. R. E. King 

(1931, p. 14) found that most of the brachiopod species 

in his collections from the Bone Spring occur in the type 

Leonard. Also, most of his collections ascribed to the 

"Hess limestone" were from basal ledges of the Bone 

Spring as now defined; he found that many brachiopod 

species from it occur in the Hess Limestone of the Glass 

Mountains, now known to be a f acies of the lower Leonard. According to Stehli (1954, p. 276 ) 

It must be noted that in the Sierra Diablo the lower Bone 

Spring contains a few forms which in the Glass Mountains are 

seemingly restricted to the Wolfcamp, and a possibility exists 

that these rocks are somewhat older than the Leonardian in 

the Glass Mountains.

STRATIGRAPHIC RELATIONS

Throughout the Sierra Diablo region the varied deposits of the Bone Spring Limestone are overlain conformably by the light-gray thick-bedded Victorio Peak 

Limestone.

The Victorio Peak Limestone also intergrades extensively with the upper part of the black limestone 

of the Bone Spring, both by intertonguing and by
PERMIAN 73

abrupt passage from light-gray into black strata in units 

several hundred feet thick. Intergradation of the two 

formations is prominently exposed on the south slope 

of Victorio Peak, on the escarpment just north of Victorio Canyon, and in Apache Canyon (sections U~U', 

F-F', W-W, and Y-Y', pi. 4). At all such places 

gray limestone changes to black northeastward, toward 

the basin area. Well out in the basin area, in the Delaware Mountains in the northeast corner of the report 

area, black limestone extends to the top of the Leonard 

interval and probably includes equivalents of the Victorio Peak (fig. 7).

However, the Victorio Peak Limestone does not replace the whole Bone Spring Limestone away from the 

basin area. In the marginal belts it overlies thickbedded gray limestone layers of different character, 

which were laid down as reefs or banks during Bone 

Spring time. In the platform areas these lower strata 

wedge out, and the Victorio Peak lies with hiatus on 

the Hueco Limestone.

VICTORIO PEAK LIMESTONE

The Victorio Peak Limestone is named for Victorio 

Peak (King, P. B., and King, E. E., 1929, p. 922), the 

prominent detached summit about midway along the 

east-facing escarpment of the Sierra Diablo (upper 

view, pi. 10). The Victorio Peak is a formation of later 

Leonard age which is thick and extensive around the 

margins of the basin area in the Guadalupe Mountains, 

the Sierra Diablo, and the Wylie Mountains.

The Victorio Peak Limestone forms the summits of 

the Sierra Diablo north of the Victorio flexure (pi. 14), 

breaking off on the east-facing escarpment into prominent light-gray cliffs that surmount slopes carved from 

the Bone Spring Limestone (lower view, pi. 10). North 

of the Babb flexure it descends to the edge of the Salt 

Basin, where it forms a low bench capped by younger 

formations that extends northward beyond the report 

area (upper view, pi. 12; section B-Bf, pi. 16). A 

small remnant of the Victorio Peak is preserved at the 

northeast corner of the Baylor Mountains, and a large 

outlier forms the eastern slope of the Wylie Mountains 

(geologic section 13; Hay-Koe, 1957).

The Victorio Peak Limestone is overlain by higher 

Permian formations at the north end of the Sierra 

Diablo and in the Wylie Mountains. On the Babb flexure at the north end of the Sierra Diablo its full thickness is 975 feet; in the Wylie Mountains it is about 

1,600 feet but includes undifferentiated beds of Guadalupe age at the top. Elsewhere in the Sierra Diablo, 

the Victorio Peak Limestone is the highest Permian 

formation and its full sequence is undetermined; here 

500 to 1,000 feet of beds are commonly preserved. On

the south slope of Victorio Peak it is nearly 1,500 feet 

thick, but the lower half intergrades with black limestone in the northern part of the mountain. Even 

allowing for erosion after Permian time, the formation 

thus varies much in thickness from place to place, 

probably mainly by intertonguing with the Bone Spring 

Limestone beneath.

NORTHEASTERN CALCIIIC FACIES

Along the east-facing escarpment of the Sierra Diablo, the Victorio Peak is a light-gray thick-bedded 

limestone, mainly calcitic but slightly dolomitic in part, 

which stands in sheer cliffs that in places are remarkably fluted and pinnacled. Beds are a few feet or tens 

of feet thick, and in places are irregularly inclined at 

low angles in different directions. Near Apache Peak 

and Apache Canyon, where the gray limestone extensively intergrades northeastward with the black 

limestone of the Bone Spring, long tongues of gray 

limestone extend into the black and descend several 

hundred feet from the main body toward their outer 

ends (section U-U', pi. 4). The calcitic limestone of 

the Victorio Peak is probably mainly a bank deposit 

(King, P. B., 1948, p. 27), although it may contain 

some small reef masses along its northeastern margin.

In places the Victorio Peak Limestone is separable 

into lithologically distinct subdivisions, but these are of 

local extent. Between Victorio Canyon and Mine Canyon the lower 250 feet is massive gray limestone, with 

indistinct bedding planes, that stands in a prominent 

cliff. Above is thinner-bedded gray limestone, with 

much interbedded buff marl, sandy and cherty limestone, and platy siliceous limestone. Many of these 

upper beds are fossiliferous, and contain productids, 

other brachiopods, sponges, and crinoid stems, some of 

which are silicified.

On the Babb flexure (geologic section 43, pi. 8) the 

Victorio Peak is separable into three divisions. The 

thick lower division is gray thick-bedded dolomitic 

limestone, in part cherty, which weathers gray brown 

and splits along closely spaced joints. About halfway 

up is a thin layer of fine-grained sandstone. The middle 

division, 100 feet thick, is thin-bedded dolomitic limestone, which weathers white and porcelaneous and forms 

a persistent light-colored slope. The upper division, 

50-65 feet thick, is dark-gray calcitic fossiliferous limestone, which is overlain by the Cutoff shale. The three 

divisions of this area are significant, because they are 

nearly identical with divisions of the Victorio Peak 

Limestone in the Guadalupe Mountains to the north 

(King, P. B., 1948, p. 17), and assist in correlation of 

the formation between the two areas.
74 GEOLOGY OF THE SIERKA DIABLO REGION, TEXAS

SOUTHWESTERN DOLOMITIC FACIES

West of the front of the Sierra Diablo the dominantly 

calcitic thick-bedded f ossilif erous limestone of the Victorio Peak changes to dolomitic thin-bedded poorly fossiliferous limestone. One facies gives place to the other 

in about a mile along a well-defined boundary that extends north-northwest across the mountains from Victorio Canyon to a little east of Sierra Prieta (fig. 7).

The dolomitic limestone includes white 6-inch to 1- 

foot layers with crinkled laminae that weather to jagged 

surfaces and dull-gray thicker layers. Analysis of a 

typical specimen from near the Slaughter Ranch by 

K. J. Murata (written commun., 1940) indicates a content of 50.25 percent CaCO3 , 38.75 percent MgCO3 , and 

1.34 percent insoluable material; the carbonate fraction 

is close to the composition of the mineral dolomite. 

Most of the dolomitic limestone beds are probably unfossiliferous, but some contain ghosts of fusulinids, 

crinoid stems, and bellerophontids.

The Victorio Peak Limestone of the small remnant 

in the Baylor Mountains and the larger body in the 

Wylie Mountains is of the same dolomitic f acies as that 

in the western Sierra Diablo.

The thin-bedded dolomitic limestone of this facies of 

the Victorio Peak somewhat resembles the dolomitic 

limestone beds of the underlying Hueco in the northeastern Sierra Diablo; it closely resembles Permian limestones of other ages elsewhere in the West Texas region 

that have been interpreted as back-reef or lagoonal deposits the Hess Limestone Member of the Leonard Formation and Gilliam Limestone of the Glass Mountains 

and the Carlsbad Limestone of former usage of the 

Guadalupe Mountains. The dolomitic limestone of the 

Victorio Peak was laid down on platform areas, which 

were probably separated from the basin area by low 

banks of the calcitic limestone facies.

FOSSILS

Nearly all the fossils that have been collected from 

the Victorio Peak Limestone are from the calcitic facies, 

on the rim of the Sierra Diablo escarpment or near the 

Babb flexure (table 8). The fauna indicated by these 

collections is less extensive than that of the Bone Spring 

Limestone, but it is less known because of poorer preservation and the relative inaccessibility of the outcrops. 

For these reasons the faunal makeup also differs much 

from one collection to another, but probably no collection approaches the whole biota of its locality.

Fusulinids are dominated by large parafusulinids 

and pseudofusulinids, such as Pamfusulina fountaini 

Dunbar and Skinner and Pseudofusulina setum (Dunbar and Skinner). The somewhat smaller Parafusulina diabloensis Dunbar and Skinner and P. scfiucherti

Dunbar and Skinner occur also, although they are more 

characteristic of the Bone Spring beneath.

Sponges which occur at many places are mostly 

Defordia-like forms and are probably a significant feature of the whole fauna in bulk (Finks, 1960, p. 28-32). 

Corals are less common. Dasycladacean algae, mostly 

Macroporella, are abundant at one locality, and indicate an environment of shallow tropical to subtropical 

water.

The fauna is dominated by brachiopods, and especially by productids, such as Buxtonia (KocJiiproductus) victorioensis King.4 Of the nonproductids, perhaps the most abundant genera are Enteletes and Neospirifer. Bryozoans are mostly rare, but massive fistuliporoids occur here and there, and at one place numerous Batostomella. Mollusks are likewise uncommon 

and are mostly moderate- to large-sized gastropods.

STKATIGRAPHIC RELATIONS

The top of the Victorio Peak Limestone is not preserved in most of the Sierra Diablo region, but north 

of the Babb flexure it is followed by the Cutoff Shale. 

Over the wide area in which the contact between the 

two units is exposed, thick-bedded calcitic limestone of 

the Victorio Peak is overlain by thin-bedded shaly 

limestone of the Cutoff, and although the two rocks 

are not interbedded, they appear to be conformable. 

In the Wylie Mountains southeast of the report area 

the Cutoff Shale is not recognizable, and beds mapped 

as Victorio Peak are succeeded by the Seven Rivers 

Limestone of Guadalupe age (Hay-Roe, 1957). The 

equivalent of the top of the Victorio Peak Limestone 

of other areas however, must lie within the dolomitic 

limestone beds beneath, as parafusulinids of Guadalupe 

type are reported from their upper part.

CUTOFF SHALE

The Cutoff Shale is named for Cutoff Mountain 

(King, P. B., 1942, p. 569-570), in the Guadalupe 

Mountains near the Texas-New Mexico boundary. Like 

the Victorio Peak Limestone, the unit is characteristic

4 Earlier identifications by R. B. King in the Sierra Diablo and by 

G. H. Girty in the Guadalupe Mountains suggested that a common 

brachiopod species of the Victorio Peak Limestone is Dictyodostus 

(called "Productus") ivesi. However, according to P. E. Cloud, Jr., 

(written commun., 1960) :

"The brachiopod that R. E. King figured as Productus ivesi in his 

Glass Mountains memoir (and of which I have the figured specimens 

before me) is a Leonard species that somewhat resembles Dictyoclostus 

bassi of the Kaibab Limestone, but which is not present in any Sierra 

Diablo collection examined by me.

"I have also studied Newberry's three cotype specimens of Productus 

ivesi, which are presumably also from the Kaibab, and regard them as 

unidentifiable productids. Possibly they are small specimens of Dictyodostus has si and perhaps they are the same as D. hessensis, but there 

is no way to tell, and D. ivesi, unhappily, must be relegated to the 

limbo. I can only guess that the Sierra Diablo specimens identified by 

R. E. King as D. ivesi represent the same species I have referred to D. 

cf. hessensis."
PERMIAN 75

EXPLANATION

OUTCROP AREAS

Black limestone of Bone Spring

Contains equivalents of Victorio Peak

Older and younger Permian rocks

Rocks older and younger than 

Permian rocks

OTHER SYMBOLS

600 +

975

Thickness of Victorio Peak Limestone, in feet, where measured

Most determinations an partial, due to 

erosion of top; thickness of the only complete sequence is underscored

Observed intertonguing between 

gray Victorio Peak Limestone 

and black Bone Spring Limestone

Arrow points toward black limestone 

fades

Observed boundary between thinbedded dolomitic limestone on 

southwest and thick-bedded calcitic limestone on northeast

Inferred boundary between gray 

Victorio Peak Limestone on southwest and black Bone Spring Limestone on northeast

FIGURE 7. Map of Sierra Diablo region showing paleotectonics of Victorio Peak Limestone.
76 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

TAELE 8. Fossils identified from Victoria Peak Limestone in central and northern Sierra Diablo

{Identifications by P. E. Cloud, Jr., Helen Duncan, R. M. Finks, L. G. Henbest, and E. L. Yochelson. Explanation of symbols. Under Foraminifera: X. species or 

genus present; var, variety of species present; afl, specimen related to species but probably different; ?, specimen doubtfully assigned to genus or species. Under other 

biological groups: A, abundant; C, common; X, present; R, rare]

Distribution of fossils in stratigraphic section, locality, and collection number indicated

Foraminifera:

Parafusulina bakeri D unbar and

Parafusulina? bosei var. attenuata

Parafusulina diabloensis Dunbar and

cfr. diabloensis Dunbar and SkinIParafumlina fountaini Dunbar and

Parafusulina linearis (Dunbar and 

Skinner). ___ . ___ ..... .....

Pseudofusulina setum (Dunbar and

Schubertella kingi Dunbar and

Porifera:

Coelenterata:

Echinodermata:

Bryozoa:

Brachiopoda: 

Avonia sp. ("Avonia" sp., Avonia

Buxtonia (Kochiproductus) victorioDictt/oclostus (Chaoidla) guadalupensis 

(Girty) .. ... ................. .

"Dictyoclostus" afl. D. semistriatus 

(Meek).............................

Enteletes dumblei Girty ...............

Neospirifer cf. N. pseudocameratus 

(Girty)...- .-... __. . _..

Rhynchopora sp...... _______ ...

29a 

Victorio 

Peak

8545

X

C 

X

X

X 

C

X

A

C 

X 

X

31 

North 

of 

Victorio 

Canyon

8546

X

X

X

C

32 

Marble 

Canyon

7011 

14444

X 

X

X

C

C

R 

X

Northeastern Sierra Diablo

7006

C

X

X

X

X

X

R

X

X

X 

X

X

14470 

F9837

X

X 

X

R 

X

X

A

R

C 

C

X

C

X 

C

R

X 

R 

R 

X

C

C 

X

14445 

F9818

C

F9820 

14448 

F9821 

14449

X 

X 

X

aff 

X

X

? 

X

X 

X

37 

First 

section 

in 

Apache 

Canyon

14461

X

X

X

X

X

X

38 

Second 

section 

to 

Apache 

Canyon

F9836

X

39 

Third 

section 

in 

Apache 

Canyon

F9825

X

X

X

var 

var

var

40 South Mesa

8534 

F2691

X

?

R

R

C

X

C

8535 

F2698

X 

X

? var

X

- X

C

X

C 

X

R 

X 

C

X

Southeast of South Mesa

8536

X

------

C

8537 

F2709

?

X 

X

X

R 

R

X

X

X

8541

R

8547

X
PERMIAN 77

TABLE 8. Fossils indentified from Victoria Peak Limestone in central and northern Sierra Diablo Continued 

Distribution of fossils in stratigraphic section, locality, and collection number indicated

Brachnpoda Continued

Welleretta of. W.degans (Qirty) ___

Lamellibranchiata:

Parallelodontid indet _________

Gastropoda:

Scaphopoda:

Cephalopoda:

Arthropoda:

Vertebrata:

Alga (dasycladacean):

29a 

Victorio 

Peak

8545

R

X

31 

North 

of 

Victorio 

Canyon

8546

X C

X 

X 

X 

R

X 

X

32 

Marble 

Canyon

7011 

14444

Northeastern Sierra Diablo

7006

X

14470 

F9837

C 

X 

R

X

X

X

14445 

F9818

X

A

F9820 

14448 

F 9821 

14449

0>7 __

First 

section 

in 

Apache 

Canyon

14461

X 

X 

X

38 

Second 

section 

in 

Apache 

Canyon

F9836

39 

Third 

section 

to 

Apache 

Canyon

F9825

40-South Mesa

8534 

F2691

8535 

F2698

X 

X

X

Southeast of South Mesa

8536

X

8537 

F2709

X

X

X 

X

8541 8547

of the platform areas where it was probably once extensive, although it is now exposed only in the western 

part of the Guadalupe Mountains (King, P. B., 1948, 

p. 18; Boyd, 1958, p. 13-14) and north of the Sierra 

Diablo. Its equivalents in the basin area are uncertain; 

the beds there that were once tentatively assigned to 

the Cutoff (King, P. B., 1948, p. 16) are here classed as 

a member of the Brushy Canyon Formation.

1ITHOLOGIC FEATURES

In the report area the Cutoff Shale is preserved only 

north of the Babb flexure and northeast of Sierra 

Prieta, from whence it extends northward for about 12 

miles, (pi. 1). Here it surmounts the ledges of Victorio 

Peak Limestone and forms rolling hills, or lower slopes 

of mesas that are capped by Goat Seep Limestone. The 

Cutoff of this area is 250-275 feet thick, or somewhat 

thicker than in the Guadalupe Mountains.

The Cutoff of the Sierra Diablo region is interbedded 

thin-bedded or platy gray to black limestone, brown 

siliceous or sandy shale, and thin-bedded fine-grained 

sandstone. The limestone layers weather into lightgray or buff hackly fragments. At South Mesa thicker

beds of black limestone occur near the middle, and north 

of North Mesa the top bed is a granular dolomitic limestone containing crinoid stems and small limestone pebbles. The Cutoff contains very few fossils. It much 

resembles the black limestone f acies of the Bone SpringLimestone and probably formed during a brief incursion of basin deposits over the platform, area (Stehli, 

1954, p. 275).

North of South Mesa, shale and limestone beds of the 

Cutoff are separated by thin layers of earthy gypsum 

in which coarser crystals are embedded. The shale and 

limestone beds are turned up and broken, suggesting 

growth of the gypsum between them. The gypsum occurs only in the Cutoff Shale and not in formations below or above it; but it forms no definite layers so that 

the term "Dos Alamos gypsum member" that was once 

applied to it (King, P. B., and King, R. E., 1929, p. 922) 

is unwarranted. Mohr (1929) believed that the gypsum was introduced by circulating ground water from 

the gypsiferous deposits of the Salt Basin, but the gypsum is more likely an original constituent of the Cutoff 

that has been reconstituted and disordered by modern 

processes of weathering.
78 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

FOSSILS

The Cutoff Shale is very meageiiy fossiliferous, and 

it has yielded no well-defined fauna. Most of the layers 

contain only a few brachiopods or other shells; where 

shells are abundant, they are apt to be of a single genus. 

During field investigations in the Sierra Diablo and the 

Guadalupe Mountains, the writer and his colleagues observed or collected the brachiopods Squamularia, 

Chonetes, and Composita, and poorly preserved mollusks. A somewhat larger collection of brachiopods 

was made near Bone Spring in the Guadalupe Mountains from strata of Cutoff type (King, P. B., 1948, p. 

24); but these strata are not physically connected with 

the type Cutoff, and their precise relations to it are 

unknown.

A similar meager fossil assemblage has been observed 

by Boyd (1958, p. 59-60) in the Cutoff Shale of the central Guadalupe Mountains in New Mexico. Here, 

Chonetes and several genera of gastropods are the most 

common shells, but one locality yielded nautiloids and 

the ammonites Pseudogastrioceras sp. and Perrinites 

hilli ( Smith). From the same area paraf usulinids have 

been collected at several localities and have been identified as of Guadalupe type (Warren, 1955, p. 12; Boyd, 

1958, p. 60-61). A possible similar occurrence is a collection of Dunbar and Skinner (1937, p. 725, loc. 140) 

near Dos Alamos north of the Sierra Diablo, from 

"cherty beds in basal part of Delaware Mountain sandstone a few feet above the Bone Spring [Victorio 

Peak(?)] Formation," which contains Parafusulina 

rothi Dunbar and Skinner.

AGE

The Cutoff Shale has been interpreted as a unit of 

late Leonard age (King, P. B., 1948, p. 18; Newell and 

others, 1953, p. 22-23; Boyd, 1958, p. 60-61), but some 

geologists (Warren, 1955, p. 12) have suggested that it 

is of Guadalupe age.

Most of the scanty fauna of the Cutoff is not a diagnostic of either series; although the ammonite Perrinites 

suggests a Leonard age, and the fusuliiiids are reported 

to suggest a Guadalupe age. This situation should be 

expected in beds lying near a boundary between series 

which contain similar and gradational faunas. Thus, 

much of the basis for judging the proper classification 

of the Cutoff must be in physical evidence, and especially in correlation of the sequence in the platform 

area with that in the basin, where the Leonard and 

Guadalupe Series are more clearly differentiated.

One reason for the original assignment of the Cutoff 

Shale to the Leonard Series was that its southern edge 

in the Guadalupe Mountains is eroded and is overlain 

by the Brushy Canyon Formation of early Guadalupe

age. Elsewhere in that area it is overlain by the sandstone tongue of the Cherry Canyon Formation of middle Guadalupe age. Although there is little indication of erosion at the contact, there was apparently 

a hiatus. North of the Sierra Diablo the upper surface of the Cutoff is eroded and is overlain by the sandstone tongue of the Cherry Canyon Formation.

Correlation of the Cutoff Shale with the sequence in 

the basin area is uncertain. It was originally suggested 

(King, P. B., 1948, p. 16) that its equivalent is in shaly 

strata between the black limestone of the Bone Spring 

and the sandstone of the Brushy Canyon (the Pipeline 

Shale Member of the Brushy Canyon Formation of this 

report), but this correlation now appears less likely. 

Alternatively, Newell and others (1953, p. 23, fig. 10) 

proposed that the Cutoff is equivalent to shaly beds 

below the uppermost black limestone of the Bone Spring 

in the Delaware Mountains (geologic section 44, unit 

10), and they imply that this uppermost black limestone 

is younger than the Cutoff. Their proposal, although 

interesting, involves tracing of beds across the very confused rocks of the Bone Spring flexure, where tracing 

by the writer (King, P. B., 1948, p. 17) has yielded different results. Correlation of the Cutoff with the 

Brushy Canyon Formation or higher units of the Guadalupe Series (Warren, 1955, p. 12) has little basis in 

known field relations.

In summary, faunal evidence as to the classification 

of the Cutoff Shale is equivocal; physical evidence, 

however, indicates that it is more likely a part of the 

Leonard Series than the Guadalupe Series, although its 

precise equivalent in the Leonard sequence of the basin 

area is undetermined.

STRATIGRAPHIC RELATIONS

In the Sierra Diablo region the Cutoff Shale is overlain unconformably by the sandstone tongue of the 

Cherry Canyon Formation. On South Mesa a mediumgrained sandstone bed of variable thickness at the base 

of the sandstone tongue lies on an eroded surface of the 

Cutoff. On North Mesa the sandstone tongue nearly or 

completely wedges out on the unconformity. This unconformity is probably the boundary between the 

Leonard and Guadalupe Series; it also may express a 

hiatus during which the Brushy Canyon Formation was 

deposited in the basin area to the east during early 

Guadalupe time.

BRUSHY CANYON FORMATION

The Brushy Canyon Formation is missing in the 

Sierra Diablo and the area north of it, but it occurs in 

the Delaware Mountains to the east, as in the northeast 

corner of the report area (pi. 1) (geologic section 44, pi. 

8). The Brushy Canyon, a formation of the basin area,
PERMIAN 79

overlaps the edges of the basin (King, 1948, p. 28-32). 

It is the basal formation of the Guadalupe Series.

The most prominently exposed parts of .the Brushy 

Canyon Formation are thick beds of relatively coarse 

sandstone, which are separated by units of thinner bedded finer grained sandstone and sandy shale. The formation is about 1,000 feet thick, but its top is not exposed within the report area in the Delaware Mountains 

and is only preserved farther east.

At the base of the Brushy Canyon Formation in the 

Delaware Mountains is a persistent unit, 30-150 feet 

thick (geologic section 44, unit 12), of black platy shale 

and shaly sandstone, interbedded with layers of limestone and sandstone. This unit lies with abrupt contact on black limestone of the Bone Spring and is overlain with gradational contact by the Brushy Canyon. It 

was tentatively correlated with the Cutoff Shale of the 

platform area (King, P. B., 1948, p. 16), but although 

it lies in the same general stratigraphic position, it now 

seems unlikely that the two units could be equivalent. 

A rather abundant brachiopod fauna in parts of the 

shaly unit has affinities with both Leonard and Guadalupe faunas (King, P. B., 1948, p. 24). The unit also 

contains large species of Pa/rafusulina and species of the 

ammonites Waagenoceras and Medlicottia (Newell and 

others, 1953, p. 23), which are more clearly of Guadalupe 

affinity.

Both physical relations and fossils indicate that the 

shaly unit is more closely related to the Brushy Canyon 

Formation above than to the Bone Spring Limestone 

beneath. It is therefore termed the Pipeline Shale 

Member, following Warren (1955, p. 11), and is classed 

as a basal member of the Brushy Canyon Formation.

SANDSTONE TONGUE OF CHEBBY CANYON FOBMATION

The Cutoff Shale of the northern part of the report 

area is followed by the sandstone tongue of the Cherry 

Canyon Formation (King, P. B., 1942, p. 588), which 

forms the upper part of the slope of South Mesa, and 

other summits farther north that are capped by Goat 

Seep Limestone (pi. 1).

On South Mesa the unit is 150-190 feet thick, and 

most of it is buff fine-grained thin-bedded sandstone. 

At the base, however, is a more massive layer of brown 

medium-grained sandstone that contains poorly preserved fusulinids, as well as shale and limestone pebbles 

derived from the underlying Cutoff. The layer rests on 

a channeled surface of the Cutoff Shale, and its thickness varies within short distances from 5 to 40 feet. On 

North Mesa, north of the report area, the sandstone 

tongue is not exposed; it is either missing by overlap 

on the Cutoff, or is very thin and covered by talus from 

the Goat Seep Limestone above.

As shown by outcrops in the southern Guadalupe 

Mountains (King, P. B., 1948, p. 38), the sandstone 

tongue is equivalent to the lowest part of the typical 

Cherry Canyon Formation of the Delaware Mountains, 

and represents an extension of its sandy beds from the 

Delaware basin across the marginal areas; in the marginal areas, the place of higher parts of the Cherry 

Canyon Formation is taken by the Goat Seep Limestone. 

Typical Cherry Canyon Formation is apparently exposed at the foot of the Delaware Mountains in the 

northeastern part of the report area (pi. 1), but these 

exposures were not visted during the present investigation. In the northern part of the report area the sandstone tongue of the Cherry Canyon Formation is overlain conformably by the Goat Seep Limestone. In 

places, layers of the Goat Seep seemingly intertongue 

with the sandstone.

GOAT SEEP LIMESTONE

The Goat Seep Limestone is named for Goat Seep 

on the west side of the Guadalupe Mountains (King, 

P. B., 1942, p. 588), where it is a succession of massive 

limestone banks and reefs that are equivalent to the middle and upper parts of the Cherry Canyon Formation 

of the basin area. Northward on the west side of the 

Guadalupe Mountains, the Goat Seep loses its massive 

character and passes into back-reef or platform deposits, 

which are thick-bedded dolomitic limestone with many 

thin-bedded or sandy partings. These back-reef deposits extend into the central Guadalupe Mountains of 

New Mexico, where they have been termed the "Grayburg-Queen sequence" (Boyd, 1958, p. 15-16), after 

formations whose type areas are in the northern Guadalupe Mountains.

The equivalent of the Goat Seep Limestone in the 

northern part of the Sierra Diablo region resembles the 

back-reef beds of the Guadalupe Mountains, and formation names of the northern Guadalupe Mountains might 

be applied to it, as was done by Stehli (1954, p. 275). 

However, it is somewhat more convenient to retain the 

term Goat Seep for it in the same manner as has been 

done for back-reef beds in the southern Guadalupe 

Mountains (King, P. B., 1948, p. 40).

LITHOLOGIC FEATURES

In the report area the Goat Seep Limestone is preserved only north of the Babb flexure, where it forms 

the resistant caps of South Mesa and Middle Mesa (pi. 

1 and upper view pi. 12). Other outliers occur farther 

north, on North Mesa and the hills west of Dos Alamos. 

On South Mesa the Goat Seep is about 200 feet thick 

(geologic section 43b, unit 24), but its top is not preserved, either here or elsewhere in the region.

On South Mesa the Goat Seep is mainly light-gray 

or pink dolomitic limestone in beds a few feet thick
80 GEOLOGY OF THE SIERRA DIABLO REGION", TEXAS

containing irregular knotted small to large chert masses 

and poorly preserved fossils. Most of the fossils are 

silicified, and many form voids lined by crystalline calcite.

Thicker layers of gray-brown dolomitic limestone and 

medium-grained dolomitic sandstone are interbedded 

whose surfaces weather dark gray and pitted. Some 

of the more sandy layers are crossbedded. Bedding in 

the Goat Seep is very irregular, in places chaotic, in 

others inclined in a consistent direction, the beds extending with primary dip to the base of the formation where 

they seemingly intergrade with the upper part of the 

sandstone tongue of the Cherry Canyon Formation.

On North Mesa, beds like those on South Mesa are 

overlain by a unit of thicker bedded dolomitic limestone 

containing many fusulinids, which forms prominent 

dark jagged ledges.

FOSSILS AND AGE

The Goat Seep Limestone of the Sierra Diablo region 

contains a rather abundant fauna (table 9), mainly of

TABLE 9. Fossils identified from Goat Seep Limestone, 

northern Sierra Diablo

{Identifications by P. E. Cloud, Jr., Helen Duncan, R. M. Finks, L. G. Henbest, and 

E. L. Yochelson. Explanation of symbols: X, species or genus present; C, common; A, abundant; R, rare]

Distribution of fossils in stratigraphic section, locality, and collection number 

indicated

Foraminifera:

Porifera:

Coelenterata:

Bryozoa:

Brachiopoda:

Dictyodostus (Chaoiella) cf, D. guadalupensis (Girty)..

Marginifera aft. M. lasallensisl (Norwood and Pratten) . 

"Marginifera" aft. "M." occidental!* Sehwellwein of

Wellerella sp ____ __________________

Lamellibranchiata:

Gastropoda:

43-

South 

Mesa 8548- 

F2688

X

X 

X 

X

X

c

X 

A 

X 

X 

R 

C 

C

C 

X

C 

X

R 

C 

R

X 

X

North 

Mesa 

8549

X

X 

X

X 

X

R

X

R

X

Dos 

Alamos 

2697

X

brachiopods, but adequate collections are difficult to 

obtain because of poor preservation of the fossils.

Available collections include 15 genera of brachiopods, of which Composite, Stenocisma, Neospirifer, 

Leptodus, and "Marginifera," are most significant. 

They also contain a few sponges, corals, bryozoans, and 

mollusks. Fusulinids are abundant in many layers and 

are probably mainly large forms of Parafusulina, although specific ^identification can be made of only a few 

specimens.

Physical matching of sections and tracing of beds in 

the Guadalupe Mountains indicate that the Goat Seep 

Limestone is equivalent to part of the Cherry Canyon 

Formation of middle Guadalupe age. This fact is confirmed by what is known of its fauna. The large 

parafusulinids are characteristic of beds of early and 

middle Guadalupe age, and according to R. E. King 

(1931, p. 15), most of the brachiopods are like those of 

the Word Formation of the Glass Mountains, which is 

of early and middle Guadalupe age.

STRATIGRAPHIC RELATIONS

In the Sierra Diablo region the Goat Seep Limestone 

is the highest Permian formation preserved, and it is 

unknown whether higher strata of the system were ever 

laid down there. Any such strata have long since been 

removed by erosion, because the Permian of the region 

is overlain unconformably by rocks of the Cretaceous 

System. The Goat Seep Limestone itself is not in contact with Cretaceous rocks, but its upper surface on 

South, Middle, and North Mesa is accordant with a surface elsewhere in the region on which Cretaceous rocks 

were deposited and later removed. This accordant surface extends westward from South Mesa, across the 

Goat Seep Limestone onto the Victorio Peak Limestone, 

which is overlain by Cretaceous rocks at Sierra Prieta.

CRETACEOUS

Rocks of the Cretaceous System in the Sierra Diablo 

region are mainly preserved in the western part of the 

report area. They border the Sierra Diablo on the west, 

down the dip from the Paleozoic and Precambrian rocks, 

although they are preserved in a few small outliers 

farther east (pi. 1). They also form the whole of the 

bedrock in the southwest corner of the report area southwest of Eagle Flat, along the southeastward extension 

of Devil Ridge and in the foothills of the Eagle Mountains. The Cretaceous rocks of the Sierra Diablo are 

the fringe of a much more extensive body to the west, 

southwest, and south, in the Finlay, Quitman, Eagle, 

Van Horn, and other mountain ranges.

The Cretaceous formations of northern Trans-Pecos 

Texas were first defined and described by Richardson
CRETACEOUS 81

(1904, p. 46-50), but modern conceptions of their stratigraphy are based largely on work done here and elsewhere in the State by Adkins (1933, p. 272-400). Cretaceous rocks west and southwest of the Sierra Diablo 

region have been reported on for the U.S. Geological 

Survey by Albritton and Smith (1964) and by Gillerman (1953, p. 15-33); those to the south are currently 

under study by DeFord and associates (Brand and 

DeFord, 1958; DeFord and Brand, 1958; Twiss, 1959). 

The description given in this report of the Cretaceous 

rocks southwest of Eagle Flat is based on publications 

of Smith (1940), Gillerman (1953), and Albritton and 

Smith (1965).

Cretaceous rocks of the Sierra Diablo region belong 

mainly to the Comanche, or Lower Cretaceous Series. 

Bocks of the Gulf, or Upper Cretaceous Series, are preserved only southwest of Eagle Flat, although they may 

once have extended over the region farther north. The 

formations recognized in the region are listed in the 

table below.

Cretaceous formations of the Sierra Diablo region

Gulf 

Series

Comanche 

Series

Southwest of 

Eagle Flat

Eagle Ford 

Formation

Washita 

Group

Kiamichi 

Formation a

Finlay 

Limestone

Cox

Sandstone

Bluff Mesa 

Formation

Yucca 

Formation

Western Sierra 

Diablo

0

(0

Kiamichi 

Formation

Finlay 

Limestone

Cox 

Sandstone

Campagrande 

Limestone

(*)

Sierra Prieta

(')

Washita 

Group

Cox

Sandstone

Campagrande 

Limestone

(3)

' Not preserved.

* Not exposed.

* Absent.

Lower Cretaceous rocks of the Sierra Diablo region 

resemble those of the classic area of the Comanche 

Series in central and north-central Texas, and like them, 

record an overlap of Cretaceous deposits on an eroded 

surface of the Paleozoic rocks the Wichita paleoplain 

of Hill (1901, p. 363). Thus, the Yucca Formation resembles the Travis Peak of central Texas; the Bluff 

Mesa Formation and Campagrande Limestone, the Glen 

Rose; the Cox Sandstone, the Paluxy; and the Finlay

Limestone, the Edwards. The Washita Group shows 

the same northward change from dominant limestone in 

the south into shale, marl, and sandstone to the north. 

In the Sierra Diablo region, however, the surface of 

overlap is more steeply canted; variations which occur 

along the outcrop in distances of several hundred miles 

in central and north-central Texas are compressed here 

to within a few scores of miles (pi. 13).

Not far southwest of the Sierra Diablo region, geosynclinal conditions prevailed during Cretaceous time, 

and a great thickness of Early Cretaceous sediments 

was deposited, in places following on the latest Jurassic. 

The Yucca and Bluff Mesa Formations of the southwestern part of the report area were deposited along the 

margins of this geosyncline. Cretaceous rocks farther 

north, along the west edge of the Sierra Diablo, were 

deposited on a shelf area that bordered the geosyncline 

toward the northeast.

Overlap relations in the shelf area along the west edge 

of the Sierra Diablo are not completely preserved, because of fragmentation of the Cretaceous rocks by erosion. It is clear, however, that the Yucca Formation is 

missing by overlap, and that the Bluff Mesa has passed 

into a thinned equivalent, the Campagrande Limestone. 

The overlying Cox Sandstone, a thick extensive sheet of 

quartzose sands, must replace the Finlay Limestone and 

Kiamichi Formation northward, for at Sierra Prieta, 

sandstone like the Cox is overlain directly by basal 

strata of the Washita Group, of Duck Creek age. A 

further extension of the same overlap north of the report area is indicated in the Cornudas Mountains, near 

the Texas-New Mexico boundary, where Adkins (1932, 

p. 354) observed Duck Creek fossils in sandstone less 

than 30 feet above the base of the Cretaceous sequence.

PRE-CRETACEOUS SURFACE

Cretaceous rocks of the Sierra Diablo region were 

deposited on a surface that evenly bevels the rocks beneath. For the most part the Cretaceous lies on Permian 

rocks, although in an area in the Sierra Diablo foothills 

northeast of Eagle Flat it lies directly on the Precambrian Hazel and Allamoore Formations. This area was 

the locus of greatest uplift during pre-Permian deformation, where the pre-Permian Paleozoic formations 

had been removed by erosion, and where the Permian 

itself was deposited in a smaller thickness than elsewhere. Rather oddly, the Cretaceous rocks have nowhere been observed in contact with any of the Paleozoic 

formations which elsewhere intervene between the Precambrian and Permian.

South of the Victorio flexure the Cretaceous lies on 

the Hueco Limestone, and in places on Precambrian 

rocks (section K-K'', pi. 16); north of the flexure it lies 

on the higher Victorio Peak Limestone (section A-A',
82 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

pi. 16). North of the Babb flexure the Cretaceous was 

probably deposited on younger Permian formations of 

the Guadalupe Series, but it is not now preserved above 

them. In contrast with the earlier unconformable surfaces in the Sierra Diablo region (as at the base of the 

Van Horn Sandstone and at the base of the Hueco Limestone) , the surface at the base of the Cretaceous is remarkably even. Except in the area where it lies on 

Precambrian rocks in the Sierra Diablo foothills, no 

hills or hollows occur. The surface of the pre-Cretaceous rocks was reduced to a peneplain, formed in part 

by prolonged subaerial erosion during early Mesozoic 

time, and afterwards perfected by marine erosion of the 

advancing Cretaceous seas.

Over wide areas in the Sierra Diablo, Cretaceous 

rocks are no longer preserved, but its topographic summits are an accordant surface which is probably the 

peneplain upon which the Cretaceous was once deposited and later removed by erosion. Some remnants of 

Cretaceous rocks are perched on this surface, as on the 

west rim of Victorio Canyon and at Black Knobs, and 

it seemingly extends beneath the larger bodies of Cretaceous farther west. The summits of the downfaulted 

Baylor Mountains to the east are probably parts of the 

same surface, for a few remnants of Cretaceous sandstone are preserved there in downfaulted blocks.

The pre-Cretaceous peneplain in the Sierra Diablo is 

preserved on accordant divides, some at altitudes greater 

than 6,000 feet. These divides were not produced by 

stripping of the bedding planes of the underlying 

Permian rocks as they truncate the bedding at a low 

angle in most places, but more steeply on the Victorio 

and Babb flexures. The peneplain is preserved most 

extensively on the Victorio Peak Limestone in the northeastern part of the Sierra Diablo, between Victorio and 

Apache Canyons, where many of the valleys are separated by nearly level summits as much as half a square 

mile in area. On these summits, the underlying limestone is thinly covered by red-brown residual clay, 

through which limestone pinnacles project, and in 

which large quantities of residual chert are embedded, 

different from the sparser chert that occurs in the limestone is the adjacent valleys. The residual clay and 

chert were surely formed at a time earlier than that 

during which the adjacent valleys were cut, and they 

may have been produced by weathering before the 

Cretaceous deposits were laid over the region.

Albritton and Smith (1950, p. 1440) have described 

features on the basal Cretaceous surface in the Finlay 

Mountains which they believe are "part of an ancient 

soil profile, probably reworked and similar in origin to 

lime-enriched zones of the southwestern United States, 

and developed by weathering of calcareous parent material in a semiarid or arid climate." They suggest 

(Albritton and Smith, 1965) that the features observed 

on the summit areas in the Sierra Diablo are not compatible with those in the Finlay Mountains, and probably were formed by weathering under more humid 

conditions. Clearly, knowledge regarding pre-Cretaceous conditions of weathering remains elusive, and 

further evidence must be awaited.

YUCCA FORMATION

The Yucca Formation, or oldest Cretaceous unit in 

the Sierra Diablo region, occurs only southwest of 

Eagle Flat (pi. 1), where its exposures are segments of 

two belts of outcrop that are extensive beyond the report area. The Yucca in Love Hogback and the Red 

Hills lies above the Devil Eidge thrust and is exposed 

thence northwestward along Devil Eidge (Smith, 1940, 

p. 604). The Yucca farther east, north of Eagle 

Spring, lies beneath the Devil Eidge thrust and is at 

the end of a belt of outcrop which extends southward 

along the foothills of the Eagle Mountains (Gillerman, 

1953, p. 15).

The Yucca Formation consists of interbedded limestone, conglomeratic sandstone, and shale, all of red, 

brown, or gray colors. The sequence above the Devil 

Eidge thrust is more than 1,600 feet thick, but the 

base is not exposed (geologic section A, pi. 13). The 

full sequence below the Devil Eidge thrust near Eagle 

Spring is 330 feet thick (geologic section B, pi. 13), 

but farther south the formation wedges out entirely in 

places by overlap on the Hueco Limestone.

The Yucca Formation contains few fossils, but it is 

clearly of early Comanche age, and is perhaps approximately equivalent to the Travis Peak Formation of central Texas. Southwest of the report area it may include 

strata of earliest Cretaceous age, or older than the base 

of the Comanche Series in its type area.

BLUFF MESA FORMATION

The Bluff Mesa Formation, which overlies the Yucca, 

is also differentiated only southwest of Eagle Flat (pi. 

1); but strata equivalent to its upper part extends 

farther north, where they are termed the Campagrande 

Limestone. Like the Yucca, the Bluff Mesa is exposed 

above the Devil Eidge thrust in the southwest corner 

of the report area and below the Devil Eidge thrust near 

Eagle Spring farther east.

The Bluff Mesa consists of massive limestone beds, 

with some marl partings and minor units of sandstone 

and shale. Above the Devil Eidge thrust near the report area it is about 1,000 feet thick (geologic section 

A, pi. 13), but it thickens northwestward to as much as 

1,600 feet at the type locality on Bluff Mesa south of
CRETACEOUS 83

Sierra Blanca. Below the Devil Ridge thrust near 

Eagle Spring, the Bluff Mesa is no more than 250 feet 

thick, and the limestone is interbedded with much shale, 

sandstone, and conglomerate (geologic section C, pi. 13). 

The Bluff Mesa is rather abundantly fossiliferous 

throughout, and contains a fauna like that of the Glen 

Rose Formation in central Texas. Exogyra quitmanensis Cragin is common in the lower part, and Orbitolina 

texana (Roemer) occurs from base to top.

CAMPAGRANDE LIMESTONE

The Campagrande Limestone is the basal Cretaceous 

unit in the Sierra Diablo and farther west in the Diablo 

Plateau, although it is equivalent to strata well above 

the base of the Cretaceous in the area southwest of 

Eagle Flat, that is, to the upper part of the Bluff Mesa 

Formation.

The Campagrande Limestone is named for the feature 

shown on modern maps as Campo Grande Arroyo 

(Richardson, 1904, p. 47), in the Finlay Mountains 

about 25 miles west of the report area. At its type 

locality it is 630 feet thick, but it varies from 375 to 800 

feet elsewhere in the Finlay Mountains (Albritton and 

Smith, 1965.) In the foothills south of the Sierra 

Diablo it is as much as 200 feet thick in places (geologic 

sections 45, 46, p. 174-175) but is generally less. 

Farther north it is mostly less than 50 feet thick, although it attains 80 feet on the east side of Sierra Prieta 

(geologic section 53, pl.13 and p. 170-171).

SIERRA DIABLO FOOTHILLS

The Campagrande Limestone forms a nearly continuous band of outcrop south of the south-facing 

escarpment of the Sierra Diablo, where it is overlain 

toward the west by Cox Sandstone (pi. 1). It is also 

preserved in smaller outliers in the Bean and Streeruwitz Hills farther south. Toward the north and west 

the Campagrande lies on the Hueco Limestone, but in 

most of the foothills it bevels the Hueco and lies directly on the Precambrian Hazel and Allamoore Formations.

Basal beds of the Campagrande are conglomerate 

with a limestone matrix, containing numerous pebbles 

of Hueco Limestone, minor pebbles of chert, and toward 

the base, fragments of Precambrian rocks. In places 

the conglomerate is as much as 80 feet thick; but it 

varies abruptly in thickness within short distances by 

overlap on irregularities of the pre-Cretaceous surface, 

and in places is missing entirely.

The overlying part of the formation, about 100 feet 

thick, has a more regular stratigraphy, and includes 

two beds of ledge-making limestone. The lower ledge 

maker, informally termed the "cap ledge," is a massive 

bed of light-gray limestone 25-50 feet thick. Parts

are lumpy and perhaps contain algal balls, but no other 

fossils were observed. Analysis of a specimen from 

the Bean Hills indicates 93.66 percent CaCO3 ,1.18 percent MgCOs, and 5.50 percent insoluble material (K. J. 

Murata, written commun., 1940). In most of the Bean 

and Streeruwitz Hills the "cap ledge" is the highest bed 

preserved. The upper ledge maker, informally termed 

the "IsTodosaria bed," is a darker gray, more distinctly 

bedded, more fossiliferous limestone 15-25 feet thick. 

At a few places its weathered surfaces are studded with 

shells of the medium-sized foraminifer Haplostwhe 

("Nodosaria"), and in many places it contains oyster 

and echmoid fragments.

Between and above the two ledge-making beds are 

shale, marl, and nodular limestone, parts of which are 

bioclastic and contain oyster fragments and traces of 

rudistids.

WESTERN SIERRA DIABLO

In the plateau country west of the Sierra Diablo the 

basal Cretaceous is a set of calcareous strata, no more 

than 25 feet thick in most places, but thickening to 50 

feet at Black Knobs and to 80 feet on the east side of 

Sierra Prieta. These strata are not easily recognized 

on first view: in some places they resemble the underlying Permian and in others, modern caliche and limestone gravel. Their nature as a basal Cretaceous deposit is made clear in favorable exposures.

These calcareous strata are classed with the Campagrande Limestone, because field relations suggest that 

they were once physically joined to the Campagrande 

farther south. However, they are not only thinner 

than the Campagrande in its more typical exposures, 

but they lack its regular stratigraphy, are nearly without fossils, and may be partly of younger age. They 

much resemble the Yearwood Formation of the Apache 

Mountains east of the report area, as described by 

Brand and DeFord (1958, p. 373-376), which is also 

a thin basal Cretaceous unit, mainly limestone, with a 

basal conglomerate.

Near Cox Mountain (geologic section 49, pi. 13) the 

Campagrande is limestone, partly nodular and marly, 

containing limestone and chert pebbles in its lower part; 

in places it has a strong ledge at the top. Most of the 

limestone is light gray or white, but it is commonly 

mottled yellow or red, so that it has a "burnt" appearance. On the east side of Sierra Prieta (geologic section 53, pi. 13), where the formation is somewhat thicker, limestone of the sort described forms ledges several 

feet thick, separated by white or buff marl and clay. 

Poorly preserved oysters and gastropods occur at various levels, and nodules or lumps in the marly layers may 

be of algal origin.

Relations of these basal Cretaceous strata in the western Sierra Diablo are puzzling. At Cox Mountain and
84 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

farther south they are overlain by many hundreds of 

feet of Cox Sandstone, Finlay Limestone, and Kiamichi 

Formation; whereas at Sierra Prieta to the north they 

are overlain by less than 200 feet of sandstone, part or 

all of which is of Finlay and Kiamichi age. Either the 

calcareous strata are a transgressive deposit which becomes younger toward the north, or they are separated 

from the overlying sandstones by a disconformity, the 

magnitude of whose hiatus increases northward. A disconformity is reported between the calcareous Yearwood Formation and the overlying Cox Sandstone in 

the Apache Mountains (Brand and De Ford, 1958, p. 

376-377).

FOSSILS AND AGE

The Campagrande Limestone in the Sierra Diablo 

foothills is fossiliferous, but no significant collections 

were obtained during the present investigation. In the 

type area in the Finlay Mountains it contains many 

foraminifers and various megafossils, including Porocystis globularis (Giebel), corals, pelecypods, various 

rudistids, and gastropods, such as Turritella (Albritton and Smith, 1965). This fauna, like that of the Bluff 

Mesa Formation, is of Glen Rose or late Trinity age.

COX SANDSTONE

The Cox Sandstone is named for Cox Mountain 

(Richardson, 1904, p. 47), west of the Sierra Diablo 

within the report area; but a better reference locality 

is perhaps in the Finlay Mountains beyond the report 

area, where it lies in sequence between the type Campagrande Limestone and type Finlay Limestone.

Toward the north the Cox is a nearly continuous 

body of sandstone, which is a little more than 400 feet 

thick on Cox Mountain and 540-675 feet thick in the 

Finlay Mountains. The Cox Sandstone thickens southward, attaining more than a thousand feet southwest 

of Eagle Flat; as it thickens, it becomes finer grained 

and acquires many interbedded layers of limestone and 

shale. The Cox is one of the most prominently exposed 

parts of the Cretaceous sequence, projecting in buttes, 

mesas, and hogbacks, on which its sandstone beds form 

massive ledges.

SOUTHWEST OF EAGLE FLAT

The Cox Sandstone is 1,066 feet thick in a measured 

section a little west of the edge of the report area (geologic section A, pi. 13), and is as thick or thicker in the 

belt of outcrop farther east near Eagle Spring (geologic section C, pi. 13). It consists of brown sandstone 

that is finer grained and more quartzitic than farther 

north, with fewer crossbeds and ripple marks, and with 

much interbedded shale, siltstone, and fossiliferous limestone (Smith, 1940, p. 612).

SIEBBA DIABLO FOOTHILLS AND COX MOUNTAIN

The most extensive exposures of the Cox Sandstone 

are along the base of the south-facing escarpment of 

the Sierra Diablo in its western half (pi. 1). Small to 

large outliers occur farther east, near the Gifford-Hill 

rock crusher in the northwestern Carrizo Mountains, 

and to the north in the plateau country, in the area near 

Cox Mountain. The top of the formation is preserved 

only on Cox Mountain (geologic section 49, pi. 13), 

where it is overlain by Finlay Limestone; but the part 

of the formation which is preserved on Dome Peak 

(geologic section 47, pi. 13) and in the northwestern 

Carrizo Mountains (geologic section 48, p. 171) is as 

thick or thicker.

The most conspicuous parts of the formation are 

massive sandstone beds, forming units 15 to more than 

100 feet thick. The sandstone beds weather brown and 

break out in great rectangular or cubical blocks that 

strew the slopes below. These blocks tend to overwhelm 

and obscure any interbedded less resistant units, which 

actually form a considerable part of the formation toward the south, although they are probably less important near Cox Mountain.

The massive sandstone beds, which are formed of 

medium- to coarse-grained quartz sand, have great variations in texture and structure from layer to layer. 

Many parts are crossbedded, in part on a large scale, 

and some bedding surfaces are ripple marked. Much 

of the sandstone contains dispersed well-rounded quartz 

and chert pebbles as much as an inch in diameter; in 

places these pebbles are concentrated in streaks or lenses, 

or in beds of conglomerate. The sandstone is characteristically dotted with small brown ferruginous spots 

or nodules, which are especially conspicuous on weathered surfaces and which may have originated from 

pyritic segregations in the original rock.

In the Sierra Diablo foothills less resistant interbedded units 10 to 25 feet thick occur throughout the 

formation, but they are thicker and more prominent in 

the lower few hundred feet. In the upper part most 

of the interbedded units are thinner bedded finer 

grained lighter brown sandstone; but lower down they 

include red and purple silty shale and marl and scattered 

beds of nodular gray limestone or dense brown to red 

limestone. Within the report area none of the limestone 

beds are fossiliferous, but near Sierra Blanca farther 

west they contain the thick-shelled gastropod Actaeonetta and various oysters (geologic section P, pi. 13). 

On Cox Mountain the interbedded units are apparently 

thinner, but some beds of purplish shale were observed; 

15 feet of nodular limestone has been reported 225 feet 

below the top (DeFord and Brand, 1958, p. 23, pi. 7).
CRETACEOUS 85

OUTLYING AREAS

East of the exposures described, smaller outliers of 

the Cox are preserved in places atop the dominant terrain of Permian carbonate rocks (pi. 1). A small patch 

of sandstone no more than 10 feet thick overlies the 

tilted Bone Spring Limestone of the Victorio flexure on 

the west rim of Victorio Canyon (northwestern part 

of sec. 14, block 43) (section X-X', pi. 4) and is capped 

by a remnant of Tertiary vesicular basalt. Farther west 

in the same vincinity sandstone patches are scattered 

over the upland. Some of these patches may be layers 

in the Bone Spring Limestone, but some are certainly 

outliers of the Cretaceous. Cretaceous fossils have been 

collected in this area by the local ranchmen, but none 

were observed during the present investigation.

Similar outliers of the Cretaceous occur in the Baylor 

Mountains, in Red Tank Canyon a mile east of Red 

Tank (west-central part of sec. 8, Block 66), where 

steeply dipping sandstone overlies the Hueco Limestone 

and is downfaulted against it on the south.

In all these outlying areas sandstone lies directly on 

the Permian rocks, and the Campagrande Limestone 

that intervenes on the western slopes of the Sierra 

Diablo is missing.

SIERRA PRIETA

At Sierra Prieta, 18 miles north of Cox Mountain, 

the lower part of the Cretaceous includes a unit of massive sandstone which is mapped with the Cox (pi. 1), 

although its relations are somewhat different from those 

of the Cox farther south. The sandstone is underlain 

by Campagrande Limestone, but it is overlain directly 

by the Washita Group. The Finlay Limestone and 

Kiamichi Formation which should intervene are not 

represented as such. Physical connection of the sandstone on Sierra Prieta with the typical Cox is 

not demonstrated, as a wide alluvial-covered area intervenes ; nevertheless, the two sandstones are probably 

parts of the same transgressive body.

In the eastern part of Sierra Prieta the sandstone is 

135 feet thick (geologic section 53, pi. 13), but in the 

western part it is as much as 190 feet (geologic section 

54, pi. 13). The upper part includes 50 or 60 feet of 

massive brown medium- to coarse-grained sandstone, 

in part crossbedded and pebbly like the Cox. Above it 

is a smaller thickness of lighter brown finer grained thinner bedded sandstone; below it is a greater thickness 

of friable buff sandstone, marly sandstone, and gray, 

buff, or purple shaly sandstone.

Many of the sandstone beds contain fragments of 

silicified wood, and some of their bedding surface show 

fucoidal markings. In the western part of Sierra Prieta invertebrate shells occur in the upper half of the 

sandstone, and are especialy abundant in massive beds

120 feet below the top where Exogym teseana Roemer, 

Alectryonia carinata (Lamarck), and various pelecypods and gastropods of Fredericksburg type are reported (Adkins, 1932, p. 354).

Presumably part or all of the sandstone on Sierra 

Prieta is equivalent to the Finlay Limestone and Kiamichi Formation elsewhere in the Diablo Plateau, although it might include equivalents of the typical Cox 

Sandstone in its lower part. Disappearance of the 

Finlay toward Sierra Prieta seems abrupt on first view, 

as mesas capped by its limestone beds occur within 6 

miles to the southwest, and at only slightly greater distances to the south and west. However, these limestone 

beds are no more than a few feet thick, and most of the 

Finlay on the mesas is marl and sandy marl, with several conspicuous sandstone beds. The Kiamichi (?) 

Formation which overlies the Finlay in an outlier 9 

miles southwest of Sierra Prieta (Block 35, west of report area) is all sandstone.

FOSSILS AND AGE

No fossils were observed in the Cox Sandstone in the 

report area, except for those in beds probably younger 

than the typical Cox on Sierra Prieta. To the west, 

near Sierra Blanca and in the Finlay Mountains, gastropods and pelecypods of marine origin occur in limestone and marl that is interbedded with the massive 

sandstone of the upper half, whereas the silty shale 

units of the lower half contain charophytes, ostracodes, 

and silicified wood, probably of littoral origin (Albritton and Smith, 1965). The thick-shelled gastropod 

Actaeonella is the most abundant marine invertebrate 

fossil.

The poorly fossiliferous Cox Sandstone intervenes 

between fossiliferous beds of Trinity age (Bluff Mesa 

and Campagrande) and of Fredericksburg age (Finlay) , indicating that it lies near the boundary between 

these two groups. Evidence is insufficient to prove 

whether the Cox is of Trinity age, of Fredericksburg 

age, or includes beds of both ages.

FINLAY LJMESTONB

The Finlay Limestone is named for the Finlay Mountains (Richardson, 1904, p. 47-48), about 25 miles west 

of the report area, where it overlies the Cox Sandstone 

with the top not preserved; elsewhere, as near Sierra 

Blanca and on Cox Mountain, it is followed by the 

Kiamichi Formation. The Finlay characteristically 

includes ledge-making beds of rudistid-bearing limestone, but these beds vary greatly in number and thickness; they form most of the unit southwest of Eagle 

Flat, but are interbedded northward with increasing 

thicknesses of nodular limestone, marl, and sandstone. 

Like the underlying Cretaceous formations, the Finlay 

thins northeastward. It is more than 350 feet thick
86 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

southwest of Eagle Flat and as much as 200 feet thick 

in the Finlay Mountains; the full thickness north of 

Sierra Blanca, however, is 150 feet and on Cox Mountain, 60 feet.

The Finlay Limestone is only scantily preserved in 

the report area (pi. 1), and its outcrops are mainly extensions of larger ones farther west those southwest 

of Eagle Flat of the outcrops in Devil Ridge, and those 

west of the Sierra Diablo of the outcrops in the Diablo 

Plateau (Albritton and Smith, 1965). A small isolated 

outlier surmounts the Cox Sandstone on Cox Mountain.

LOCAL FEATURES

Southwest of Eagle Flat, the Finlay above the Devil 

Eidge thrust is a nearly continuous sequence of limestone 

beds a few feet to more than 5 feet thick with only a few 

marly partings; fossils are abundant but poorly preserved. About 350 feet of Finlay overlies the Cox on 

Devil Ridge just west of the report area, but the top is 

missing (geologic section A, pi. 13). The Finlay is 

more extensively exposed on the pediment northeast of 

the Devil Ridge thrust; however, outcrops are low and 

obscure, and little is known of the sequence.

On Cox Mountain (geologic section 49, pi. 13) where 

the full thickness of the Finlay is 60 feet, it includes two 

ledge-making beds of gray limestone, one at the top and 

another near the middle, with slope-making nodular 

limestone, sandy limestone, and marl between and below. 

The ledge-making beds contain rudistids, the slope-making beds contain oysters and gastropods.

Northwest of Cox Mountain the Finlay Limestone 

forms Roberts Mesa (Block 39) and Norton Mesa 

(Block 34), each several square miles in area, which are 

outliers of more extensive tablelands farther west (pi. 

1). Only about 80 feet of the formation is exposed 

(geologic sections 51,52, p. 173-174), the base being concealed by alluvium and the top being a stripped surface 

of the limestone caprock. This caprock is probably near 

the top of the formation, for it is overlain by sandstone 

of the Kiamichi( ?) Formation west of the report area 

(Block 35).

Near Roberts and Norton Mesas the only strong limestone bed is the caprock at the top, which is no more 

than 6 feet thick. Below is marl and calcareous sandstone, with several beds of brown massive sandstone, the 

most conspicuous of which is 8 or 10 feet thick and has 

been separately mapped (pi. 1). The sandstone is 

medium grained, crossbedded, and ripple marked, the 

ripples commonly trending northwestward. Tracing of 

the sandstone beds from mesa to mesa along the west 

edge of the report area indicates that they wedge out 

southward. The limestone caprock contains poorly preserved rudistids; the marl beneath, abundant pelecypods

and gastropods; and the sandstone beds, fragments of 

silicified wood.

FOSSILS AND AGE

In the Finlay Mountains the Finlay Limestone contains a varied invertebrate fauna, including the f oraminifer Dictyoconus ("Orbitolina") walnutensis Carseyj 

Exogyra, Gryphaea, rudistids, and other pelecypods; 

the ammonite Engonoceras; gastropods; and echinoids. 

(Albritton, and Smith 1965). Collections from the 

report area, largely from the marl beds, are more restricted, consisting of pelecypods, gastropods, and a 

few echinoids; rudistids are common in the ledgemaking beds but are poorly preserved. The fauna of 

the Finlay Limestone is of Fredericksburg age, and the 

formation is equivalent to part or all of the Edwards 

Limestone farther east in Texas.

Table 10 indicates the fossils of the Finlay Limestonewhich have been identified from collections made west 

of the Sierra Diablo, in or near the report area. All 

but the first lot were identified by R. W. Imlay (written 

commun., 1940,1950).

TABLE 10. Fossils identified from Finlay Limestone, western

part of Sierra Diablo region, Texas

[Identifications by E. W. Imlay]

Lamellibranchiata:

Pecten (Neithea) occidental}* ConModidus concentrice-castellatus

Gastropoda:

ori

Nation1! cf. N.I pedernalis Roemer.

Turrttella seriatim-granulata

Cerithiumt cf. C.I pecosense StanEchinoidea:

Locality and fossil collection number

Cox Mountain 

(De 

Ford 

and 

Brand, 

1958)

X

X

X

Southwest of Roberts 

Ranch 

(USGS 

17844, 

17843)

X

X

X

X

X

X

Roberts 

Mesa 

(USGS 

17844, 

17843)

X 

X

X

X

X

X

Norton 

Mesa 

(USGS 

17281, 

17900)

X

X 

X

X

X

X

X 

X

X

X

X

Northeastern 

part of 

Triple 

Hill 

quad. 

(Albritton and 

Smith, 

1965)

X 

X

X

X

X 

X 

X 

X 

X

X

X 

X

X

X

X 

X
CRETACEOUS 87

KIAMICHI FORMATION

The KiamicM Formation is named for the Kiamichi 

River in southeastern Oklahoma, from whence it extends southward into north-central Texas as far as the 

Brazos Eiver. Adkins (1932, p. 351-355) has demonstrated the wide extent of the same unit in Trans-Pecos 

Texas.

Within the report area the Kiamichi Formation is 

preserved only on Cox Mountain (geologic section 49, 

pi. 13), where 65 feet of fossiliferous marly limestone, 

marl, and thin-bedded sandstone overlie the Finlay 

limestone and are followed unconformably by Tertiary 

basalt. Similar strata with the same fauna, 100 feet 

thick, occur farther west near Flat Mesa north of Sierra 

Blanca (geologic section D, pi. 13), and are capped by 

sandstone with a Duck Creek fauna (Adkins, 1932, p. 

352).

The Kiamichi evidently passes northward into sandstone, because at Sierra Prieta the Washita Group is 

underlain directly by sandstone whose upper part contains a Fredericksburg fauna (see under "Cox Sandstone") . In the area between Cox Mountain and Sierra 

Prieta, a little west of the report area (Block 35), 34 

feet of fossiliferous sandstone, probably the Kiamichi 

Formation, is preserved in an outlier on the Finlay 

Limestone (Albritton and Smith, 1965).

The Kiamichi Formation is not exposed southwest 

of Eagle Flat within the report area, its position being 

occupied by an alluvial-covered swale (section 19, Block 

69, Twp. 8; pi. 1). However, it probably exists in this 

area, as Gillerman (1953, p. 25) observed the formation, 

with its characteristic fossils, farther southeast in the 

same outcrop belt in the foothills of the Eagle Mountains (geologic section C, pi. 13).

On Cox Mountain the Kiamichi Formation contains 

a varied fauna of pelecypods, gastropods, and cephalopods, and minor corals and echinoids. The most characteristic fossils are various species of the cephalopod 

Ossytropidoceras and the oyster G-ryphaea navia Hall, 

the first indicating broadly a late Fredericksburg age, 

and the second more specifically a Kiamichi age.

Table 11 lists fossils that have been identified from 

the collections made in the Kiamichi Formation on Cox 

Mountain. The first four lots were identified by E. W. 

Imlay (written commun., 1940).

WASHITA GROUP

Within the report area the Wasliita Group, or highest unit of the Comanche Series, is preserved only southwest of Eagle Flat and on Sierra Prieta (pi. 1), 

although outcrops are more extensive in the surrounding region. Within the region all three facies of the 

group that were distinguished by Adkins (1932, p. 361) 

occur the marginal sandy facies; the normal neritic

TABLE 11. Fossils identified from KiamicM Formation, Cox 

Mountain, Tens.

[Identifications by E. W. Imlay, except in last two columns]

Coelenterata: 

Parasmilia sp., and other

Lamellibranchiata:

cf. O. corrugata Gabb _ 

Exogyra texana Eoemer __

Trigonia emoryi Conrad 

Of)

Pecten (Neithea) subalplnus

(Neithea) irregularis 

Bose

Gastropoda:

Cephalopoda: 

Oxytropidoceras acwticarinacf. O. supani (LassEchinoidea: 

Enallaster texanus (Eoemer).

Fossil collection number

USGS 

17838

X 

X 

X

X

X

X

X

X 

X

USGS 

17837

X

X

X

X

X

X

USGS 

17836

X

USGS 

17280

X

X 

X

X

X

X

Adkins 

1932, 

p. 353

X 

X

X 

X

X

X 

X

X 

X 

X

DeFord 

and 

Brand, 

1958

X

X

X 

X

X

X 

X

facies of limestone, marl, and shale; and the reef limestone facies but they are compressed within a shorter 

distance than in central and north-central Texas. On 

Sierra Prieta the group consists largely of the marginal 

facies; southwest of Eagle Flat, the neritic facies; and 

farther to the south, the reef facies.

Various formations of the Washita Group have been 

differentiated in adjoining areas to the south and east 

(Gillerman, 1953, p. 25-31; Brand and DeFord, 1958,5 

p. 379-386; Twiss, 1959). In the report area varied 

ages of different parts of the group are indicated by the 

fossil collections, but it has not been feasible to subdivide the group on any other than a zonal basis.

SOUTHWEST OF EAGLE FLAT

The Washita Group occurs below the Devil Ridge 

thrust southwest of Eagle Flat, where it crops out in 

low parallel ridges and forms a band of outcrop several 

miles wide (pi. 1). About a thousand feet of strata lies 

beneath the Eagle Ford Formation, but although the 

Finlay Limestone underlies them on the northeast, the 

intervening Kiamichi Formation and the basal beds of 

the Washita Group are concealed.

6 Brand and DeFord (1958, p. 378) have proposed a "Sixshooter 

Group" to encompass the Finlay Limestone of Fredericksburg age and 

the overlying formations of Washita age, but justification for supplanting the long-established Washita Group in this region is not apparent.
88 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Here the Washita Group is chiefly thin-bedded limestone, in part marly and sandy (geologic section B, pi. 

13). The lower 680 feet is limestone and marly limestone; the middle 150 feet, sandstone, calcareous sandstone, and shale; and the upper 200 feet, limestone and 

sandy limestone (Albritton and Smith, 1965). Fossils 

are abundant in marly beds of the lower unit 480 to 580 

feet below the top of the group and include such diagnostic species as Alectryonia quadriplicata (Shumard), 

Turrilites brazoensis Roemer, and Mortoniceras wintoni 

(Adkins) (Smith, 1940, p. 616-617), which occur in 

north-central Texas at levels between the Weno and 

Mainstreet Formations. The three units southwest of 

Eagle Flat may correspond approximately to the 

Georgetown Limestone, Grayson Formation, and Buda 

Limestone as differentiated by Gillerman (1953, p. 25- 

31) in the foothills of the Eagle Mountains a few miles 

to the southeast (geologic section C, pi. 13), but this 

correlation has not been verified.

SIERRA PRIETA

On Sierra Prieta the Washita Group overlies the 

sandstone mapped as Cox, and is variably truncated 

above by the thick sill of igneous rock which caps the 

mountain (pi. 1; section A-A', pi. 16). As the beds 

are poorly resistant to erosion, they are extensively 

masked by landslides and float from the igneous rock 

and are exposed mainly in ravines (upper view, pi. 12). 

However, fairly complete sections can be measured in 

several places. At the east end of Sierra Prieta (geologic section 53, pi. 13) 350 feet of Washita beds is 

preserved below the sill, and at the west end (geologic 

section 54, pi. 13), 175 feet.

Most of the group is marl, nodular limestone, sandy 

shale, and thin-bedded sandstone. No very distinctive 

lithologic subdivisions are apparent, although a considerable range in age is indicated by the fossils, which are 

abundant throughout. At all localities the basal 40 or 

50 feet of beds is of Duck Creek age; these beds contain abundant Eopachydiscus, Mortoniceras, Pervinqueria, and other ammonites, some of which must have 

been of exceptional size, for preserved fragments are 

several feet across. Higher in the section, layers of 

oyster shell coquina are interbedded at various levels, 

composed mainly of G-ryphaea washitaensis Hill. The 

age of the strata above the Duck Creek horizon can be 

determined only approximately. Imlay (written commun., 1940) suggests correlation of successive collections in the thick sequence at the east end of the mountain with the "Denton or Weno," and the "Fort Worth 

or Denton," and states that the highest collection is 

"not younger than Mainstreet." Adkins (1932, p. 354) 

tentatively correlated the highest beds in the thinner

TABLE 12. Fossils identified from "beds of Duck Creek age 

Washita Group of Sierra Prieta, Tex.

[Identifications by R. W. Imlay, except In last column]

Lamellibranchiata:

Inoceramus cf. I. comancheanus 

Cragin ________________

Alectryonia aff. A. carinata Lamarck.

Pecten (Neithea) subalpinus Bose. ... 

(Neithea.) sp. ___________

Pholadomya cf. P. shattwki Bose ..... 

Homomya cf. H. ligeriensis (d'OrTapfs? cf. T.I chihuahuensis Bose ....

Gastropoda:

Cephalopoda: 

Cymatoceras texanum (Shumard) .... 

C.?sp... __ .. ......................

Idiohamites cf. L.fremonti (Marcou).. 

cf. 7. comancheanus (Adkins and 

Winton) .......................

Eopachydiscus brazoense (Shumard)-. 

Eopachydiscus? cf. E.I laevicaniculasp. juv

Mortoniceras cf. M. leonensis (Conrad).... __ . __...... ___ ..

Pervinqueria cf. P. kiliani (Lasswitz).

sp...............................

Echinoidea:

Pkymosa cf. P. maxicanum Bose .....

Pliotaxaster whUei (Clark) .._ .....

Brarhiopoda: 

Kingenal cf. K3 leontnsis (Conrad)..

Fossil collection number

17904

X

X 

X 

X

X 

X

X 

X 

X

X

X 

X

X 

X

X 

X

X

X 

X

X

X 

X

X 

X 

X

X

17905

X

X

X

X

X

17915

X 

X

X

X

17801- 

18091

X 

X 

X 

X 

X

X

X 

X

X 

X

X

X 

X

X

X 

X

X

X 

X 

X 

X 

X

X 

X 

X

Adkins, 

1932

X

X

X 

X

X

X 

X

sequence at the west end of the mountain with the

Weno.

FOSSILS

Tables 12 and 13 indicate fossils which have been 

identified from collections made in the Washita Group 

on Sierra Prieta. Table 12 shows the fossils from the 

Duck Creek horizon; table 13 shows those from higher 

strata that are known to include faunas of several horizons, probably ranging from Fort Worth to Mainstreet. 

All the identifications are by R. W. Imlay (written 

commun., 1940), except those by W. S. Adkins in the 

last column.

EAGUB FORD FORMATION

The Eagle Ford Formation, the only unit of the Gulf 

Series in the report area, is preserved southwest of 

Eagle Flat, where it forms a belt of outcrop about a 

mile wide between the Washita Group and the Devil 

Ridge thrust, which truncates its top (pi. 1). About
IGNEOUS ROCKS 89

TABLE 13. Fossils identified from beds younger than Duck Creek age in Washita Group of Sierra Prieta, Test.

[Identifications by R. W. Imlay, except in last column]

Lameilibrancbiata:

SD

Gastropoda:

Cephalopoda:

Ecbinoidea:

Pseudopyrina clarki (B5se). _______________________________

cf. P. inaudUa (Bbse). ________________________________

Brachiopoda:

Fossil collection number

17907

X

X

X

17908

X 

X

X

X

X

17909

X 

X

X

X

X 

X 

X

X 

X 

X 

X 

X 

X

X 

X

X

X 

X

X

X

X

X

X 

X

X

17910

X

X

X

X 

X 

X

X

X

X

17911

X

X

17912

X

17913

X

17914

X 

X

X

X

X 

X

X

X

X 

X

17902

X

X

X 

X

X

Adkins 

1932

X

X

X

X

X 

X 

X

X

X

X

X

1,400 feet of strata is preserved, which is black fissile 

bituminous shale that passes upward into buff sandstone, in part quartzitic, interbedded with some shale 

and chalky limestone. Fossils are not abundant, but 

various foraminifers, Inoceramus, Ostrea, and other 

pelecypods, and a few genera of gastropods have been 

reported (Smith, 1940, p. 618).

IGNEOUS ROCKS

In the Sierra Diablo region igneous rocks occupy 

much smaller areas than the sedimentary rocks, but they 

are varied and widely distributed (pi. 1). Some lie in 

the Precambrian sedimentary and metamorphic rocks 

arid are themselves of Precambrian age; these rocks 

have been described above (p. 22-23,24). Others, which 

intrude or lie on rocks as young as of Permian and

Cretaceous ages, are probably of Tertiary age. They are 

outliers of much more extensive Tertiary intrusive and 

extrusive igneous rocks to the west and south (Albritton 

and Smith, 1965, Gillerman, 1953, p. 34-49; Twiss, 1959; 

Hay-Roe, 1957).

The largest bodies of intrusive rocks are near Marble 

and Mine Canyons in the northeastern Sierra Diablo 

and at Sierra Prieta northwest of the Sierra Diablo; 

smaller bodies occur farther south (pi. 1). The only 

extrusive rock is basalt, which is preserved in a few 

small outliers in the western Sierra Diablo. Compositions and relations of the various intrusive and extrusive rocks differ so much that they were probably formed 

during widely separated parts of Tertiary time, and at 

least one body, that at Mine Canyon, may include igneous rocks of several different ages.
90 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

MAEBLE CANYON-MINE CANYON INTRUSIVE 

COMPLEX

The most varied assemblage of intrusive rocks is in 

the northeastern part of the Sierra Diablo west of the 

Figure Two Eanch, on the lower slope of the escarpment near Marble Canyon and Mine Canyon (pi. 14). 

Here, the Permian rocks are invaded by two stocks, each 

about half a mile in diameter, and by various outlying 

dikes and sills. One of the stocks, at the head of Marble 

Canyon, is composed of coarse plutonic rocks of granitic 

texture, and has been eroded into a basin. The other 

stock, south of the portal of Mine Canyon, is composed 

largely of finer grained porphyries and breccias, and 

projects in Cave Peak, a conical summit prominently in 

view from Texas Highway 54 (lower view, pi. 10).

At their present levels of erosion both stocks invade 

mainly the dolomitic strata of the Hueco Limestone; 

in places however, their contacts extend as low as the 

basal clastic Powwow Member of the Hueco, and in 

others as high as the siliceous black limestone beds of 

the Bone Spring Limestone. Neither stock has notably 

deformed the country rock beyond a few feet from its 

contact. Nevertheless, the country rock has been metamorphosed for distances as much as 400 feet from the 

igneous rocks the main body of the Hueco Limestone 

to varieties of marble, and the rocks below and above it 

to various complex lime and magnesian silicate hornfelses.

The intrusive complex near Marble and Mine Canyons was studied by the writer at various times during 

the present investigation. It was also studied for the 

U.S. Geological Survey, in the field or laboratory, by 

W. T. Holser (in Warner and others, 1959, p. 140-143, 

pi. 5), Earl Ingerson (written commun., 1937), S. J. 

Lasky (oral commun., 1938; written commun., 1940), 

and Charles Milton (written commun., 1940). Chemical analyses of some of the rocks were made by K. J. 

Murata (written commun., 1937, 1940). The present 

account is compiled from these various observations.

MARBLE CANYON STOCK

The Marble Canyon stock is oval in plan, about threequarters of a mile long and a quarter of a mile wide, 

and is elongated north-south (pi. 14). Where the contact of the stock with the country rock is exposed, it 

is nearly vertical. The core of the stock, comprising 

most of its volume, is a quartz-bearing syenite of coarse 

granitic texture. The syenite is bordered by a discontinuous band of darker gabbroic rock; both are traversed by many dikes of aplite and pegmatite, some of 

which extend short distances into the country rock on 

the west.

The syenite has been eroded into a basin, partly 

covered by arkosic sand and soil, from which project

rounded knobs and boulders. It is cut by several sets 

of joints, spaced tens of feet apart, of which the most 

prominent in the southern part trend east-west. Specimens of the syenite which were examined in thin section 

by Ingerson and Milton are dominantly potassium feldspar and sodic plagioclase (oligoclase), the proportions 

varying from specimen to specimen. Quartz is minor, 

comprising less than 6 percent of the rock, and mainly 

forms graphic intergrowths with the potassium feldspar. Mafic minerals include brown biotite, brownishgreen hornblende, and gray-violet diopsidic pyroxene. 

Some specimens contain minor amounts of calcite, in 

crystals as much as 0.5 mm in diameter, which extinguish uniformly. Ingerson suggests that the calcite is 

not an alteration product, but was dissolved in the 

magma and crystallized during the orthomagmatic 

stage.

Between syenite and country rock is a band of darker 

gabbroic igneous rock of granitic texture like the syenite, although somewhat finer grained. Specimens that 

have been studied in thin section by Ingerson and Milton are dominantly intermediate plagioclase (andesine); 

potassium feldspar is subordinate. Mafic minerals include brown biotite, diopsidic pyroxene, and olivine and 

minor quantities of magnetite, ilmenite, and spliene.

The dark gabbroic rock is somewhat more resistant 

to erosion than the syenite, and in places projects as a 

low wall between it and the country rock. The outcrop 

of the gabbroic rock in the northern and southern parts 

of the stock is as much as 400 feet wide; elsewhere, it 

is narrower, and at several places on the east and west 

sides is missing altogether. Throughout its extent it 

maintains its entity as a distinct rock unit, and no gradational phases between it and the syenite were observed. The contact between them is nowhere exposed, 

but in a few float boulders a syenitic rock was observed 

to intrude gabbroic rock. Apparently the gabbroic 

rock is an early phase of the intrusion of the stock and is 

not merely a border phase of the syenite produced by 

assimilation of the adjacent country rock.

On the east side of the stock, for 8 to 10 inches from 

the country rock, the dark gabbroic rock is finer grained 

than the remainder, indicating a chilled contact. Within 

15 feet of the contact at the same locality it contains 

several aplite and pegmatite dikes, as well as inclusions 

of a dark hornfels of different composition from the 

adjacent country rock, which was probably brought up 

from a lower level. On the north side of the stock the 

dark gabbroic rock (or the syenite where this is missing) is separated from the country rock by a zone 10 

or 20 feet wide, which is a confused mass of stringers of 

coarse igneous rock, aplite and pegmatite, and hornfels.

Both the syenite and the dark gabbroic rock are traversed by widely spaced dikes a few inches to as much as 

8 inches across, mainly of fine-grained aplite but includ-
IGNEOUS ROCKS 91

ing some coarse pegmatite. Specimens from the dikes, 

according to Ingerson and Milton, consist mostly of potassium feldspar and a little quartz, plagioclase feldspar 

being nearly or wholly lacking. However, one of the 

dikes in the dark gabbroic rock on the east side of the 

stock contains abundant nepheline, its only occurrence 

in the complex; it is associated with potassium feldspar, 

partly replaced by "chessboard" albite.

MINE CANYON STOCK

The Mine Canyon stock is three-quarters of a mile 

northeast of the Marble Canyon stock and superficially 

resembles it, as it lies in Permian carbonate rocks and 

has a diameter of about three-quarters of a mile (pi. 14). 

Nevertheless, its internal character is almost wholly different, as it includes few rocks of granitic texture, and 

is formed mainly of units of fine-grained porphyry and 

breccia. Observed contacts with the country rock are 

nearly vertical, like those in the Marble Canyon stock, 

but the light rhyolite breccia of the stock projects in 

several bosses on the slope of Marble Canyon to the 

south, suggesting a low dip of the contact away from 

the main stock. However, the light rhyolite breccia 

is a late component of the stock and probably invaded 

the country rock more irregularly than the earlier 

components.

The components of the Mine Canyon stock are discrete units of light rhyolite porphyry, dark rhyolite 

porphyry, porphyritic granite, and light rhyolite breccia, which are ringed concentrically around a center on 

the slope north of Cave Peak. Not all the units are 

progressively younger from the periphery inward, as 

one might assume. The dominant rock of the stock, or 

light rhyolite breccia, occurs mainly toward the periphery, yet it is the youngest major igneous unit in the 

complex.

Light rhyolite porphyry forms irregular masses as 

much as 400 feet wide against the country rock on the 

south and east sides of the stock; it is also preserved as 

inclusions in the light rhyolite breccia farther west. 

Much of the porphyry is poorly exposed and is covered 

extensively by float from the adjacent light rhyolite 

breccia. Most of it is aphanitic, greenish gray where 

fresh, and weathers light gray or buff. In places it contains phenocrysts of feldspar and quartz as much as 

3 mm in diameter, but elsewhere these are smaller or 

lacking altogether. According to Milton, the groundmass is an aggregate of randomly oriented feldspar 

laths, strewn with brown biotite and opaque minerals.

Dark rhyolite porphyry crops out in a band about 500 

feet wide on the north slope of Cave Peak, encircling the 

core of porphyritic granite. The porphyry is dense, 

dark gray to black, and breaks along joints into 

straight-sided blocks. It contains abundant phenocrysts of feldspar, and a few of quartz, about 2 mm in

7.57-105

diameter. Microscopic examination by Milton indicates that the feldspar is slightly albitized orthoclase, 

and that the groundmass is formed of interlocking 

feldspar and quartz, many small euhedral plates and 

patches of biotite, and minor sphene. The porphyry 

grades irregularly into a breccia of the same material 

whose fragments are as much as 1 inch across. In a 

band about 10 feet wide next to the central core of 

porphyritic granite, the porphyry has been silicified and 

traversed by quartz veinlets, producing a rock that resembles an aplite.

The core of the Mine Canyon stock is prophyritic 

granite which forms a cylindrical mass about 500 feet 

in diameter, exposed on the north slope of Cave Peak. 

The porphyritic granite is medium grained and is composed of quartz and orthoclase phenocrysts in a finer 

grained groundmass. Microscopic examination by 

Milton indicates that the orthoclase phenocrysts are 

somewhat albitized, and that the groundmass is an interlocking aggregate of quartz and feldspar, with a few 

epidotized skeletons of biotite.

Light rhyolite breccia forms the greatest surface area, 

and probably the greatest volume, of any of the intrusive units in the Mine Canyon stock. Cave Peak is 

formed of it, and its weathered blocks are the principal 

constituents of the out wash from the stock. The breccia 

occupies a wide band around the periphery of the stock; 

nevertheless it intrudes and crosscuts all the igneous 

units previously described and it must have the structure of a ring dike. On the east side of the stock the 

breccia lies within concentric bands of light rhyolite 

porphyry and metamorphosed country rock. On the 

west side it crosses these bands and invades little-altered 

country rock; here, light rhyolite porphyry and metamorphosed country rock remain only as inclusions in 

the breccia. The light rhyolite breccia was evidently 

intruded after the climax of the contact metamorphism.

The light rhyolite breccia is an aphanitic light-gray 

or white igenous rock which contains closely to widely 

spaced angular fragments an inch to several feet across. 

Many of the fragments are like the matrix, others are 

rhyolite porphyry with conspicous flow structure, and 

a few are metamorphosed limestone and other country 

rocks. Inclusions of other rocks of the stock 10 feet or 

more across occur in places, especially on the west side 

and near the summit of Cave Peak. Microscopic examination by Ingerson of speciments from an outlying boss 

of the breccia on the north slope of Marble Canyon indicates that the matrix is mainly quartz and potassium 

feldspar, partly forming small phenocrysts, but chiefly 

a groundmass which also includes much secondary 

calcite.

The light rhyolite breccia has been somewhat mineralized throughout, as indicated by extensive iron oxide 

staining of weathered surfaces. Most of the introduced
92 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

minerals form threads or narrow veinlets which trend 

westward, northwestward, or northward. Mineralization is most extensive on the east side near the contact 

with the dark rhyolite porphyry and on the west side 

near the contact with light rhyolite porphyry inclusions. The dominant mineral is pyrite, but there is also 

chalcopyrite, fluorite, and huebnerite (iron-manganese 

tungstate). According to Holser, some of the veinlets 

contain minor amounts of beryllium (less than 0.1 percent BeO).

Rocks of the Mine Canyon stock are cut by widely 

spaced vertical dikes, some as much as 4 feet wide. A 

specimen from one of the dikes on the east side of the 

stock is described by Milton as a dull light-gray finegrained rock, composed of interlocking particles of alkali feldspar with sparing phenocrysts of the same 

feldspar and a few embayed phenocrysts of quartz, 

and apparently without mafic minerals.

OUTLYING IGNEOUS ROCKS

East and north of the Marble Canyon and Mine 

Canyon stocks are numerous smaller bodies of intrusive rocks, mainly dikes and sills (pi. 14). Except for 

minor aplite dikes, none seem to be related to the Marble 

Canyon stock. Most of them probably originated during later phases of the intrusion of the Mine Canyon 

stock.

On the north slope of Marble Canyon, a boss of light 

rhyolite breccia, which is an offshoot of the main breccia intrusion, projects into the Hueco Limestone. Not 

far away the marl and thin limestone beds of the Hueco 

are traversed by sills less than a foot thick of lightgray aphanitic igneous rock, whose affinity to the main 

breccia mass is suggested by their content of breccia 

fragments. South of Marble Canyon aphanitic igneous rock forms a dike that follows a northwest-trending fault.

Outlying intrusions are extensive from Mine Canyon 

northward for 4 miles, nearly to Apache Canyon (pi. 

1). Most of them are sills which follow the relatively 

weak strata of the Powwow Member of the Hueco 

Limestone, but two plugs invade the fossiliferous shale 

of Pennsylvanian age just north of Mine Canyon. In 

the segment between Mine Canyon and Apache Canyon 

the strata have been displaced by block faulting and 

the sills have been similarly displaced, indicating that 

the igneous rocks were intruded before the faulting.

Most of the igneous rocks of the outlying masses are 

light-gray aphanitic much-jointed felsite. The felsite 

has been greatly kaolinized and iron stained by weathering, so that no fresh specimens could be collected that 

would be suitable for petrographic study.

METAMORPHIC ROCKS

Intrusion of both the Marble Canyon and Mine Canyon stocks produced much contact metamorphism in the

adjacent host rocks, mainly the Hueco Limestone. Most 

of the contact metamorphism is related to the emplacement of the coarse-grained intrusive rocks and is less 

related to the finer grained porphyries and breccias. 

Effects of the metamorphism vary not only with distance from the stocks, but also with the compositions of 

the rocks in the stratigraphic sequence. Most of the 

country rock that has been metamorphosed is dolomite 

and limestone of the main body of the Hueco Limestone ; in some places, however, the clastic rocks of the 

Powwow Member are involved, in others the siliceous 

black limestone of the Bone Spring Limestone.

Close to the stocks the metamorphic rocks are varieties of hornfels.

A dark heavy hornfels forms large inclusions in the 

dark gabbroic rock on the east side of the Marble Canyon stock. Its sedimentary origin is shown by varying 

mineral compositions of its bedding laminae. According to microscopic determinations by Milton and Ingerson, it is composed of tiny grains of diopside and a 

little calcite, quartz, and sphene, which are poikilitically 

enclosed in a groundmass of andesine feldspar. This 

hornfels differs so much from the adjacent country rock 

that it has either been carried up from a lower stratigraphic level, or has absorbed much material from the 

igneous rock in which it lies.

Nearby on the east side of the Marble Canyon stock, 

the country rock close to the intrusive has been altered 

to a white or light-gray hornfels that is difficult to 

distinguish from the more extensive marble adjacent to 

it. Microscopic examination by Milton indicates that 

this hornfels is a mosaic of equidimensional quartz 

grains crowded with tiny diopside crystals and with 

veinlets and irregular areas of zeolite.

A more complex hornfels has been formed from the 

marl and marly limestone of the Powwow Member of 

the Hueco Limestone within a few feet of the intrusive 

contact of the Mine Canyon stock on its east side. 

Chemical composition of this rock is as follows:

Chemical analyses, in percent, of hornfels from Powwow Member 

of Hueco Limestone on east border of Mine Canyon stock 

{Analyst, K. J. Murata, 1940]

797 A 797B 

(white (gray 

phase) phase)

Insoluble____.________ 5.56 ______________ 6.28

SiO2________-__-_--_--_- 25.38 _________-_--_ 24.56

CaO___-_-_____________ 55.00 _-_______----_ 54.04

MgO-----------_-------- 3.93 ______________ 3.06

R2O3_-_----------_------- 1.62 ______________ 2.80

CO____ __ -_-- - 5.95 ______________ 7.00

H2O + _.____________--_- 2.03 ______________ 2.09

H_O-____ _ __ _ .29 ______________ .09

Total___________ 99.76 99.92

SiO2 in insoluble_______ 3.60 ________----_. 1.00

F__________-__-___._-_- .21 ______________ .05

SO3 _________________ .14 ____________ None
IGNEOUS ROCKS 93

An intensive study of this hornf els was made by Milton. Most of it is very fine grained, consisting for the 

most part of sharply defined areas that vary from white 

to shades of green or gray, each variation indicating 

a different mineral composition. Much of the hornfels is spurrite (CaCO3 -2Ca2SiO4 ) and merwinite 

(Ca3Mg(SiO4 ) 2 ), but some assemblages contain variable amounts of calcite (CaCO3 ), periclase (MgO), 

vesuvianite (Ca6 [Al(OH,F)]Al2 (SiO4 ) 5 ), wollastonite 

(CaSiOs), and grossularite (3CaO A12O3 3SiO2 ). The 

spurrite and merwinite are replaced by radiophyllite 

(CaSiOS 'H2O), and there are minute veinlets of thaumasite (CaSiO3 -CaCO3 -CaSO4 -15H_O). Some specimens include breccia fragments of diopside and quartz, 

probably altered from chert. The principal assemblages 

belong to the sanidine facies of metamorphism, which 

according to Turner (in Fyfe, Turner, and Verhoogen, 

1958, p. 213-215), is conditioned by very high temperature (600°-1000° C) and very low pressure (pH2O generally less than a few hundred bars). Alteration of the 

assemblages to the hydrous minerals radiophyllite and 

thaumasite represents a retrogression from the intense 

initial metamorphism.

Another variant of the hornfels occurs on the south 

side of the Marble Canyon stock, where black limestone 

extends into the zone of metamorphism. Original bedding, which is still preserved, is indicated by alternating 

thin white and gray layers. Chemical composition of 

this rock is as follows:

Chemical analyses, in percent, of hornfels from Bone Spring

This hornfels is largely akermanite (Ca2MgSi2O7 ) 

and merwinite (Ca3Mg(SiO4 ) 2 ), proportions of which 

vary from one specimen to another, and minor calcite. 

Part of the merwinite forms large crystals which poikilitically enclose the smaller grains of akermanite. One 

specimen contains thick light-gray veins of wollastonite.

Beyond the hornfels zone around the Marble Canyon 

and Mine Canyon stocks a much larger volume of the 

country rock has been altered to white marble. The 

white marble forms a band around the Marble Canyon

stock 200-400 feet wide. The marble band is somewhat 

narrower around the Mine Canyon stock, and is truncated in the western part of its periphery by the younger 

intrusive mass of light rhyolite breccia.

The following analyses indicate the nature of the 

marble surrounding the Marble Canyon stock. The 

first group of analyses is of marble from various places 

around the periphery. The second group illustrates 

variations in the composition of altered and unaltered 

rocks at about the same stratigraphic level, eastward 

along Marble Canyon from the stock.

Chemical analyses, in percent, of white marble around the 

periphery of the Marble Canyon stock

[Analyst, K.J. Murata, 1937, 1940]

Inorganic insoluble. 

Soluble R2O3 __ ..

MgCOs-. _ ... ..

Mg(OH)j.._ .....

Total. __ ...

788

0.42 

0) 61.14

12.79

25.57

99.92

772

0.60 

.60

64.89

33.21

99.30

783

0.50 (')

64.73

2.67

31.88

99.78

784

0.18 

0) 85.25

14.02

99.45

785

0.29 

0) 61.80

6.02

31.92

100.03

786

0.73 

0)63.98

5.49

29.82

100.02

1 Not determined.

788. White marble, southeast side of stock, high on slope and 50 ft below top of Hueco 

Limestone.

772. White marble, east side of stock not far from contact, lower part of Hueco Limestone.

783. White marble, north side of stock, 2-10 ft from contact, upper part of Hueco 

Limestone.

784. White marble, northwest side of stock, 15-30 ft from contact, Hueco Limestone 

or basal Bone Spring Limestone.

785. White marble, west side of stock, not far from contact, upper part of Hueco 

Limestone or basal Bone Spring Limestone.

786. White marble, west side of stock south of preceding locality, not far from contact, upper part of Hueco Limestone or basal Bone Spring Limestone.

Chemical analyses, in percent, of marble and unaltered limestone 

on east side of Marble Canyon stock along Marble Canyon

[Analyst, K. J. Murata, 1937J

[Analyst, K. J. Murata, 1940

787 A 787 B

SiO2 ___ .__...._-..-... 44.20 ______________ 36.90

CaO....__. _______________ 45.00 .._-__.-_.__-. 48.01

MgO__---_ ___ __________ 6.29 ______________ 12.25

T> r\ i on o AQ

CO2__---__-_--__------_- 2.06 ._._._.__-___. .43

H.O + .77 ______________ .26

H2O ____________________ .34 ______________ .08

Total ____ ________ 100.56 ... _______ 100.41

Soluble R2 O3 - -----

CaCO3 --------------

MgCOs. __ - ------

Mg(OH) 2 . _____________

Total _____ _

CaO_____---____---_-

MgO_ ___---_----._-

772

0.60

/»rv

64.89

None

33.21

QQ qrj

36.35

22.95

773

1.28

 £t\j

27

68.56

30.07

None

inn 4.4.

38.42

14.38

774 A

1.26

. Oo 

12

86.88

11.69

None

100. 01

46.68

5.59

774 B

0.27

.10

oc

55.49

44.01

None

100. 12

31.09

21.05

772. White marble, east side of stock not far from contact, lower part of Hueco Limestone.

773. Black "baked" limestone at gateway in Marble Canyon, east of intrusive. 

774 A. Unaltered Hueco Limestone from about same horizon as specimen 773,

north slope of Marble Canyon several hundred yards east of gateway; from

lower beds of calcitic limestone. 

774 B. Same locality as preceding: from upper beds of dolomitic limestone.

The marble is uniformly white and fine grained. 

Chemical analyses of five of the specimens tabulated 

above show a content of 61-66 percent calcite (CaCO3 ) 

and 21-33 percent brucite (Mg(OH) 2 ). Much of the 

marble probably has a similar composition, as it was 

derived from original dolomitic limestone beds of the 

Hueco and Bone Spring. However, one specimen con-
94 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

tains no brucite and much more calcite, and was probably derived from a calcitic limestone bed. According 

to Ingerson, the brucite was derived from serpentine, 

which formed from hydrothermal alteration of olivine, 

the olivine having developed by action of siliceous 

vapors on the original magnesian limestone. Much of 

the brucite still retains the serpentine structure, and 

many of the brucite patches enclose remnants of olivine 

in the serpentine mesh.

Just beyond the band of white marble is a somewhat 

narrower band of finely crystalline black limestone with 

a "baked" or calcined appearance, which is less altered 

than the marble although thoroughly recrystallized. 

This is prominently exposed on the slopes of Marble 

Canyon east of the Marble Canyon stock, but is less 

conspicuous elsewhere. Its black color is caused by an 

enrichment of organic matter, now carbonized, as shown 

by the 0.26 percent of organic insoluble in the analyzed 

specimen (773), as compared with none in the marble 

and 0.06-0.10 percent in the unaltered limestone. The 

organic matter was probably expelled from the original 

limestone of the marble zone during metamorphism. 

The black limestone contains traces of original bedding, 

chert concretions, and fossils. The boundary between 

it and the marble is abrupt, but it fades gradually into 

unaltered limestone and extends farther away from the 

stocks in some strata than in others.

INTERPRETATION

The Marble Canyon and Mine Canyon stocks were 

emplaced before the block faulting of the Sierra Diablo. 

Outlying sills are faulted, and the proximity of the 

stocks themselves to the fault scarp at the edge of the 

range is incompatible with their relatively deep-seated 

origin. During intrusion of the stocks they were probably at least covered by the Permian carbonate rocks of 

the Sierra Diablo which now extend 1,500 feet or more 

above the present outcrops of the stocks. During part 

of the intrusive epoch the Permian rocks themselves 

were probably covered by several thousand feet of sandy 

and shaly Cretaceous strata.

The Marble Canyon and Mine Canyon stocks must 

have been formed initially during a single intrusive 

epoch, but they have had different subsequent histories. 

The zones of contact metamorphism around these stocks 

were formed during the initial epoch, at a time of maximum burial. The postulated maximum depth of cover 

is compatible with the spurrite and other minerals of 

the metamorphic suite, which indicate recrystallization 

under conditions of high temperature and low pressure. 

The stocks were emplaced without deforming the country rock more than a few feet from their contacts. Their 

mode of intrusion has not been determined. Evidence

for assimilation of the country rock is inconclusive, but 

not much assimilation is likely to have occurred in such 

shallow intrusives. The dark gabbroic rock around the 

Mable Canyon stock is not a contaminated border f acies 

of the central syenite but a somewhat earlier intrusive. 

There is no indication of stoping, as the stocks contain 

few or no inclusions of country rock; but possibly blocks 

of country rock were pushed upward ahead of the intrusives.

During the initial intrusive epoch the magma of the 

Marble Canyon stock solidified as a coarse-grained 

granitic rock, and the stock has had no subsequent 

igneous history. By contrast, the Mine Canyon stock 

became a conduit that was utilized by later ascending 

magmas, producing a complex of later porphyries and 

breccias. At least the latest of these, the light rhyolite 

breccia, was emplaced under conditions of much lower 

temperature and pressure than the initial intrusions, as 

it crosscuts the earlier metamorphic 'aureole and in 

places is in contact with little-altered limestone.

The brecciated nature of both the light rhyolite 

breccia and the earlier dark rhyolite breccia suggests 

that the Mine Canyon stock was open to the surf ace during their emplacement, and formed a volcanic conduit. 

Perhaps by this time the surface had been stripped of 

its cover of poorly resistant Cretaceous strata, down to 

the top of the resistant Permian carbonate rocks whose 

top is little more than 1,500 feet above the present exposures of the stock. Two epochs of later intrusion and 

possible volcanism are indicated. The first marked the 

time of emplacement of the dark rhyolite porphyry and 

breccia and ended with solidification of the core of 

porphyritic 'granite. During the second, the light 

rhyolite breccia invaded the periphery of the earlier core 

as a ring dike and irregularly invaded the country rock. 

Perhaps at about the same time the surrounding country 

rocks were intruded by f elsite dikes and sills, some as 

much as 2 or 3 miles north of the Mine Canyon stock.

SIERRA PRIETA INTRUSIVE

In the Diablo Plateau northwest of the Sierra Diablo 

is the Sierra Prieta, a crescentic mass of intrusive rock 

about 4 miles long, which projects 500-1,000 feet above 

its surroundings (pi. 1). The igneous rock of Sierra 

Prieta forms a thick sill of complex structure, which 

dips beneath Hueco Limestone of Permian age on the 

south side and overlies shale, marl, and sandstone of 

the Washita Group of Cretaceous age on the north and 

east sides (section A-A', pi. 16). In places the intrusive rock crops out in cliffs and ragged ledges; but 

in many others it has broken down into blocks and 

boulders, some of which are nearly in place, others of
IGNEOUS ROCKS 95

which have moved varying distances from their original 

positions. On the north and east sides of the mountain 

are extensive masses of disordered, land-slipped blocks 

of igneous rock, now in process of dissection, produced 

by undercutting of the weak strata of the Washita 

Group beneath the sill. Some of these land-slipped 

masses are as much as a mile from the present outcrops 

of igneous rock on the mountain and were probably derived from greater extensions of the sill during an 

earlier time.

IGNEOUS HOCKS

The igneous rock of the Sierra Prieta is an alkalic 

porphyry, whose main body is conspicuously spotted by 

phenocrysts of dark-green mafic minerals that lie in a 

gray finely crystalline felsic groundmass. In the central part of the intrusive the spots are half an inch 

across, but they are smaller toward the margins. The 

rock splits into plates and flags whose surfaces have a 

lustrous schistose appearance. A specimen examined 

under the microscope by C. S. Ross (written commun., 

1938) consists of 

a coarsely felted groundmass of sodic plagioclase, with >a few 

phenocrysts of nepheline. Ferromagnesian minerals are 

aegerite-augite and an amphibole resembling riebeckite. The 

latter commonly forms a reaction rim around the nepheline 

grains, or even occurs within them. An'alcite and another 

zeolite are associated with the nepheline.

At the margins of the intrusive the coarse spotted 

igneous rock gives place to a uniformly fine-textured 

rock 25 feet or more thick, which in places forms massive ledges. According to D. E. Lee (written commun., 

1959) 

An estimated 80 percent of the rock is made up of a finely felted 

groundmass of feldspar blades. An X-ray diffraction pattern 

of crushed material indicates that this groundmass is mostly 

sodic plagioclase but includes perhaps as much as 25 percent 

orthoclase. The rock also contains smaller amounts of analcite 

and a mineral that may be chabazite. Tiny grains of unidentified pyroxene are scattered throughout the rock.

METAMORPHIC BOCKS

The Hueco Limestone that overlies the igneous rock 

on the south side has been metamorphosed to marble for 

3-25 feet from the contact, beyond which it is blackened 

and "baked" for as much as 50 feet farther. In places 

marble also extends beyond the main body as dikelike 

masses, probably adjacent to joints or fractures. Inliers 

of altered limestone are exposed in valleys south of the 

intrusive contact, indicating a low dip of the igneous 

rock beneath the limestone. The following analyses 

indicate that the marble consists of variable amounts of 

calcite and brucite, so that the Hueco Limestone has 

been altered in much the same manner as it has been 

near the Marble Canyon and Mine Canyon stocks.

Analyses of marble and altered limestone from Hueco Limestone on 

south side of Sierra Prieta intrusive

[Analyst, K. J. Murata, 1940]

Insoluble.- _ ____ _ ___

R2O3 ---- _ _.._ _ . __ _______

CaCO. _________________________

MgCOs--.. - --_ _______

Mg(OH) 2_______________________

Total. ____ __ ___ __

809

1.16

1.16

67.23

None

29.72

qq 27

810

1.66

.16

96.30

2.82

None

100. 94

811

0.19

n. det.

64.03

None

35.15

99.37

809. Marble from just above Igneous contact, three-quarters of a mile northwest of 

Black Mountain Tank (center of sec. 17, block N).

810. Black "baked" limestone, 30 ft above contact, same locality as preceding.

811. Marble, forming a dikelike mass in limestone, half a mile east of preceding 

locality.

The Cretaceous rocks which underlie the intrusive 

are little altered, except for slight induration of the 

shale of the Washita Group close to the contact. The 

Cox Sandstone, where it is in contact with the intrusive 

on the west side of the southeastern prong of the mountain, contains cavities coated by concentric growths of a 

blue mineral which C. S. Ross has determined to be 

fluorite.

STRUCTURE

The igneous rock of the Sierra Prieta forms a thick 

south-dipping sill that is broadly accordant with the 

strata adjacent to it (section A-A', pi. 16). However, 

the sill overlies the Washita Group of Cretaceous age 

on its north side and underlies the Hueco Limestone of 

Permian age on its south side. The intrusive must, 

therefore, have zigzagged through the strata during 

its ascent, partly following the bedding, partly breaking across it.

These inferred general relations are illustrated by outcrops in the eastern prong of the mountain. In much 

of the prong the intrusive is a sill that overlies strata 

near the top of the Washita Group. Farther west, 

however, the base of the intrusive descends abruptly 

across the edges of the Washita Group and all the underlying formations down to the Hueco Limestone (lower 

view, pi. 12). The abruptly descending contact is bordered by a ledge 25 feet or more thick of the finegrained phase of the intrusive, which is broken by 

joints normal to the contact.

A tabular inclusion of Hueco Limestone 300 feet long 

and 75 feet thick was observed near the center of the 

intrusive (center of sec. 25, block N); this inclusion 

may be a part of a septum connected with the main body 

of the Hueco farther south. Other inclusions of Hueco 

may exist in the intrusive, but if so, they are covered by 

the extensive surface debris of the igneous rock.

The igneous rock is broken by many vertical joints, 

spaced 10 or 15 feet apart, and by flat or gently dipping 

joints a few feet apart. These joints outline the
96 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

weathered blocks which strew the surface. Many of 

the vertical joints trend west or west-northwest, and 

some faults of the same trend drop the igneous rocks 

and the Cretaceous strata northward. Possibly these 

faults are not fundamental displacements, and instead, 

resulted from superficial settling of joint-bounded 

blocks of the massive sill over the weaker underlying 

strata of the Washita Group.

REGIONAL RELATIONS

The Sierra Prieta intrusive is part of an extensive 

group of alkalic intrusive of Tertiary age in TransPecos Texas (Warner and others, 1959, p. 131). It is 

the southeasternmost of a chain of sills, laccoliths, and 

stocks which extend 40 miles northwestward across the 

Diablo Plateau beyond the report area and include those 

of Antelope Hill, Sierra Tinaj a Pinta, Cerro Diablo, 

and the Cornudas Mountains (King, P. B., 1949). Beyond this chain are similar intrusives of alkalic igneous 

rocks in the Hueco Mountains (King, P. B., King, R. 

E., and Knight, J. B., 1945, sheet 1), and a small plug in 

the southern part of the report area (see below).

INTRUSIVE BOCKS OF SOUTHERN PART OF 

REPORT AREA

Small bodies of intrusive rocks of probable Tertiary 

age occur at widely separated places in the southern 

part of the report area (pi. 1).

On the east side of the Carrizo Mountains (sec. 5, 

Block 6, Twp. 9) are several small dikes and sills of 

diabase, the largest of which follows the unconformable contact between the Carrizo Mountain Formation 

and Van Horn Sandstone (Flawn, in King, P. B., and 

Flawn, P. T., 1953, p. 67).

At the southwest end of the Streeruwitz Hills 2i/£ 

miles west-northwest of Eagle Flat section house (center of east line of sec. 3, Block 69, Twp. 8) a small plug 

of massive unsheared spotted igneous rock lies in 

metarhyolite of Precambrian age (King, P. B., in King, 

R. E., and Flawn, P. T., 1953, p. 100). Although the 

rock was not examined microscopically, it much resembles the alkalic intrusive rocks of Sierra Prieta and 

elsewhere in the Diablo Plateau.

Southwest of Eagle Flat, small sills of rhyolite 

porphyry intrude the Washita Group and Eagle Ford 

Formation (sec. 20, Block 67^; sec. 3, Block 69, Twp. 

9; Smith, 1940, p. 619-620). They are probably related to the more extensive igneous masses of the Eagle 

Mountains adjacent to the south.

BASALTIC VOLCANIC ROCKS

Small bodies of basalt of surface or near-surface 

origin occur at widely separated places in the western 

part of the report area (pi. 1).

Eemnants of a flow of vesicular basalt form the summit of Cox Mountain (sees. 19 and 20, Block 45^), and 

a remnant of another flow is preserved on the west rim 

of Victorio Canyon (sec. 14, Block 43). The flows at 

both places lie on an eroded surface of the Cretaceous 

rocks at Cox Mountain on the Kiamichi Formation 

with a few feet of intervening limestone gravel and at 

Victorio Canyon on a small thickness of Cox Sandstone. Regarding the rock at Cox Mountain, D. E. Lee 

reports (written commun., 1960) 

The rock is a porphyritic olivine basalt. The phenocrysts are 

olivine and calcic plagioclase as much as 2 mm across. Most 

crystals in the groundrnass are less than 0.2 mm in size, and some 

are as small as 0.03 mm. The dominant molecule in the olivine 

phenocrysts must be forsterite. Most of these phenocrysts are 

in process of alteration to a bowlingitelike- mineral. In part 

this alteration is complete; elsewhere the altered material forms 

a rim around the olivine. The groundmass, in estimated order 

of abundance, consists of calcic plagioclase, magnetite-ilmenite, 

clinopyroxene, olivine, and carbonate. Some of the carbonate 

is concentrated in ill-defined patches including other minerals. 

Apatite is also present.

In the Sierra Diablo foothills farther south are several basalt plugs, one northeast of England Tank in the 

Cox Sandstone (northwestern part of sec. 24, Block 

51), two others northwest of the Keen Ranch in the 

Campagrande Limestone (sec. 6, Block 56). The latter 

were examined by Flawn (in King, P. B., and Flawn, 

P. T., 1953, p. 100), who reports that the plugs consist 

of black aphanitic basalt that contains small phenocrysts 

of black glassy augite and spinel. Associated with the 

plugs are basalt sills less than 5 feet thick which contain numerous phenocrysts of olivine, spinel, and augite 

as much as 1-2 cm in diameter and a few augite phenocrysts with the surprising dimensions of 4-5 cm. However, some of this basaltic rock is vesicular, indicating 

that it was intruded near the surface.

UNCONSOLIDATED DEPOSITS OF QUATERNARY AGE

Unconsolidated deposits of Quaternary age cover 

about a third of the report area; they are separated into 

a number of units on the geologic map (pi. 1) based 

more on differences in character, surface form, and 

origin than on chronological sequence. The unconsolidated deposits were mapped partly by cursory field 

study and partly from air photographs.

The environment and origin of the unconsolidated 

deposits has already been discussed in this report (see 

section on "Geography"), and the similar unconsolidated deposits in the nearby southern Guadalupe Mountains were treated at length in an earlier publication 

(King, P. B., 1948, p. 127-160). Here, the unconsolidated deposits in the Sierra Diablo region are described 

briefly as map units.
UNCONSOLIDATED DEPOSITS OF QUATERNARY AGE 97

The unconsolidated deposits that lie at the surface in 

the Sierra Diablo region are all of Quaternary age. 

Some of these, on the alluvial fans at the edges of the 

mountains and on the valley bottoms and pediment surfaces within the mountains, are of Recent age and are 

in process of formation today. Others, which have 

been dissected by modern drainage or buried beneath 

the surface deposits, are of earlier and probable Pleistocene age. In the intermontane areas of the Salt Basin 

and Eagle Flat, where the unconsolidated deposits are 

known from well drilling to be hundreds or thousands 

of feet thick, the older and deeper deposits may be of 

late Tertiary age. However, no unconsolidated deposits 

of late Tertiary age are exposed in the region, and no 

means are at present available to distinguish possible 

buried unconsolidated deposits at this age from those of 

Quaternary age.

LANDSLIDE DEPOSITS

Among the oldest unconsolidated deposits in the region are landslides on the slopes of the intrusive igneous 

body of Sierra Prieta, in the northwestern part of the 

map area. They are disordered bouldery masses of 

igneous rock derived from the intrusive, and occur on 

its west, north, and southeast sides. Those on the north 

side are especially extensive, and conceal the bedrock 

over an area of several square miles. All the landslides 

occur where the intrusive lies as a sill on shale and other 

weak beds of the Washita Group of Cretaceous age; 

they were formed by undermining of the massive 

igneous rock by erosion of the weak beds. Talus and 

small landslides of igneous rock are forming today on 

outcrops of the Washita Group by such undermining, 

but the main landslides are much older, are much dissected, and in part are preserved as detached erosion 

remnants. Moreover, some of the landslide masses 

north of Sierra Prieta are as much as a mile from present outcrops of the igneous sill on the mountain, and 

probably formed when it was more extensive than now. 

All the main landslides appear to be of the same general 

age, and they may have formed at a time when the 

erosional and climatic regime differed considerably 

from that of today.

DEPOSITS OP PLOOB OP SALT BASIN

The Salt Basin, the large intermontane area along the 

east side of the Sierra Diablo region, is deeply filled by 

unconsolidated deposits washed in from the higher lands 

around it. A well in the basin north of the Sierra 

Diablo region is reported to have been drilled in the 

deposits to a depth of 1,620 feet without reaching their 

base (Baker, 1927, p. 40). The West & Armour, I 

Davis Investment et al. oil test, between the Baylor

Mountains and Apache Mountains, drilled 1,150 feet 

in the deposits before reaching Permian bedrock. Most 

of the wells drilled near Van Horn and in the Wildhorse Valley irrigation district to the east are less than 

600 feet deep and fail to reach the base of the deposits 

(Richardson, 1914, p. 9; Follett, 1954, p. 6-9), but two 

wells about 950 feet deep that were drilled 8 miles eastnortheast of Van Horn (sec. 19, Block 63) are reported 

to have entered limestone bedrock (Leonard A. Wood, 

written commun., 1959). The age of the deeper unconsolicated deposits of the Salt Basin is undetermined, but 

those at the surface are of Pleistocene and Recent age.

The surface of the lowest part of the Salt Basin, north 

of the Baylor Mountains, is a nearly level floor more 

than 5 miles wide, formed of clay, silt, and sand which 

are shown as a unit on the map (pi. 1). The clay, silt, 

and sand were probably deposited on the bottom of a 

lake or succession of lakes during Pleistocene time 

(King, P. B., 1948, p. 137, 156-157). Their nearly level 

surface may be a relatively old feature, inherited from 

the lake bottom and modified only by minor shifting of 

material by the wind. No material derived from the 

adjacent mountains seems to be in process of deposition 

on the floor today.

The floor of the Salt Basin is diversified by alkali 

flats, hills of gypsiferous clay, and areas of drifted 

quartz sand which are differentiated on the map (pi. 1), 

all of which have been partly or wholly shaped by the 

wind.

One set of alkali flats (locally called "salt lakes") is 

east of the northern part of the Sierra Diablo, another 

is just north of the end of the range. Grayton Lake, 

an alkali flat of similar character, forms the lowest part 

of the closed depression of Eagle Flat in the southwestern part of the map area. The alkali flats may be the 

final remnants of more extensive lakes of an earlier period, yet today they contain water only at long intervals; 

they are maintained principally by the wind, which 

sweeps material from their surfaces down to groundwater level, an effective limit to downward erosion.

The hills of gypsiferous clay have no clearly discernible pattern over extensive areas toward the north; but 

on the east side of the floor opposite the northern part of 

the Sierra Diablo, they form a remarkable set of closely 

spaced parallel ridges, trending north-northwestward, 

which curve westward just north of the Baylor Mountains. These ridges, and others like them farther north, 

probably mark the shores of one of the latest shallow 

lakes of Pleistocene time (King, P. B., 1948, p. 156-157, 

pi. 23), along which the clays were raised into low 

dunes. Later modifications of the clay hills by the wind 

is indicated by superposition on the gross features of a 

more delicate grain trending eastward or east-southeast-
98 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

ward. Between the alkali flats and hills of gypsiferous 

clay, the floor of the basin is a level meadowland, underlain by brown clay.

The areas of drifted quartz sand occur only in the 

northeastern part of the map area, at the lower ends of 

alluvial fans extending out from the Delaware Mountains east of the Salt Basin. The sand was probably 

derived ultimately from erosion of sandstones of the 

Delaware Mountain Group which form a conspicuous 

part of these mountains; the absence of sand adjacent to 

the Sierra Diablo and other mountains west of the Salt 

Basin is due to these mountains being composed largely 

of carbonate rocks. Within the report area the drifted 

sands form a relatively featureless expanse without dune 

forms, although conspicuous dunes of the same material 

occur farther north (King. P. B., 1948, p. 138).

FANGLOMERATE

Along the edges of the Salt Basin are deposits of 

fanglomerate which are built into alluvial fans that 

slope toward the basin from the adjacent mountains. 

The fans have coalesced into an alluvial slope less than 

1 mile to more than 5 miles wide that is nearly continuous along the edges of the Sierra Diablo and other 

mountains west of the Salt Basin. East of Beach 

Mountain and the Baylor Mountains the alluvial slopes 

extend from the mountains on either side of the Salt 

Basin to its axis, where Wildhorse Creek drains northward. Farther north the alluvial slopes on the two sides 

do not meet, because they are separated by the basin 

floor, discussed above.

The fanglomerate, which has been in process of formation since the mountains assumed their present form, 

probably has a wide range in age. The older fanglomerate, now buried, is probably of Pleistocene or even 

earlier age; but part of the fanglomerate at the surface 

is in process of accumulation today, the moderately 

dissected remainder being only a little older. The fanglomerate at the surface must be younger than the bulk 

of the deposits on the floor of the Salt Basin, as the 

alluvial fans are being prograded toward the floor.

The fanglomerate varies in composition, depending 

on the bedrock of the source areas in the mountains from 

which it was derived, and in texture, depending on the 

sizes and gradients of the streams which supplied it. 

The fanglomerate of large fans of low gradient, composed of relatively fine material, is differentiated on the 

map (pi. 1) from that of fanglomerate of lesser fans 

with steeper gradients built by smaller streams, composed of coarser materials. Large fans have been built 

by Hackberry and Sulphur Creeks near Van Horn and 

by Ked "Wash farther north. Lesser fans with the steepest gradients and the coarsest fanglomerate are along

the segment of the Sierra Diablo north of the Baylor 

Mountains, where relatively recent faulting has created 

a regime of active erosion and deposition.

OLDER ALLUVIAL DEPOSITS

Within the mountains small thicknesses of alluvial 

deposits have been spread over the bottoms of valleys or 

over more extensive rock-cut plains and pediments. 

Most of these deposits are near the levels of modern 

drainage and are of relatively young age, but earlier 

periods of alluviation are indicated by gravel-capped 

remnants as much as a hundred feet above modern 

drainage.

These remnants are most extensive in the foothills 

south and southeast of the southeastern angle of the 

Sierra Diablo, where they overlie former pediments 

that were cut on red sandstone of the Hazel and Van 

Horn Formations. For the most part the pediments 

and gravel deposits were formed by tributaries of 

Sulphur and Hackberry Creeks which drain eastward 

into the Salt Basin; but the western ones, north of the 

Millican Hills, were formed by streams draining into 

the east end of Eagle Flat. Toward the west the older 

gravel deposits merge with the younger alluvial cover 

of Eagle Flat, so that the two sets of deposits cannot be 

differentiated. Dissection of the older gravel deposits 

southeast of the Sierra Diablo may be related to renewed 

downfaulting of the Salt Basin, which revived erosion 

in the mountain areas.

Within the Sierra Diablo the bottoms of many 

canyons and valleys have been filled by alluvial deposits, 

which were later dissected to depths of 50 or 100 feet 

and partly removed. In many of the valleys that drain 

westward from the mountains, dissection has no more 

than trenched the alluvium; but in most of those which 

drain eastward into the Salt Basin, the older alluvial 

deposits have been reduced to terrace remnants. Most 

of these older deposits are not recorded on the map (pi. 

1), being either omitted or not differentiated from the 

younger alluvial deposits, but they are sufficiently extensive and prominent to be shown separately in Apache 

Canyon. Causes of the canyon filling and subsequent 

dissection indicated by these deposits are undetermined. 

They may be related to a time of tectonic stability, followed by one of renewed downfaulting; in the Salt 

Basin, or they may be related to climatic fluctuations 

during Pleistocene time.

YOUNGER ALLUVIAL DEPOSITS

Most of the unconsolidated deposits within the Sierra 

Diablo and west of it, as well as in Eagle Flat, are 

mapped as an undifferentiated unit of younger alluvial 

deposits (pi. 1). Deposits included in the unit are un-
TECTONICS 99

doubtedly complex, but data obtained from field investigation and study of air photographs are insufficient 

to provide a meaningful separation. Most of the 

alluvial deposits at the surface that are included in the 

unit must be relatively young, as they lie at or near the 

levels of modern drainage and are partly in process of 

formation today; some that are moderately dissected 

are slightly older. The younger alluvial deposits in 

some areas probably overlie deposits of Pleistocene age, 

and in Eagle Flat perhaps still older deposits.

The younger alluvial deposits accumulated in three 

drainage areas, one on the east side of the Sierra Diablo 

and adjacent ranges leading directly into the Salt Basin, 

another on the west slope of the Sierra Diablo in the 

northwestern part of the map area leading northwestward by circuitous route into the Salt Basin, and a third 

in the southwestern part of the map area leading into 

Eagle Flat.

The younger alluvial deposits in the drainage area on 

the east side of the Sierra Diablo are mostly of small 

extent and fill the bottoms of valleys that indent the 

escarpments. Their composition and texture is like that 

of the fanglomerate in the fans down the slope, beyond 

the edges of the mountains, but they are differentiated 

because they are relatively thin and were deposited on 

eroded bedrock. The most extensive alluvial deposits 

in this drainage area lie between the Baylor Mountains 

on the east and the higher escarpments of the Sierra 

Diablo on the west, where the bedrock is mainly sandstone rather than carbonate rocks. Here, tributaries of 

Sulphur Creek and Red Wash have cut extensive pediments which were subsequently covered by a small thickness of sand and gravel.

On the west slope of the Sierra Diablo, narrow strips 

of alluvium extend up the valleys in places nearly to 

the mountain crest and expand down the slope west 

of the mountains into broad alluvial plains separated 

by widely dispersed rock hills and mesas. The bedrock 

in parts of this western area has been folded and faulted, 

but so long ago as not to have shaped the present topography. The plains are thus erosional rather than tectonic depressions, and their alluvial cover, although extensive, is probably rather thin. The alluvial deposits 

toward the south have nearly featureless gently sloping 

surfaces, but north of the Victorio flexure they are dissected to depths as great as 50 feet. Along some of the 

larger drainage courses are alluvial flats lower than the 

tops of the dissected deposits, so that there have been 

several cycles of cutting and filling.

In the drainage area of Eagle Flat modern erosional 

depositional processes are less active than in the Salt 

Basin, partly because of the circuitous drainage connection between them, and partly because of the great7571-108 65 8

er tectonic stability of Eagle Flat in the recent past. 

The central part of Eagle Flat is doubtless a tectonic 

depression like the Salt Basin; but because of its present stability, its unconsolidated deposits are not capable 

of an obvious subdivision like that in the main basin. 

They are therefore mapped as undifferentiated younger alluvial deposits (pi. 1). Along the northern and 

southwestern margins of the flat, the alluvial deposits 

cover broad rock-cut plains or pediments that extend 

between and through low hills of deformed Precambrian and Cretaceous rocks. Within the flat itself the 

alluvial slopes extend from either side of the axis. Alluviation has cut off the western part of the flat from 

the remainder to form a closed depression surrounding 

the alkali flat of Grayton Lake. The sandy surface 

materials in many parts of the flat have been raised by 

the wind into low dunes, shown by a stippled pattern on 

the topographic base (pis. 1,9).

Like the Salt Basin, the tectonic depression of Eagle 

Flat, within its encircling pediments, must be thickly 

filled by unconsolidated deposits of Pleistocene or even 

earlier age. At Hot Wells these deposits have been 

penetrated to a depth of 1,000 feet without reaching 

their base (Baker, 1927, p. 40), but little other data are 

available as to their thickness, nature, or extent.

TECTONICS

The Sierra Diablo region lies within the Basin and 

Range province. Present topographic features have 

largely been shaped by block faulting that originated 

during Cenozoic time, which produced mountains and 

plateaus in places, and intermontane lowlands in others that are now for the most part filled by erosional 

debris.

Nevertheless, the Sierra Diablo region had a considerable prior tectonic history, so that the geologic structure varies, not only from one place to another, but 

between rock systems of different ages. Successive times 

of disturbance are indicated by the several angular 

unconformities that interrupt the rock sequence between the formations of Precambrian age and the Van 

Horn Sandstone of Precambrian (?) age, between the 

Van Horn Sandstone and the Bliss Sandstone of Ordoviciaii age, between the rocks of Pennsylvanian age and 

the Hueco Limestone of Permian age, and between 

formations of Permian age and those of Cretaceous 

asre. At least two of these unconformities that beo

neath the Van Horn Sandstone and that beneath the 

Hueco Limestone record times of major orogeny.

By Permian time the Sierra Diablo region had evolved 

into a positive area, the Diablo platform, which subsided less than the Delaware basin to the northeast, 

and perhaps other basins to the southwest. Once ere-
100 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

ated, this positive area persisted into later times, so that 

Cretaceous deposits overlapped it from the southwest 

and were later strongly deformed on the southwest side; 

whereas the rocks of the Sierra Diablo region itself 

remained little disturbed until later in Cenozoic time.

The block-faulted structure produced during later 

Cenozoic time was thus not newly born, but had its 

antecedents in the complex events of earlier times.

The tectonic history of the Sierra Diablo region is 

summarized in table 14.

TABLE 14. Tectonic history of Sierra Diablo region, Texas

Age

Late Tertiary to Pleistocene.

Early Tertiary

Early Mesozoic

Permian

Late Pennsylvanian

Between Ordovician and 

Precambrian(?)

Between Precambrian(?) 

and Precambrian

Later Precambrian

Earlier Precambrian

Record in the rock sequence

Bolson deposits.

Unconformity between Cretaceous sedimentary rocks and Tertiary volcanic 

rocks south of the report area.

Angular unconformity between Cretaceous 

and Permian rocks.

Fdcies variations in Permian rocks

Angular unconformity between Hueco Limestone and older rocks.

Unconformity between Bliss Sandstone and 

Van Horn Sandstone.

Angular unconformity between Van Horn 

Sandstone and older rocks.

Probable unconformity between Hazel and 

Allamoore Formations; coarse conglomerate in Hazel Formation.

Kind of structure

Block faulting along north-trending and west-northwest-trending faults; uplift of mountain areas and 

depression of Salt Basin and Eagle Flat.

Folding and thrusting of Cretaceous rocks southwest of 

Eagle Flat.

Mild regional deformation and local flexing.

Greater subsidence of Delaware basin than Diablo platform; local flexing.

Deformation of pre-Permian rocks into broad anticlines 

and synclines; local displacement along west-northwest-trending faults and flexures.

Tilting and local faulting.

Faulting of west-northwest trend with strike-slip displacement.

Intense folding and faulting of Allamoore and Hazel 

Formations; emplacement of Streeruwitz thrust sheet.

Probable deformation.

Deformation of Carrizo Mountain Formation, progressive and retrogressive metamorphism, injection of 

rhyolite and greenstone into sedimentary rocks.

Structural features of the Sierra Diablo region are 

illustrated in horizontal dimensions by the tectonic map 

(pi. 15), which shows the same items of structure as on 

the geologic map (pi. 1), except for omission of those 

in the Precambrian Hazel, Allamoore, and Carrizo 

Mountain Formations that formed before Van Horn 

time. In addition, the tectonic map shows known or inferred structure contours on the top of Precambrian 

and Precambrian (?) rocks and data on the nature and 

trends of joints. Structural features are also illustrated in vertical dimension by 10 structure sections 

extending generally eastward across the northern 

and eastern parts of the region (pi. 16) and by 10 structure sections extending generally northward across the 

southern part of the region (pi. 16).

STRUCTURE OP PRECAMBRIAN AND 

PRECAMBRIAKX?) ROCKS

STREERUWITZ THRUST FAULT

The major structural feature of the Precambrian 

rocks of the Sierra Diablo foothills and the Carrizo

Mountains is the Streeruwitz thrust fault (King, P. B., 

in King P. B., and Flawn, P. T., 1953, p. 102-103), 

which forms a boundary between the much-metamorphosed Carrizo Mountain Formation and its associated 

intrusive rocks on the south and the disturbed but littlemetamorphosed Allamoore and Hazel Formations on 

the north (pi. 1). The fault is exposed discontinuously 

along the south edge of the Sierra Diablo foothills from 

the Streeruwitz Hills eastward to a locality 2 miles 

northeast of Allamoore (sec. 16, Block 67, Twp. 8), 

and it reappears in a small area near the Texas and 

Pacific Railway in the northern Carrizo Mountains 

(sec. 17, Block 66, Twp. 8), thus having a known strike 

length of about 15 miles. Besides, several small patches 

of metarhyolite lie amidst the Allamoore Formation in 

the Millican Hills more than iy2 miles north of the 

trace of the Streeruwitz fault (sec. 5, Block 67, Twp. 

8), and are probably klippen of its thrust sheet (section 

<9-<9',pl.l6).

At all places the overriding rocks along the Streeruwitz fault are metarhyolite, which is cataclastically
TECTONICS 101

altered, with strongly developed lineation and streaks 

of mylonite. Lineation trends generally southward, 

normal to the trace of the thrust, and is probably parallel to the a fabric axis. In the Carrizo Mountains" 

this metarhyolite intrudes the base of the Carrizo 

Mountain Formation, a metasedimentaiy sequence some 

19,000 feet thick (section T-T', pi. 16). The Carrizo 

Mountain Formation probably forms most of the overriding block of the thrust, although it is nowhere known 

to be in contact with it. The steeply dipping homoclinal beds of the formation strike northeastward (pi. 

1), whereas the Streeruwitz fault strikes west-northward. Presumably the northeast-striking homocline is 

truncated by the fault.

The Streeruwitz fault overrides the Allamoore Formation, which is extensively silicified and marmorized 

near it, and for a greater distance away from it is intensely deformed by folds with a west-northwest strike 

parallel to the fault trace. The Hazel Formation is 

nowhere in contact with the fault but is preserved a 

short distance to the north where it is as much deformed 

as the Allamoore (sections K-K', 0-0', P-P', and 

others, pi. 16). Emplacement of the Streeruwitz thrust 

sheet must have occurred after Hazel time.

Actual contacts between the overriding metarhyolite 

and the overriden Allamoore Formation are exposed in 

many ravines or hillsides in the Sierra Diablo foothills, 

but there is no sharply marked cleancut surface. Near 

the contact the metarhyolite is lineated and mylonitized, 

the Allamoore is schistose and marmorized, and both 

units are strongly silicified; but in many places the contact is masked by schistose amphibolite or by quartz 

veins. Aberrant dips of foliation and trends of lineation in the metarhyolite near the contact attest further 

movement after the creation of the cataclastic structure.

The Streeruwitz fault is clearly older than the Hueco 

Limestone of Permian age, as the Hueco lies unconf ormably on the fault trace in the Streeruwitz Hills (section 

K-Kf, pi. 16). The fault must also be older than the 

Van Horn Sandstone of Precambrian (?) age, as the Van 

Horn lies unconf ormably on Hazel, Allamoore, and Carrizo Mountain Formations that were deformed during 

the thrusting, and as it contains fragments of metarhyolite that was lineated and mylonitized during these 

movements.

STRUCTURE OF ALLAMOORE AND HAZEL FORMATIONS

The Allamoore and Hazel Formations for 3 miles 

north of the trace of the Streeruwitz fault are intensely 

folded and faulted as a result of forces directed from 

the south; presumably the disturbance in this belt is 

related to emplacement of the Streeruwitz thrust sheet. 

Rocks of the disturbed belt have been altered by dynamic and hydrothermal processes; but little of the 

original sedimentary structure has been lost, and there is 

no trace of the cataclastic metamorphism that is prominent in the metarhyolite south of the thrust. Further 

north the disturbance decreases, and the Hazel Formation along the eastern and southern escarpments of the 

Sierra Diablo dips at low angles.

The coarse thick conglomerate of the lower part of 

the Hazel Formation attests that the Allamoore Formation was deformed just before and during the early part 

of Hazel time. Part of the complex structure now visible in the Allamoore Formation must have been produced by this deformation; but this cannot be unraveled 

from the dominant structure, shared by both the Allamoore and Hazel, which is of post-Hazel and pre-Van 

Horn age.

The exposed contact between the Allamoore and 

Hazel Formations is of complex origin. In places the 

original unconformable upper surface of the Allamoore 

may be preserved, but in most places there has been 

movement between the two formations of undetermined 

magnitude, caused mainly by differences in competency 

of their rocks. In some places the Allamoore Formation 

even overlies parts of the Hazel Formation well above 

its base, and the two are separated by a low-angle thrust 

fault of large displacement. These conditions vary from 

place to place along the contact in a manner that cannot easily be differentiated. Rather than introduce possibly unjustified interpretations on the geologic map 

(pi. 1) and structure sections (pi. 16), the contact between the Allamoore and Hazel is therefore indicated 

as a "surface of movement."

Just north of the Streeruwitz thrust fault in the 

Sierra Diablo foothills is a belt of Allamoore Formation 

a mile or more wide (pi. 1). In this belt the Allamoore 

is strongly folded and faulted in a manner that has not 

been completely worked out. In the Millican and Bean 

Hills some downfolds preserve bodies of conglomerate 

of the Hazel Formation, and in the Millican Hills other 

downfolds preserve bodies of metarhyolite which are 

klippen of the Streeruwitz thrust sheet. Toward the 

east, between Buck Spring and Carrizo Spring, the 

structures plunge eastward and the Allamoore and 

Hazel Formations are folded together into several 

steeply dipping anticlines.

The southern belt of Allamoore Formation is bordered on the north by the Hazel Formation. In both 

the Millican Hills and Streeruwitz Hills the adjacent 

Hazel is a massive coarse conglomerate as much as 2,000 

feet thick, which is probably a basal deposit. In the 

Streeruwitz Hills successive units of limestone, phyllite, 

and volcanics are cut off against the conglomerate (pi. 

1), due either to an angular unconformity or to thrust-
102 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

ing. In other places, notably in the Bean Hills, Allamoore Formation lies against red sandstone of the Hazel 

without conglomerate, and the contact is more clearly a 

thrust fault.

Thrusting of Allamoore over Hazel at the north edge 

of the southern belt is most convincingly displayed west 

of the Garren Kanch in the Millican Hills (sec. 4, Block 

67, Twp. 8) where a "subsidiary nappe," or recumbent 

fold of Allamoore Formation, overrides the Hazel Formation across a breadth of about a mile (section 0-0', 

pi. 16). The carapace of the nappe is limestone which 

is traceable, with a few interruptions, from its lower to 

its upper limb. The core of the nappe is volcanic rock 

and phyllite. The nappe is enclosed by conglomerate 

of the Hazel Formation, which is discordant below and 

accordant above. The discordant conglomerate beds 

beneath the nappe contain numerous tourmalinized 

slickensided surfaces.

North of the southern belt of Allamoore Formation 

is a belt of Hazel Formation, whose south edge in the 

Millican and Streeruwitz Hills includes the thick bodies 

of coarse conglomerate already mentioned. In most 

places the Hazel dips homoclinally northward, with 

gradually flattening dips, but greater complexity than 

would otherwise be inferred is indicated by reappearance of bodies of Allamoore Formation north of the 

belt.

Most of these northern bodies of Allamoore Formation have a synclinal structure and overlie the Hazel 

Formation adjacent to them. This feature is well displayed in an area of high relief near Tumbledown 

Mountain (sec. 27, Block 66, Twp. 7; section R-R, 

pi. 16; upper view, pi. 10), where about 2,000 feet of 

Allamoore is synclinally dowiifolded in the Hazel and 

is repeated by a thrust in its lower part. A much 

larger body of Allamoore Formation with similar structure is preserved in the Bean Hills (section Z-Z/, pi. 

16). In the Millican Hills a northern body of Allamoore Formation likewise has a synclinal structure 

(section P-P1', pi. 16), but is still tenuously connected 

with the southern belt by a narrow band of limestone, 

indicating that this body is the inverted forward edge 

of a recumbent fold. In an exceptional area near the 

Garren Kanch (northwestern part of sec. 3, Block 67, 

Twp. 8) Allamoore of the northern body dips 20° W. 

in normal order beneath conglomerate of the Hazel 

Formation, but tracing of the contact indicates that 

these strata have been rotated nearly 360° from their 

original position.

Some of the northern bodies of the Allamoore Formation lie far to the north, over gently dipping red sandstone that is probably high in the Hazel sequence. Several of them occur at the foot of the south-facing escarpment of the Sierra Diablo 3 to 6 miles west of the Old 

Circle Kanch (sections L-L' and M-M'', pi. 16), but the 

body of greatest interest is near the Sancho Panza, St. 

Elmo, and Blackshaft mines (sec. 16, Block 67, Twp. 

7; pi. 1) where a thin layer of Allamoore is tectonically 

intercalated in the Hazel. Toward the southeast this 

layer dips steeply or is overturned, but to the northwest 

it dips at low angles eastward or northeastward. The 

layer is not more than 10 feet thick and is highly sheared 

and sporadically mineralized. As shown in mine workings, the under surface is marked by grooves or steps 

parallel to the strike, and includes horses of the underlying sandstone. The upper surface is a strong firm 

sandstone, which may itself have been sheared over the 

Allamoore beneath.

North of the main northern outliers of the Allamoore 

Formation, the Hazel Formation stands steeply in 

places, as along Hackberry Creek, where vertical beds 

of red sandstone and interbedded conglomerate are well 

exposed. Farther north the structure flattens abruptly, 

forming the "north edge of the steep-dip zone" of the 

geologic map (pi. 1). Near the Hazel mine (sec. 14, 

Block 66, T. 7) the red sandstone layers are nearly 

horizontal, but from there northward toward Victorio 

Peak they dip at angles of 30° or less toward the south 

(section P-P', pi. 16). Similar low dips of the red 

sandstone are visible at various places farther west, 

even where the sandstone is overlain by displaced masses 

of Allamoore Formation (section M-M', pi. 16).

FAULTS WITH STRIKE-SLIP DISPLACEMENT

The Sierra Diablo foothills are crossed by westnorthwestward-trending faults, most of the longer of 

which displace Van Horn and Paleozoic formations, 

but some of the shorter of which occur only in the Allamoore and Hazel Formations. The obvious larger displacements on these faults are of Cenozoic age, although 

some have moved earlier, between Cretaceous and Van 

Horn time. Displacement during these Cenozoic and 

earlier times was dominantly dip slip.

However, some of these faults may have had still 

earlier strike-slip displacements. Such earlier strikeslip displacements are indicated most convincingly along 

the Grapevine fault, where there is a left-lateral offset 

of the "north edge of the steep-dip zone" in the Hazel 

Formation by about half a mile (pi. 1). Elsewhere in 

the area of outcrop of Hazel and Allamoore Formations 

are shorter faults of the same trend which do not extend 

into younger rocks, and which displace nearly vertical 

Allamore and Hazel Formations in the same sense. 

Perhaps these were displaced during the same epoch 

of strike-slip movement.
TECTONICS 103

The left-lateral strike-slip displacements along the 

faults of west-northwestward trend do not seem to be 

related to dip-slip displacements on these and similar 

faults seen in the Van Horn and younger formations. 

A period of strike-slip faulting is thus suggested, at 

some time after deformation of the Allamore and Hazel 

Formations and before deposition of the Van Horn 

Sandstone. Strike-slip displacement of the west-northwestward-trending faults may have established a 

"grain" in the region which was utilized during later 

times of deformation by differently directed forces.

FRACTURE ZONES IN HAZEL FORMATION

In the gently dipping red sandstone of the Hazel Formation just south and east of the southeast corner of the 

Sierra Diablo are the Hazel and Pecos fracture zones. 

The Hazel fracture zone is a set of en echelon fractures 

31/2 miles in length, trending nearly eastward from the 

Mohawk mine. The Pecos fracture zone extends 2 

miles north-northeastward, past the Pecos mine and 

Eureka prospect.

The fractures are vertical mineralized fissures on 

which the ore bodies of the Hazel mine and other mines 

and prospects are located. Within the zones, the fractures lie parallel or en echelon, or diverge at acute 

angles. Outcrops of the fractures are commonly indicated by bleaching of the red sandstone immediately 

adjacent. In vertical section the fractures are zones a 

few feet to 40 feet wide of bleached, brecciated, and 

sliced country rock, interlaced with a gangue of barite, 

calcite, and quartz, which contains sulfides of copper, 

silver, and other metals.

The relative ages of these fracture zones and the highangle faults and joints of adjacent areas are uncertain. 

The fracture zones extend across the dominant westnorthwestward-trending faults and joints, apparently 

without offsetting them or being offset by them, yet 

the west-northwestward-trending faults seem to have 

been displaced intermittently from late Precambrian to 

late Tertiary time. Moreover, emplacement of the 

metallic-mineral deposits may have occurred much later 

than the time of formation of the fractures themselves, 

in zones of weakness already created. It has been suggested (King, P. T., and Flawn, P. T., 1953, p. 151) that 

the metallic mineral deposits were emplaced in Tertiary 

time, but the fractures themselves might have been 

created at any time following the deposition and deformation of the Hazel Formation.

STRUCTURE OF VAN HORN SANDSTONE

The Van Horn Sandstone of Precambrian (?) age 

does not share the structure of the Carrizo Mountain, 

Allamoore, and Hazel Formations, but lies on their 

deeply eroded surfaces and truncates their folds and

faults. The Van Horn itself was tilted and faulted 

before Early Ordovician (Bliss) time, as shown where 

the contact is exposed in Beach Mountain and the Baylor Mountains. Discordance between the Van Horn 

and Bliss is generally only a few degrees, but it is as 

much as 20° on the north face of Beach Mountain. 

Faulting before Bliss time is shown on Tumbledown 

Mountain where the Van Horn was dislocated by the 

Dallas and Grapevine faults. The Dallas fault and 

the Van Horn and Allamoore Formations that were 

displaced by it are truncated by the Bliss Sandstone 

and no later movement occurred along the fault. The 

Grapevine fault was downthrown to the south both before and after Bliss time, so that the Van Horn is preserved only on its south side, whereas the displaced Bliss 

occurs on both sides. Along the Carrizo Spring fault 

to the south, tilted Van Horn is truncated by Bliss, suggesting that it likewise was displaced before Bliss time.

Throughout most of its extent the Van Horn is overlain unconformably by the Hueco Limestone of 

Permian age. The Hueco truncates the several widely 

dispersed basinlike areas in which the Van Horn is now 

preserved. These basinlike areas conform broadly to 

the structure of the succeeding pre-Permian formations, 

suggesting that they were formed at least partly during 

the late Paleozoic pre-Hueco deformation.

The Van Horn Sandstone is tilted and broadly 

warped, so that it dips commonly at angles of 5° or 10°, 

although in places it lies nearly horizontal, and in parts 

of the Eed Valley it dips as steeply as 45°. In the Red 

Valley there appear to be several broad folds or eastward-plunging noses. To the north near Carrizo 

Spring, dips are northeastward or eastward; near 

Threemile Mountain they are generally southeastward; 

south of Threemile Mountain they are again northward.

STRUCTURE OF THE PRECAMBRIAN SURFACE

The known or inferred configuration of the upper 

surface of the Precambrian and Precambrian (?) rocks 

in the Sierra Diablo region is illustrated by structure 

contours on plate 15. The regional configuration of the 

surface in northern Trans-Pecos Texas was presented 

earlier (King, P. B., and Flawn, P. T., 1953, pi. 19B; 

Flawn, 1956, pi. 1; DeFord and Brand, 1958, p. 38).

The surface chosen for contouring is the top of the 

Carrizo Mountain, Allamoore, Hazel, and Van Horn 

Formations. For the most part this is not the surface 

of a "basement," as most of the rocks which form the 

surface are sedimentary and toward the north are little 

altered or deformed; moreover, one unit, the Van Horn 

Sandstone, is unconformable on the remainder. The 

Van Horn Sandstone must be included with the formations contoured because its erratic thickness is unpre-
104 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

dictable away from areas of outcrop. Information on 

the configuration of the surface is reliable in the southern half of the Sierra Diablo region, where the top of 

the Precambrian and Precambrian (?) rocks is exposed 

in many places. The configuration farther north can 

only be inferred, and the contours there are extrapolated from higher formations. Such extrapolation is 

fairly accurate where pre-Permian formations are 

exposed, as these have nearly constant thicknesses 

throughout the region. It is much less accurate where 

only Permian or younger formations are exposed, because of their variable thicknesses and the one or more 

angular unconformities beneath them.

Contours on the upper surface of the Precambrian 

and Precambrian(?) rocks of the report area (pi. 15) 

show that it stands high throughout the southern half 

of the Sierra Diablo, as well as in the foothills to the 

south and the Carrizo Mountains beyond. The surface 

culminates at an altitude of somewhat more than 6,000 

feet near the southeastern angle of the Sierra Diablo 

and lies at more than 5,000 feet over extensive areas 

nearby. In the northern half of the Sierra Diablo and 

in the Baylor Mountains, the surface is generally much 

lower, in the former area standing at altitudes between 

1,000 and 2,000 feet, and perhaps descending to sea level 

near the north end of the range. The border between 

the high-standing and low-standing parts of the surface 

in the southern and northern parts of the Sierra Diablo 

is seemingly near the Victorio flexure in the exposed 

rocks, where the surface may have been abruptly flexed 

or faulted.

Configuration of the surface of the Precambrian and 

Precambrian (?) rocks is a product of all the deformations to which it was subsequently subjected. Many of 

its complexities in the map area are an obvious result 

of the block faulting of later Cenozoic time, yet most 

of its gross features were produced by the pre-Hueco 

deformation of later Paleozoic time, during which the 

rocks of earlier Paleozoic, Precambrian(?), and Precambrian age were uplifted and deeply eroded before 

the Permian was deposited over them (fig. 2).

Features of the Precambrian surface within the map 

area are part of a larger pattern of positive and negative areas in northern Trans-Pecos Texas which were 

also produced by successive deformations during Paleozoic and later times. Precambrian rocks are exposed 

not only in the southern part of the Sierra Diablo, but 

in several mountain areas adjacent to it on the south 

(fig. 8), where their upper surface rises to an altitude 

of more than 5,000 feet. This high-standing area has 

been called the "Van Horn dome" by Baker (1927, p. 

41; 1934a, p. 182), who interpreted it as "the highest 

uplift in Texas." Certainly it is the highest-standing

regional feature in the State, although Precambrian 

rocks project higher in the much narrower more localized uplift of the Franklin Mountains farther west 

(Adams, 1944). Northeast of the high-standing area 

the Precambrian surface probably descends below sea 

level beneath a thick body of Paleozoic rocks in the 

Delaware basin; southwest of the high-standing area it 

probably descends to as great a depth beneath a thick 

body of geosynclinal Mesozoic rocks.

The area of high-standing Precambrian rocks is 

domical only in the broadest sense, as it now consists of 

a number of distinct but closely adjacent mountain uplifts, separated by downf aulted areas; it may have been 

a more continuous feature before block faulting of later 

Cenozoic time. It probably originated mainly during 

the pre-Hueco deformation of later Paleozoic time. 

The pre-Permian Paleozoic sequence of the region is like 

that elsewhere in northern Trans-Pecos Texas and southern New Mexico, and provides no indication of any 

nearby positive area. Moreover, the high-standing area 

does not appear to be related to any special part of the 

Precambrian complex, as it crosscuts diverse Precambrian rocks and structures. The positive area, once 

created, manifested itself in various guises during later 

times during Permian and Mesozoic times when it received smaller thicknesses of sediments than surrounding areas, during Late Cretaceous and early Tertiary 

time when it was less deformed than the area to the 

southwest, and in late Tertiary and Quaternary time 

when it was raised by block faulting. During these 

times its role was perhaps relatively passive or even 

accidental. For example, uplift was probably greater 

during the late Cenozoic block faulting in the Guadalupe 

Mountains than in the area of high-standing Precambrian rocks, yet the uplift there was insufficient to raise 

the Precambrian rocks as high because of the much 

thicker overburden of Paleozoic strata.

STRUCTURE OF PRE-PERMIAN PALEOZOIC ROCKS

Much of the complexity of the map pattern of the 

pre-Permian Paleozoic rocks in the Sierra Diablo region results from the unconformity at the base of the 

Hueco Limestone, which causes the Hueco, at one place 

or another, to lie on all the older rocks of the sequence 

(pi. 1). This unconformity resulted from folding, 

faulting, and deep erosion of the underlying rocks 

events that were of Late Pennsylvanian age, as rocks of 

Early Pennsylvanian age lie unconf ormably beneath the 

Hueco in the northern Sierra Diablo.

The pre-Hueco deformation is strikingly illustrated 

by the distribution of the Ordovician rocks in the southeastern foothills of the Sierra Diablo (pi. 1). On Beach 

Mountain they overlie the Van Horn Sandstone and
TECTONICS 105

comprise the Bliss Sandstone, El Paso Limestone, and 

Montoya Dolomite, a mass nearly 2,000 feet thick. 

Three miles to the northwest, at the southeast corner of 

the Sierra Diablo, the Hueco Limestone lies on red sandstone of the Hazel Formation; all the Ordovician rocks 

and the Van Horn Sandstone are missing. A paleogeologic map of the surface on which the Hueco was deposited (fig. 2) indicates that Beach Mountain lay near 

the southwest end of a broad syncline that plunged 

northeastward, whereas the southeast corner of the 

Sierra Diablo lay on the crest of the next broad anticline 

to the northwest.

Another syncline is indicated farther north, in the 

northeastern part of the Sierra Diablo where Barnett 

Shale of Mississippian age and limestone and shale of 

Pennsylvanian age are preserved beneath the Hueco 

Limestone. In most of this syncline the angular divergence between the Hueco and older rocks is only a 

few degrees; but on the south flank, at an inlier in Victorio Canyon (sec. 13, Block 43), the Montoya Dolomite 

dips 75° N., whereas the overlying Hueco dips only 

gently in the same direction. On the north flank the 

Fusselman Dolomite and beds of Devonian age diverge 

at only slight angles from the Hueco, except at a locality l^j miles northwest of the Figure Two Ranch (sec. 

12, Block 66, Twp. 5) where the Fusselman is nearly 

vertical, and is either faulted or sheared against the 

Montoya and Devonian beds on either side.

Abrupt truncation of pre-Hueco formations near 

some of the west-northwestward-trending faults of the 

region suggests that these faults were dislocated during 

the pre-Hueco deformation. This is most strikingly 

shown along the Hillside fault (section Q-Q'', pi. 16). 

On the northern or downthrown side of the fault, the 

Powwow Member of the Hueco Limestone lies on the 

Van Horn Sandstone, but contains coarse angular fragments of Precambrian metarhyolite; these fragments 

were obviously derived from south of the fault and decrease in abundance away from it. Presumably the 

metarhyolite projected as a scarp along the Hillside 

fault during deposition of the Powwow Member. 

Where the Sulphur Creek fault crosses the Sierra Diablo escarpment 1 mile north of the Hazel mine, the 

Hueco Limestone of the northern or upthrown side 

overlies 750 feet of Van Horn Sandstone, whereas on the 

southern or downthrown side it lies on red sandstone 

of the Hazel Formation (section Q-Q', pi. 16). The 

Van Horn is folded into a syncline whose correspondence with the fault may be partly coincidental, as the 

syncline seemingly diverges from the fault farther east. 

On the South Diablo fault west of the Old Circle Ranch, 

the Hueco Limestone again lies on the Van Horn Sandstone on the upthrown side, whereas some miles to the

south it lies on Hazel and Allamoore Formations. The 

pre-Hueco structure thus indicated had much the same 

position as the later South Diablo fault, although it may 

have been no more than a broad flexure.

Other faults or abrupt flexures were probably displaced at this time, some of which are indicated hypothetically on the paleogeologic map (fig. 2) and the 

structure sections (pi. 16). A fault along the Victorio 

flexure is likely, because on the escarpment south of 

Victorio Peak, Hueco Limestone is known to lie on 

Precambrian Hazel Formation at least part of the distance across the flexure (section Y-Y', pi. 4), whereas 2 

miles to the west in Victorio Canyon the Hueco on the 

flexure lies on steeply tilted Upper Ordovician Montoya 

Dolomite (section K-X', pi. 4). This tilting may be 

related to a fault of pre-Hueco age, downthrown to the 

north (section N-N', pi. 16). A fault or flexure nearly 

coinciding with the present Cox Mountain fault is also 

possible (sections K-K', L-L'', and M-M', pi. 16). 

North of the fault, Hueco Limestone lies on Lower Ordovician El Paso Limestone, whereas in the nearest exposures to the south it lies on Precambrian (?) Van 

Horn Sandstone or Precambrian Hazel Formation.

All these faults or abrupt flexures, known or inferred, are downthrown northward, toward the dominantly negative area that resulted from the pre-Hueco 

deformation, whereas in Cenozoic time the displacement on most of the faults was southward.

STRUCTURES OF PERMIAN" AND EARLY MESOZOIC

AGE

Cretaceous formations of the Sierra Diablo region 

lie unconformably on the older rocks in the same manner as the Hueco Limestone at the base of the Permian. 

Where the Cretaceous is no longer preserved, an extension of its basal unconformity is indicated by wide areas 

of even-crested summits from which an original Cretaceous cover has been removed by erosion. The preserved base of the Cretaceous and its exhumed surface 

show that truncation of rocks beneath is less than at the 

base of the Permian. In most of the Sierra Diablo 

region the Cretaceous was deposited on Permian 

rocks on Guadalupe Series in the north, on Leonard 

Series in the middle, and on Wolfcamp Series in the 

south. The only exception is in the western part of the 

Sierra Diablo foothills where the Cretaceous lies on 

Precambrian rocks (pi. 1). Curiously, the Cretaceous 

at no place lies directly on earlier Paleozoic formations 

which intervene elsewhere in the region between the 

Permian and the Precambrian.

In most places the angular discordance between the 

Cretaceous and older rocks is slight, but it is greater on 

several monoclinal flexures that extend west-northwest-
106 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

ward across the region, on which Permian strata are 

downbent north-northeastward (pis. 1,15; fig. 8).

The northernmost, or Babb flexure, is at the north 

end of the Sierra Diablo and is named for the old Babb 

Ranch, west of which it is prominently exposed (upper view, pi. 12). It has been traced thence west-northwest into the Diablo Plateau for more than 10 miles, 

past the north side of Sierra Prieta. It may also extend east-southeastward for nearly the same distance 

to the mouth of Apache Canyon, but here its course 

is obscured by the North Diablo fault zone of Cenozoic 

age. The Victorio flexure is about 12 miles farther 

south and is named for Victorio Peak, south of which 

it is exposed on the Sierra Diablo escarpment (upper 

view, pi. 10). It has been traced tftence west-northwest 

into the Sierra Diablo and east-southeast into the Baylor Mountains for a distance of 21 miles.

Both the Babb and Victorio flexures are a mile or 

two wide. On the flexures Permian rocks dip mostly 

10° northward, but they dip less in places and more 

than 15° in others. Structure on the flexures is obscured by irregular bedding of many units involved, but 

some evenly bedded units cross them, such as 'the Hueco 

Limestone on the Victorio flexure and the Victorio Peak 

Limestone on the Babb flexure (sections B-B', N-N', 

and P-P', pi. 16; sections X-X' and T-Tf, pi. 4). Displacement on the flexures, as determined by differences 

in height of the evenly bedded units at the upper and 

lower ends, is 1,700 feet on the Victorio flexure and 1,000 

feet on the Babb flexure.

A third flexure that was truncated by the unconformity at the base of the Cretaceous is indicated farther south, along the South Diablo fault, where the 

possibility of pre-Hueco flexing has already been noted. 

At a place S1/^ miles west of the Old Circle Ranch (sec. 

2, Block 56) about 900 feet of Van Horn Sandstone and 

Hueco Limestone form an escarpment north of the fault, 

whereas Campagrande Limestone lies directly on red 

sandstone of the Hazel Formation to the south (section 

M-M', pi. 16). This must have been caused by northward downflexing in pre-Cretaceous time, in the same 

direction as on the Babb and Victorio flexures, but 

opposite from the downthrow on the later South Diablo 

fault. The flexure evidently diverged westward from 

the fault, as in this direction the Van Horn and Hueco 

extend a short distance south of it (section Z-Z', pi. 16).

The flexures and other features just described developed at some time after deposition of the Permian 

rocks now preserved in the Sierra Diablo region and before deposition of the Cretaceous rocks. Tilted Permian rocks on the Babb and Victorio flexures are truncated by the pre-Cretaceous surface, and on the Victorio 

flexure west of the rim of Victorio Canyon a small

remnant of Cretaceous sandstone overlies the tilted 

Permian rocks (section N-N', pi. 16; section X-X', 

pi. 4).

Nevertheless, the flexures are an accentuation of features existing in the region during Permian time, which 

were themselves inherited from the pre-Hueco deformation. Pre-Hueco deformation caused the southern part 

of the Sierra Diablo region to become a positive area and 

the part to the north a negative area (fig. 2). During 

Permian time the positive area, or Diablo platform, received relatively shallow-water deposits, mainly carbonates ; whereas the negative area, or Delaware basin, 

received relatively deep-water deposits, including black 

limestone and siliceous shale during Leonard time (figs. 

6,7) and fine-grained sandstone during Guadalupe time. 

During Leonard time limestone reefs and banks formed 

along the boundary between the platform and basin 

(sections Z7-Z7', X-X', and Y-Y', pi. 4). The Hueco 

Limestone extends with little change across these flexures, as well as the flexure near the South Diablo fault 

zone. Initial flexing must have occurred immediately 

after Hueco time, as there is a prominent unconformity 

at the top of the formation on the Babb and Victorio 

flexures. Inequalities of relief produced by this unconformity probably influenced location of reefs and banks 

during Leonard time, although flexing may have continued during deposition of the Leonard Series itself.

STBUCTUBES OF LATE CBETACEOUS OB EABLY 

TEBTIABY AGE

Southwest of Eagle Flat, in the southwest corner of 

the map area, Cretaceous rocks are strongly deformed, 

as first observed by Baker (1927, p. 5). These rocks 

and structures are a small segment of the northeastern 

front of the Chihuahua tectonic belt (DeFord and 

Brand, 1958, p. 72), which was deformed after the Cretaceous rocks were deposited, and mainly before volcanic rocks of probable Tertiary age were spread over 

them. The front of the Chihuahua tectonic belt extends 

northwestward beyond the report area through Devil 

Ridge, the Quitman Mountains, and Malone Mountain 

(Albritton and Smith, 1965) (figs. 3, 8), and southeastward through the Eagle Mountains and Indio 

Mountains (Gillerman, 1953, p. 39-40; DeFord and 

Brand, 1958, p. 72-85). The area of deformed rocks in 

the United States is only a small part of the Chihuahua 

tectonic belt, most of which lies in Mexico.

Two major faults break the rocks southwest of Eagle 

Flat the Devil Ridge thrust and the Red Hills thrust, 

about 2 miles farther southwest (Smith, 1940, p. 630- 

631) (pis. 1, 15.) These faults are exposed in few 

places; but the Devil Ridge thrust at one place dips 

54° SW., and the Red Hills thrust at another dips 22°
TECTONIC& 107

SW. Smith estimates that the minimum displacement 

of the Devil Eidge thrust is about 4% miles and that 

of the Eed Hills thrust about 3 miles.

The Devil Eidge thrust carries Yucca and Bluff 

Mesa Formations over Washita Group and Eagle Ford 

Formation. The Washita and Eagle Ford are thrown 

into complex minor folds for a mile or two northeast 

of the fault trace, beyond which the underlying Cretaceaus rocks are less deformed. The Yucca, Bluff Mesa, 

Cox, and Finlay Formations above the Devil Kidge 

thrust dip homoclinally southwestward, mainly at 

angles of 15°-30°, but in places an overturned syncline 

is preserved next to the Eed Hills thrust.

In the Sierra Diablo region northeast of the Chihuahua tectonic belt neither the Cretaceous nor the underlying Paleozoic rocks contain structures like those 

southwest of Eagle Flat, and this region probably remained little disturbed until later in Tertiary time.

STRUCTURES OP LATE TERTIARY AND 

QUATERNARY AGE

GENERAL. FEATURES

The Sierra Diablo is one of a group of ranges in 

northern Trans-Pecos Texas in which the surface features have been shaped largely by tectonic movements 

during late Tertiary and Quaternary time as elsewhere in the Basin and Eange province of which the 

region is a part. On the east is the upheaved block of 

the Guadalupe, Delaware, and Apache Mountains; next 

to the west is the depressed block of the Salt Basin; beyond is the upheaved block of the Sierra Diablo (fig. 8).

Faults are the dominant structural features of the 

boundaries between the mountains, or areas of upheaval, 

and the Salt Basin, or area of depression. Most of 

the steep escarpments that face the basin have been 

outlined by such faults, which have dropped the strata 

thousands of feet toward the basin. It places between 

the mountains and basin are foothills of downdropped 

strata, such as the Patterson Hills west of the Guadalupe Mountains, and Beach Mountain and the Baylor 

Mountains east of the Sierra Diablo.

The general trend of the faults along the edges of the 

basin is northerly, although there are offsets along faults 

that trend in other directions. Faults of the northerly 

system on the east side of the Sierra Diablo trend 

irregularly in various directions east and west of north 

(fig. 8). Many faults of the northerly system moved 

several times during late Tertiary and Quaternary time. 

The last movements were of late Pleistocene age and o

produced low scarps that still persist in the older 

alluvial deposits and the adjacent bedrock. In the 

Guadalupe Mountains the dominant joint set is parallel

to the dominant north-northwestward-trending faults 

of the area.

In the southern part of the region another fault system trending west-northwestward crosses the northerly 

system. Its faults are most abundant in the Sierra 

Diablo, but some occur in the Apache Mountains and 

southern Delaware Mountains east of the Salt Basin 

(fig. 8). Like the northward-trending faults, they 

moved in late Tertiary time; but they are generally in 

the interiors of the ranges rather than along their 

borders, and they do not share the latest movements of 

the northerly faults. Some of them have had a considerable pre-Cenozoic history, as discussed above. In 

the Sierra Diablo the dominant joint set is parallel to 

the west-northwesterly faults, rather than to the northerly faults that border the range (pi. 15). The westnorthwesterly faults seemingly follow lines of weakness in the crust more ancient than those followed by 

the northerly faults.

FAULTS BORDERING THE MOUNTAINS

The Sierra Diablo and adjacent mountains and foothills are probably bordered continuously by faults along 

the edge of the Salt Basin, although these are generally 

concealed by Quaternary deposits and are exposed at 

only a few places. The longest segments, on the East 

Diablo and East Baylor faults, are parts of the northerly fault system; but these segments are separated by 

others on the North Diablo and North Baylor faults belonging to the west-northwesterly fault system, whose 

positions nearly coincide with the Babb and Victorio 

flexures. Small segments of the faulted margins of the 

Delaware and Wylie Mountains along the east side of 

the Salt Basin also extend into the report area.

NORTH DIABLO FAULT ZONE

The North Diablo fault zone extends east-southeastward for 8 miles from near the old Babb Eanch to the 

salient of the Sierra Diablo near Apache Peak. The 

zone consists of subparallel interlacing faults that enclose narrow wedges, mainly of Victorio Peak Limestone, dropped 1,000-1,500 feet below equivalent strata 

on the main escarpment to the south (upper view, pi. 

12), which are intermediate in structural height between the bedrock of the escarpment and that beneath 

the Salt Basin. The principal faults are downthrown 

toward the Salt Basin; but complications are produced 

by minor faults downthrown toward the escarpment 

and by steep tilting or folding of the rocks in some of 

the fault blocks, so that black limestone of the Bone 

Spring Formation emerges in places (section C-C', pi. 

16).

The surface of the large fault at the foot of the Sierra 

Diablo escarpment is exposed 1% miles west of the
108 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

105° 104*

31

EXPLANATION

Igneous, metamorphic, 

and sedimentary 

rocks of Precambrian age

Sedimentary rocks of 

Paleozoic and Mesozoic age

Volcanic rocks of early Intrusive igneous rocks 

Tertiary age of Tertiary age

Bolson deposits and 

thick alluvial fill of 

late Tertiary and 

. .Quaternary age

Dotted where concealed by 

younger deposits

Low-angle thrust faults High-angle faults, Monoclinal flexures of Anticlinal axis and 

of early Tertiary age mainly of late Terti- Permian and early domes 

ary and Quaternary Mesozoic age 

age In part followed by reef 

Dotted where concealed by zones of Permian age 

bolson deposits; major 

faults in heavy thick 

lines

FIGDEB 8. Map of Sierra Diablo region and adjacent areas showing faults and related structural features. Faults and flexures 

of west-northwesterly trend extend across the width of the map, and are crossed by other faults of diverse trend.
TECTONICS 109

portal of Apache Canyon, and dips 70°-80° toward the 

downthrow, with flat-lying black limestone of the Bone 

Spring on the upthrown side and gently tilted Victorio 

Peak Limestone on the downthrown side.

At the west and east ends of the North Diablo fault 

zone, the displacement at the border of the mountains 

continues along northward-trending faults to the west 

along a fault which extends northward at the bases of 

South, Middle, and North Mesas and to the east along 

the East Diablo fault which extends southward. The 

western prolongation of the North Diablo fault zone 

itself coincides with the Babb flexure, which is broken 

in places by small faults of the same trend (section 

B-B', pi. -6). The fault zone was probably formed by 

renewed movement along one segment of the flexure in 

late Tertiary and Quaternary time. The steep tilting 

and folding of the Permian rocks in parts of the fault 

zone may antedate the faulting and be related to the 

earlier flexing.

EAST DIABLO FAULT

The East Diablo fault borders the Sierra Diablo on 

the east for 25 miles. It has a bight and cusp pattern, 

with three cusps or salients near the Hazel Mine, Victorio Peak, and Apache Peak separated by two curved 

bights, each about 10 miles across.

East of the southern bight the Sierra Diablo is separated from the Salt Basin by the intermediate block 

of the Baylor Mountains, whose summits stand a thousand feet or more below those of the Sierra Diablo. 

Opposite the Baylor Mountains the East Diablo fault 

is bordered by pediments and bedrock hills, rather than 

by thick alluvial deposits.

In the central and northern salients and the intervening northern bight, the East Diablo fault borders on 

the Salt Basin, and its displacement is greater than in 

the southern bight. In most places bedrock on the 

downthrown side is concealed by a series of coalesced 

alluvial fans, many of which are still in process of 

growth. At a few places between Victorio Canyon and 

Marble Canyon, however, small patches of steeply 

dragged bedrock emerge on the downthrown side of the 

fault (section G-G', pi. 16). Some contain Victorio 

Peak Limestone, whose base is 1,200 feet lower than at 

the nearest point on the escarpment to the west. Total 

displacement in the zone of the East Diablo fault is 

probably much greater, the remainder being accounted 

for by drag of the downthrown beds and displacement 

on probable faults to the east, which are concealed by 

the Quaternary deposits.

The East Diablo fault follows the base of the eastfacing escarpment of the Sierra Diablo, 2,000 feet or 

more high (pi. 10). In the northern bight the crest of 

the escarpment has receded a mile or so from the fault,

but the bench of Hueco Limestone at the base ends on an 

even line along the fault and is little dented by the heads 

of alluvial fans. In the southern bight the Hueco Limestone, which forms the rim of the escarpment, has 

receded a mile or two from the fault; the slopes below 

it, which are formed of poorly resistant red standstone 

of the Hazel Formation, have been carved into a concave surface, with pediments at the base.

Landforms of the Sierra Diablo escarpment suggest 

that the East Diablo fault along its base moved rather 

late in geologic time the even base line of the outer 

bench, the actively growing alluvial fans in front, and 

the small length of most of the canyons behind. Late 

movements are further indicated by low fault scarps a 

short distance east of the main fault (pis. 1,15). One 

crosses the alluvial fans northeast of Apache Peak, 

somewhat north of the end of the East Diablo fault. 

It extends for 3 miles with a trend slightly west of north 

and is about 15 feet high. Another scarp of about the 

same height occurs in the southern bight east of the 

Pecos mine, in alluvium overlying Ordovician rocks of 

the Baylor Mountains block.

The surface of the East Diablo fault, or of rocks 

closely adjacent to this surface, is exposed between 

Marble and Victorio Canyons in the northern bight, 

adjacent to the outcrops of downfaulted bedrock. The 

Hueco Limestone of the upthrown block extends horizontally to the fault and is not internally disturbed except for north-trending vertical joints, some veined by 

calcite, which are nearly parallel to the main fault. 

By contrast, the downthrown strata are steeply dragged, 

greatly jointed, shattered, and silicified. Best exposures 

of the fault surface are three-quarters of a mile north 

of the portal of Victorio Canyon (opposite elevation 

point 4550, sec. 3, Block 66, Twp. 6), where it is followed 

by a breccia zone 25-50 feet wide, of angular fragments 

of black limestone derived from the downthrown block. 

The fault surface is nearly vertical, or dips eastward 

at a steep angle.

Rocks near the East Diablo fault are exposed in the 

southern bight 1% miles northwest of Red Tank (sec. 

21, Block 54%), where the fault is adjoined on the 

downthrown side by low hills of El Paso Limestone. 

Close to the fault the limestone is much brecciated and 

is traversed by north-trending vertical joints and wide 

calcite veins that are probably nearly parallel to the 

main fault.

NORTH BAYLOR FAULT

The Baylor Mountains project northeastward into 

the Salt Basin as an acute-angled salient, on the north 

side of which are much eroded hills that extend westward with a nearly straight front for 9 miles to the 

East Baylor fault. These hills are probably bordered
110 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

on the north, beneath the adjacent alluvium, by the 

North Baylor fault, which separates the Baylor Mountains block from the deeply depressed part of the Salt 

Basin beyond.

The North Baylor fault produces an easterly offset 

of the mountain front similar to that on the North 

Diablo fault zone, and like it, nearly coincides with a 

major structure in the Permian rocks, the Victorio 

flexure. The flexure is prominently exposed on the 

Sierra Diablo escarpment just west of the terminus 

of the North Baylor fault; its easterly extension is indicated in the Permian rocks of the northeastern Baylor 

Mountains, where there are depositional features and 

northward-tilted beds similar to those on the flexure 

farther west. The inferred trace of the North Baylor 

fault would lie within the prolongation of the flexure, 

although it seemingly trends eastward and the flexure 

east-southeastward.

EAST BAYLOR FAULT

The East Baylor fault, like the East Diablo fault, 

forms a boundary between bedrock of the mountains 

and unconsolidated deposits of the Salt Basin. It follows the east side of the Baylor Mountains, Beach 

Mountain, Threemile Mountain, and the Carrizo 

Mountains for a distance of about 20 miles, probably 

terminating a few miles south of the edge of the map 

area near the line of the Southern Pacific railroad. 

Unlike the East Diablo fault, its course is nearly 

straight in a north-northeasterly direction (pis. 1, 15), 

although minor irregularities are suggested by recesses 

in the base line of the adjoining mountains.

The East Baylor fault is nowhere exposed, but its 

presence is indicated by the steep faces of the adjoining 

mountains; the Baylor Mountains rise nearly as high 

above the Salt Basin, and with nearly as even a base 

line, as the Sierra Diablo along the East Diablo fault. 

Moreover, some miles out in the basin southeast of the 

Baylor Mountains (sec. 25, Block 65, Twp. 7) is an isolated flat-topped hill, composed of Hueco Limestone 

that stands at least 1,200 feet lower than in the mountains (pis. 1, 15; section /-/', pi. 16). Although the 

rock spurs along the fault terminate on an even line, 

they are variously indented by the heads of alluvial 

fans, and there are large reentrants where Sulphur 

Creek and Hackberry Creek enter the Salt Basin. 

Nevertheless, some late faulting may have occurred in 

places. In the northeastern Baylor Mountains narrow 

pediments at the base of the scarp are slightly higher 

than adjacent alluvial deposits on the east; farther 

south the wide pediment cut on Van Horn Sandstone 

near Hackberry Creek terminates in a scarp about 25 

feet high along the edge of the Salt Basin.

Some of the bedrock exposed at the foot of the Baylor 

Mountains, mostly El Paso Limestone, is probably close 

to the East Baylor fault. Northeast of the high point 

of the mountains (BM 5568) the limestone is stained 

red and yellow, is sliced by closely spaced joints, dips 

steeply and erratically, and in places is much brecciated. South of Eed Tank Canyon the El Paso near 

the mountain base dips steeply northwestward, perhaps 

mainly as a result of pre-Hueco deformation. It is 

cut by closely spaced northeastward-trending joints, 

some nearly vertical, others dipping 50°-60° SE., and 

is offset by minor faults downthrown toward the Salt 

Basin, probably related to the main fault at the edge 

of the mountains.

FAULTS ON EAST SIDE OF SALT BASIN

Short segments of faults which border the mountains 

along the east side of the Salt Basin extend into the 

map area in places, one along the Delaware Mountains 

in the northeast corner, another along the Wylie Mountains in the southeast corner (pis. 1, 15).

The part of the Delaware Mountains in the northeast 

corner of the map area is a prominent salient that 

projects westward into the Salt Basin at about midlength in the range (fig. 8). Bedrock ends toward the 

basin along a remarkably even baseline, strikingly 

shown on air photographs, different parts of which 

trend northward, northeastward, and west-northwestward. Behind the base line the mountains rise 1,500 

feet, and are formed nearly to their tops by poorly 

resistant thin-bedded black limestone of the Bone 

Spring Formation. The salient was probably upf aulted 

relatively late in geologic time.

In a canyon about a mile south of the north end of 

the salient (sec. 9, Block 65, Twp. 4), where the faulted 

contact between the black limestone of the mountains 

and the f anglomerate of the basin is well exposed, the 

fault surface is nearly vertical and is followed by a zone 

of calcite 5 feet wide, containing angular fragments of 

black limestone. Stratification in the adjacent bedrock 

is nearly horizontal and shows little indication of internal disturbance.

South of the salient, downfaulted bedrock forms low 

hills at the foot of the high scarp and is tilted toward 

the Salt Basin, although it may be faulted beneath the 

alluvium farther out.

The Wylie Mountains, part of which form the southeast corner of the map area (pis. 1, 15), are bordered 

on the west by the West Wylie fault, which has been 

discussed by Baker (192T, p. 42; 1928, p. 370-371), 

Hay-Eoe (1957), and others. East of the fault is an 

escarpment about 1,200 feet high, at whose base the 

Precambrian Carrizo Mountain Formation emerges
TECTONICS 111

from beneath the Hueco Limestone. West of the fault, 

toward a southern arm of the Salt Basin drained by 

Wildhorse Creek, are hills of downfaulted west-tilted 

Hueco Limestone, partly separated by alluvium. HayRoe (1957) estimates that displacement of the Hueco 

Limestone on the West Wylie fault is about 480 feet. 

The north side of the Wylie Mountains, facing the 

main part of the Salt Basin, forms a moderately 

straight front, much frayed by erosion and indented by 

alluvial valleys. It may be bordered beneath the adjacent alluvium by a fault of nearly east-west trend, as 

suggested on figure 8. However, the throw of this presumed fault cannot be great, as limestone was penetrated above a depth of 950 feet in two wells drilled 

about 4 miles north of the mountains and 8 miles eastnortheast of Van Horn (sec. 19, Block 63) (Leonard A. 

Wood, written commun., 1959).

FAULTS AND RELATED STRUCTURES WITHIN THE 

MOUNTAINS

Many parts of the interiors of the mountains are 

faulted. Faulting is greatest in the mountain salients, 

especially in the northeast corners of the Sierra Diablo 

and Baylor Mountains, where the rocks are split into 

narrow parallel fault blocks. Elsewhere near the 

mountain borders in the Baylor Mountains and Beach 

Mountain, the rocks are broken into rectangular blocks, 

bounded by faults trending in various directions. The 

southern part of the Sierra Diablo is broken into blocks 

several miles wide along parallel faults which die out 

westward, but the northern part is less broken.

The faults in the interiors of the mountains had less 

direct influence on shaping the topography than the 

faults along the borders. Many of the interior faults 

are followed by scarps on their upthrown sides, but 

these scarps are resequent fault-line scarps formed of 

resistant limestones and caused by removal of weak 

beds from the downthrown sides by differential erosion. 

Moreover, along a few faults where rocks on the upthrown sides are weaker, obsequent fault-line scarps 

have formed on resistant rocks on the downthrown sides. 

Probably the faults in the interiors of the mountains 

participated in the main epoch of faulting in late Tertiary time, but they were largely inactive later, when 

there was further displacement on the faults along the 

mountain borders.

Most of the faults in the interior of the Sierra Diablo 

trend west-northwestward. Indications of earlier 

movements on the west-northwesterly faults, discussed 

above, and the prominence of joints of the same trend 

suggest that these faults formed by reactivation of a 

long-persistent grain. Minor west-northwesterly faults 

in the northern part of the Sierra Diablo are downthrown northward, and major west-northwesterly 

faults in the southern part are downthrown southward, 

perhaps on opposite flanks of the area of maximum upheaval during the main period of block faulting. By 

contrast, all the earlier faults and flexures along the 

same trend were downthrown northward, away from a 

positive area on the south.

Toward the east in the Baylor Mountains and Beach 

Mountain, the west-northwesterly faults give place to 

faults trending northeastward and northwestward, 

which variously offset or intersect each other. These 

trends are also reflected in the joint pattern (pi. 15). 

Evidently this expresses a fundamental change in the 

fracture pattern from that in the Sierra Diablo, as 

many of the west-northwesterly faults of that area 

curve eastward into northeasterly or northwesterly 

faults.

NORTHERN PART OF SIERRA DIABLO

The northern half of the Sierra Diablo, north of the 

Victorio flexure, is formed of a thick mass of Permian 

carbonate rocks, with the Victorio Peak Limestone at 

the top. Even-crested ridge summits on this limestone 

are remnants of an exhumed surface on which Cretaceous rocks were once deposited, from which can be 

reconstructed a half dome that was produced by warping after Cretaceous time. The summits rise from an 

altitude of 5,000 feet on the west and southwest to 

6,638 feet at the apex near the North Diablo triangulation station in the northeastern part of the mountains. 

The remainder of the dome beyond, if it ever existed, is 

now broken off along the North Diablo and East Diablo 

faults. Permian rocks of the half dome are warped in 

the same manner as the summits, and the warping probably influenced the configuration of the top of the Precambrian. (See structure contours, pi. 15). Cretaceous rocks form widely spaced outcrops down the slope 

of the half dome on the west, and may underlie the 

alluvium-covered trough which separates it from the 

Victorio flexure on the southwest.

Most of the half dome is little broken, but it is crossed 

by widely spaced faults of small displacement (section 

F-F', pi. 16), trending west-northwestward and downthrown to the north, and by prominent joints trending 

west-northwestward and north-northeastward (pi. 15). 

Some of the faults are prominently exposed on the walls 

of Apache Canyon (pi. 11), where they stand nearly 

vertical; but elsewhere they are expressed by faint 

scarps or alined topographic sags and are less easy to 

trace on-the ground than on air photographs. The 

longest fault zone extends 12 miles east-southeastward 

across the mountains to the north rim of Victorio Oanyon, where it fades out before reaching the edge of the
112 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

mountains in an area of pervasive jointing (pis. 1, 15). 

Weathering along the joints causes a remarkable fluting in the cliffs of Victorio Peak Limestone north of 

Viotorio Canyon.

A small tract in the salient of the Sierra Diablo east 

of Apache Peak has a much more complex structure 

than the rest of the northern part of the Sierra Diablo. 

Here, Permian and earlier Paleozoic rocks are broken 

by as many as six faults in a breadth of a mile or less, 

most of which trend northwestward but with a few ait 

right angles. They are downthrown alternately northeastward and southwestward to create narrow intervening horsts and grabens (section E-E'', pi. 16). The 

faulted tract is bordered on the northeast and east by 

the North Diablo and East Diablo faults, at the edge 

of the Salt Basin, and is separated from the main part 

of the Sierra Diablo on the southwest by a large northwestward-trending fault along which the rocks are 

downthrown as much as 500 feet northeastward.

Location of the tract in a salient between the North 

Diablo and East Diablo faults suggests that it was 

broken during displacement of these faults, perhaps 

rather late in geologic time. The only direct indication 

of late displacements in the tract is the offsetting of 

f elsite sills which lie at the same stratigraphic position 

in adjacent fault blocks. The sills are probably of 

Tertiary age and were injected late in the history of 

the adjacent Marble Canyon-Mine Canyon intrusive 

complex. (See section, "Igneous rocks," p. 92.)

SOUTHERN PART OF SIERRA DIABLO

In the southern half of the Sierra Diablo, south of 

the Victorio flexure, Hueco Limestone at the base of the 

Permian sequence forms the country rock over extensive 

areas and Precambrian and Precambrian (?) rocks, 

mainly sandstones of the Hazel and Van Horn Formations, lie near the surface. Structurally the southern 

half of the Sierra Diablo differs much from the northern, being a succession of north-tilted blocks several 

miles broad trending west-northwest and downthrown 

to the south (pis. 1,15,16).

On the Victorio flexure between the two halves of the 

Sierra Diablo, Permian rocks are tilted northward. The 

flexed Permian rocks may overlie a larger fault or flexure beneath (fig. 2; section N-N', pi. 16), which separates an area of high-standing Precambrian rocks on 

the south from one of low-standing Precambrian rocks 

on the north. (See structure contours, pi. 15.) Unlike 

the other structures of the southern half of the Sierra 

Diablo, the flexure is largely a pre-Cretaceous feature. 

(See p. 105-106.) Although it trends in the same direction as the faults farther south, it is not faulted. 

Toward the east its tilted Permian rocks are truncated

by the exhumed pre-Cretaceous surface, on which a few 

outliers of Cretaceous rocks are preserved. Toward the 

west, however, broad flexures and folds in the Cretaceous rocks follow the same trend (pis. 1, 15) and continue beyond the map area (fig. 8).

The faults of the southern part of the Sierra Diablo 

involve mainly the Hueco Limestone, which forms maturely dissected scarps on their upthrown sides, the 

height of some of which nearly equals the fault displacement. Along a few of the faults Cretaceous rocks 

are preserved on the downthrown sides. These may 

have covered much of the Sierra Diablo region at the 

time of the faulting, but were afterwards largely removed by erosion to produce resequent fault-line scarps 

in the limestone. Dissection of the scarps is enhanced 

where formations beneath the Hueco emerge especially 

the poorly resistant red sandstone of the Hazel Formation. Where the red sandstone is exposed, the scarps 

are irregularly frayed and in places have retreated a 

mile or more from the faults.

The faults are named, from north to south, the Bat 

Cave fault, Cox Mountain fault, Sulphur Creek fault, 

Sheep Peak fault, Circle Ranch fault zone, and South 

Diablo fault. Each fault originates near the eastern 

border of the mountain block and dies out westward in 

plateau country beyond the mountains (pis. 1, 15). 

The Cox Mountain and South Diablo faults extend 20 

miles across the map area and the latter continues at 

least 10 miles farther west, but the other faults are 

shorter. The Cox Mountain, Sheep Peak, and South 

Diablo faults are displaced more than a thousand feet 

in places, but most of the others were displaced a few 

hundred feet or less (pi. 16).

Long segments of the faults have nearly straight or 

gently curved traces, but the Sheep Peak and Sulphur 

Creek faults branch eastward. The Circle Ranch fault 

zone is not a continuous line of displacement, but consists of many minor faults, lying partly parallel, partly 

en echelon or branched, which separate two blocks that 

are less disturbed. The South Diablo fault, although a 

zone of continuous major displacement, consists of many 

segments of slightly different trend from which minor 

faults branch eastward on each side.

Toward the east the faults pass from the Hueco Limestone into the homogeneous red sandstone of the Hazel 

Formation, where their courses are difficult to trace on 

the ground. The Bat Cave and Cox Mountain faults 

may abut the East Diablo fault at the edge of the mountain block at nearly right angles, but the junctions are 

covered by alluvium. The Sulphur Creek fault is readily traceable on air photographs through the red sandstone to an acute-angled junction with the south end of 

the East Diablo fault between Beach Mountain and the
TECTONICS 113

Baylor Mountains. The Sheep Peak, Circle Ranch, and 

South Diablo faults appear from air photographs to 

die out in the red sandstone within short distances east 

of the scarps of Hueco Limestone, but other faults of 

similar trend, lying en echelon, continue into Beach 

Mountain (pis. 1,15).

Westward, all the faults except the South Diablo fault 

lose displacement and die out within the map area, but 

the disturbance on some is extended a short distance 

farther by flexures or folds. An abrupt flexure continues 2 miles beyond the end of the Sheep Peak fault, 

and a broad anticline occurs at the end of the Cox Mountain fault.

The planes of all the faults dip steeply, where visible. 

A steep dip toward the downthrow was observed on the 

Sheep Peak fault south of Sheep Peak and on the South 

Diablo fault north of the Keen Eanch. Similar steep 

dips may be inferred where the Bat Cave, Cox Mountain, and Sulphur Creek faults cross the cliffs of Hueco 

Limestone on the east-facing escarpment of the Sierra 

Diablo. However, a fault on the^xtension of the Sheep 

Peak fault, where exposed in a Hueco Limestone cliff 

ly^ miles west of the Hazel mine, dips 60° N. toward 

the upthrown block. In a few places, as on the Cox 

Mountain fault west of the Pecos mine and the Sheep 

Peak fault west of Sheep Peak, calcite veins occur in 

the Hueco Limestone at or near the fault planes. The 

veins contain limonite and hematite, perhaps weathered 

from original sulfide minerals. Where the faults involve Hueco Limestone and Cretaceous formations, these 

rocks are dragged steeply on the downthrown sides, 

whereas the rocks on the upthrown sides are little disturbed. In some places, as on faults of the Circle 

Eanch zone southeast of the Circle Eanch, displacement 

by drag is greater than on the fault itself.

BAYLOR MOUNTAINS

The Baylor Mountains form an irregular quadrilateral block 9 miles long and 7 miles wide, implanted in 

the southern bight of the East Diablo fault. Their 

summits are about a thousand feet lower than those of 

the Sierra Diablo on the west and about a thousand feet 

higher than the floor of the Salt Basin on the east and 

north. The mountains are bordered on all sides by 

faults the East Diablo, North Baylor, and East Baylor faults and are a block that stands at an intermediate level between the heights of the Sierra Diablo 

and the depths of the Salt Basin. They consist of a 

plate of Permian rocks, whose foundation of earlier 

Paleozoic rocks crops out around the edges (pi. 1). 

The Permian rocks are flat lying or gently tilted, except 

at the northeast corner of the mountains where they dip

more steeply northward, probably along an eastward 

extension of the Victorio flexure.

The rocks of the interior of the Baylor Mountains are 

greatly faulted on the northeastern and southeastern 

sides, where many narrow blocks have been downdropped away from a less disturbed nucleus in the westcentral part. As in the greatly faulted northeastern 

salient of the Sierra Diablo, these blocks seemingly 

broke away from the more stable mountain area during 

displacement of the major faults on the northern and 

eastern sides of the mountains.

The internal faults are of two systems, one in the 

northeastern part which trends northwest, the other in 

the southeastern part which trends northeast. Those in 

the northeastern part are a quarter of a mile to a mile 

apart, but branch or interlace. Most are downthrown 

toward the northeast, dropping the intervening blocks 

toward the salient of the mountains (section $-/S", pi. 

16). The traces of the faults across steep hills indicate 

that they stand nearly vertical. One of the longer 

faults near the center of the mountains extends northwestward to the East Diablo fault, where it apparently 

matches a fault of west-northwest trend on the Sierra 

Diablo escarpment to the west. Exposures are insufficient to determine the exact relations of the two faults 

to each other, or to the East Diablo fault. The faults 

in the southeastern part are fewer. One pair, with a 

curvature convex toward the southeast, bounds a narrow 

outlying block of Montoya Dolomite, and another set 

extends discontinuously along Eed Tank Canyon. On 

one of the faults in Eed Tank Canyon a small remnant 

of Cretaceous sandstone is preserved on the downthrown 

side. The faults of the two trends intersect near Eed 

Tank Canyon on the eastern side of the mountains, 

where many of the northwest-trending faults abut the 

northeast-trending faults.

BEACH MOUNTAIN AND VICINITY

Beach Mountain, which borders the Salt Basin south 

of the Baylor Mountains, is a smaller mass which projects as high as or higher than the latter (pi. 2). Unlike the Baylor Mountains it is formed largely of Ordovician carbonate rocks. It is an erosion remnant rather 

than a fault block and is not structurally separated from 

the main block of the Sierra Diablo on the west. Like 

the Baylor Mountains it is much broken internally by 

two systems of faults trending nearly at right angles 

(pis. 1,15).

One system includes the Grapevine and Carrizo 

Spring faults (sections R-R' and S-Sf, pi. 16). Faults 

of the system originate in the Precambrian rocks west 

of Beach Mountain, where they trend west-northwest 

or west, but in the mountain they curve into east-north-
114 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

eastward or northeastward courses. The traces of the 

faults across the steep western face of the mountain indicate that they stand nearly vertical. In Beach Mountain the faults involve Ordovician formations and Hueco 

Limestone and were probably displaced during late 

Tertiary time, but the Grapevine fault and perhaps the 

Carrizo Spring fault had a considerable prior history. 

(See p. 103.) On the Grapevine fault deformed Hazel 

Formation was offset with left-lateral strike-slip displacement, probably during late Precambrian time, and 

the Van Horn Sandstone was downthrown to the south 

before Bliss time.

The faults of the second system, like those of the first, 

seemingly originate toward the west in the west-northwesterly system of the Sierra Diablo, but in Beach 

Mountain they curve into northwestward or northnorthwestward courses. This is shown most clearly by 

a branch of the Sulphur Creek fault which curves southwUrd into the northern part of Beach Mountain, where 

a thick sequence of El Paso and Montoya Formations 

is preserved on its downthrown eastern side (lower 

view, pi. 2). Like faults of the first system, some of 

those of the second were displaced before late Tertiary 

time. The Van Horn Sandstone was downthrown to 

the east along the Dallas fault before Bliss time and the 

fault was not displaced again later (see p. 102-103), yet 

it is parallel to others of the same trend which displace 

Ordovician formations and the Hueco Limestone.

The two fault systems meet complexly in the eastcentral part of Beach Mountain (pis. 1, 15). Faults 

trending north-northwest terminate against the Grapevine fault, but the Carrizo Spring fault terminates eastward against a fault of north-northwest trend. The 

Hueco Limestone at the east end of the mountain (section J-J', pi. 16) is preserved in a block that is bounded 

on the west and north by faults of the two intersecting 

systems.

HILLSIDE FAULT AND RELATED STRUCTURES

The Hillside fault forms a major line of discontinuity 

in the southern part of the map area, between the Carrizo Mountain Formation and associated igneous rocks 

on the south and the Van Horn Sandstone, Hueco Limestone, and Cretaceous formations on the north. It extends west-northwest along the northern side of the 

Carrizo Mountains for a known distance of 8 miles, terminating eastward against the East Baylor fault near 

Van Horn and disappearing westward beneath the alluvium of Eagle Flat near Allamoore (pis. 1, 15).

Through most of its course the Hillside fault is followed on its northern downthrown side by a prominent 

escarpment of Hueco Limestone and Cretaceous formations as much as 500 feet high. This is an obsequent 

fault-line scarp, formed by more rapid erosion of the

Carrizo Mountain Formation and associated igneous 

rocks on the southern upthrown side. The valley which 

has been eroded south of the scarp is followed by the 

line of the Texas and Pacific Railway in its course 

through the Carrizo Mountains from the Salt Basin to 

Eagle Flat. A major displacement on the fault occurred after Cretaceous time, perhaps during the late 

Tertiary, but erosional features along it indicate that 

it has been inactive since.

An earlier movement on the Hillside fault is indicated by the Powwow Member at the base of the Hueco 

Limestone north of the fault, in which fragments of 

metarhyolite derived from south of the fault increase 

in size and abundance toward it. Presumably newly upfaulted metarhyolite projected as a scarp along the fault 

at the time of deposition of the Powwow Member (fig. 

2). These relations show further that no significant 

strike-slip displacement could have occurred along the 

fault during or since Hueco time, for the fragments in 

the Powwow Member on the northern side match rocks 

in place on the immediately adjacent southern side.

The Hillside fault forms the southern boundary of 

the thick bodies of Van Horn Sandstone in the Sierra 

Diablo region (pi. 1), and to the south the Powwow 

Member of the Hueco Limestone generally lies on the 

Carrizo Mountain Formation and associated igneous 

rocks. The boundary is not absolute, however, as a few 

thin remnants of Van Horn are preserved south of the 

fault along the eastern side of the Carrizo Mountains.

Toward the western end of the Hillside fault near 

the Gifford-Hill rock crusher (sec. 28, Block 67, Twp. 

8), Cretaceous formations are downthrown northward 

against metarhyolite, and the displacement probably 

much exceeds 1,000 feet (section T-T1', pi. 16). Equally great displacement must have occurred several miles 

farther east (sec. 16, Block 66, Twp. 9) where Hueco 

Limestone, lying on Van Horn Sandstone and topped 

by a Cretaceous outlier, forms a high scarp north of 

the fault (section Q-Q'', pi. 16). Flawn (in King, P. 

B., and Flawn, P. T., 1953, p. 115) reports that on the 

south side of the fault a mile east of the rock crusher, 

a small patch of Powwow Member of the Hueco Limestone lies on metarhyolite, indicating not only that part 

of the displacement occured before Hueco time, but 

that the post-Hueco displacement is less than at nearby 

localities; however, the patch of Powwow may lie in 

a wedge that was displaced less than the main fault 

block to the south.

The surface of the Hillside fault, or rocks close to it, 

is exposed at several places in the segment extending 

2 miles east from the rock crusher. In the easternmost 

exposure, metarhyolite is separated from the Van Horn 

Sandstone by a nearly vertical zone of brecciated quartz
TECTONICS 115

along the fault plane, the Van Horn to the north being 

bleached and closely jointed. Farther west the metarhyolite close to the fault contains several steeply dipping zones of breccia, which crop out in wall-like ridges. 

One zone dips 70° S., but may follow the foliation 

planes of the metarhyolite, rather than the fault plane. 

In this vicinity fragments in the Powwow Member 

north of the fault have been shattered by later deformation.

North of the Hillside fault in the eastern half of its 

trace, the Hueco Limestone and adjacent Van Horn 

Sandstone are broken by four or five minor 

faults trending north-northwest, the western group of 

which extends nearly across the Ked Valley to the Carrizo Spring fault. In an exposure of one of the western minor faults, its surface dips 80° E., toward the 

downthrow. The minor faults reflect a pervasive fracturing of the block north of the fault along the same 

trend, as shown by abundant joints in the Hueco Limestone and Van Horn Sandstone which also trend northnorthwest (pi. 15).

The Hillside fault may be part of a zone of faulting 

which extends somewhat farther east and west. It is 

nearly in line with the north side of the Wylie Mountains across the Salt Basin to the east, which may be 

bordered beneath the alluvium by a minor fault, likewise downthrown to the north (fig. 8). About 10 miles 

west of the known terminus of the Hillside fault, along 

the southern edge of the Streemwitz Hills, are ridges 

and knobs of Hueco Limestone, tilted southward, 

which may lie in a fault zone between the hills and the 

tectonic depression of Eagle Flat (sections K-K', pi. 

16). This fault zone may continue farther east and 

west, but relations are concealed beneath the alluvial 

plains along the north side of the flat. The inferred 

fault zone has about the same trend as the Hillside 

fault, but is downthrown southward, in the opposite 

direction.

The Hillside fault lias been ascribed an inordinate 

role in the tectonics of the region by Moody and Hill 

(1956, p. 1223-1224), who interpret it as a major element in the "Texas lineament" (Kaiisome, 1915, p. 295; 

Baker, 1935a, p. 211-214; Albritton and Smith, 1957), 

extending westward through the gap between Sierra 

Blanca and the Quitman Mountains (fig. 1), and perhaps past the south end of the Franklin Mountains near 

El Paso. They believe that it "represents a large-scale 

left-lateral wrench fault" and that the structures in the 

Mesozoic rocks south of Sierra Blanca are "secondorder drag folds relative to this wrench."

This interpretation is not supported by local geologic 

relations. The composition of the Powwow Member 

north of the Hillside fault indicates that no significant 

strike-slip movement could have occurred on the fault

during or since Hueco time. There is no indication of 

an extension of the Hillside fault zone west of the 

Streemwitz Hills or east of Wylie Mountains. Neither 

in the gap between Sierra Blanca and the Quitman 

Mountains on the west; nor between the Apache Mountains and Davis Mountains on the east does the structure permit the existence of a throughgoing strike-slip 

fault. The folds and faults in the Mesozoic rocks south 

of Sierra Blanca are part of the Chihuahua tectonic 

belt, a regional feature that extends far south westward 

and southeastward from the Hillside fault. Left-lateral strike-slip displacements have been observed on 

minor faults in the Precambrian rocks north of the 

Hillside fault (see p. 102-103), but there is no indication that these faults were displaced in this manner 

after Precambrian time.

JOINTS

The writer made systematic observations on the joints 

in the Sierra Diablo region, similar to those made earlier in the southern Guadalupe Mountains (King, P. B., 

1948, p. 114-117, pi. 20). Summaries of the joints iii 

the Sierra Diablo region have been published previously (King, P. B., and Knight, J. B., 1944, structure 

map; King, P. B,., and Flawii, P. T., 1953 pi. 10), but 

further details are given here (pi. 15).

All the rocks of the Sierra Diablo region are cut by 

many joints. Those in the greatly deformed Precambrian formations trend in diverse directions, dip at all 

angles from horizontal to vertical, and are so complex 

that it was not considered worth the effort to record or 

analyze them. Those in the younger gently dipping 

stratified rocks the Van Horn Sandstone, the Paleo'- 

zoic formations, and the Cretaceous formations dip 

steeply and are arranged in systematic patterns that are 

susceptible of measurement and study. Steeply dipping joints also occur in the gently tilted parts of the 

Hazel Formation, along with other joints inclined at 

lower angles, and some of these are recorded 011 the 

map (pi. 15).

Most of the steeply dipping joints in all the stratified formations are straight and smooth, even where 

they cut through irregularly bedded rocks or alternations of hard and soft strata. At the surface some 

of the joints are open fissures, but these probably were 

enlarged by weathering, and most of them narrow and 

tighten at depth. Single joints commonly extend across 

the entire breadth of any exposure, and where several 

sets occur, most of them, cross one another without deflection. Spacing of the joints depends on the nature 

of the rock; they are widely spaced in massive rocks, 

such as the Van Horn and Cox Sandstones, and are 

closely spaced in thin-bedded brittle rocks, such as the 

Ordovician and Permian limestones and dolomites.
116 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Nearly all the joints dip steeply or stand nearly vertical. During the field investigation, conspicuous deviations of the joints from the vertical were recorded, 

but it was found that such deviations were so slight 

that they could be ignored. The most significant features of the joints appear to be their trends in horizontal plan, and the largest number of observations 

were made on these trends. On the map (pi. 15) the 

trends of joints are summarized by two methods:

1. Joints at individual stations are shown by lines of 

various lengths, radiating from the point of observation. Records made at the stations commonly consisted 

of measurements at two or more points in the immediate 

vicinity, at each of which all joints were recorded, and 

notations were made of the dip and prominence of each; 

observations at a station may include as many as 20 

individual measurements. It is impossible to represent 

all these measurements on the map (pi. 15); joints at 

each station are accordingly summarized, the most abundant four or five joint sets being plotted, with lengths 

of lines indicating their relative prominence. Besides 

the joints which were measured on the ground, joints 

which are prominent in air photographs are also indicated.

2. Joints are further summarized statistically by 

rosettes, which are overprinted at various places on the 

map (pi. 15). For purposes of summary the observations are grouped according to tectonic units of different ages and according to locality. Separate statistical summaries were made for joints of the Van Horn 

Sandstone, the Ordovician to Pennsylvanian rocks, the 

Permian rocks, and the Cretaceous rocks, each rock 

group representing a tectonic unit separated from the 

others by a significant structural unconformity. Occurrence of joints in the different tectonic units was 

further segregated into structurally significant units 

of area, whose boundaries are shown in an inset map 

accompanying plate 15.

Each rosette shows the relative abundance and prominence of the joints of various trends that were measured in each stratigraphic and areal unit. A tally was 

made of the number of joints in each 5° of arc, and 

each tally was converted into a percentage of the total 

number recorded. As a check, a tally was also made of 

the prominence of the different joint sets observed. 

This tally was found to agree closely with the number 

of joints of each set which were observed, indicating 

that the most abundant joints also tend to be the most 

prominent joints. As originally worked out, wide variations were found between percentages at some of the 

adjacent points on the arcs, probably because of a personal equation in making the observations. The percentages were therefore evened by means of moving

averages. Each figure used in plotting the rosettes is 

thus the average of the original percentage for the 

direction shown, and the percentage of the two directions lying 5° on each side of it. To indicate the amount 

of information available for each unit summarized, the 

number of stations and number of observations used 

are marked by the different rosettes.

Observations on the trends of the joints are of interest, for they amplify and fill in the fracture pattern of 

the rocks which is otherwise only partly suggested by 

the fault pattern.

In the fault block formed by the Sierra Diablo and 

its foothills to the north and south, the dominant joints 

trend west-northwest, parallel to the west-northwesttrending faults and flexures of the same area. These 

joints dominate, not only near the faults and flexures, 

but also where the rocks are otherwise little disturbed. 

The next most abundant joints, in places of nearly equal 

magnitude, trend nearly at right angles to the northnortheast. Ordinarily, these joints are not followed by 

any faults, suggesting some fundamental difference in 

their nature. The remaining joints trend in all directions between those of the dominant sets, but in many of 

the units summarized two maxima are indicated on the 

rosettes that are about midway between the trends of 

the two dominant sets. A striking feature in the Sierra 

Diablo block is the subordination of joints trending 

northward parallel to the faults of northerly trend 

which border the range. As shown on the map (pi. 15), 

some north-trending joints are recorded close to the East 

Diablo fault, but their number is insufficient to influence 

significantly the form of the rosettes.

Eastward in the Baylor Mountains and Beach Mountain, the joint pattern changes significantly in the same 

manner as the fault pattern. Here, two joint sets of 

nearly equal magnitude trend northeast and northwest, 

in the same directions as the faults. In the Red Valley 

north of the Hillside fault, where minor faults trend 

north to north-northwest, a prominent joint set in the 

same direction is recorded by the rosettes (pi. 15).

Subdivision of the recorded joints according to tectonic units was made primarily to test the possibility 

of significant differences between jointing in rocks of 

different ages, but the results are inconclusive. Although there are differences in the patterns of rosettes 

in rocks of various ages in the same units of area, these 

seem less likely to be caused by differences in age than 

by differences in amounts of data, or by differences in 

susceptibility to jointing of the rocks themselves. In 

many areas, for example, the rosette for the Permian 

rocks shows many joints in all directions with poorly 

defined maxima, whereas rosettes for the Van Horn 

Sandstone and the Cretaceous rocks show much better
TECTONICS 117

defined maxima. This is partly because more observations were made on the extensively exposed Permian 

rocks, partly because the Permian carbonate rocks fractured more diversely than the dominant sandstones of 

the other two units. The dominant joint trends in rocks 

of different ages in the same unit areas thus appear to 

bo nearly alike.

This suggests that the dominant joint pattern in all 

the rocks might be less closely related to the earlier 

orogenies than it is to the upheaval of the mountain 

blocks in late Tertiary and Quaternary time. It seems 

unlikely, however, that rocks which have been in process of accumulation and deformation since Precambrian 

time could have remained without fractures until such 

a late period. Moreover, evidence so far presented indicates that faulting and flexing along a west-northwest 

trend has recurred many times in the history of the area. 

It would thus appear that joints related to this trend, 

and perhaps others, formed long before the latest upheaval, and were renewed in successively younger rocks 

that were laid down unconformably over the older.

BEGIONAL INTEBPBETATIOET AND SYNTHESIS

The structure of the Sierra Diablo and surrounding 

regions is dominated by a network of faults (pi. 15, 

fig. 8) that formed in later Cenozoic time. The faults 

are a product of the stress pattern which existed at the 

time, and would seem to be capable of mechanical 

analysis on that basis. Such an analysis is made difficult, however, by the extensive prior tectonic history of 

the region. At least part of the faulting resulted from 

reactivation of earlier faults and flexures, which were 

created by forces different from those which prevailed 

during later Cenozoic time. Once created, these earlier 

faults and flexures became zones of weakness which 

could be utilized afterwards by new forces with new 

orientations.

The fault network of the region consists principally 

of two sets of faults and related features, one trending 

northward, the other west-northwestward, which cross 

or intersect in a complex manner (fig. 8). The northward-trending set dominates, and may be most closely 

related to the stresses existing during later Cenozoic 

time; the west-northwestward-trending set is mainly 

subordinate, and may have formed principally by reactivation of earlier zones of weakness.

The northward-trending structures extend far northwestward beyond the Sierra Diablo into New Mexico, 

and perhaps westward into Chihuahua, but they die out 

southward in Trans-Pecos Texas. Throughout their 

extent they largely control the modern topography, 

attesting the relative recency of their formation. They 

thus outline the Salt Basin and the mountains which

adjoin it, such as the Sierra Diablo. Along the edges 

of the Salt Basin the latest faults of Pleistocene age are 

of northerly trend. In the Guadalupe and Delaware 

Mountains the principal northward-trending structure 

is an arch, fractured along its crest by longitudinal 

faults and joints (King, P. B., 1948, p. 109), but in the 

Sierra Diablo and adjacent mountains, the principal 

structures are fault blocks which have been little arched 

or flexed. The northward-trending structures of 

Trans-Pecos Texas and New Mexico are seemingly 

products of a regional tension, whose axis of least stress 

was oriented approximately east and west.

Along the edges of the Sierra Diablo the northwardtrending structures break across the west-northwestward-trending structures, as though these largely 

originated earlier. Within the range the dominant 

faults and joints trend west-northwest, and northwardtrending structures are scantily represented, if at all 

(pi. 15). Nevertheless, west-northwestward-trending 

structures significantly truncate or offset northwardtrending structures in other places, especially in the 

Apache Mountains east of the Sierra Diablo. Also, the 

Salt Basin is peculiarly segmented, apparently by westnorthwestward-trending faults that extend short distances into the ranges which border it (fig. 8). Each 

segment is offset left laterally from the ones on either 

side, suggesting a possible strike-slip displacement 

along the west-northwestward-trending faults which 

bound them. Nevertheless, no such displacements can 

be observed where these faults enter the adjoining 

ranges. It seems more likely that the northward-trending structures, during their formation, reactivated an 

earlier west-northwestward-trending grain, and were 

modified by it.

Evidence has been presented (p. 102-103, 105-106, 

111-115) that the west-northwestward-trending structures were intermittently displaced between late Precambrian and late Cenozoic time. Faults of this trend 

that are of late Precambrian age can be proved with 

certainty at only a few places, yet the fact that they 

exist at all suggests that a grain of this trend originated 

in the Precambrian basement early in the history of the 

region and controlled the structures formed during later 

tectonic episodes, in strata of younger ages laid down 

over the basement. Many of the faults of west-northwesterly trend that are of late Precambrian age have 

left-lateral strike-slip displacements of a mile or less; 

but no strike-slip displacement can be proved on faults 

of similar trend in the younger rocks, and on some of the 

faults there is evidence against such a displacement. 

The conglomerate of the Powwow Member of the Hueco 

Limestone on the north side of the Hillside fault was 

derived from a source just south of the fault, and dem-
118 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

onstrates that no strike-slip displacement occurred along 

it during Permian time or later.

Seemingly, then, the forces which caused the subsequent flexing and faulting of the west-northwestwardtrending structures were of a different kind and orientation from those of late Precambrian time, and were 

merely guided by the lines of weakness already established. Some of the structures, as those formed during 

the pre-Hueco deformation of later Pennsylvanian time, 

were products of a mild compressional folding. Succeeding structures may have been dominantly tensional 

and the incidental products of dominantly vertical 

movements that created major positive and negative 

areas. During Permian time such vertical movements 

differentiated the positive area of the Diablo platform 

from the negative area of the Delaware basin on the 

northeast; during Cretaceous time similar movements 

differentiated the positive area from a geosynclinal area 

on the southwest.

The discussion so far indicates the local causes for the 

west-northwestward-trending structures. Are they 

also a product of more fundamental regional causes, 

and are they merely a segment of a large regional feature? Some geologists (Hill, 1902, p. 173; Ransome, 

1915, p. 295; Baker, 1935a, p. 211-214; Moody and Hill, 

1956, p. 1223-1224; Albritton and Smith, 195T) ascribe 

them to the "Texas lineament," a supposed major structure that is believed to extend across south-centra] 

North America from the Pacific to the Gulf Coast. 

The original definition of this structure by Ransome 

(op. cit.) is of interest:

[It] coincides in general with the southwest boundary of the 

Colorado Plateaus and with the valley of the Rio Grande. It is 

along this general line that the uplifted masses of Paleozoic 

rocks of the Colorado Plateau province, as in the Franklin 

Mountains near El Paso, look out to the south over the Cretaceous terrain of the Mexican Plateau. Mr. R. T. Hill has called 

attention to this feature in several of his papers and points out 

that in the Trans-Pecos Region it coincides with a zone of faulting which is older than the north-south faults to which the 

bolder topographic features are due. The entire, rather vaguely 

defined and perhaps in part imaginary, zone from the Pacific 

to the Gulf of Mexico may be called the Texas lineament.

Subsequent proponents of the Texas lineament do 

not mention Ransome's filial unflattering, but probably 

just, characterization of this feature.

Baker (1935a, p. 212) extends the Texas lineament 

as described by Ransome "from Point Conception on 

the Pacific coast of southern California to Cape San 

Roque, the easternmost point of South America, the 

zone determining the northeastern coast line of South 

America and passing through the island of Cuba"; he 

proposes that it be renamed the "Hill intercontinental 

lineament." Moody and Hill (1956, fig. 11) believe 

that the lineament is a zone of "wrench faults" with

left-lateral strike-slip displacement. Albritton and 

Smith (1957, p. 515) conclude that "after more than 

half a century, the idea of the Texas lineament remains 

in the class of plausible hypothesis."

The substance of these proposals seems to be that the 

alleged lineament forms a zone between more stable and 

less stable parts of the continental crust between a 

mainly cratonic area on the north, as in the Colorado 

Plateau, and a mobile area on the south, in the southern 

part of the Basin and Range province and the ranges 

of Mexico. In places, as in the Transverse Ranges of 

California, the zone contains faults with left-lateral 

strike-slip displacement. In others, as in Arizona and 

Trans-Pecos Texas, the zone marks the passage from a 

dominantly thrust-faulted terrain on the south to a 

dominantly block-faulted terrain on the north. Moreover, the Transverse Ranges of California are alined 

with the lengthy Murray f racture zone of the Pacific 

Ocean basin on the west, which probably involves a 

strike-slip displacement of the oceanic crust (Menard, 

1955, p. 1164-1167).

Whether any persistent throughgoing structures exist 

along the lineament in the continental crust is doubtful. 

Even conceding transverse faults in gaps between the 

ranges of the southern part of the Basin and Range 

province, which would now be concealed from detection 

by unconsolidated deposits, no lengthy structures, due 

to more than local causes, can be proved. No rift features comparable to those along active faults with 

strike-slip displacement occur east of California.

It would therefore appear that the Texas lineament 

marks rather vaguely a boundary between parts of the 

continental crust of North America that have possessed 

different degrees of mobility through geologic time, 

that these differences in mobility have influenced the 

development of varied local structures, such as those of 

west-northwest trend in the Sierra Diablo region, but 

that the differentiation has not been of sufficient magnitude to produce any throughgoing structures comparable to the great faults of California or the fracture 

zones of the Pacific Ocean basin.

ECONOMIC GEOLOGY

Metallic and nonmetallic mineral deposits of the 

Sierra Diablo region are varied. Some of these deposits 

have yielded or continue to yield profitable production, 

and others may be capable of later exploitation; but 

many are too small or of too low a grade to be of economic interest. The region has also been extensively 

drilled with varying success for water, and in a few 

places unsuccessfully for oil and gas. Most of these resources have been described in various earlier publications, and are merely summarized here.
ECONOMIC GEOLOGY 119

COPPER AND SILVER 6

Vein deposits containing metallic sulfide minerals 

occur in a number of places in the Precambrian rocks in 

the eastern part of the foothills of the Sierra Diablo, 

and to a lesser extent in the Carrizo Mountains. Ore has 

been produced intermittently from several mines since 

1880, and the veins in other places have been explored 

by many prospects. The principal metals of the deposits are copper and silver, but some deposits also contain zinc and lead. Some rich pockets of ore were discovered during the early days of mining, but most of 

the ores of the district are of low grade, averaging about 

21^3 to 3 percent of copper.

The most prolific mine in the district is the Hazel, 

which lies near the foot of the Sierra Diablo 10 miles 

northwest of Van Horn (sec. 14, Block 66, Twp. 7). It 

is one of the oldest mines in Texas, and the largest proucer of copper in the State. Moderate amounts of ore 

have also been produced from the Blackshaft and 

Sancho Panza mines a few miles to the southwest, but 

production from the remaining mines and prospects has 

been much less. Total production of the district is difficult to estimate because records are fragmentary, and 

are generally lacking for the period before 1900. A 

possible 'approximation is 140,000 tons of ore, yielding 

2,700,000 pounds of copper and 4,000,000 ounces of 

silver.

The copper and silver deposits occur in four principal 

associations, of which only two have yielded production:

1. Deposits of Hazel type lie in the northern part of 

the district, near the foot of the scarps of the southeastern angle of the Sierra Diablo. These deposits are 

in vertical fissure veins or mineralized fractures, lying 

in gently dipping compact red sandstone of the Hazel 

Formation. The veins are commonly indicated in surface outcrops by bleaching of the red sandstones immediately adjacent. They consist of zones a few feet 

to 40 feet wide of bleached, brecciated, and sliced country rock, interlaced with a gangue of barite and other 

minerals, which contain sulfides of copper, silver, and 

other metals. The deposits of Hazel type are not haphazardly located, but occur along two fracture zones. 

The Hazel fracture zone, about &y2 miles in length, 

trends nearly east and west and contains deposits of the 

Hazel mine, Marvin-Judson prospect, and Mohawk 

mine (pis. 1, 15). The Pecos fracture zone, about 2 

miles in length, trends north-northeast and contains the 

deposits of the Pecos mine and Eureka prospect.

2. Deposits of Blackshaft type occur in a belt about 

iy2 miles long just north of the Millican Hills, and

"See King, P. B., and Flawn, P. T. (1953, p. 149-168), which contains detailed descriptions of the mines and prospects and references 

to earlier publications.

have been worked in the Blackshaft, St. Elmo, and 

Sancho Panza mines (pi. 1). Deposits of Blackshaft 

type are in crushed, sheared, and silicified limestone, 

phyllite, and igneous rock of the Allamoore Formation, 

and in associated fault gouge, which together form a 

bed a few feet thick along a low-angle thrust fault, enclosed by the Hazel Formation. The bed is folded into 

an irregular east-plunging syncline, so that it dips 

steeply in the southeastern part and very gently in the 

northwestern part, where it crops out over a wide area 

and is susceptible to opencut mining. The crushed and 

sheared rock of the Allamoore Formation has been 

veined and replaced by gangue minerals and metallic 

sulfides, principally of copper, although there are scattered rich silver-bearing pockets.

3. Other deposits have been prospected in the Allamoore Formation of the Millican Hills and the Carrizo 

Mountain Formation of the Carrizo Mountains. In the 

workings of all these prospects mineralization seems to 

have taken place in narrow unsystematic veins and veinlets, with little replacement of limestone or other host 

rocks. Prospecting so far has failed to yield any 

sizable ore bodies, and no ore is known to have been 

produced from the deposits.

4. Another type of deposit occurs only at the Dallas 

mine on the west side of Beach Mountain (pi. 1). Here, 

a fault of pre-Ordovician (pre-Bliss) age has thrown 

the Van Horn Sandstone down against the Allamoore 

Formation, and the limestone of the Allamoore adjacent 

to the fault has been veined and mineralized. No ore 

is known to have been produced from this deposit.

Although these deposits occur in varied structural 

situations, the deposits themselves are of such a similar 

makeup as to suggest that they all formed from a common cause at the same time. The deposits are dominantly in Precambrian rocks, and similar deposits are 

only scantily developed in the adjacent Paleozoic and 

Cretaceous rocks. In all the deposits, narrow previously formed zones of weakness in the country rock 

were later veined and replaced by gangue and metallic 

minerals brought in by hydrothermal solutions. The 

zones of weakness in the Blackshaft type of deposits 

were formed during Precambrian time; those of the 

Dallas mine originated between Precambrian (?) and 

Ordovician time; the age of the zones of weakness of 

the Hazel type of deposits is unknown.

Regional considerations suggest that the metallic ore 

deposits of the district were emplaced hi the zones of 

weakness during Tertiary time. Paleozoic and Cretaceous rocks contain mineral deposits in the Eagle and 

Quitman Mountains not far to the southwest in TransPecos Texas, and similar deposits are widely distributed 

in adjacent parts of Chihuahua and New Mexico.
120 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Tertiary intrusive and volcanic rocks are also common 

throughout the region. The ore deposits in the district 

may be principally in the Precambrian rocks, not because the deposits are old, but because the Precambrian 

rocks were lower and nearer the source of hydrothermal 

solutions, and because the Precambrian rocks have been 

much more deformed and fractured than the Paleozoic 

and later rocks which overlie them.

TUNGSTEN AND BERYLLIUM

The Mine Canyon stock in the northeastern part of 

the Sierra Diablo (sec. 20, Block 66, Twp. 5) has been 

sporadically prospected for many years for tungsten 

and other metals. The most extensive work was done 

in 1940 and 1941, by William Eossman of Pecos, Tex., 

who put more than a thousand feet of adits and shafts 

into the slopes of Cave Peak.

The light rhyolite breccia of the stock has been somewhat mineralized throughout, as indicated by extensive 

iron staining of weathered surfaces. Most of the introduced minerals occur in narrow veinlets which trend 

westward, northwestward, and northward; the veinlets 

are 3 inches or less thick, and fray out into joints within 

50 or 100 feet along the strike. According to S. G. 

Lasky (written commun., 1941), the dominant mineral 

is pyrite, but there is also chalcopyrite, fluorite, and 

huebnerite (iron-manganese tungstate); in addition, 

Richardson (1914, p. 9) reports the presence of wolfframite. None of the outcrops or workings on Cave 

Peak show sufficient quantities of tungsten minerals to 

make the deposit of economic interest.

In 1948 the outcrops and workings on Cave Peak 

were sampled for beryllium by W. T. Holser, as part 

of an investigation of nonpegmatitic occurrences of this 

metal in the United States (Warner and others, 1959, 

p. 140-143). Analyses of samples indicate that the 

veinlets and rocks adjoining them in places contain as 

much as 0.1 percent BeO, but mostly much less, and 

that none occurs in the other rocks of the area.

TALC ^

Talc was discovered in the Allamoore Formation 

south of the Sierra Diablo in 1952, and has since been 

mined and prospected in the Streeruwitz, Bean, and 

Millican Hills and on Tumbledown Mountain, for a 

distance along the strike of 17 miles.

The talc occurs in phyllite units that are interbedded 

with the limestone and volcanic units of the formation. 

On the geologic map (pi. 1) the phyllite units are 

grouped with the limestone units, but they were shown 

separately in an earlier publication (King, P. B., and

7 See King, P. B., and Flawn, P. T., (1953, p. 170-172) and Flawn 

(1958, p.104-105).

Flawn, P. T., 1953, pis. 2, 3). The phyllite units are 

generally less than 100 feet thick, but are as much, as 

300 feet thick in places; individual units vary in thickness along the strike as a result of crumpling and flowage of the incompetent rock. The amount of talc in 

the units varies from place to place. The mineral may 

have formed from an original fine-grained magnesiumbearing tuff or marl. Carbonate rocks adjacent to the 

phyllite units contain little magnesium, and are mainly 

limestone rather than dolomite, but dolomite forms inclusions in the talc bodies. Large masses of pure 

ceramic-grade foliated to fibrous talc as much as 150 

feet thick occur in places, but in others the talc bodies 

contain layers or irregular masses of chert and carbonate rock.

Six companies are operating in the district, and 

through 1958 these had produced a total of 120,000 tons 

of talc; in 1960 they produced 60,000 tons. In 1960 a 

processing mill was installed at Allamoore. About 90 

percent of the talc produced in the district is sold for 

ceramic purposes and is used for manufacture of wall 

tile, the remainder being marketed as an insecticide 

carrier.

CRUSHED STONE 8

Crushed stone is produced by Gifford-Hill Co. of 

Dallas, Texas, at its Holley plant 2^ miles east of Allamoore (sec. 27, Block 67, Twp. 8). The plant and workings are in the northwestern part of the Carrizo Mountains just southwest of the Texas and Pacific Eailway, 

between the railroad and U.S. Highway 80. The plant 

was opened in 1926, and has been in nearly continuous 

operation since that date.

The stone used for crushing is the metarhyolite that 

intrudes the Carrizo Mountain Formation. In the 

workings this is pink or reddish, siliceous, and considerably more massive and blocky than elsewhere in the 

area. As elsewhere, it contains broken and elongated 

phenocrysts of quartz and feldspar, and some layering, 

defined by different colors and varying composition, but 

the rock does not split readily along the layering. 

Large reserves of metarhyolite remain in the neighborhood, although most of it is more foliated, and hence 

more slabby and less massive than that which is now 

quarried.

The crushed metarhyolite has been used to ballast the 

line of the Texas and Pacific Eailway between Dallas 

and Sierra Blanca, and has also been used to a more 

limited extent in highway construction.

MARBLE AND BRUCITE

In the Sierra Diablo region, marble occurs sporadically in limestone units of the Precambrian Allamoore

See King, P. B., and Flawn, P. T., (1963, p. 172-173).
ECONOMIC GEOLOGY 121

Formation, but its main occurrence is in the Permian 

Hueco Limestone in contact metamorphic zones adjacent to igneous intrusives of Tertiary age. A zone of 

marble in the Hueco, 200-400 feet wide, encircles the 

Marble Canyon stock, and a slightly narrower zone extends part of the way around the periphery of the Mine 

Canyon stock; a zone 3-25 feet thick overlies the sill of 

Sierra Prieta on its south side.

Marbles derived from the Hueco Limestone are white, 

uniformally crystalline and massive, seldom retaining 

any relic bedding structures, although they are obscurely jointed. Analyses indicate that they vary in 

composition from nearly pure CaCO3 to mixtures of 

CaCO3 with MgCO3 and Mg(OH) 2 . The latter forms 

the mineral brucite, and in some specimens amounts to 

as much as 30 percent of the rock. The magnesiumbearing marbles were obviously derived from the more 

dolomitic layers of the original limestone.

The marbles of the Sierra Diablo region have been 

little developed until recently. A "marble quarry" was 

shown on the east side of the Marble Canyon stock on 

the topographic map of the Van Horn quadrangle, 

which was surveyed in 1904 and 1905, but only a little 

surface stripping was done during this period, and very 

little marble was taken out (Richardson, 1914, p. 9). 

In the winter and spring of 1961 and 1962 this deposit 

was being reopened and prospected by the Texas Construction Materials Co. of Houston, Tex., with plans for 

production of dimension stone and for use of broken 

material in terrazzo tile. The brucite which occurs in 

many of the marbles is a possible source of metallic 

magnesium, but it is intermixed with the carbonate 

minerals of the marble.

NITRATE AND TURQUOISE

A few very minor mineral deposits have been recorded 

in the Sierra Diablo region. Nitrate has been prospected on an overhanging cliff of Van Horn Sandstone, 

7 miles northwest of Van Horn (sec. 24, Block 67, Twp. 

8), but it is a superficial coating produced from disintegration of bat guano (Mansfield and Boardman, 

1932, p. 66-68). Thin films of turquoise were reported 

by Eichardson (1914, p. 9) in some of the copper prospects in the Carrizo Mountain Formation of the Carrizo 

Mountains west of Van Horn, but probably in very 

small amounts, as none was observed there during the 

present investigation.

GROUND WATER

In the Sierra Diablo region, ground water has been 

explored by drilling from the time of the first American 

settlements to the present, but with results which have 

varied according to the geologic conditions at different 

localities. Geologic conditions which govern accumulation of ground water in the region have been summarized 

by Eichardson (1914, p. 9). Eichardson (1914; 1904, 

p. 89-95) and Baker (1935b, p. 373-380) have reported 

on the earlier results of drilling for water. Later results of drilling have been investigated by the Texas 

Board of Water Engineers, in cooperation with the U.S. 

Geological Survey, and have been reported on in part 

(Broadhurst and others, 1951, p. 37, 97; Hood and 

Scalapino, 1951; Follett, 1954, p. 6-15).

The principal source of ground water in the region 

is the unconsolidated deposits of Cenozoic age in the 

intermontane basins, especially in the Salt Basin and to 

a lesser extent in Eagle Flat. Water in the Salt Basin 

varies widely in quality, as illustrated by two analyses 

published by Eichardson (1914, p. 9), one from Van 

Horn, the other from the Figure Two Eanch which contain, respectively, 425 and 2,366 parts per million of 

dissolved solids.

The analysis of water from Van Horn is representative of that in the southern part of the Salt Basin, where 

alluvial slopes extend out from the mountains on either 

side to a central axis, along which Wildhorse Creek 

drains northward. Water was discovered at Van Horn 

shortly after construction of the Texas and Pacific Eailway, and has proved to be of the best quality of any 

along the line west of the Pecos Eiver. It is obtained 

from unconsolidated deposits at a depth of about 600 

feet in several wells drilled by the railroad and by the 

town of Van Horn; the municipal wells yield 100,000 

gallons per day (Broadhurst and others, 1951, p. 37).

Since World War II, ground water in the southern 

part of the Salt Basin has been further exploited by 

drilling in the Lobo Flats district about 12 miles south 

of Van Horn and in the Wildhorse Valley district about 

8 miles northeast of Van Horn (each a little beyond the 

edge of the map area, pi. 1). In both districts a dozen 

or more wells supply sufficient water to irrigate areas of 

more than 10 square miles (Hood and Scalapino, 1951; 

Leonard A. Wood, written commun., 1959); a few 

square miles are also irrigated by wells on the east side 

of the Salt Basin 5 miles northeast of the northeast 

corner of the Baylor Mountains. Wells in the Wildhorse Valley district yield 800 to 1,200 gallons per minute from unconsolidated deposits at depths of 200 to 

600 feet. The most productive areas are seemingly 

nearest Wildhorse Creek, and wells several miles on 

each side of it have yielded insufficient water for practical irrigation. Two wells in the southern part of the 

district (sec. 19, Block 63) were drilled into limestone 

bedrock when they failed to obtain water in the unconsolidated deposits; one of these is reported to have 

yielded 350 gallons per minute at 1,000 feet and 400 gallons per minute at 1,500 feet.
122 GEOLOGY OF THE SIEKRA DIABLO REGION, TEXAS

Ground water at Van Horn, in the Lobo Flats district, in the Wildhorse Valley district, and elsewhere in 

the southern part of the Salt Basin is evidently derived 

from water moving northward through the unconsolidated deposits in a manner comparable to the surface 

drainage of Wlldhorse Creek and its tributaries. These 

streams drain extensive areas in the high relatively well 

watered Davis Mountains (fig. 1). These mountains 

evidently provide a large recharge area, so that ground 

water in the southern part of the Salt Basin is probably 

capable of continued exploitation.

The analysis of water from the Figure Two Ranch, 

mentioned above, is representative of that in the main 

part of the Salt Basin, where alluvial slopes extend only 

a few miles out from the mountains on each side, with a 

nearly level alkaline floor 5 miles or more wide between 

them. On the floor, ground water is reached at a depth 

of 30 feet of less, and is taken out by ranch wells for 

watering stock. As indicated by the analysis, it is of 

poor quality, all of it being so saline or gypseous that it 

would be valueless for irrigation purposes. It is unlikely that water of better quality could be discovered in 

the unconsolidatecl deposits at any depth in the main 

part of the Salt Basin, for this has been an area of concentration of mineral salts throughout the history of 

the basin as a topographic feature.

The unconsolidated deposits of Eagle Flat, the intermontane basin south of the Sierra Diatlo} have been 

less extensively drilled for water than the Salt Basin. 

Besides scattered ranch wells, wells about 1,000 feet 

deep have obtained water at Hot Wells and Torbert on 

the line of the Southern Pacific railroad in the southern 

part of the report area (pi. 1), and at the town of Sierra 

Blanca west of the report area (Baker, 1935b, p. 374- 

375). The wells at Sierra Blanca yield 36,000 gallons 

of water per day which contains 1,655 ppm of dissolved 

solids (Broadhurst and others, 1951, p. 97); hence, the 

yield is smaller and of poorer quality than at Van Horn. 

As noted by Baker (op. cit.) ground water at Hot Wells 

and Torbert stands less than 100 feet higher than at Van 

Horn, suggesting that the ground water, like the surface 

water, drains from Eagle Flat into the Salt Basin. Reserves of water in Eagle Flat are probably much less 

than those in the Salt Basin, as the drainage area tributary to it is smaller and is largely country with scanty 

rainfall. Along the northern border of Eagle Flat, in 

the southern foothills of the Sierra Diablo, where Precambrian rocks lie near the surface, ranch wells obtain 

small supplies of water from the overlying unconsolidated deposits; some of the earlier of these wells were 

noted by Richardson (1914r, p. 9).

The mountain areas, including the large Sierra Diablo 

and the smaller Baylor Mountains and Beach Mountain,

are formed largely of various formations of carbonate 

rock, which are less likely to contain accumulations of 

ground water than the surrounding unconsolidated deposits. A few successful wells have been drilled, mainly in the alluvium of the valleys, but many others have 

proved to be dry. One of the deeper unsuccessful wells, 

drilled at the Slaughter Ranch in the northern part 

of the Sierra Diablo, is reported to have been sunk to 

a depth of more than a thousand feet in Permian carbonate rocks. In the Sierra Diablo and the other mountain areas the chief supplies of water will probably continue to be from artificial surface reservoirs (locally 

termed "tanks"), many of which have been constructed, 

as shown on the topographic base map (pis. 1, 9).

OIL AND GAS

Possibilities for accumulations of oil or gas in the 

Sierra Diablo region appear to be remote.

Possibilities are least likely in the southern half of 

the region, south of the Victorio flexure. Here, Precambrian and Precambrian (?) rocks lie either at the 

surface or within a thousand feet of the surface (pis. 15, 

16). Moreover, in much of this part of the region 

Permian Hueco Limestone rests directly on Precambrian and Precambrian (?) rocks, with the earlier 

Paleozoic sequence removed by pre-Hueco erosion.

Possibilities are somewhat greater north of the Victorio flexure, as the Precambrian and Precambrian (?) 

rocks lie at greater depth beneath the surface, and as 

both the Permian and pre-Permian Paleozoic sequences 

are more completely preserved (pis. 15,16). Two wells 

have been drilled in this structural situation about 10 

miles north of the northwest corner of the report area 

to depths of 4,518 and 4,794 feet (A. R. Jones, 1 E. W. 

Mowry in sec. 36, Block 70, Twp. 2; General Crude Oil, 

1 Merrill & Voyles in sec. 8, Block 69, Twp. 2) (Haigh 

and others, 1953, p. 78-81), both of which passed 

through a complete sequence of Paleozoic formations 

beneath the Permian, but apparently without showings 

of oil or gas.

Possibilities are greatest northeast and east of the 

Sierra Diablo region, within the former Delaware basin 

area, where both Permian and Pennsylvanian strata attain great thickness, as shown by both surface exposures 

and drill records (King, P. B., 1948, p. 12-13). In the 

Apache Mountains east of the Sierra Diablo, several 

wells have drilled through these strata into lower 

Paleozoic formations, including the Middle Ordovician 

Simpson Group (Maley, 1945; M. E. Upson, in DeFord 

and others, 1951, p. 50-52). This group is productive 

of oil in the West Texas basin farther east, but is 

missing in most parts of the Sierra Diablo region on 

the west. In the Salt Basin, between the Apache Moun-
STRATIGRAPHIC SECTIONS, ORDOVICIAN, SILURIAN, AND DEVONIAN ROCKS 123

tains and the Baylor Mountains (sec. 5, Block 86) the 

West & Armour, 1 Davis Investment et al. test was completed in 1960 at a depth of 8,201 feet, but reports are 

conflicting as to the rocks penetrated whether the well 

entered "Ellenburger( ?)," that is, El Paso Limestone, 

at total depth (Horak and others, 1961, p. 834), or 

whether it failed to reach the base of the Permian. It 

is not known whether showings of oil or gas were found 

in this well.

DESCRIPTIONS OF STRATIGRAPHIC SECTIONS AND 

FOSSIL COLLECTIONS

STRATIGRAPHIC SECTIONS AND FOSSIL COLLECTIONS 

OF ORDOVICIAN, SILURIAN, AND DEVONIAN ROCKS

SECTION 1. SIXMILE MOUNTAIN

The following is a section of the basal part of the El 

Paso Limestone and of the Bliss Sandstone, at the south 

end of Beach Mountain, on the west side of Sixmile 

Mountain (with BM 5315 at top), near SW cor. sec. 

10, Block 66, Twp. 8. The section was measured by P. 

B. King and J. Brookes Knight in 1931; fossils were 

observed in the field but were not collected.

Top of mountain; no higher beds exposed. 

El Paso Limestone:

Division B : Feet

19. Limestone, granular; possibly slightly 

sandy, but not mottled ; in 1- to 4-in. beds; 

contains small chert masses. Forms a 

great cliff, the full height of which was 

not ascended. Estimated thickness 250

18. Limestone, buff, sandy, thin-bedded; thinly 

laminated in some beds; gastropod imprints observed ________________ 28

17. Sandstone, buff, friable____________ 1

16. Limestone, buff, sandy; in 6-in to 1-ft beds;

contains lenses of nonsandy limestone_ 45 

Division A:

15. Sandstone, coarse-grained, calcareous, 

white; weathers gray; forms massive 

ledge______________________ 21

14. Sandstone, calcareous, thin-bedded; forms

a slope_____________________ 32

13. Limestone, brown, sandy____________ 26

12. Sandstone, fine-grained, calcareous, buff to 

white; top bed glauconitic. Cystid stems 

abundant in lower part. Mostly forms 

thin ledges, but locally projects in a cliff 31

11. Limestone, brown, sandy; in 1-ft beds,

weathers pitted- _ __ _ 24

10. Sandstone, fine-grained, white; in 6-in to 

3-f t beds; mostly thinly laminated, but 

crossbedded in part. Forms prominent 

rounded ledges_________________ 36 

9. Sandstone, somewhat calcareous, brown; 

with widely spaced laminae. Five feet 

above base of unit is a layer of brown 

sandy thin-bedded limestone, partly nodular and mottled, whose base is crowded 

with gastropod casts_____________ 36

757-108 65 9

Feet

Disconformity. 

Bliss Sandstone:

8. Sandstone, brown; in 1- to 3-in. beds; with partings of sandy marl or marly shale, the upper 

of which are greenish. Sandstone beds contain Scolithus; an open-coiled euomphalid gastropod and various trails observed on bedding 

surfaces______ ___ . 55 

7. Sandstone, fine-grained to gritty; in 6-in. beds; 

parts crossbedded, other parts containing Scolithus; forms ledges _ _ 7 

6. Sandstone, brown, marly____ _ ____ 1 

5. Sandstone, fine-grained to gritty; in 1- to 2-ft 

beds; thinly laminated to thinly crossbedded, 

with abundant Scolithus in upper part; forms 

ledges______________ _________ 16 

4. Sandstone, gray to brown, coarse-grained to conglomeratic; contains quartz pebbles______ 2 

3. Covered_________________.________ 7 

2. Sandstone, gritty, laminated to crossbedded; with 

thin seams of quartz pebbles; mainly gray but 

partly pink, due to content of red detritus derived from Van Horn sandstone________ 26 

1. Conglomerate, gray; composed of rounded quartz 

and chert pebbles in a coarse poorly sorted 

sand matrix_ _______ ___ ____ . 5 

Angular unconformity. 

Van Horn Sandstone at base of section.

El Paso Limestone: 

Part of division B 

Division A____.

Summary of section 1

exposed____________ 324 

_________________ 206

Part of El Paso Limestone exposed______ 530 

Bliss Sandstone_________________________ 114. 5

SECTION 2. YATES RANCH

The following is a section of the basal part of the El 

Paso Limestone and of the Bliss Sandstone on the west 

side of Beach Mountain, on a spur half a mile east of 

Yates Ranch, near SW cor. sec. 3, Block 66, Twp. 8. 

The section was measured by J. Brookes Knight and 

Josiah Bridge in 1938; fossils were observed in the 

field but not collected.

Summit of spur; higher beds not measured. 

El Paso Limestone:

Division B: peet 

34. Dolomite_________________ ._____ 15 

33. Limestone, dolomitic; contains poorly preserved fossils ; forms a ledge________ 4 

32. Limestone, dolomitic, thin-bedded; forms a

slope_____________.__________ 23 

Division A:

31. Sandstone, dolomitic; forms a massive ledge_ 7 

30. Marl, sandy, yellow; forms a slope_______ 5 

29. Sandstone, dolomitic; forms a massive ledge_ 27 

28. Dolomite, yellow; contains poorly preserved

gastropods and cephalopoda; forms ledges- 27 

27. Limestone, dolomitic, yellow; contains silicified gastropods; forms a ledge________ 4 

26. Limestone, mottled, dolomitic, yellow___ . _ 7
124 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

El Paso Limestone Continued

Division A Continued Feet 

25. Limestone, mottled gray; forms thin ledges. 

Bedding surfaces covered with brown dolomitic fucoidal markings; contains gastropods and cephalopods 45 

24. Limestone, marly, dolomitic; forms a slope 7 

23. Sandstone, calcareous; forms a ledge 2 

22. Sandstone, marly; forms a slope 4 

21. Sandstone, dolomitic, light-gray, massive; 

forms a prominent ledge. Fucoidal markings abundant near base and faint Scolithusl 

tubes occur near top 45 

20. Limestone, sandy, marly, dolomitic; forms

a slope__________ 12

19. Limestone, sandy, dolomitic; forms a ledge_ 3 

18. Sandstone, marly__ _ 10 

17. Sandstone; contains Lytospira; forms a

ledge_ 3 

16. Marl; forms a slope_ _ 7 

15. Sandstone, dolomitic; forms a ledge _ 2 

14. Sandstone, dolomitic, marly; forms a slope 12 

13. Sandstone; contains poorly preserved fossils;

forms a ledge_ 1 

12. Mainly covered on slope; a few ledges and 

much float of coarse brownish-red sandstone__________ _____ _- 14

Disconformity. 

Bliss Sandstone:

11. Sandstone, coarse, reddish, thin-bedded; contains rare Scolithus, as well as Lytospira 

and linguloid brachiopods near top_____ 31 

10. Sandstone, coarse, reddish; contains abundant Scolithus; forms prominent ledges___ 15 

9. Sandstone, with many conglomerate layers_ 15 

8. Sandstone______.______________ 3 

7. Conglomerate___________________ 20 

6. Sandstone______._______________ 20 

5. Conglomerate___________________ 1 

4. Sandstone, thin-bedded; contains rare

Scolithus ___. __________, 11 

3. Conglomerate____._______________ 2 

2. Sandstone, thin-bedded; contains rare

Scolithus_________.______________ 12

1. Conglomerate, coarser than any rocks above_ 1 

Angular unconformity. 

Van Horn Sandstone at base of section.

Summary of section 2

El Paso Limestone:

Part of division B exposed____________ 42 

Division A________________________ 244

Part of El Paso Limestone exposed_________ 286 

Bliss Sandstone___________________________ 113

SECTION 3. DALLAS MINE

The following is a section of the basal part of the El 

Paso Limestone and of the Bliss Sandstone, on the 

northwest side of Beach Mountain, on the slope east of 

Tumbledown Mountain above the abandoned Dallas 

mine, near the center of the western part of section 28, 

Block 66, Twp. 7. The section was measured in 1936 

by J. Brookes Knight and reviewed in 1938 in company with Josiah Bridge. Fossil identifications are by

P. E. Cloud, Jr., and Josiah Bridge (written commun., 

1954). (See also Cloud and Barnes, 1948, p. 67-68.)

El Paso Limestone:

Division A: Feet 

6. Dolomite; forms ledges; continues up the slope

of mountain____ _ (?) 

5. Sandstone, coarse, pinkish, somewhat dolomitic; in part crossbedded. Contains faint 

markings on bedding surfaces 36 

4. Limestone, brownish, slightly sandy, dolomitic; in 1- to 2-ft beds; interbedded with 

marl_________.________ 75 

3. Sandstone, pink, dolomitic; forms a massive 

ledge. Piloceras observed at top, and elsewhere worm borings and fucoidal markings___________________ 18 

Disconformity. 

Bliss Sandstone:

2. Sandstone, light-brown to red-purple; in 3-in. to 

2-ft beds; with thin shaly partings, containing abundant Scolithus and obscure fucoidal 

markings. A fragment of ClarJcoceras, Lytospira sp., Ophileta sp., Helicotoma cf. H. uniangulata (Hall), gastropod cross sections, and 

archaeostracan crustaceans were collected 5-8 

ft below top (TF 437; Oe 4, USGS 2751; X 3, 

TJSGS 3589) ; Hystricursus"! sp. and Lytospira 

gyrocera from same general level (B 173); 

Lingulepis sp. and gastropod cross sections 27 ft 

below top (TF 438)_________________ 88 

1. Sandstone, quartzitic, with rare Scolithus. Some 

beds are red, because of content of detritus 

derived from Van Horn__ _ _ 17 

Angular unconformity.

Van Horn Sandstone at base of section. A short distance to the southwest the Bliss overlaps the Dallas 

fault and lies on Allamoore Formation beyond it. 

Summary of section 3

El Paso Limestone:

Part of division A exposed_______________ 129 

Bliss Sandstone_ _______ _ _ ____ 105

SECTION 4. NORTH SIDE OF BEACH MOUNTAIN

The following is a section of Montoya Dolomite, El 

Paso Limestone, and Bliss Sandstone on the north side 

of Beach Mountain, on a blunt spur projecting northnorthwest from elevation point 5,590, in the east half 

of sec. 22, Block 66, Twp. 7. This section was originally measured by King in 1931. It was measured 

again in 1936 by Knight, who revisited it with Josiah 

Bridge in 1938, when further collections and observations were made. The section of El Paso Limestone 

and Bliss Sandstone was remeasured in great detail 

by P. E. Cloud, Jr., and V. E. Barnes in 1944 and 1945 

(Cloud and Barnes, 1946, p. 352-361).

In the text given here, description of the Montoya 

Dolomite is from Knight's section, and descriptions of 

the El Paso Limestone and Bliss Sandstone are 

abridged from the published section of Cloud and 

Barnes; however, lists of fossils collected by Knight,
STRATIGRAPHIC SECTIONS, ORDOVICIAN, SILURIAN, AND DEVONIAN ROCKS 125

Bridge, and others are added at the appropriate places. 

Unit numbers for the El Paso and Bliss are the same 

as those in the published section of Cloud and Barnes, 

which were given in descending order, or the reverse 

of the usual arrangement. The Bliss Sandstone is further illustrated by section 4a, by Knight, measured at 

nearly the same place as the main section, and by section 4b, by King, measured about half a mile to the 

southwest, in the southwestern part of sec. 22, on 

the opposite, or upthrown side of a fault. Fossil identifications are by P. E. Cloud, Jr., but they include 

some earlier determinations by Josiah Bridge (written 

comnmn., 1954).

Top of mountain; no higher beds exposed. 

Montoya Dolomite:

Aleman(?) Oherty Member or Fusselman(?) 

Dolomite: Feet 

8. Dolomite, light-gray, unfossiliferous; without 

chert; forms upper cliff on mountain. This 

unit might be Fusselman Dolomite rather 

than Montoya, but until fossil evidence for 

such an assignment is available, it is retained in the Montoya____________ 110 

Aleman Cherty Member:

7. Dolomite, thin-bedded, purplish-pink to lightgray ; without chert; forms a slope between 

cliffs above and below. DinortMs (Plaesiomys) large n. sp. collected (Om 1, USGS 

2761) _________________________ 28 

6. Limestone, dolomitic, hackly, light-gray to

pink; without chert______________ 25 

5. Limestone, dolomitic, massive, pinkish-gray;

with chert bands_________________ 25 

4. Limestone, dolomitic, massive, pinkish-gray; 

without chert. Poorly preserved corals and 

brachiopods observed_____________ 58 

3. Limestone, dolomitic, gray to slightly pink,

very cherty; parts very thin bedded____ 40 

Upham Member:

2. Limestone, dolomitic, light-gray to slightly 

pink; forms massive 3- to 7-ft beds that 

stand in a cliff. Contains a few dolomitized poorly preserved brachiopods, including Lepidocyclus________________ 95 

Cable Canyon (?) Sandstone Member:

1. Sandstone, massive, pinkish, saccharoidal, 

dolomitic. Forms a cliff and breaks off in 

huge blocks. A few poorly preserved cup 

corals observed________________ 35 

Disconformity. 

El Paso Limestone: 

Division C:

1. Dolomite and limestone, earthy, nodular, 

brownish-gray; with interbedded 4- to 

14-in. layers of compact dolomite; forms 

a gently sloping bench between the ledges 

and cliffs above and below. Small Maclurites, poorly preserved high-spired gastropods, sponges, and a probable Buttsoceras collected 7-12 ft above base (TF 

327; Oe 14, USGS 2760)____________ 50

El Paso Limestone Continued

Division B: Feet

2. Dolomite, fine-grained, brown to grayishbrown; in 1-in to 3-ft beds; some interbedded shaly dolomite; mostly forms steep 

slopes and ledges; some small chert nodules in lower part, and minor chert and 

siliceous masses elsewhere. Ceratopea sp., 

Hormotoma sp., and large gastropods collected 45 ft above base (TF 441) ; Lophonema sp. and longicone siphuncles 85 ft 

above base (Oe 12, USGS 2758) ; Ceratopea anJcylosa Cullison 142-144 ft above 

base (TF 326) ; Lophonema? sp., Hormotoma spp., Ceratopea aff. C. anklosa 

Cullison, and C. spp.? near top (Oe 13). 

Ceratopea and Hormotoma observed elsewhere_______.___ 160

3. Covered on bench; probably argillaceous

dolomite_____ 20

4. Dolomite, fine-grained, grayish-brown to 

brown; well bedded, but forming thick 

ledges; a thin intraformational conglomerate 51 ft above base, a few layers of chert 

nodules. Dolomite is markedly sandy 

in lower 48 ft. Two genera of high-spired 

gastropods collected 48 ft above base (TF 

439). Ceratopea observed 85 ft above 

base________-_________ 101

5. Dolomite; similar to overlying beds, but 

with sand only in a thin layer 12 ft above 

base. Contains some chert nodules. 

Hormotoma and other small gastropods 

observed___ 24

6. Dolomite; coarser grained than beds above

or below; light-pink to brownish____ 2.5

7. Dolomite; like beds above, except in lower 

8 ft, which is fine grained, grayish 

brown; yields a weak petroliferous odor 

when broken. Some beds contain chert, 

in part oolitic; others contain scattered 

sand grains. A siphuncle of a probable 

Mcqueenoceras observed 12 ft above 

base; Hormotoma, sp. and another siphuncle 37 ft above base_______ 184.5

8. Dolomite, very fine grained, grayishbrown; irregularly bedded in layers as 

much as 3 ft thick; forms lower part of a 

prominent bluff. Chert lenses in lower 

part and minor chert elsewhere. Dolomite contains abundant sand grains in 

lower 3 ft-_________ __________ 53

9. Dolomite, mostly very fine grained, gray to 

brownish-gray; irregularly bedded in 

layers as much as 3 ft thick; considerably less cherty than beds beneath. 

Ceratopea tennesseensis Oder and piloceratid siphuncles collected 80 ft above 

base (TF 436) ; Ceratopea cf. C. tennesseensis Oder and C. cf. C. keitM Ulrich 

95 ft above base (TF 324) ; C. cf. C. tennesseensis Oder, C., sp., and an endoceratid siphuncle 118 ft above base (TF 

325) ; and from several beds in about the
126 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

El Paso Limestone Continued

Division B Continued Feet 

same part of the section Ceratopea aff. 

0. tennesseensis Oder and C. jenJcinensis 

Cullison, and C. spp. (Oe 11, USGS 2757) _ 120

10. Dolomite, very fine grained to dense, gray 

to brownish-gray; irregularly bedded in 

layers as much as 3 ft thick. Chert forms 

abundant nodules and masses in lower half, 

and some beds higher up. A siphuncle of 

Mcqueenoceras type and a large Ceratopea 

observed 9 ft above base; Calathium, Ceratopea, sp., a Mcqueenoceras siphuncle, and 

another endoceratid siphuncle collected 18 

ft above base (TF 322) ; Callathium sp., 

Helicotomal sp., a small gastropod, Mcqueenoceras sp., and a piloceratid? 

siphuncle from same general level (Oe 10, 

USGS 2756) ; Calathium, a Ceratopea, gastropods, and a fragment of a cephalopod 

from chert at top (TF 323) _______ 85

11. Dolomite, fine-grained, brownish, yellowish, 

or pinkish, thin-bedded; in 1- to 20-in. 

beds; interbedded with dolomitic and argillaceous limestone in upper 18 ft; forms 

benches. Some chert lenses in lower part 

and a thin bed of cherty sandstone near 

middle. ArchaeO'Scyphia cf. A. annulata 

Cullison, and a fragment of a probable 

Pynoceras collected 18-20 ft above base 

(TF 320) ; Archaeorthfe costellata Ulrich 

and Cooper and cystid plates at top (TF 

321; Oe 9, USGS 2755). Hormotoma, 

Ceratopea, siphuncles of brevicone cephalopods, ArchaeortMs, Firikelnburgia,, and Calathium were observed at various other 

levels______________________ 50

12. Dolomite, fine- to medium-grained, vuggy; 

calcitic in upper part; yellowish gray to 

light gray; in 1- to 30-in. beds; some scattered sand grains in lower part. Xenelasma 

syntrophiodes Ulrich and Cooper, a sponge, 

Hormotoma sp., and Polhemia"! collected 

4-6 ft above base (TF 319) ; Calathium 

sp., Hormotoma sp., Ceratopea sp., and 

Mcqueenoceras sp. at about the same level 

(Oe 8, USGS 2754). Orospiral and Hormotoma, were also observed_________ 13 

Division A:

13. Sandstone, dolomitic, fine- to mediumgrained ; quartz grains well-rounded, some 

feldspar grains_________________ 4

14. Dolomite, moderately sandy, very fine 

grained, gray; in 1-in. to 2-ft beds; quartz 

grains well rounded and frosted. Polhemia, small brevicone cephalopods, and syntrophioid brachiopods like Diaphelasma 

observed 3 ft above base__________ 8

15. Dolomite, sandy and shaly; dolomitic sandstone; yellowish to brownish gray, with a 

greenish shaly layer at top. Gastropods 

suggesting Euconia and Polhemia observed 

near middle___________________ 11

El Paso Limestone Continued 

Division A Continued Feet

16. Sandstone, dolomitic, yellowish to pinkish, 

medium- to fine-grained, crossbedded; in 

beds as much as 5 ft thick; forms a prominent persistent ledge. Some feldspar 

grains_______________________ 29

17. Siltstone, dolomitic; interbedded with fine to 

coarse sandstone; yellowish to pinkish; 

in beds as much as 4.5 ft thick; forms a 

ledge. Some glauconite at base______ 21

18. Dolomite, silty and sandy, fine-grained, yellowish- to brownish-gray; weathers earthy_ 15

19. Dolomite, partly calcitic, very fine grained, 

yellowish- to brownish-gray ; in 1-in. to 4-ft 

beds; forms a prominent ledge in lower 

part. Some glauconite in middle. Cystid 

plates and columnals observed 29 ft above 

base______________________ 40

20. Limestone, dolomitic, fine-grained, gray to 

yellowish-gray; in 1-in to 1-ft beds. Contains abundant chert in lower 3 ft. A 

sponge like Archaeoscyphia, Diaphelasma, 

Allopiloceras sp., and a trilobite were collected 12 ft above base (TF 318)_____ 17

21. Limestone, fine-grained, gray, nodular; interbedded with calcareous shale__ _ 6

22. Limestone, medium- to fine-grained, gray; 

with dolomitic streaks; weathers to thin 

beds; abundant glauconite in lower part. 

Piloceratid siphuncles abundant in lower 

3 ft. Lytospira, "Euconia," Ophileta 

(OzarTcispira) cf. 0. rotuliformis (Meek), 

Diaphelasma cf. D. OJclahomense Ulrich 

and Cooper, and other brachiopods collected 2 ft above base (TF 315; Oe 7, part; 

B 39, USGS 3590) ; Ophileta (Ozarlcispira) 

rotuliformis Meek, Lytospira! Hormotoma 

small sp., Bucanella sp., Euconia sp., Pelagiellal sp., Holopea-like gastropod, a 

raphistomoid gastropod. Endocycloceras 

sp., and Hystricurus sp. from 9 ft above 

base (Oe 7, USGS 2753; C 39, USGS 3591) ; 

Diaphelasma oTtlahomense Ulrich and 

Cooper, Syntrophina sp., Ophileta (OzarJcispira) cf. O. rotuliformis (Meek), 

Ophileta sp., Hormotoma sp., a raphistomoid gastropod, and a small cyrtendoceratid cephalopod from higher up (TF 

317) ________-_______________ 16

23. Dolomite, fine-grained, brownish-gray; in 

beds a few inches thick; interbedded with 

gray limestone. Clarkella sp., Syntrophina 

sp., Ophileta (Ozarkispira) cf. 0. rotuliformis (Meek), and Homotoma sp. were 

collected 9-11 ft above base (TF 433), and 

poorly preserved Rhomtiellal and Lecanospiral were observed at the same level. 

Cystid plates, Tetralo^ula sp., OzarJcispira 

sp., Lytosplral Piloceras sp., Allopiloceras 

sp., and Kirkocerast were collected 15-17 

ft above base (TF 434) ____________ 26
STRATIGRAPHIC SECTIONS, ORDOVICIAN, SILURIAN, AND DEVONIAN ROCKS 127

El Paso Limestone Continued

Division A Continued Feet

24. Sandstone, dolomitic, medium- to coarsegrained, crossbedded, yellowish-gray to 

pink; forms a prominent ledge_____ 9

25. Siltstone, and very fine grained dolomitic

sandstone___________________ 12

26. Dolomite, silty and sandy; interbedded with 

siltstone, sandstone, and green shale; forms 

a light-colored slope. At base is a 4- to 10- 

in. bed of reddish sandy dolomite, containing rounded pebbles and cobbles of sandstone, the largest 10 in. in diameter. Lies 

with abrupt contact on Bliss Sandstone 38

Disconformity.

Bliss Sandstone:

27. Sandstone, fine- to coarse-grained; contains 

pebbly layers in lower half; pinkish or yellowish ; friable to quartzitic, slightly calcareous throughout; in 1-in. to 2-ft beds. 

Is interbedded with argillaceous sandstone 

and shale, the latter of greenish or purplish 

color. The well-indurated sandstone 

layers contain vertical Scolithus tubes. 

Lingulepis, Lingulella, a possible Lytospira, 

and archaeostracan crustaceans were colcollected 98-105 ft above base (TF 432) ; 

many beds show impressions or molds of 

various unidentified gastropods______ 125

Angular unconformity.

Van Horn Sandstone at base of section.

Section 4a

[Section of Bliss Sandstone measured at approximately the same 

place as lower part of preceding, by J. Brookes Knight, 1936]

El Paso Limestone: 

Division A:

4. Sandstone, fine-grained, friable, dolomitic; 

with obscure winding tubules on bedding; 

forms a ledge__________________ 10 

Disconformity. 

Bliss Sandstone:

Calcareous division:

3. Sandstone; a little more massive and dolomitic 

than beds below, with finer grained sand; 

gray to yellow; no Scolithus_______________ 28

Main body of formation:

2. Sandstone; forms ledges on slope. Some layers, which are more quartzitic than remainder, contain Scolithus; others are crossbedded. Between the sandstone layers are 

partings of soft marly sandstone. Sandstones and marls are light gray, brown, and 

purplish red; some marls are green_____ 72 

1. Sandstone, pebbly and gritty, gray to reddishbrown, crossbedded. At base is a quartzpebble conglomerate which lies with sharp 

contact on Van Horn Sandstone_______ 22 

Angular unconformity. 

Van Horn Sandstone at base of section.

Section 4b

[Section of Bliss Sandstone measured about half a mile southwest of 

preceding section on opposite, or upthrown side, of a fault, by P. B. 

King, 1931]

El Paso Limestone:

Division A: Feet 

7. Sandstone, friable; with partings of greenish 

marly shale; becomes calcareous 10-15 ft , above base _______ _________ 30

Disconformity.

Bliss Sandstone:

Calcareous division:

6. Sandstone, quartzitic, brown, thinly laminated; forms a ledge____________ 2

5. Sandstone, friable, buff; in 1-ft beds; full of

calcareous tubular structures________ 13

4. Limestone, buff, sandy__ ______ _ 5 

Main body of formation:

3. Sandstone, gray, friable; in 1- to 3-in. beds;

all contain Scolithus______________ 37

2. Sandstone, less resistant than beds above

or below_____ _ _ _ 26

1. Sandstone gritty, quartzitic; weathers brown; 

brown; crossbedded on a small scale. Contains seams of rounded quartz pebbles as 

much as half an inch in diameter_____ 10

Angular unconformity.

Van Horn Sandstone at base of section.

Summary of section 4

Montoya Dolomite:

Aleman(?) Cherty Member or Fusselman

limestone (?) ________._______ 110 

Aleman Cherty Member________ 177

TJpham Member_______ 95 

Cable Canyon (?) Sandstone Member__ 35

Total Montoya Dolomite-___________________

El Paso Limestone:

Division C_____________________ 50 

Division B__________ __ 813 

Division A_ 252

417

Total El Paso Limestone 1,115 

Bliss Sandstone:

Main section __ 125 

Section 4a__________ 125 

Section 4b____________________ 93

SECTION 5. UNCONFORMITY LOCAUTY

The following is a section of the basal part of the El 

Paso Limestone and of the Bliss Sandstone in the southern part of Baylor Mountains, on a prominent bluff that 

faces into a reentrant valley north of Sulphur Creek, 

near the middle of the south line of sec. 22, Block 65, 

Twp. 7. This bluff is prominently in view from Texas 

Highway 54 to the south and is illustrated in figure 5A. 

The bluff of El Paso and Bliss is overlapped on the west 

by the Hueco Limestone, whose base stands several 

hundred feet lower, and which contains talus blocks derived from unit 8 and other resistant beds of the Ordovician sequence; the place was hence referred to during 

the field investigation as the "unconformity locality,"
128 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

and that title is retained here. The section was measured by J. Brookes Knight in 1936; fossil identifications are by P. E. Cloud, Jr., (written commun., 1954).

Top of section; higher beds of El Paso Limestone occur 

to northeast, but the whole Ordovician sequence is 

overlapped on the west by Hueco Limestone. 

El Paso Limestone:

Division A: Feet 

14. Limestone, dolomitic_________ (?) 

13. Sandstone, crossbedded, light-brown to pink,

dolomitic; forms a ledge_ ____ _ 12.5 

12. Limestone, marly and sandy, mottled, lightgray __ 25 

11. Limestone, dolomitic; interbedded with 

marly layers; contains poorly preserved 

gastropods__________________ 22 

10. Not exposed in line of section; to east is 

yellow sandy limestone, slightly mottled, 

containing poorly preserved Ophileta, 

with interbedded marl layers________ 25 

9. Limestone, dolomitic, slightly sandy; in

1-ft beds; contains Piloceras___________ 16

8. Limestone, dolomitic, slightly sandy, thinbedded, dark-gray; weathers brown. 

Piloceras and other cephalopods collected 

(Oe 2). Forms top of a projecting promontory that overlooks valley to the south. 20 

Disconformity. 

Bliss Sandstone:

Calcareous division:

7. Sandstone, coarse, crossbedded; interbedded 

with finely sandy dolomitic limestone, and 

marl___ _________ _________ 15

6. Limestone, dolomitic, finely sandy, yellowishgray; in part with ramifying mottlings; 

interbedded with marl_____________ 28 

Main body of formation:

5. Sandstone, quartzitic; in 6-in to 1-ft beds; 

interbedded with softer more argillaceous 

sandstone and blue-green shaly sandstone. 

Many of the sandstone layers are crossbedded and ripple marked, and the quartzose layers contain ScolitJius. Lingulepis n. 

sp. and Lytospira! collected from near base 

(Oe 1, TJSGS 2748; Oe 5, USGS 2765; Oe 

6, USGS 2752) __________________ 30 

4. Sandstone, shaly, brown, white, and green; 

forms a slope. One thin bed contains 

Scolithus_______________________________ 10

3. Sandstone, quartzitic, brown; in 1-ft beds;

contains Scolithus__________________ 20

2. Sandstone, quartzitic, red-brown, purplish, 

and white; forms somewhat thinner layers 

than beds above; interbedded with white 

and green marly sandstone. The quartzitic 

sandstone layers are crossbedded in part, 

contain Scolithus, and have fucoidal markings on bedding_________________ 25 

1. Sandstone, coarse, crossbedded, reddish to 

white; contains quartz pebbles in lower 3 

ft. Scolithus occurs 4 ft above base, and 

in a few beds higher up. To east, basal

Bliss Sandstone Continued

Main body of formation Continued Feet 

beds contain rounded cobbles 3 in. across, 

mostly of vein quartz, but a few of schist 

and quartzite 17 

Angular unconformity. 

Van Horn Sandstone at base of section.

Summary of section 5 

El Paso Limestone:

Part of division A exposed 120. 5 

Bliss Sandstone:

Calcareous division 43 

Main body of formation- 102

Total Bliss Sandstone 145 

SECTION 6. SOUTHEASTERN BAYL.OR MOUNTAINS

The following is a section of Fusselman Dolomite, 

Montoya Dolomite, beds of Middle (?) Ordovician age, 

and the upper part of the El Paso Limestone on the 

southeast face of Baylor Mountains 1 mile southsouthwest of the portal of Eed Tank Canyon in the 

northwestern part of sec. 6, Block 122. A generalized 

section was measured in this vicinity by P. B. King 

and E. E. King in 1928, but the sequence was studied 

in more detail later by H. J. Howe (1959, p. 2312-2313, 

2328), when two sections were measured about half a 

mile apart, termed "B-l and B-2." The descriptions 

of the Montoya and Fusselman Dolomites given here 

are from Howe's section B-l (1959, fig. 29, p. 2328); 

that of the beds of Middle(?) Ordovician age is from 

his section B-2 (written commun., 1959); some observations by P. B. King and E. E. King have been added. 

Fossil identifications are by H. J. Howe.

Hueco Limestone at top of section. 

Angular unconformity.

Fusselman Dolomite: Feet 

10. Dolomite, very fine grained, very light gray; 

weathers brownish orange and sugary. Massive, 

except for basal few feet, which is faintly laminated_________._ _ 70 

Disconformity (?). 

Montoya Dolomite:

Aleman Cherty Member:

9. Dolomite, microgranular, faintly thinly laminated, brownish-gray; weathers light olive 

gray. About 40 percent of unit consists of 

elongated irregular white chert nodules that 

weather light brown_ ___________ 18 

8. Dolomite, very fine grained, thick-bedded to 

very thick bedded, light-gray; weathers 

brownish orange. Near top, contains Hypsiptycha, Streptelasma, and favositids; Paleophyllum thomi (Hall) zone is well developed lower down; near base, contains Thaerodonta and Lepidosyclus_______________ 24

7. Dolomite, very fine grained, light-gray. About 

15-20 percent of unit consists of chert nodules, 

elongated parallel to bedding_________ 15
STRATIGEAPHIC SECTIONS, ORDOVICIAN, SILURIAN, AND DEVONIAN ROCKS 129

Montoya Dolomite Continued

Aleman Cherty Member Continued Feet 

6. Dolomite, very fine grained, thick-bedded to 

very thick bedded, light-gray; weathers 

brownish orange; contains sparse chert nodules. Horn corals are scattered throughout 

and Lepidocyclus was observed near top__ 40 

5. Dolomite, microgranular, homogeneous to 

faintly laminated, light-gray; about 30 percent of unit consists of light-gray elongated 

chert nodules__________________ 20 

4. Dolomite, microgranular, light-gray. "Key 

chert" horizon occurs at top; remaining 

part of unit consists of about 10 percent elongated chert nodules. "Key chert" 

contains Lepidocyclus manniensis (Foerste), 

L. laddi Wang, L. capax (Conrad), L. sp., 

Onniella sp.,Thaerodonta sp., Plaesiomys bellistriatus Wang., Rhynchotrema sp., Austinella sp., Glyptorthis sp., and fragments of 

other fossils____________________ 30 

Upham Member:

3. Dolomite, like unit 1; contains very common 

fossil fragments, and Onniella sp., TUaerodonta sp., Lepidocyclus sp., and Glyptorthis 

sp _ __________ 29 

2. "Key chert," containing 15-20 percent small 

irregular chert nodules, arranged in closely 

spaced layers__________________ 6 

1. Dolomite, fine-grained to very fine grained, 

thick-bedded to very thick bedded, lightgray; weathers brownish orange. Contains Receptaculites and Halysites, nearly 

obliterated by dolomitization_________ 66 

Cable Cany on (?) Sandstone Member:

h. Dolomite, sandy___________________ 2 

Disconformity. 

Beds of Middle (?) Ordovician age:

g. Sandstone, fine-grained, brown; forms a ledge_ 10 

f. Shale and argillaceous dolomite_________ 17 

e. Sandstone, dolomitic________________ 3 

d. Shale and argillaceous dolomite_________ 26 

c. Sandstone, fine-grained, brown; forms a ledge_ 10

El Paso Limestone: 

Division C:

b. Shale and argillaceous dolomite, probably equivalent to division C of geologic section 4___ 40 

Division B:

a. Limestone, dolomitic, finely crystalline; weathers light gray and contains a few irregular 

chert masses; in beds a few feet thick; forms 

conspicuous ledges. Contains Ceratopea near 

top _. ________ 200

Similar strata below base of section, forming less conspicuous ledges, dipping more steeply and cut by closely spaced joints; one or more faults downthrown toward the southeast probably duplicate the sequence.

Summary of section 6

Fusselman Dolomite______________________ 70 

Montoya Dolomite:

Aleman Cherty Member___________________ 147

Summary of section 6 Continued

Montoya Dolomite Continued Feet 

Upham Member___ _________ 101 

Cable Cany on (?) Sandstone Member_ 2

Total Montoya Dolomite ___ 250

Beds of Middle(?) Ordovician age______ ______ 66 

Part of El Paso Limestone exposed- ____ _ 240

SECTION 7. NORTHEASTERN BAYLOR MOUNTAINS

The following is a section of beds of Devonian age, 

Fusselman Dolomite, Montoya Dolomite, and beds of 

Middle (?) Ordovician age on the southeast spur of the 

high point of Baylor Mountains (BM 5568), a mile 

northeast of the portal of Red Tank Canyon, in the 

northwestern part of sec. 9, Block 65, Twp. 7. The section was measured by J. Brookes Knight in 1938, but 

notes made by Knight and the writer during earlier 

years have been incorporated. Fossils were not collected, but were observed during measurement of section.

Section 7a illustrates further features of the beds of 

Middle(?) Ordovician age and the upper part of the 

El Paso Limestone at a locality half a mile to the northeast, near the center of sec. 2, Block 65, Twp. 7; it was 

furnished through the courtesy of C. C. Branson (written commun. 1950), who measured it in 1947. Fossils 

noted in the section were identified by G. A. Cooper.

Hueco Limestone at top of section. 

Angular unconformity.

Beds of Devonian age: Feet 

14. Limstone, dolomitic, gray-brown, buff, or pink, 

thin-bedded or nodular; contains very abundant irregular nodules and lenses of black or 

brown chert; preserved beneath Hueco Limestone only on southwestern of two spurs of 

the mountain___________________ 30-50 

Disconformity ( ?). 

Fusselman Dolomite:

13. Beds like those below, occurring on southwestern of two spurs of mountain; not preserved 

on northeastern spur where main part of 

section was measured. Approximate thickness_____ 25 

12. Dolomite, fine-grained light-gray; weathers salmon gray and pitted; forms massive ledges 

several feet thick. A few beds are indistinctly mottled, and some in upper part are thin 

bedded and hackly. No chert or fossils observed _ 275 

Disconformity (?). 

Montoya Dolomite:

Aleman Cherty Member:

11. Limestone, dolomitic, light-gray; contains

thick chert lenses_____ 20 

10. Limestone, dolomitic, light-gray, thinbedded; contains sparse chert nodules 

and lenses. Poorly preserved Lepidocyclus, "OrtMs," and other brachiopods observed . 75
130 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Montoya Dolomite Continued

Aleman Cherty Member Continued

9. Limestone, dolomitic, gray, thin-bedded; 

contains abundant ramifying chert 

masses__________._ _ 28 

8. Limestone, dolomitic, gray; contains moderately abundant chert nodules and lenses. 

Poorly preserved brachipods observed 55 

7. Limestone, dolomitic, light-gray; in 6- to 18- 

in. beds; contains many silicifled Lepidocyclus, "Orthis," other brachiopods, and 

cup corals _ _ ___ _ 50 

6. Limestone, dolomitic, very cherty______ 10 

Upham Member:

5. Limestone, dolomitic, gray; thinner bedded

than below___________________ 18 

4. Limestone, dolomitic, very cherty; forms a 

ledge. Probably the same as lower "key 

chert" interval, unit 2 of section 6_ _ 3 

3. Limestone, dolomitic, gray; in 3- to 5-ft 

beds; mottled, with mottlings projecting 

in relief on weathered surfaces. Haclurites, Lepidocyclus, Favosites, halysitid 

corals, cup corals, and Receptaculites observed. Base concealed on spur, but exposed in ravine to north__________ 40 

Cable Canyon ( ?) Sandstone Member:

2. Sandstone, brown, crossbedded________ 7-25 

Disconformity. 

Beds of Middle (?) Ordovician age:

1. Limestone, earthy, yellow, pink, and brown; 

without sandstone beds; exposed in ravine 

north of spur_____________________ (?) 

Base of section covered by alluvium.

Section 7a

[Section of beds of Middle(?) Ordovician age and upper part of 

El Paso Limestone measured half a mile northeast of preceding 

section; by C. C. Branson, 1947]

Montoya Dolomite at top of section, with a 2-ft bed of

sandstone at base. 

Disconformity. 

Beds of Middle (?) Ordovician age:

9. Dolomite, yellow, very sandy; contains frosted 

sand grains, with a green shale parting a 

little above base___________________ 8 

8. Shale, green, with thin layers of buff fucoidal

sandstone_______________________ 4 

7. Siltstone, fine-grained, buff, well-bedded; contains frosted sand grains_____________ 5 

6. Sandstone, saccharoidal, crossbedded; white,

with greenish areas_________________ 7 

5. Sandstone, dolomitic, silty, yellow_________ 18 

4. Limestone, shaly and silty, platy, yellow_____ 26 

3. Sandstone, calcareous, nodular; contains frosted

sand grains, also Desmorthis ? and cystid plates- 18 

El Paso Limestone: 

Division C:

2. Dolomite, calcitic, sandy, knotty, buff to yellow, sparsely fossilferous, poorly exposed_ 59

Feet

El Paso Limestone Continued 

Division B:

1. Dolomite, dense, slightly cherty and sandy, 

gray to pink; contains scattered frosted 

sand grains___________ 50

Base of section covered by alluvium.

Summary of section 7

Beds of Devonian age_____________ _ 30-50

Pusselman Dolomite___ __ 300 

Montoya Dolomite:

Aleman Cherty Member___ _ 238 

Upham Member___ _ 61 

Cable Cany on (?) Sandstone Member- __ 7-25

Total Montoya Dolomite________ _ 306-324 

Beds of Middle (?) Ordovician age (in section 7a) 86 

El Paso Limestone (in section 7a) :

Division C_____________ _ _ 59 

Part of division B exposed-_ _ 50

Part of El Paso Limestone exposed. 109

SECTION 8. HAWKINS TANK

The following is a section of the basal part of the El 

Paso Limestone, and of the Bliss Sandstone and Van 

Horn Sandstone, in a group of hills between the northwest corner of the Bay lor Mountains and Sierra Diablo 

scarp, west of Texas Highway 54. The section was 

measured on a conical butte half a mile southwest of 

Hawkins Tank, near the center of the north line of sec. 

10, Block 54%, but some observations made on adjacent 

hills have been added. The section was measured by 

P. B. King in 1936 ; fossils were noted in field, but have 

not been formally identified.

Top of butte ; higher beds exposed in gome of hills farther 

east, probably including parts of division B of El Paso 

Limestone, but could not be placed in sequence ; many 

of hills are capped by Hueco Limestone, which oversteps all the earlier strata down to the Hazel Formation.

El Paso Limestone : 

Division A :

21. Limestone, sandy, marly, brown __ _ 

20. Limestone, gray ; forms ledges ______ _ _

19. Limestone, marly, brown ; forms a slope. _

18. Limestone ; forms thin ledges, with marl

partings _____ .___ ____ _ _ _ _ 

17. Limestone, evenly layered, gray; in 6-in.

beds ; contains abundant silicified fossils,

including Piloceras, Ophileta, Lytospira,

Hormotoma, and possible sponges (Oe3)_

16. Limestone, nodular, marly; forms a slope _

15. Limestone, forming a slope below and passing into prominent ledges above ; lower

part sandy, brown or gray-brown, thin

bedded; upper part gray, in 1-ft beds,

mottled or lumpy, containing spongy lightbrown chert that forms networks of tubules on bedding, and nodules of compact

bluish chert ___________________ 28

7

4

5

12

4

13
STRATIGRAPHIC SECTIONS, ORDOVICIAN, SILURIAN, AND DEVONIAN ROCKS 131

El Paso Limestone Continued

Division A Continued Feet 

14. Sandstone, fine-grained, calcareous, brown 

or buff; in 6-in to 1-ft beds; in part laminated, in part crossbedded; forms massive 

ledges______.______________ 17 

Disconformity. 

Bliss Sandstone:

Calcareous division:

13. Sandstone, finer grained than below; slightly calcareous, buff or brown; forms ledges 

a foot thick, separated by slopes______ 40 

12. Sandstone, coarse, quartzose, slightly calcareous 'and glauconitic; weathers brown; in 

massive ledge________________ 3 

11. Sandstone, thin-bedded, soft, buff______ 6 

10. Sandstone, coarse, quartzose, calcareous;

weathers brown_______________ 3

Main body of formation :

9. Sandstone, quartzitic, noncalcareous, gray;

forms ledges__________________ 4 

8. Sandstone, thin-bedded, friable, buff_____ 13 

7. Sandstone, quartzitic; in part crossbedded; 

weathers brown; in 1- to 3-ft beds with 

marly partings; forms ledges________ 10 

6. Sandstone, thin-bedded, quartzose, apparently glauconitic__________________ 16 

5. Sandstone, quartzitic, gray; weathers red 

brown ; forms two groups of ledges; in part 

crossbedded and in part containing Scolithus________________________ 10 

4. Sandstone, medium-grained, quartose, white 

or buff; mostly in beds a few inches thick, 

but with some 1-f t beds near middle. Beds 

contain dark laminae and many contain 

Scolithus _____________________________ 50

Angular unconformity. 

Van Horn Sandstone:

3. Sandstone, coarse, arkosic, red-purple to maroonred ; in massive rounded 5- to 10-ft ledges, with 

scattered pebbles, and interbedded conglomerate layers made up of closely packed wellrounded pebbles and cobbles as much as 6 in. 

in diameter, of same composition as those in 

unit 1. Toward top, sandstone is irregularly 

decolorized to brown adjacent to joints. Thickness exposed, to base of slope__________ 100 

2. Poorly exposed across flat, toward hill to northwest; dip changes from less than 5° in unit 

above to 20° in unit below, and several faults 

may occur, but interval is probably small___ (?) 

1. Conglomerate, coarse; interbedded with friable 

coarse maroon-red sandstone. Conglomerate 

consists of closely packed well-rounded pebbles 

and cobbles of vein quartz, mafic volcanic rocks, 

chert, limestone, massive red rhyolite, and 

schistose lineated metarhyolite__________ 50 

Angular unconformity.

Hazel formation, fine-grained red sandstone at base of 

section.

Summary of section 8 

El Paso Limestone:

Part of division A exposed____________ 90

Part of El Paso Limestone exposed_____ 90

757-108 65 10

Summary of section 8 Continued

Bliss Sandstone: Feet 

Calcareous division 52 

Main body of formation 103

Total Bliss Sandstone- 159 

Van Horn Sandstone______ >150

SECTION 9. POINT OF MOUNTAINS

The following is a section of the Montoya Dolomite, 

and parts of the overlying Fusselman Dolomite and 

underlying El Paso Limestone, on a projecting salient 

of the Sierra Diablo escarpment 1% miles northwest of 

Figure Two Ranch, on a ridge projecting northeast 

from a flat-topped butte capped by Hueco Limestone, 

near the center of the southern part of sec. 9, Block 66, 

Twp. 5. The section was measured by P. B. King in 

1931; fossils were noted in the field, but have not been 

formally identified.

Hueco Limestone at top of section. 

Angular unconformity (Barnett Shale and beds of 

Devonian age are preserved beneath the unconformity at nearby localities).

Fusselman Dolomite: Feet 

11. Dolomite, white to light-gray, finely crystalline ; with veins, patches, and vugs of crystalline calcite. A poorly preserved favosite 

coral noted. Forms obscure massive beds, 

which dip steeply and stand in a wall-like 

ridge. Approximate preserved thickness 100-200 

Disconformity (?). 

Montoya Dolomite:

Aleman Cherty Member:

10. Limestone, dolomitic; in 3- to 4-ft beds; 

weathers to drab gray jagged surfaces. 

Contains abundant nodules, knotted 

lenses, and long beds of light-gray to 

brown chert, weathering rusty. Brachiopods observed- 38 

9. Limestone, dolomitic; thinner bedded than

below and above 30 

8. Limestone, dolomitic; in 2- to 3-ft beds; 

weathers to dark gray jagged surfaces. 

Toward top, nodular layers of brown 

chert several inches thick are interbedded. Contains abundant brachiopods_______________. 21 

7. Limestone, dolomitic; in 1- to 2-ft beds; 

weathers to dark gray jagged surfaces, 

with a few chert nodules. Contains 

abundant brachiopods, in part silicified, 

including Lepidocyclus and "Orthis"__ 21 

Upham Member:

6. Limestone, dolomitic, finely crystalline, 

dark-gray; in 2- to 3-ft beds containing knotted nodules and lenses of brown 

chert____________________ 20 

5. Limestone, dolomitic; weathers jagged and 

pitted; forms a slope. Contains brachiopods and corals 11
132 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Montoya Dolomite Continued

Upham Member Continued Feet 

4. Limestone, dolomitic, finely crystalline, 

dark-gray; weathers to drab-gray pitted 

surfaces. Forms massive beds and prominent ledges, cut by vertical joints. 

Contains abundant corals, especially in 

upper part, including Streptelasma and 

halysitid corals________________ 37 

Cable Canyon (?) Sandstone Member:

3. Sandstone, marly, thin-bedded, buff;

bedded with thin quartzitic layers 30 

2. Sandstone, saccharoidal, pale-brown; 

weathers dark brown; in thick beds 

breaking out in large blocks________ 25 

Disconformity. 

El Paso Limestone: 

Division C:

1. Limestone, marly, mottled, yellow; obscured in part by sandstone blocks from 

above. Exposed thickness about_ 10-15 

Base of section cut off by fault; rocks of Devonian and 

Mississippian age on downthrown side to northeast.

Summary of section 9

Part of Fusselinan Dolomite exposed________ 100-200

Montoya Dolomite:

Aleman Cherty Member_________ 110 

Upham Member________ _____ 68 

Cable Canyon (?) Sandstone Member__ 55

Total Montoya Dolomite__________ 233 

Part of El Paso Limestone exposed_________ 10-15

SECTION 10. APACHE SPRING

The following is a section of the Fusselman Dolomite 

and the upper part of the Montoya Dolomite on the 

ridges north of Apache Spring. The section is in two 

parts. Section lOa, of the Montoya Dolomite and the 

lower part of the Fusselman Dolomite, was measured 

on the ridge half a mile north of the spring, in the 

southeastern part of sec. 4, Block 66, Twp. 5. It is imperfectly tied by a cherty unit in the Fusselman Dolomite with the lower part of section lOb, which was 

measured on the ridge just northwest of the spring, in 

the northeastern part of sec. 7, Block 66, Twp. 5. The 

section was measured by J". Brookes Knight and Josiah 

Bridge in 1938; fossils were collected and identified in 

the field, but are not now available for reexamination.

Section lOb

Hueco Limestone at top of section. 

Angular unconformity.

Fusselman Dolomite: Feet 

11. Dolomite, massive, without chert. Stromatopora

observed near base__________________ 85 

10. Limestone, forming ledges and cliffs. Contains 

silicified fossils near top, including Favosites, 

several species of cup corals, and Stromatopora 

(X 9) ____________________________ 60

Fusselman Dolomite Continued Feet 

9. Limestone, in part cherty; contains Favosites and

cup corals (X 8)______ _ 37 

8. Limestone, dolomitic ; without chert-_-_ 37 

7. Limestone, somewhat dolomitic, medium-bedded; 

in part brecciatecl, with numerous chert masses. 

Contains brachiopods and the trilobite Dalmanites (X 7)_____________________ 38 

6. Limestone, massive; forms a coral reef. Corals 

include several species of Favosites, Halysites, 

and cup corals (X 6) _ _ 37 

5. Limestone, dolomitic; contains brecciated chert,

also Favosites, Halysites, and cup corals (X 5) 18 

4. Dolomite, without chert_ _ 8 

3. Limestone, dolomitic, very cherty; contains Halysites and other corals (X 4)________ 25 

2. Dolomite, white; forms ledges_______ 50 

1. Dolomite, white; weathers light buff; without chert 

or fossils; forms prominent ledge in ravine at 

northeast base of spur____________ 21 

Base of section concealed by alluvium. 

Section lOa

Top of spur; higher beds not measured. 

Fusselman Dolomite:

k. Dolomite; weathers to pitted surfaces; silicified along joints 6 

j. Dolomite; not so massive as bed below. Walking of beds between sections lOb and lOa indicates that cherty units 3 and 5 of the former 

should lie in this unit about 30 ft above 

base ________________________ 100 

i. Dolomite, finely crystalline massive, light-gray;

weathers to light-buff pitted surfaces____ 38 

Disconformity (?). 

Montoya Dolomite:

Aleman Cherty Member :

h. Covered______________________ 6 

g. Limestone, dolomitic; with abundant chert

layers; forms ledges_______________ 14 

f. Limestone, dolomitic; contains rounded chert

nodules 2-3 in. in diameter; forms a slope 4 

e. Limestone, dolomitic, very cherty; forms prominent ledges_______ ______-_ 22 

d. Limestone, dolomitic ; with sparse chert layers. 

At top, contains a branching colonial coral, 

Lepidocyclus, "Orthis," and other brachiopods_________________________ 20 

c. Limestone, dolomitic; silicified Streptelasma

at base______________________ 21 

b. Limestone, dolomitic, gray; without chert; 

forms ledges; contains poorly preserved 

silicified brachiopods_______________ 21 

Upham Member:

a. Limestone, dolomitic; contains some chert 

bands and nodules; forms a massive cliff at 

base of exposure_________________ 32 

Base of section concealed by alluvium.

Summary of section 10

Fusselman Dolomite:

In section lOb_____________________ 416 

In section lOa_____________________ 144

Approximate total Fusselman Dolomite in overlapping sections_____________________ 420
STRATIGRAPHIC SECTIONS OF MISSISSIPPIAN AND PENNSYLVANIAN ROCKS 133

Summary of section 10 Continued

Montoya Dolomite: Feet

Aleman Cherty Member______________ 108

Part of Upham Member exposed________ 32

Part of Montoya Dolomite exposed______ 140

OKDOVICIAN AND SILURIAN FOSSILS, NOT COLLECTED 

ALONG COURSES OF STBATIGBAPHIC SECTIONS

The following fossils were collected from Ordovician 

and Silurian rocks but not in any measured section:

X 1 and X 2 (USGS 3594, S595, 3596, and 3597). El Paso 

Limestone, lower part of division B. Inlier within the Sierra 

Diablo northeast of Cox Mountain; low hills between the two 

county roads, in northwestern part of sec. 14 and northeastern 

part of sec. 15, Block 54%. A sequence 340-400 ft thick is 

exposed, between sandstone beds at or near the top of division 

A on the southeast, and unconformably overlying Hueco Limestone on the northwest (Cloud and Barnes, 1946, p. 71), but the 

nature of the exposures are such that no section could be 

measured. Two sets of collections are available: The first set 

(X 1 and X 2) consists of a lot from the lower beds and another 

lot from the higher, made by J. Brookes Knight in 1938. The 

second set X2a-X2e) consists of five lots from the same succession of beds, made by Josiah Bridge, J. Brookes Knight, and 

others, later in the same field season. In addition, collections 

TF 329 to TF 335 were made in 1944 by Cloud and Barnes 

(1946, p. 71), but the fossils identified from them are not reproduced here. Identifications are by P. E. Cloud, Jr. (written 

commun., 1954). Each set of collections is given in descending 

stratigraphic order.

X 2. Higher beds to northwest, near saddle. CalatMum sp., 

Orospira sp., Bamesella"!, Hormotoma sp., bellerophontid? 

sp., other gastropods, endoceratid cephalopods, Xenelasma? sp., TritoecMa"!

X 1. Lower beds, between saddle and county road. CalatMum sp., Ceratopea n. sp., C. sp.?, Hormotoma sp., 

Orospira cf. 0. elegantula Cullison, gastropod gen. and 

sp.? orthoid brachiopods gen. and sp.?, trilobite gen. and 

sp.?

X 2 e. Near saddle, at top of sequence from which collections were made. Brachiopod gen. and sp. ? 

X 2 d. Gastropod unident.; Mcqueenoceras siphuncle; coiled 

nautiloid aff. Curtoceras, Tarphyceras, and Eurystomites; 

Hystericurusl, Jeffersonia sp., archaeostracan crustacean? 

gen. and sp.?

X 2 c. CalatMum, Bamesella sp. aff. B. lecanospiroides 

Bridge and Cloud, Bolbocephalus"! sp., Jeffersonia sp. aff. 

J. missouriensis Cullison. 

X 2 b. Pelmatozoan columnal, Orospiral sp., Diparelasmal

sp.

X 2 a. Near county road, not far above sandstone exposure. 

Ceratopea n. sp., Orospira sp., gastropod gen. and sp.? 

orthoid gen. and sp. ?

X 15 (USGS 3599). El Paso Limestone, upper part of division B, which is here overlain unconformably by Hueco Limestone. Northeastern Baylor Mountains, half a mile northeast 

of stratigraphic section 7a, on northeast side of next ridge. 

Collected by J. B. Knight in 1938; identified by P. E. Cloud, Jr. 

(written commun., 1954).

Ceratopea cf. C. ankylosa Cullison, Hormotoma sp., Raphistoma sp.

X 10 (USGS 3598). Montoya Dolomite, probably Aleman 

Cherty Member. Inlier of steeply dipping strata projecting 

amidst outcrops of Hueco Limestone, in Victorio Canyon 2 miles 

west-southwest of summit of Victorio Peak, near eastern center 

of sec. 14, block 43. Collected by J. B. Knight, 1938; identified 

by P. E. Cloud, Jr., Jean Berdan, and Helen Dunean (written 

commun., 1954).

Streptelasmatid corals, one specimen probably related to 

8. foerstei group; "Rafinesquina" sp.; Hypsiptycha sp.; 

Lepidocyclus sp.; dinorthid brachiopods gen. and sp. ? 

Om 2 (USGS 2762). Montoya Dolomite, Aleman Cherty 

Member. West slope low ridge on west side of Baylor Mountains, a quarter of a mile east of Texas Highway 54, near center 

of sec. 6, Block 66, Twp. 8. Collected by P. B. King and J. 

Brookes Knight, 1936; identified by Helen Dunean and Jean 

Berdan (written commun., 1954).

Streptelasmatid corals, in part probably related to S. foerstei

group.

OmS (USGS 2763). Montoya Dolomite, Aleman Cherty 

Member. East slope of Baylor Mountains a quarter of a mile 

south of eastern portal of Bed Tank Canyon, in east-central 

part of sec. 4, Block 122. Collected by J. B. Knight, 1936; 

identified by P. E. Cloud, Jr., Jean Berdan, and Helen Dunean 

(written commu., 1954).

Palaeophyllum thomii (Hall) ; FoerstepJiylluml sp. undet.; 

Streptelasmatid corals, in part probably related to S. 

prolongatum group; PlatystropMa sp.; DinortMs (Austinella) sp.; HypsiptycMa sp.; Lepidocyclus sp., trepostomatous bryozoans.

Om 4 (USGS 2764). Fusselman(?) Dolomite; light-gray 

bedded limestone, several hundred feet higher stratigraphically 

than Om 3, in same sequence. Originally mapped as upper part 

of Montoya Dolomite, but later interpreted as a calcitic facies 

of Fusselman. Southeast slope of Bed Tank Canyon, a quarter 

of a mile above its eastern portal, in west-central part of sec. 

4, Block 122. Collected by J. B Knight, 1936; identified by 

Helen Dunean, and Jean Berdan (written commun., 1954). 

Streptelasmatid coral gen. and sp. ?

STRATIGRAPHIC SECTIONS AND FOSSIL COLLECTIONS 

OF MISSISSIPPIAN AND PENNSYLVANIAN ROCKS

SECTION 11. MINE CANYON

The following is a section of part of the Barnett 

Shale exposed in a ravine about half a mile north of 

the portal of Mine Canyon, in the southwestern part 

of sec. 12, Block 66, Twp. 5. The section was measured 

by J. Brookes Knight in 1931. Fossils collected from 

units 2, 3, and 4 have been identified by Mackenzie 

Gordon, Jr., and E. L. Yochelson, and are discussed 

on pages 41-42.

Hueco Limestone at top of section. 

Unconformity.

Barnett Shale: Feet 

9. Limestone, white, impure 5 

8. Shale, green 10 

7. Shale, purplish-brown; interbedded with shaly

limestone- 10 

6. Limestone, buff, shaly, friable; contains poorly

preserved fossils 10
134 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Barnett Shale Continued Feet

5. Shale, purplish, carbonaceous; interbedded with 

thin limestone beds that contain poorly preserved fossils_________________ 20

4. Shale like that above, but containing limestone 

lenses and concretions as much as 3 ft in diameter; these and similar limestone lenses beneath contain well-preserved fossils 10

3. Shale, dark-gray; contains pyrite and selenite, also 

phosphatic nodules; lenticular limestone beds 

near top__ _ 20

2. Shale, purplish, carbonaceous; limestone concretions and lenses at top and 20 ft below top 50

1. Shale, black, massive, to base of exposure (?) 

Base concealed by alluvium. 

Part of Barnett Shale exposed______________ 135-fSECTION 12. MARBLE CANYON

The following is a section of part of the beds of 

Pennsylvanian age exposed along the base of the Sierra 

Diablo escarpment south of Marble Canyon, along the 

east edge of sec. 21, Block 66, Twp. 5. The section was 

measured by P. B. King and E. E. King in 1928, and 

fossils were collected from units 5 and 6 by J. Brookes 

Knight and P. B. King in 1931. Identification of these 

fossils by Mackenzie Gordon, Jr., and E. L. Yochelson 

is given on page 45.

Hueco Limestone at top of section. 

Angular unconformity.

Beds of Pennsylvanian age: Feet 

10. Limestone, gray, thin-bedded; forms a slope _ 22 

9. Limestone, light-gray, granular; forms a ledge 22 

8. Limestone, light-gray, thin-bedded; forms a slope. 24 

7. Limestone, light-gray, granular; forms a ledge 25 

6. Slope on which bedrock is concealed; Spirifer,

cup corals, and other fossils on surface___ 5 

5. Limestone; forms a ledge; contains bellerophontids and cup corals________________ 3 

4. Covered ___________________ 11 

3. Limestone, light-gray, granular; contains crinoid

columnals______________________ 22

2. Covered___________________________ 6

1. Limestone, light-gray, granular; forms a ledge__ 30

Base concealed by alluvium.

Part of beds of Pennsylvanian age exposed_______ 170

STRATIGRAPHIC SECTIONS AND FOSSIL COLLECTIONS 

OF PERMIAN BOCKS

The sections and fossil lists which follow describe 

fossils which were collected and identified during both 

the earlier and later phases of this investigation. As 

many revisions of fossil terminology and taxonomy 

have been made between the times of the earlier and 

later investigations, the names for the same fossils are 

likely to vary from one collection to another. It has 

not been feasible to revise the earlier identifications to 

agree with the later, but the earlier listings are given

here because they are of some descriptive and historical 

interest.

From collections made during the earlier phases of 

the investigation, brachiopods were identified by R. E. 

King (1931) and fusulinids by Dunbar and Skinner 

(1937). Collection numbers are preceded by REK for 

the brachiopods so identified and by D & S for the 

fusulinids so identified. These collections are deposited 

at Peabody Museum, Yale University.

Fossils in collections made during the later phases of 

the investigation were identified by paleontologists of 

the U.S. Geological Survey (P. E. Cloud, Jr., and E. L. 

Yochelson, written commun., 1954; L. G. Henbest, written commun., 1955). They are indicated by accession 

numbers prefixed by USGS, and the Foraminifera by 

additional accession numbers prefixed by "F." In addition, the field labels of J. Brookes Knight and the 

writer are also generally indicated. These collections 

are deposited with the U.S. Geological Survey.

SECTION 13. WYUCB MOUNTAINS

The following is a section of the Hueco and Victorio 

Peak Limestones in the Wylie Mountains, beginning in 

the southeast corner of the report area, and proceeding 

eastward across the mountains about 10 miles. Sections of the Hueco Limestone on the west face of the 

Wylie Mountains were measured by P. B. King and 

E. E. King in 1928, and by P. B. King and J. Brookes 

Knight in 1931, at which time scattered observations 

were also made on higher strata farther east. Subsequently, the whole mountain area has been mapped 

and described by Hay-Eoe (1957). Fossils collected in 

1928 were identified by E. E. King (1931) and Dunbar 

and Skinner (1937); those collected in 1931 were identified by E. L. Yochelson (written commun., 1959); those 

collected by Hay-Eoe were identified by E. V. Hollingsworth and D. A. Drake (Hay-Eoe, 1957). Some collections from the same area were made earlier by G. B. 

Eichardson and identified by G. H. Girty (Eichardson, 

1914, p. 5).

The section given here is compiled from these sources. 

Data on the Powwow Member of the Hueco Limestone 

combine observations by King and his associates and 

by Hay-Roe. Units 3-7 of the main body of the Hueco 

Limestone are generalized from the sections by P. B. 

King and E. E. King and by P. B. King and J. Brookes 

Knight, which were measured on the slope west of elevation point 5039 (sec. 3, Block 64). The section of 

Victorio Peak Limestone is from Hay-Eoe, with the 

addition of some observations by P. B. King and J. 

Brookes Knight.
STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 135

Seven Rivers Formation in eastern foothills of

Wylie Mountains, and farther east. 

Conformity (?). 

Victorio Peak Limestone:

Dolomite member: Feet 

12. Dolomite, granular; with calcite 

vugs; pale brownish gray; weathers deeply pitted; in thick massive 

beds. Contains abundant species of 

Parafusulina (identified by R. V. 

Hollingsworth), which are said to 

be of Leonard type in lower part 

and of Guadalupe type in the upper 

part. Most of these weather to 

cavities, but part are silicifled. 

Forms eastern third of Wylie 

Mountains__________..____ 1,100 

Marl member:

11. Marl, dolomitic; poorly exposed because of slumping of overlying 

beds; wedges out along strike south 

of mountains______________ 15 

Limestone member:

10. Limestone and dolomite, yellowish- to 

brownish-gray; weathers to lightgray pitted surfaces; in 4- to 6-in. 

beds; contains rare poorly preserved fossils. In 1931, bellerophontid gastropods as much as 3 in. 

in diameter were collected in basal 

beds, and in higher beds a large 

coarsely ribbed spiriferoid (USGS 

7052) ___________________ 4 TO 

Basal member:

9. Marl, dolomitic, thin-bedded, yellowgray to pale-brown; with thin 

ledge-making dolomite layers, interbedded with red silty shale and 

crossbedded limestone-pebble conglomerate. Forms a light-colored 

slope-making band between the 

ledges that extends southward 

across the mountains________ 30-60 

Unconformity. 

Hueco Limestone:

Main body of formation:

8. Limestone, similar to that below, 

forming summits of western third 

of Wylie Mountains. Thickness indeterminate on outcrop because of 

numerous closely spaced faults of 

small displacement. Amount given 

is obtained by subtracting measured 

thickness of lower beds from total 

thickness of main body of formation (1,240 ft) in Cosden Petro 

leum Oockrell 1 well at east edge 

of mountains (sec. 7, Block 80)__ 450 

7. Limestone, dense, dark-gray to graybrown; in 6-in to 2-ft beds; forms 

ledges 5-30 ft thick, separated by 

slopes, in which platy limestone 

and shale are interbedded. Many 

of the limestone beds contain short

Hueco Limestone Continued

Main body of formation Continued

chert nodules and lenses. Spicules, 

fusulinids, productids, gastropods, 

and echinoid spines observed in 

various layers. Forms summit of 

west face of Wylie Mountains south 

of elevation point 5039_________

6. Limestone. In upper part thinner 

bedded and darker gray than beds 

above and below, forming thin 

ledges on slope; in lower part, 

some thicker, lighter gray ledges. 

A few beds in upper part contain 

small chert nodules. Fossils are 

abundant in many beds, but are 

mostly visible in cross section, 

and are partly destroyed by dolomitization. From collections of 1928 

have been identified Staffella sp., 

Pseudoschwagerina texana Dunbar 

and Skinner, Productus incal 

d'Orbigny, and Productus invest 

Newberry (D & S 141, 142; REK 

508). Collection of 1931 contains 

Polypora sp., Composita sp., and 

Omphalotrochus sp. (USGS 7005x) ; 

echinoid spines, a pinnid pelecypod, 

and bellerophontid gastropods also 

observed___________________

5. Limestone, dolomitic, fine-grained to 

dense, gray to dark-gray; in 1- to 

4-ft beds; forms ledges and cliffs. 

Some beds are laminated and a few 

are brecciated. Some poorly preserved echinoid spines and bellerophontid gastropods observed_______

4. Limestone, partly dolomitic, gray to 

pink; weathers gray; in 1- to 3-ft 

beds; forms ledges and slopes, with 

a covered interval at base______ 

3. Limestone, gray to gray-brown; mainly 

in 6-in. to 1-ft beds; forms slopes 

and thin ledges below, where there 

are many marl partings, but passing into a strong ledge at top, which 

is prominent at about midheight on 

west face of mountains. A few beds 

contain chert nodules and lenses. 

Fossils are abundant, but are mostly 

poorly preserved and fragmented. 

Productus hessensis King and 

Composita subtilita (Hall) have been 

been identified from collection of 

1928 (REK 507). Collection of 1931 

includes echinoid spines; the brachiopods Composita cf. C. sultilita 

(Hall), and Dictyoclostus (n. subgen.) cf. D. hessensis (King), D. 

wolfcampensis (King) ; the gastropods Omphalotrochusl sp. and a bellerophontid ; and the pelecypod AviFeet

173

211

196

75
136 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Feet

139

Hueco Limestone Continued

Main body of formation Continued

culopecten sp. (USGS 7005) ; staffellid foraminifers also observed______

Powwow Member:

2. Marl and nodular limestone, buff, 

poorly consolidated. Abundant staffellid foraminifers, Composita, productid brachiopods, euomphalid gastropods, pectenoid pelecypods, and 

echinoid spines and plates observed. 

Also contains the ostracodes Ellipsellal distenda Kellett, Healdia! sp., 

ParaparcMtes humerosus Ulrich and 

Bassler, and P. magnus Kellett, and 

the foraminifer Globovalvulina sp. 

(identified by D. A. Drake)_______

1. Sandstone, siltstone, and shale, arkosic 

and conglomeratic, poorly consolidated, dark-red-brown to orange. 

Thickness varies abruptly within 

short distances, as a result of deposition on an irregularly eroded surface 

of underlying rocks_______________

Angular unconformity.

Metamorphic rocks of Carrizo Mountain Formation at base of section.

Summary of section 13

Victorio Peak Limestone_______________ 1, 615-1, 645

Hueco limestone:

Main body of formation________ 1, 244 

Powwow Member___________ 40-170

20

20-150

Total Hueco Limestone__________ 1,284-1,414 

SECTION 14. BASS CANYON

The following is a section of the Hueco Limestone in 

the southern Carrizo Mountains, on the south slope of 

Bass Canyon, about 1^ miles south of the south edge 

of the report area (sec. 18, Block 66, Twp. 9). A section at this locality is given by Baker (1927, p. 9), and 

a section of the main body of the formation was measured by P. B. King and R. E. King in 1928; the area 

was later mapped by Flawn (in King, P. B., and Flawn, 

P. T., 1953, p. 67 and pi. 1). In the section given here, 

the description of the Powwow Member is by Baker 

and that of the main body of the formation by P. B. 

King and R. E. King. Fossils were identified by E. E. 

King (1931).

Top of ridge; no higher beds preserved. 

Hueco Limestone:

Main body of formation: Feet 

8. Limestone, dark-gray; in 1-ft beds; interbedded with thin-bedded yellow-brown limestone__ ___ _____ ___ 255 

7. Limestone, dark-gray, thin-bedded________ 70 

6. Limestone, dark-gray, thick-bedded; forms 

prominent ledges. Contains Productus Jiessensis King and Composita subtilita (Hall) 

(REK 510) ; staffellid foraminifers, echinoid 

spines, and gastropods also observed____ 100

Hueco Limestone Continued

Main body of formation Continued Feet 

5. Limestone, poorly exposed_________ _ 13 

Powwow Member:

4. Sandstone, calcareous, micaceous, fissile 5 

3. Sandstone, irregularly banded red and gray 20 

2. Sandstone, coarse, conglomeratic, gray; lying

unevenly on unit below- __________ 8 

1. Sandstone and conglomerate, micaceous, darkpurplish-red, containing angular fragments 

of quartz and schist. (This unit was assigned by Baker to the Van Horn sandstone; 

observations by King, confirmed by Flawn, 

indicate that it is part of the Powwow member, although Flawn has found true Van 

Horn sandstone below the Hueco a mile or 

two to the northeast.) -_______ __ 250 

Angular unconformity. 

Carrizo Mountain Formation at base of section.

Summary of section 14

Hueco Limestone:

Part of main body of formation exposed 438 

Powwow Member _ 283

Part of Hueco Limestone exposed ____ 721

SECTION 15. THREEMUJEJ MOUNTAIN

The following is a section of Hueco Limestone on 

Threemile Mountain, at the east end of the high ridge 

northwest of Van Horn, in the southeastern part of sec. 

13, Block 66, Twp. 8. The main part of the section 

(units 1-14) was measured up the east face of the 

mountain to the top of a spur, the higher beds being 

added from the summit of the mountain, 750 ft to the 

northwest, which is separated from the spur by minor 

faults, downthrown to the west. The section was measured by J. Brookes Knight in 1931, and some additional 

notes and fossil collections were made in 1938. Larger 

fossils were identified by P. E. Cloud, Jr., and E. L. 

Yochelson; foraminifers were identified by L. G. Henbest (written commun., 1954,1955). Besides the fossil 

collections from Threemile Mountain listed here, others 

were made by G. B. Eichardson in 1907, which were 

identified by G. H. Girty (USGS 7184; field loc. 37), 

and by J. W. Beede and others for the Texas Bureau of 

Economic Geology, which were identified by E. E. King 

(1931, REK Te). 

Top of mountain; no higher beds preserved.

Hueco Limestone:

Main body of formation: Feet 

19. Limestone, thinner bedded and darker than

below; near top, cross sections of pelecypods

observed- 38 

18. Limestone, massive, gray; weathers pitted_ 12 

17. Limestone, thin-bedded, light-gray; a few beds

2-3 ft thick____________________ 38 

16. Limestone, dark-gray; contains some chert and

fossils 17
STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 137

Hueco Limestone Continued

Main body of formation Continued Feet 

15. Limestone, dark-gray; forms a slope; contains chert and a few echinoid spines, and 

near base, large bellerophontids____ 23 

14. Limestone, thin-bedded; forms top of southeastern spur_____________ 10 

13. Limestone, massive, gray; contains chert and

bellerophontids__________ 55 

12. Limestone, thin-bedded; weathers yellowish; 

succeeding unit. Contains echinoid spines 

and other fossils____ _____ 25 

11. Limestone, forming a ledge; contains bryozoans______________________ 18 

10. Limestone, forming slopes and ledges; contains bryozoans and large echinoid spines_ 11

9. Limestone, gray, massive; with thin marl 

partings near base and bands of chert nodules near top. This and adjacent beds contain Wewokella (Talpaspongia) clavata (R. 

H. King), other sponges and their spicules, 

Syringopora sp. and other compound corals; 

echinoid spines and plates; Fenestella sp., 

Fistulipora sp., Polypora sp., and other 

bryozoans; the brachiopods Composita cf. C. 

subtilita (Hall), Crurithyrisl sp., Dictyoclostus wolfcampensis (King), various dielasmids including Dielasma aff. D. bovidens 

(Morton), Hustedia mormoni (Macrou), 

and Meekellal sp.; the pelecypods Alloris 

mal sp., Aviculopecten sp., Aviculopinna sp., 

Pseudomonotis sp., and Septimyalina sp.; 

the gastropods Betterophon parvicristatus 

Yochelson and other bellerophontids, 

Euconispira cf. E. missouriensis (Swallow), 

a loxonematacean, Meekospira sp., Naticopsis sp., Omphalotrochus obtusispira 

(Shumard), Stegocoelia! sp., Straparollus 

(Euomphalus) cornudanus (Shumard), and 

a subulitid; the scaphopod Plagioglyptat 

sp.; and ostracodes (USGS 6937,14437; field 

labels 11, C 14). The beds also contain 

the foraminifers Stafella sp., and Ozawainella sp. (F. 2718c, 9812), and Dunbar and 

Skinner report the presence of Schivagerina 

bellula Dunbar and Skinner (D & S 90)__ 30

8. Limestone, marly; forms a slope; poorly exposed except in ravines. Contains bellerophontids______________________ 35

7. Limestone, gray; forms a ledge________ 6

6. Marl and marly limestone ; containing bellerophontids______________________ 19

5. Limestone, thick-bedded, gray to light-gray; 

with marl partings; forms a ledge. Contains bellerophontids_____________ 20 

Powwow Member:

4. Limestone, marly; forms a slope; poorly exposed except in ravines. Fossils occur in 

the marls and are scattered on the slope, 

derived from this bed and those just above. 

They include fenestrate and branching 

bryozoans; the brachiopods Dictyoclostus 

wolfcampensis (King), Composita cf. C. 

subtilita (Hall), and Dielasma cf. D. boviHueco Limestone Continued

Powwow Member Continued Feet 

dens (Morton) ; the gastropods Straparollus (Euomphalus) cornudanus (Shumard), 

Omphalotrochus obtusispira (Shumard), 

and a large bellerophontid; and the 

scaphopod Plagioglyptal sp. (USGS 14430; 

field label C 7) ______________ 22 

3. Sandstone, arkosic, conglomeratic, yellow; 

mostly forms a slope, but with ledges toward the top_____________ 77

2. Sandstone, arkosic, red; contains scattered 

chert pebbles near base and a layer of limestone-pebble conglomerate in a red arkosic 

matrix at top_________ 37

1. Conglomerate, gray; formed of limestone 

pebbles and cobbles, probably derived from 

El Paso Limestone to north. This unit is 

a very local deposit, and thins rapidly 

westward________.._______ _ 70 

Angular unconformity.

Van Horn Sandstone in massive red ledges at base of 

section.

Summary of section 15

Hueco Limestone:

Part of main body of formation exposed_____ 357 

Powwow Member_ _ ___ __ 206

Part of Hueco Limestone exposed 563

OTHER FOSSIL COUUECTIONS FROM HUECO LIMESTONE 

IN THREEMIUE3 MOUNTAIN AREA

 The following fossils were collected by P. B. King 

and J. Brookes Knight from the Hueco Limestone in 

the Threemile Mountain area, but not in any measured 

section:

USaS 14438, F 9813 (field label C 15). About 4 miles west 

of Threemile Mountain, on south side of ridge, south of elevation point 5083 (southwestern part of sec. 16, Block 66, Twp. 8). 

Lower part of main body of Hueco Limestone contains undetermined bryozoans; the brachiopods Dictyoclostus wolfcampensis (King), D. (n. subgen.) huecoensis (King), and Composital sp.; and the gastropods Omphalotrochus"! sp., Stegocoelia"! sp., Straparollus (Euomphalus) cornudanus (Shumard) ; 

large bellerophontids, and a subulitid. The limestone is 

crowded with small foraminifers of the Spandelina group and 

Staffella sp. and with juvenaria of fusulinids, probably including Schubertella.

USGS 14426 (field label C S). About 3% miles west-northwest of Threemile Mountain, on an outlier whose summit is 

elevation point 5079 (near center of sec. 9, Block 66, Twp. 8). 

Limestone and interbedded marls of main body of Hueco 25-50 

ft above Powwow Member contain echinoid spines, the 

brachiopods Dictyoclostus wolfcampensis (King) and Composita cf. C. subtilita (Hall) ; and the gastrophod Omphalotrochus obtusispira (Shumard). Staffellid foraminifers and 

productid gastropods were observed in the field, but are not 

represented in the collection.

SECTION 16. BEACH MOUNTAIN

The following are two sections of the Hueco Limestone on the eastern flank of Beach Mountain. Section
138 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

16a was measured at the east end of a mesalike outlier 

whose summit is elevation point 5021 (near center of 

south line of sec. 6, block G). Section 16b was measured 

about three-quarters of a mile farther east, in a block 

downfaulted farther than rocks of the preceding, and 

extends south westward from outcrops of Montoya Dolomite to the crest of the ridge (southwestern part of sec. 

6, Block 65, Twp. 8). The sections were measured by 

J. Brookes Knight in 1931. Fossils were observed in the 

field, but none were collected. Small collections, which 

were made in the same area by G. B. Richardson in 

1907, have been identified by G. H. Girty (USGS 7182, 

7l82a; field Iocs. 25, 27).

Section 16a

Top of outlier; no higher beds preserved. 

Hueco Limestone:

Main body of formation : Feet 

10. Limestone, dolomitic, blue-gray, thin-bedded; 

forms 1- to 3-ft ledges; contains minute 

mollusks_ ________ _ 70 

9. Limestone, dolomitic, yellow-gray, splintery; 

forms 5- to 15-ft ledges; contains poorly preserved silicified fossils, including bellerophontids__ _._____________ ___ 105 

8. Limestone, dolomitic, yellow-gray; in 1- to 2-f t 

beds; interbedded with dolomitic marl; 

forms a slope__________________ 100 

7. Limestone, dolomitic, yellow-gray; forms 

a ledge; contains staffellid foraminifers and 

large productids_________________ 3 

6. Slope, with a thin ledge of dolomitic limestone near middle; probably mostly marl__ 15 

5. Limestone, dark blue-gray, mottled; forms a 

ledge; cross sections of small gastropods 

observed_____________________ 3 

Powwow Member:

4. Marl, sandy, poorly consolidated; yellow, below nearly white at top_____________ 8 

3. Sandstone, fine-grained, marly, red; contains

pebbles near base______________ _ 25 

2. Slope without exposures; pebbles on surface_ 17 

1. Conglomerate, made up of limestone pebbles

derived from underlying Ordovician rocks_ 2 

Angular unconformity. 

Montoya Dolomite at base of section.

Section 16b

Top of ridge; no higher beds exposed.

Hueco Limestone:

Main body of formation:

6. Limestone, dolomitic, gray; in 3- to 5-ft beds, 

becoming thinner bedded, darker, and less 

dolomitic upward. In the thinner darker 

beds cross sections of small mollusks are 

visible; the topmost Tedge contains poorly 

preserved gastropods, including Euconispira, 

euomphalids, and bellerophontids, as well as 

Composita, cup corals, and echinoid spines- 140

Section 16b Continued 

Hueco Limestone Continued

Main body of formation Continued Feet 

5. Limestone, dolomitic; gray, in 3- to 5-ft beds; 

forms receding ledges. A euomphalid gastropod observed near top; irregular siliceous 

masses lower down may in part be much 

altered fossils________ - _ 50 

4. Limestone, dolomitic, splintery; forms thin 

ledges on slope, with a 2-f t ledge near middle 

that contains poorly preserved bellerophontid 

gastropods_________ __ 35

3. Slope, with a thin ledge of splintery yellowgray dolomitic limestone at top__ __ 10 

Powwow Member:

2. Slope, poorly exposed. Some outcrops of red 

marl at top, but most of surface is covered 

by limestone pebbles and reddish wash__ 30 

1. Conglomerate, sandy, yellow, composed of limestone pebbles derived from underlying Ordovician rocks_____________________ 3 

Angular unconformity. 

Monotoya Dolomite at base of section, on northeast.

Summary of section 16 

Hueco Limestone: 

Section 16a:

Part of main body of formation exposed__ 269 

Powwow Member_________________ 52

Part of Hueco limestone exposed________ 348 

Section 16b:

Part of main body of formation exposed__ 235 

Powwow Member_________________ 33

Part of Hueco Limestone exposed_______ 268 

SECTION 17. HIGH POINT OF BAYL.OR MOUNTAINS

The following section of the Hueco and Bone 

Spring Limestones was measured on the eastern face of 

Baylor Mountains, up a southeast-trending spur, whose 

summit is the high point of the mountains, at BM 5568 

(northeastern part of sec. 1, Block 122, and southern 

part of sec. 3, Block 65, Twp. 7). A section was measured here by P. B. King and R. E. King in 1928, and 

again by J. Brookes Knight in 1931. The section 

given is that of Knight, but some notes made in 1938 

have been added, and the fossils collected in 1928 are 

placed in their approximate positions in the section. 

Fossils collected in 1928 were identified by R. E. King 

(1931), and those collected in 1931 by P. E. Cloud, Jr., 

and E. L. Yochelson (written commun., 1954).

Top of mountain ; no higher beds exposed.

Bone Spring Limestone: Feet 

17. Limestone, dolomitic, light-gray, massive; has an 

original dip to north, and forms great cliffs north 

of summit BM 5568_________________ 200 

16. Limestone, fine-grained, light-gray, thin-bedded; 

contains fossil fragments. Forms a cliff whose 

summit is BM 5568; wedges out northward beneath, and partly intergrates with unit above_ 110
STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 139

Bone Spring Limestone Continued Feet

15. Shale, calcareous or marly, yellow to pink; with 

some ledges of dark-gray limestone a foot or two 

'thick, in part fossilferous____ _ _ 55

14. Limestone, dark-gray, thin-bedded, cherty, very fossiliferous. From a collection made in 1928 at 

about this level, R. E. King identified the brachiopods Rhipidomella mesoplatys baylorensis King 

(type), Streptorhynchus pyramidalel King, Productus ivesi Newberry, Productus schucherti 

King, Linoproductus cora angustus King, Marginifera sublaevis King, Aulostegas triagonalis 

King, Spirifer (Neospirifer) pseudocameratus 

Girty, Hustedia meekana (Shumard), and Composita mira (Girty) (REK 503)_________ 10

13. Limestone, dolomitic, irregularly bedded; with siliteeous bands that contain fossils__________ 45

12. Limestone, dolomitic, gray, massive; contains

sponges at base ________________ 10

11. Limestone, granular, light-gray, thick-bedded,

cherty; contains many gilicified brachiopods_ 15

10. Limestone, light-gray, thin-bedded and laminated; 

interbedded with siliceous shale. Many cherty 

bands are fossiliferous and contain hexactinellid 

sponge spicules; the bryozoans Fistuliopora sp., 

Acanthocladia sp., and Polypora sp.; the brachiopods Buxtonia (Kochiproductus) victorioensis 

King, Chonetes sp., Composita sp., Dictyoclostus 

(Chaoiella) guadalupensis (Girty), Hustedia 

sp., Linoproductus (Cancrinella) sp., "Marginifera" sp., "Martinia" sp., Meekella sp., orthotetacean indet., "Spirifer" sp., and Stenocisma sp.; 

a nuculoid pelecypod; the gastropods Apachella 

sp., Babylonites sp., Euphemites cf. E. imperator 

Yochelson, E. sp., and Knightites (Retispira) 

sp.; the scaphopod Plagioglypta sp.; and the trilobite Delarial sp. (USGS 7048 ; field label 24 A). 

From a collection made in 1928 at about the same 

level, R. E. King identified the brachipods 

Rhipidomella mesoplatys baylorensis King, Meekella difflcilis Girty, Marginifera manzanica Girty, 

Prorichthofenia likharewi King, Camarophoria 

venusta Girty, Hustedia meekana (Shumard), 

and Composita subtillta (Hall) (REK 502)__ 50 

9. Limestone, dolomitic; contains abundant molds of 

fusulinids in parallel orientation ; weathers very 

jagged; forms ledges that alternate with 2- to 

3-ft layers of marl. To north, the dolomitic 

layers wedge out into light-gray platy fossiliferous limestone ____________________ 110 

8. Limestone, dolomitic, thin-bedded; contains poorly 

preserved large fusulinids, crinoid columnals, 

and cup corals; weathers very jagged; some interbedded marl near top______________ 55 

7. Limestone, dolomitic, massive; in part brecciated; 

weathers very jagged; forms a lens; contains 

poorly preserved large fusulinids and other fossils____________________________ 20 

6. Limestone, dolomitic; resembles beds below, but

forms receding ledges________________ 40 

5. Limestone, dolomitic, light-gray, thick-bedded; 

weathers jagged; forms cliffs; contains poorly 

preserved crinoid columnals near top______ 165

Bone Spring Limestone Continued Feet 

4. Limestone, dolomitic, light- to dark-gray; in 1- to 

4-ft beds; weathers jagged in part; forms a slope. 

Some beds contain molds of fusulinids that are 

larger than those below_ 110 

Unconformity ( ?). 

Hueco Limestone:

Main body of formation :

3. Limestone, dolomitic, light-gray, thinly and 

evenly bedded, splintery; forms cliffs in 

upper part. Most beds contain molds of 

small fusulinids, and a bed 25 ft above base 

contains nodules of probable algal origin 308 

2. Limestone, dolomitic, light gray-brown; in 2- 

to 5-ft beds; weathers somewhat pitted; 

forms a ledge; contains vugs, cavities, and 

fusulinid molds _ _ 10 

Powwow (?) Member:

1. Poorly exposed on slope; in ravines are outcrops of limestone-pebble conglomerate in 

gray-brown dolomitic matrix 35 

Angular unconformity.

Beds of Devonian age, and Fusselman Dolomite at base of 

section (see section 7).

Summary of section 17

Part of Bone Spring Limestone exposed __ _ 995

Hueco Limestone:

Main body of formation____ 318 

Powwow (?) Member-_ 35

Total Hueco Limestone_ __ _ ___ 353

OTHER FOSSIL COLLECTIONS FROM BONE SPRING 

LIMESTONE NEAR HIGH POINT OF BAYLOR MOUNTAINS

The following fossils were collected from the Bone 

Spring Limestone by P. B. King in 1931, on the ridge 

west of the high point of the Baylor Mountains; the 

collections are not in the measured section, but their 

stratigraphic positions can be approximated.

USGS 1053. Ridge west of high point of Baylor Mountains, 

near elevation point 5535 (northeastern part of sec. 2, Block 

122), from black limestone above middle reef beds (approx. 

unit 15 of section 17). Contains the coral Lophophyllum sp.; 

the bryozoan Fistulipora sp.; the brachiopods Chonetes sp., Linoproductus (Cancrinella) sp., "Marginifera" spp., Dictyoclostus 

(Chaoiella) guadalupensis (Girty), productids indet., Stenocismal sp., Neospirifer sp., and Rhipidomella sp.; the pelecypods 

Astartella sp. and a pectenoid; and a bellerophontid gastropod.

USGS 7009. North end of ridge west of high point of Baylor 

Mountains (southeastern part of sec. 4, Block 65, Twp. 7), from 

top of middle reef beds (approx. unit 14 of section 17, or at 

about same level as collection REK 503). Contains the bryozoans Fistulipora sp. and Striatopora sp.; the brachiopods 

Leptodus sp., Rhipidomella sp., and a productid; the pelecypods Astartella sp., "Cypricardinia" sp., a nuculoid, and 

Pteria! sp.; and the gastropods Apachella sp., Euphemites sp., 

Glabrocingulum sp., and a pleurotomarian.

SECTION 18. NORTHEASTERN BAYLOR MOUNTAINS

The following section of the Hueco and Bone Spring 

Limestones was measured in the northeastern part of the
140 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Baylor Mountains northwestward up the first ridge 

southwest of elevation point 4888 (north-central part of 

sec. 48, Block 65, Twp. 6), with higher beds on elevation 

point 4888 added (south-central part of sec. 37, Block 

65, Twp. 6), which are downfaulted with respect to the 

main section. The section was measured by J. Brookes 

Knight in 1931, but some additional observations were 

made in 1938. Fossils were identified by P. E. Cloud, 

Jr., and E. L. Yochelson (written commun., 1954).

Top of ridge; no higher beds exposed.

Bone Spring Limestone: Feet 

18. Limestone, dark-gray, fine-grained to dense; chert 

nodules in 6-in to 2-ft beds; weathers to 

smooth gray surfaces and forms cliffs. Resembles limestone at high point of Baylor 

Mountains (unit 16, section 17). Thickness 

given is approximately that on elevation point 

4888; on ridges at northeast, near northeast end 

of mountains, these limestones are several 

times thicker_____________________ 100 

17. Limestone, thin-bedded, black; forms a slope. 

On southeast slope of summit 4888, about 150 ft 

stratigraphically above unit 14, a thin lens of 

bioclastic limestone (or "molluscan ledge") contains a prolific dominantly molluscan fauna 

(USGS 6983, USGS 14475; field labels 27, C 

33). This includes the corala Amplexus sp., 

Cladochonus sp., and Lophophyllum sp.; the 

bryozoans Acanthocladia sp., Cystodictya sp., 

Fenestella sp., Fistulipora sp., MeeJcopora sp., 

Polypora sp., Rhom'bopora sp., Septopora sp., 

Stenopora sp., and Striatopora sp.; the brachiopods Avonia sp., Buxtonia (KocMproductus) 

victorioensis King, CJionetes sp., (large), Composita sp., Enteletes cf. E. dumblei Girty, 

Hustedia mormoni (Marcou), Leptodus sp., 

Heekella difflcilia Girty, orthotetacean indet., 

Rhipidomella sp., Squamularia sp., and Wellerella sp.; and the trilobite Delaria"! sp. The 

mollusks include the pelecypods Acanthopecten 

sp., Astartella nasuta Girty, Aviculopecten sp., 

Edmondia sp., Myalinid indet., Nucula sp., 

Nuculana spp., Paleoneilo sp., Parallelodon sp., 

PermopJiorus sp., Pseudomonotis sp., Pterial 

sp., Schizodus sp., Solenoyma sp., and Stre'blopteria sp.; the gastropods Anomphalus sp., 

Babylonites sp., Bellerophon deflectus Chronic, 

Glyptospira sp., Knightites (Retispira) sp., cf. 

Loxonema sp., Naticopsis sp., Orthonema sp., 

pleurotomarian indet., StegocoeUat sp., "Stroleus" sp., sublitid indet, Trachydomia sp., "T." 

sp., and "Worthenia" sp.; the chiton "Gryphochiton" sp.; the scaphopod Plagioglypta sp.; 

and an orthoceratid cephalopod and an ammonite___________.._-_________ 200 

16. Limestone, granular, dark-gray, evenly bedded; 

contains some poorly preserved fossils. Forms 

top of ridge southwest of summit 4888_____ 20 

15. Limestone, platy and siliceous, gray and black; 

forms a slope. Some 1-ft beds of gray granular 

limestone interbedded in lower part______ 85

Bone Spring Limestone Continued Feet 

14. Limestone, granular, gray, thick-bedded; contains

a large Enteletes and other fossils 14 

13. Limestone, dolomitic, gray, massive. Contains 

the bryozoan Fistulipora sp.; the brachiopods 

MeeJcella sp., Prorichthofenia sp., and Wellerella sp. (large) ; a pseudozygopleuran and a 

pleurotomarian gastropod, and an indeterminate nautiloid (USGS 7000; field label 25 B). 

Sponges were observed near base- 45 

12. Limestone, black, thin-bedded; with an irregular

upper contact_____-_____-__-_ _ 5 

11. Limestone, dolomitic, light-gray, massive; contains large fusulinids__ _ _ __ 35 

10. Limestone, granular, light-gray, thin-bedded, fossiliferous; mostly forms float on a slope___ 20 

9. Limestone, dolomitic, massive, in part brecciated;

forms a reefy mass; contains rare fossils- _ 35 

8. Limestone, slabby, black; forms a slope_____ 25 

7. Limestone, dolomitic; brecciated below, massive 

above; forms a reefy mass. Contains many 

silicified fossils, and near base, large fusulinids- 40 

6. Limestone, platy to thin-bedded; light-gray below 

and black above; forms a slope; several 2-ft 

beds of granular limestone interbedded near 

base __ ____________________ 110 

5. Limestone, dolomitic, light-gray, thin-bedded to 

platy; with a 10-f t ledge of granular fossilif erous limestone interbedded 17 ft above base. 

This contains the brachiopods Prorichthofenia 

>sp. and "Marginifera" sp., the gastropod Warthia waageni Yochelson, and the scaphopod 

Plagioglypta sp. (USGS 7000a; field label 25 

AA). At about the same level, large indeterminate fusulinids were collected (F 9822; field 

label C 24 B)_____________________ 66 

4. Limestone, dolomitic, siliceous, gray, thin-bedded

and laminated; forms a slope_________ 15 

3. Limestone, dolomitic, granular, light-gray; forms

a ledge, with a slope beneath_________ 8 

Erosional unconformity. 

Hueco Limestone:

2. Limestone, dolomitic, bedded, in part brecciated; 

forms massive ledges. Some 1-ft beds of lightgray compact limestone are interbedded about 

15-ft below top. The dolomitic beds contain 

numerous small or slender fusulinids, mostly 

preserved as molds and partly filled by quartz, 

which are indeterminate in the laboratory 

(F 3908; field label C 24 A). The unit varies 

in thickness, due to the unconformities at the top 

and base of the Hueco; a thickness of 100 ft was 

measured nearby to the east in 1938, but the unit 

pinches out entirely between the Bone Spring 

and El Paso a short distance to the south____ 80 

1. Conglomerate, dolomitic; contains angular pebbles 

of limestone, dolomite, and chert, derived from 

underlying Ordovician formations-___ __ 15 

Angular unconformity.

El Paso Limestone (division A) at base of section. 

Summary of section 18:

Part of Bone Spring Limestone exposed___ _ 823 

Total Hueco Limestone_ 95
STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 141

SECTION 19. NORTHWESTERN BAYIX)R MOUNTAINS

The following is a section of the Hueco and Bone 

Spring Limestones on a northwestern hill of the Baylor 

Mountains, whose summit is elevation point 4364, lying 

about half a mile east of Texas Highway 54 (southeastern part of sec. 42, Block 65, Twp. 6). The section is 

based on observations by P. B. King and J. Brookes 

Knight in 1931 and 1936. The units are incompletely 

described, and their thicknesses are estimated; the section is included mainly to indicate the relative positions 

of the fossil collections. Larger fossils were identified 

by P. E. Cloud, Jr., and E. L. Yochelson, and f oraminifers by L. G. Henbest (written commun., 1954, 1955).

Top of hill; no higher beds preserved.

Bone Spring Limestone: Feet 

6. Limestone, dolomitic; weathers brown and 

jagged; similar to unit beneath, but somewhat 

thinner bedded. Contains algae, crinoid 

stems, and abundant large fusulinids, rather 

poorly preserved as a result of dolomitization. 

Fossils are better preserved at this level a mile 

to the southeast, where the rock is a calcirudite in which many of the fusulinid shells are 

completely preserved, although most show the 

effects of attrition. Rounded pellets of limestone are abundant, some of which contain fossils that belong to a different facies from that 

represented by the matrix. This rock probably is a lithified beach sand, derived from 

nearby reefs. It contains the foraminifers 

Climacammina sp., Tetrataxis sp., Staffella 

sp., Pseudofusulina setum (Dunbar and Skinner), Parafusulina imlayi Dunbar var., fusulinids of the P. attenuata-P. bakeri series, P. 

schucherti Dunbar and Skinner, and P.I sp. 

(F 2720; field label Pb 16)__________ 50 

5. Limestone, dolomitic; weathers brown and 

jagged; thick bedded to massive, with some 

marl partings. Poorly preserved sponges, 

Geyerella, Leptodus, and productids observed, and some thin layers contain fusulinids-_______________________ 100 

4. Slope-making beds, mainly covered by blocks that 

have slumped from above. Appears to be 

mostly thin-bedded cherty fossiliferous limestone, but shale and marl are exposed in places 

near base. A fossiliferous limestone near top 

locally yields an extensive fauna, which includes indeterminate fusulinids; the corals 

Gladochonus sp. and Lophophyllum sp.; the 

bryozoans Batostomella sp., Fistulipora sp., 

and Striatopora sp.; echinoid plates; the 

brachiopods Chonetes (Chonetinella) victorianus (Girty), Crurithyris sp., Dielasma spp., 

Enteletes cf. E. dumblei Girty, Hemiptychina 

sp., Hustedia mormoni (Marcou), Leptodus 

sp., Meekella sp., Neospirifer sp., orthotetacean indet., Rhipidomella sp., and Wellerella 

sp.; the pelecypods Acanthopecten sp. and Parallelodon sp.; the gastropods Anomphaltis sp., 

Babylonites sp., Bellerophon deflectus Chronic,

Bone Spring Limestone Continued Feet 

Donaldinal sp., Platyceras sp., pseudozygopleuran indet., Stegocoelia! sp., Straparollus 

(Euomphalus) cf. S. (E). Jcaibabensis Chronic, 

Trachydomia sp., and "T." sp.; the scaphopod 

Dentalium sp.; and an ammonite (USGS 

7002b; field label 26). Ledges near the base of 

the slope contain indeterminate fusulinids; 

the sponges Fissispongia n. sp., n. gen. aff. F., 

and Girtyocoelia dunbari R. H. King; the 

bryozoan Fistulipora sp.; the brachipods Composita sp., Enteletes sp., Neospirifer sp., productid indet, ProricMhofenia sp., Squamularia sp., and Wellerella sp.; the pelecypods 

Parallelodon sp., pectenoid indet, and Pseudomonotis sp.; and the gastropods Bellerophon 

sp. and Euphemites sp. (USGS 7002a) 175 

Unconformity (angular and erosional at nearby localities). 

Hueco Limestone:

3. Limestone, dolomitic, massive; interbedded with 

thin-bedded limestone and bedded chert; forms 

ledges. In lower part contains the brachiopods Meekellal sp., "Productus" sp., Leptodus 

sp., and Hustedia hessensis King (USGS 

7002) _________________________ 100 

3. Limestone, dolomitic, gray-brown; weathers

pitted______________._________ 50 

1. Limestone, dolomitic, thin-bedded; crumpled in 

places; contains some small fusulinids. This 

unit wedges out entirely against the El Paso 

Limestone at the south end of the ridge, where 

unit 2 lies on the El Paso; a mile to the southwest, units 2 and 3 are also missing, so that 

unit 4 lies on the El Paso. Thickness to base 

of slope in northern part of hill____ __ _ 100 

Angular unconformity.

El Paso Limestone at base of section; exposed only at 

south end of hill.

Summary of section 19

Part of Bone Spring Limestone exposed 325 

Total Hueco Limestone________________ _ 150-250

SECTION 20. EAGLE FLAT

The following is a section of the Hueco Limestone 

at the east end of the high ridge north of Texas and 

Pacific Railway, about a mile northwest of Eagle Flat 

section house (center of south line of sec. 1, Block 69, 

Twp. 8). The Powwow Member was measured on the 

slope at the eastern end, where it is exposed in a gully; 

the main body of the formation was measured about 

half a mile to the northwest on the north side of the 

ridge, beginning about 500 feet east of an abandoned 

prospect pit, the higher beds (units 22-24) being added 

from a ridge top to the west. The section was measured by J. Brookes Knight in 1931. Fossils were identified by P. E. Cloud, Jr., and E. L. Yochelson (written 

commun., 1954).
142 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Top of ridge; no higher beds exposed. 

Hueco Limestone:

Main body of formation: Feet

24. Limestone, dark-gray, thin-bedded; contains

small gastropods 8

23. Limestone, forming a ledge__ _ 3

22. Limestone, thin-bedded, splintery; weathers 

gray; contains echinoid spines and a few 

other fossils___________-______- 25

21. Limestone, thin-bedded to slabby, gray to lightgray ; weathers yellow; mostly forms a 

slope, but with 2-f t ledges at intervals. Contains a few echinoid spines in upper part- 71

20. Limestone, moderately thin-bedded; forms 

cliffs; 2 or 3 cherty beds; contains mollusks like those in unit 18__________ 16

19. Limestone, gray; forms a slope, with a few

ledges toward top_______ _____ 22

18. Limestone, dark-gray, cherty; forms a cliff, 

containing abundant mollusks in upper part, 

including bellerophontids__ ____ 20

17. Limestone, thin-bedded; forms a slope____ 18

16. Limestone, dark-gray, cherty, massive; forms 

a cliff; contains echinoid spines and a few 

other silicified fossils_____________ 18

15. Limestone, dark-gray, thin-bedded; forms a 

slope; contains abundant echinoid spines 8 

ft above base- ____ __ 16

14. Limestone, dense, dark-gray; weathers mouse 

gray; forms a massive cliff; contains abundant ramifying chert nodules and silicified 

fossils. The latter include echinoid spines, 

the brachiopods Composite cf. C. subtilita 

(Hall) and Dictyoclostus wolfcampensis 

King; and the gastropods bellerophontid 

indet., KnigJitites (Retispira) sp., Naticopsis 

sp., Omphalotrochus sp., and Straparollus 

(Euomphalus) cornudanus (S h u m a r d) 

USGS 7008; field label 1 A)_________ 28 

Powwow Member:

13. Limestone, forming a slope___________ 8

12. Limestone, forming a ledge; contains large

chert nodules___________________ 3

11. Marl, forming a slope; interbedded with thin

limestone layers -_____________ 14

10. Limestone, containing large bellerophontids- 3 

9. Limestone, gray; interbedded with marl, containing abundant fossils, which include the 

bryozoans Fenestella sp., Polypora sp., and 

Rhombopora sp.; the brachiopods CleiotJiyridina sp., Composita sp., Dictyoclostus 

wolfcampensis (King), and dielasmids including Dielasma aff. D. Kovidens (Morton) ; 

myalinid and pseudomonotid pelecypods; the 

gastropods Bellerophon parvicristatus Yochelson, and other abundant but poorly preserved bellerophontids, Euconispira cf. E. 

missouriensis (Swallow), Knightites 

(Knightites) sp., a loxonematacean, Naticopsis sp., and Straparollus (Euomphalus) 

cornudanus (Shumard) ; and the scaphopod Plagioglyptal sp., (USGS 7028; field 

label 5)_____________________ 27 

8. Limestone, sandy, yellow, fossiliferous____ 2

Hueco Limestone Continued

Powwow Member Continued Feet 

7. Shale, sandy, yellow; mostly covered 18 

6. Conglomerate, red _ 2 

5. Shale, red, sandy _ 6 

4. Conglomerate, gray; formed of schist and

chert pebbles___ 7 

3. Shale, red, sandy 6 

2. Conglomerate, yellow; formed mainly of limestone from Allamoore Formation, but including a few pebbles of schist and greenstone_ ____- _ 16 

1. Conglomerate, arkosic, red; formed of pebbles of schist and greenstone 13 

Angular unconformity. 

Metarhyolite of Precambrian age at base of section.

Summary of section 20

Hueco Limestone:

Part of main body of formation exposed____ 245 

Powwow Member _ 125

Part of Hueco Limestone exposed _____ 370

SECTION 21. STREERUWITZ HILLS

The following sections of the Hueco Limestone are in 

the Streeruwitz Hills, on closely adjacent mesas, lying 

21/2 to 31^3 miles northwest of the Eagle Flat section 

house. They were measured by J. Brookes Knight 

in 1931, but additional fossils were collected from each 

section in 1938. Section 21a is at the southeastern end 

of the eastern mesa (center of sec. 26, Block 57), and 

section 21b is about three-quarters of a mile to the 

northwest, at the west end of the western mesa (eastcentral part of sec. 27, Block 57). Larger fossils were 

identified by P. E. Cloud, Jr., and E. L. Yochelson, and 

foraminifers by L. G. Henbest (written commun., 1954, 

1955).

Section 21a

Top of mesa; no higher beds exposed. 

Hueco Limestone:

Main body of formation: Feet

8. Limestone, massive; forms ledge at top of

mesa_ __ 10

7. Limestone, thin-bedded; forms a slope___ 15

6. Limestone, dark-gray, massive; forms cliff 20 

Powwow Member:

5. Limestone, dense, splintery, light-gray, thinbedded; contains much chert and is interbedded with shale. Upper beds form thin 

ledges on slope. The limestones contain the 

foraminifers Bradyinal sp., a spandelinid, 

Schubertella Tcingil Dunbar and Skinner, Tri~ 

ticites or Pseudofusulina sp., and Schwagerina Jcnighti Dunbar and Skinner; cup corals; 

the bryozoan Septopora sp.; echinoid spines; 

the brachiopods Composita cf. 0. subtilita 

(Hall), Dictyoclostus cf. D. wolfcampensis 

(King), "Dielasma" sp., and Hustedia sp.; 

the pelecypods Allorisma sp. and Pseudomonotis sp.; the gastropods OmphalotrocJius 

ol)tusispira (Shumard), KnigJitites (Retis-
STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 143

Section 2 la Continued

Hueco Limestone Continued

Powwow Member Continued Feet 

pira) sp., and large 'bellerophontids; the scaphopod Plagioglyptal sp.; and plant fragments (USGS 7003, 7003a, 14431, F 9808; 

field labels 2 B, C 8) ______________ 47 

4. Shale, marly; with a thin ledge of splintery 

limestone near middle, containing quartz 

geodes. Contains small fusulinids; the bryozoans Fistulipora sp., Polypora sp., Septopora sp., and Streblotrypa sp.; echinoid 

spines; the brachiopods Cleiothyridina sp.; 

Composita cf. C. subtilita (Hall), Cruritnyrisl sp., Dictyoclostus wolfcampensis (King), 

"Dielasma" sp., and Wellerella sp.; the pelecypods Nucula sp. and a myalinid; the gastropods Bellerophon huecoensis (Yochelson) 

and other bellerophontids, Euconispira cf. 

E. missouriensis (Swallow), Naticopsis sp., 

and Straparollus (Euomphalus) cornudanus 

(Schumard) ; a nautiloid; and the scaphopod 

Plaffiofflypta'i sp. (USGS 7003b; field label 

2D) __________________________ 30 

3. Limestone, shaly, splintery, red________ 10 

2. Shale, calcareous, red_______________ 8 

1. Conglomerate, arkosic, massive; formed of pebbles of limestone, greenstone, and schist, derived from Precambrian formations_____ 8 

Angular unconformity. 

Greenstone of Precambrian age at base of section.

Section 21b

Top of mesa ; no higher beds exposed. 

Hueco Limestone:

Main body of formation :

6. Limestone, alternating beds of which are gray, 

coarse-grained, and slabby, and pink to 

yellow, dense, and splintery. Both types 

contain echinoid spines and other fossils 20 

5. Limestone, pink-weather ing, buff, fossiliferous_ 8 

Powwow Member:

4. Limestone, gray; cherty toward top; interbedded with marl. Contains the forminifers 

Bradyinat sp., Ozawainella sp., Staffella sp., 

and spandelinids; the sponge Wewokella 

(Talpaspongia) clavata (R. H. King) and 

spicules; echinoid spines; the brachiopods 

Composita cf. G. subtilita (Hall) and Dictyoclostus wolfcampensis (King) ; and the gastropod Straparollus (Euomphalus) cornudanus (Shumard), and others (USGS 14432, 

F 9809; field label C 9)____________ 60 

3. Limestone, dense, pinkish; weathers yellow 

brown; interbedded with marl; forms ledges 

and slopes; fossiliferous at top_______ 66 

2. Limestone, shaly, pink; with a bed of splintery

limestone at top_________________ 4 

1. Conglomerate, calcareous; formed of pebbles

of limestone of Allamoore Formation____ 3 

Angular unconformity. 

Allamoore Formation at base of section.

Summary of section 21

Hueco Limestone: 

Section 21a:

Part of main body of formation exposed___. 

Powwow Member___ ___________ _.

Feet

45

103

Part of Hueco Limestone exposed _ 148 

Section 21b:

Part of main body of formation exposed- 28 

Powwow Member _ 133

Part of Hueco Limestone exposed 161

SUCTION 22. McADOO RANCH

The following is a section of the Hueco Limestone 

near the west end of the south-facing escarpment of the 

Sierra Diablo, on the east side of a gap in the ridge, 

2 miles southwest of the Gordon (formerly McAdoo) 

Ranch (center of north line of sec. 29, Block 52^). 

The section was measured by J. Brookes Knight in 1931. 

Many fossils were observed in the field but not collected ; the small collections which were made were identified by P. E. Cloud, Jr. (written commun., 1954).

Top of ridge; no higher beds exposed. 

Hueco Limestone:

Main body of formation: feet 

12. Limestone, gray, slabby; contains chert and 

calcite vugs; marly partings in lower part. 

Contains a bellerophontid and Straparollus 

(Euomphalus) cornudanus (Shumard) 

(USGS 701Sb; field label 8 C)_______ 45 

11. Limestone, forming a ledge; bellerophontids

and other fossils observed- _ 5 

10. Limestone, gray; weathers pitted; in 4-ft beds, 

alternating with thinner beds ; in part forms 

cliffs, in part ledges and slopes. Some beds 

contain chert nodules and small quartz 

geodes; a bed about 25 ft above base contains large masses of white chert. Fossils 

rare; echinoid spines observed________ 110 

Powwow Member:

9. Limestone, slabby, gray to pinkish-gray. Contains a dasycladacean alga, probably Mizzia 

(USGS 7013a; field label 8 B). Staffellid 

foraminifers observed_____________ 10

8. Limestone, slabby, pink; with a thin bed of 

arkosic sandstone in middle; minute fossils 

observed_ . _ - 11

7. Limestone, pinkish-gray; in 4-ft ledges; separated by arkosic sandstone_ _ 22

6. Limestone, dense, pink; weathers yellow; in 

1-ft ledges, separated by greater thicknesses 

of slabby arkosic sandstone. A limestone 

bed near middle contains a dasycladacean 

alga (USGS 7013; field label 8 A); minute gastropods and staffellid foraminifers 

observed_ ____ 14

5. Sandstone, arkosic, pinkish-gray, poorly consolidated; mostly forms a slope 20

4. Covered by talus; probably like adjoining

units________ . . 20
144 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Hueco Limestone Continued

Powwow Member Continued Feet 

3. Sandstone, arkosic, pinkish-gray, conglomeratic; forms a ledge____________ 7 

2. Covered by talus; probably like adjoining

units__________________ _____ 25 

1. Sandstone, arkosic, coarse, yellowish-gray,

poorly consolidated _________ 5 

Angular unconformity. 

Van Horn Sandstone at base of section.

Summary of section 22

Hueco Limestone:

Part of main body of formation exposed____ 160 

Powwow Member___________________ 134

Part of Hueco Limestone exposed__________ 294 

SECTION 23. WEST OF OLD CIRCLE RANCH

The following is a section of the Hueco Limestone on 

the south-facing escarpment of the Sierra Diablo, on 

the east side of a wide gap in the ridge, 3%miles west of 

the Old Circle Ranch (northeastern part of sec. 2, 

Block 56). The section was measured by J. Brookes 

Knight in 1931. Fusulinids were collected, and were 

examined by Dmibar and Skinner (1937), but they 

were not identified.

Top of ridge; no higher beds exposed. 

Hueco Limestone:

Main body of formation: Feet 

6. Limestone, gray, massive; contains euomphalid gastropods and large echinoid spines_ 5 

5. Limestone, gray; with indistinct bedding; 

forms a cliff. Fusulinids collected at top 

and base (D & S 92, 93; field labels 9 B, 9 

C) ; other fossils rare or obscure____ 35 

4. Limestone, gray; in 2- to 5-ft beds; contains 

abundant fusulinids (D & S 91; field label 

9 A)_________________________ 35 

3. Limestone, gray; forms a massive ledge__ 10 

Powwow Member:

2. Limestone, sandy, pink; contains calcite vugs_ 8 

1. Marl, arkosic; mostly yellow, becoming red 

below, with thin beds of yellow limestone and 

conglomeratic limestone, and with beds of 

arkosic conglomerate in lower part, whose 

pebbles have been reworked from those in 

the Van Horn Sandstone-____________ 80 

Angular unconformity. 

Van Horn Sandstone at base of section.

Summary of section 23

Hueco Limestone:

Part of main body of formation exposed______ 85 

Powwow Member_____________________ 88

Part of Hueco Limestone exposed_________ 173 

SECTION 24. OLD CIRCLE RANCH

The following is a section of the Hueco Limestone on 

the escarpment overlooking Deer Creek from the west, 

half a mile northwest of Old Circle Ranch (southwest 

corner of sec. 23, Block 531/£). The section was measured by J. Brookes Knight in 1931. Fusulinids were 

collected, and were examined by Dunbar and Skinner 

(193T), but they were identified only in part.

Top of escarpment; no higher beds exposed. 

Hueco Limestone:

Main body of formation: Feet 

11. Limestone, light-gray, thin-bedded; forms 

ledges; a few beds contain fusulinids (D & 

S 98; field label 10 D)_______ 50 

10. Limestone, containing large calcite vugs and 

some chert; forms upper part of massive 

cliff. Contains fusulinids at top (D & S 

97; field label 10 C), and large echinoid 

spines_________ . 35 

9. Limestone, light-gray; forms lower part of 

massive cliff. Contains Schivagerina linearis 

Dunbar and Skinner (D & S 96; field label 

10 B), poorly preserved productids, and at 

top, large echinoid spines and a euomphalid____________.__ 25 

8. Limestone, partly covered; forms a slope;

float contains abundant fusulinids 20 

7. Limestone, light-gray; forms a massive ledge__ 16 

6. Limestone, compact, light-gray to pink ; forms 

a massive cliff in lower half. Fusulinids 

abundant in lower part, including Schwagerina linearis Dunbar and Skinner, and 8. 

emaciata (Beede) (D & S 95; field label 

10 A) ________________________ 52 

5. Limestone, compact, gray; with some chert

nodules___ _ _ .._____ 15 

4. Limestone, poorly exposed; forms a slope 10 

3. Limestone, compact, massive, gray; contains

chert nodules___ _ 11 

Powwow member:

2. Shale, arkosic, light-yellow-gray; with thin

ledges of conglomerate in lower half__ 31 

1. Conglomerate, arkosic, yellow__ 5 

Angular unconformity. 

Red sandstone of Hazel Formation at base of section.

Summary of section 24

Hueco Limestone:

Part of main body of formation exposed_____ 234 

Powwow Member___________________ 36

Part of Hueco Limestone exposed__________ 270 

SECTION 25. HAZEL MINE

The following is a section of the Hueco Limestone on 

the southeastern angle of the Sierra Diablo escarpment, 

half a mile north-northeast of the Hazel mine (southeastern part of sec. 41, Block I). The Powwow Member was measured on the southeastward-projecting 

ridge below the upper cliffs, the higher beds up the 

northeast side of the ridge through a cleft in the cliffs, 

thence westward to the ridge summit. The section was 

measured by J. Brookes Knight and P. B. King in 1931. 

 No fossils were collected, although they were observed 

in the field.
STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 145

Top of ridge; no higher beds exposed. 

Hueco Limestone:

Main body of formation: Feet 

10. Limestone, dolomitic; somewhat thinner 

bedded and lighter gray than beds below; 

forms ledges and slopes above the main 

cliffs__________.____________ 130

9. Limestone, dolomitic, dark-gray; in even beds 

3-5 ft thick; contains fusulinid molds; forms 

cliffs. Basal part is pinkish-gray and contains some chert_________________ 150

8. Limestone, dolomitic, light-gray; contains

abundant fusulinid molds___________ 5

7. Limestone, dolomitic, light-gray; forms cliffs;

contains poorly preserved fossils_______ 31

6. Limestone, light-gray; with many calcite vugs; 

contains poorly preserved bellerophontids, 

and in upper foot, staffellid foraminifers_ 12

5. Limestone, dense, light-gray; weathers yellow;

contains fossil fragments___________ 3 

Powwow Member:

4. Sandstone, arkosic, calcareous, yellow, poorly

exposed on slope________________ 5

3. Limestone, sandy, yellow ___________ 3

2. Conglomerate, yellow; interbedded with gray 

sandy marl in upper part. Conglomerate at 

base consists of closely packed coarse pebbles and cobbles of limestone and of red 

sandstone from Hazel formation. Conglomerate above consists of smaller pebbles of 

red sandstone and resistant foreign rocks, 

with scattered seams of limestone pebbles, 

set in an arkosic sandstone matrix_____ 85

1. Conglomerate, red, arkosic; made up of pebbles of red sandstone, quartzite, and igneous 

rocks _.___ _______ 5 

Angular unconformity. 

Red sandstone of Hazel Formation at base of section.

Summary of section 25

Hueco Limestone:

Part of main body of formation exposed_____ 331 

Powwow Member__________________ 98

Part of Hueco Limestone exposed_________ 429

SECTION 26. BAT CAVE

The following is a section of the Hueco Limestone on 

the escarpment of the Sierra Diablo at Bat Cave, on the 

south side of an eastward offset of the escarpment 1% 

miles north-northeast of the Pecos Mine (northeastern 

part of sec. 13, Block 54%). The section was measured 

by J. Brookes Knight in 1936. Fusulinids and other 

foraminifers were identified by L. G. Henbest (written 

commun., 1955); other fossils were observed in the field, 

but were not collected.

Top of escarpment; no higher beds exposed. 

Hueco Limestone:

Main body of formation:

7. Limestone, dolomitic, gray, thin-bedded; with 

some interbedded very light gray layers and 

much interbedded calcitic limestone in upper

Hueco Limestone Continued

Main body of formation Continued Feet 

part. Poorly preserved fusulinids observed 

in lower part. A bed 100 ft above base contains better preserved foraminifers, including 

Staffella sp., Schubertella Mngi Dunbar and 

Skinner, PseudofusuUna? sp., and Schwagerina bellula Dunbar and Skinner (F 2703; 

field label Ph 18). Near the top occur 

Climacammina sp., Schubertella Mngi Dunbar 

and Skinner, Triticites aff. T. subventricosus 

Dunbar and Skinner, and Schwagerina sp. 

(F 2719; field label Ph 19) ; with these were 

observed poorly preserved Omphalotrochus- 165

6. Limestone, dolomitic, gray, thin-bedded; contains fusulinid molds______________ 150

5. Limestone, dolomitic, gray, thick-bedded ; forms 

lower part of a slope; contains unidentifiable 

small fusulinids (F 2696; field label Ph 12) __ 75

4. Limestone; calcitic below, dolomitic toward 

top; gray, thin-bedded; forms a great cliff. 

Fusulinids abundant in lower part and 

scarcer toward top. At base contains the 

fusulinids and other foraminifers Schubertella kingi"? Dunbar and Skinner, Pseudo 

-fmulina powwowensist (Dunbar and Skinner), Parafusulina linearis (Dunbar and 

Skinner) var., and Schwagerina bellulal 

Dunbar and Skinner (F 2693; field label 

Ph 15). Near middle contains Geinitzina 

sp., Schubertella kingil Dunbar and Skinner, 

Parafusulina, linearis (Dunbar and Skinner) 

var., and Pseudoschwagerina texana Dunbar 

and Skinner (F 2714; field label Ph 16)___ 195

3. Limestone, marly, gray ; forms ledges; contains 

abundant fusulinids in lower half. Contains 

the fusulinids and other foraminifers Osagia 

incrustata Twenhofel (algal-foraminiferal 

colonies), a tolypamminid, Trepeilopsis sp., 

textulariids, Spandelina sp., Endothyra sp., 

Tetrataxis sp., a millerellid, Staffella sp., 

Osawainella! sp., PseudofusuUna powwowensis (Dunbar and Skinner, tSchwagerina Ttellula Dunbar and Skinner, Parafusulina 

linearis (Dunbar and Skinner), and Pseudoschwagerina beedei Dunbar and Skinner (F 

2690; field label Ph 14)___ 20 

Powwow Member:

2. Limestone, dolomitic, sandy, massive; contains 

quartz pebbles in lower part. Upper part 

contains many small unidentifiable fusulinids 

(F 2711; field label Ph 13) ___________ 90

1. Conglomerate, yellow; made up of limestone

pebbles, with a dolomitic matrix toward top__ 48 

Angular unconformity. 

Bed sandstone of Hazel Formation at base of section.

Summary of section 26

Hueco Limestone:

Part of main body of formation exposed_____ 605 

Powwow Member_ __ ______ _ 138

Part of Hueco Limestone exposed_______ __ 743
146 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

FOSSIL COLLECTIONS FROM HUECO LIMESTONE NEAR 

SHEEP PEAK

No stratigraphic sections were measured on Sheep 

Peak, or near it, but the fossils listed below were collected from the Hueco Limestone on the peak, and in 

surrounding areas. Collections were made by J. 

Brookes Knight in 1936 and 1938; fusulinids and other 

foraminifers were identified by L. G. Henbest and 

larger fossils by P. E. Cloud, Jr., and E. L. Yochelson 

(written commun., 1955, 1954:).

USGS 8560, F 2112 (field, label Ph. 25). Hueco Limestone, 

lower part of main body of formation, north slope of Sheep Peak 

(northeastern part of sec. 18, Block 53%). Contains the 

fusulinids ISchwagerina bellula Dunbar and Skinner, Parafusulina cfr. P. linearis (Dunbar and Skinner), and IPseudoscJiwagerina beedei Dunbar and Skinner; the brachiopods 

Meekella sp. and Linoproductus sp.; and the gastropod Straparollus (Euomphalus) sp. indet.

USGS 8559 (field label Ph 24). Hueco Limestone, basal part 

of main body of formation, lying directly on red sandstone of 

Hazel Formation, the Powwow Member being missing at the 

locality. Knoll 1% miles north-northwest of Sheep Peak (northwestern part of sec. 13, Block 53%). Contains the brachiopod 

Linoproductus sp.

USaS 8560a, F 2701 (field label Ph 28). Hueco Limestone 

main body of formation. Three miles east-northeast of Sheep 

Peak on south side of valley of Deer Creek, south of Cox Mountain fault, in bed of a dry creek (center of sec. 15, Block 54%). 

Contains the fusulinids and other foraminifers Geinitzina sp., 

Spandelinoides sp., Schubertella sp., Triticites subventricosus 

Dunbar and Skinner, Pseudofusulinat sp., and Pseudoschwagerina beedei Dunbar and Skinner.

USGS 8560a, F 2695 (field label Ph. 29). Hueco Limestone, 

main body of formation. Four miles east-northeast of Sheep 

Peak on ridge north of valley of Deer Creek, north of Cox 

Mountain fault (center of sec. 14, Block 54%). Contains the 

fusulinids and other foraminifers Climcammina sp., Geinitzira 

sp., Spandelina sp., Tetrataxis sp., Schubertella Jcingi Dunbar 

and Skinner, Schwagerina bellula Dunbar and Skinner, Triticites spp., Parafusulina linearisl (Dunbar and Skinner), and 

Pseudoscliwagerina, texana Dunbar and Skinner var.

VSGS 8560a, F 2704 (field label Ph 27). Hueco Limestone, 

main body of formation. Four and a quarter miles east of 

Sheep Peak and 1% miles south of Bat Cave, on rim of Sierra 

Diablo escarpment, in upfaulted block south of Cox Mountain 

fault (center of east line of sec. 17, Block 54%). Contains the 

fusulinids and other foraminifers Endothyra! sp., Schubertella 

Jcingil Dunbar and Skinner, Triticites aff. T. subventricosus 

Dunbar and Skinner, and Schwagerina sp.

VSGS 14474 (field label C 32). Hueco Limestone, main body 

of formation. Four miles west-northwest of Sheep Peak at 

north end of low ridge, south of Sheep Peak fault (center of 

west line of sec. 13, Block 52%). Contains the gastropod 

Stegocoelia n. subgen. n. sp.

USGS 14424 (field label C 1). Hueco Limestone, main body 

of formation. Three miles west-northwest of Sheep Peak at 

crest of ridge, north of Sheep Peak fault (northeastern part of 

sec. 13, Block 52%). Contains the brachiopod Composita cf. 

C. subtilita. (Hall) ; a parallelodontid pelecypod; and the gastropods Bellerophon parvicristatus Yochelson, Meekospira sp., 

a murchisonid, Naticopsis sp., Peruvispira sp., Stegocoelia'j sp.,

Straparollus (Euomphalus) cornudanus (Shumard), and 

Worthenia sp.

SECTION 27. SECOND SECTION SOUTH OE1 VICTORIO

PEAK

The following is a section of the Hueco and Bone 

Spring Limestones on the escarpment of the Sierra 

Diablo at the upper end of the Victorio flexure 2^4 

miles south of Victorio Peak (southwestern part of sec. 

19, Block 43). The section was measured by J. Brookes 

Knight in 1938. Larger fossils were identified by P. E. 

Cloud, Jr., and E. L. Yochelson and fusulinids and 

other foraminifers by L. G. Henbest (written commun., 

1954,1955).

Top of ridge above escarpment; no higher beds exposed. 

Bone Spring Limestone: &eet

19. Limestone, dolomitic; forms a cliff; approximate

thickness_______-_______ 200

18. Shale, yellow; interbedded with limestone and 

limestone-pebble conglomerate, both very fossiliferous. Unit dips steeply northward and 

thins abruptly, being little more than 75 ft thick 

a quarter of a mile to the north. Contains the 

sponge Heliospongia vokesi E. H. King; colonial, 

semicolonial, and cup corals; the brachiopods 

Buxtonia (Kochiproductus) victorioenste King, 

Dictyoclostus (Chaoiella) guadalupensis (Girty), Enteletes sp., "Marginifera" cf. "M." waleottiana (Girty), and Stenocisma cf. S. inequalis 

(Girty) ; and the gastropod Bellerophon deflectus Chronic. Fusulinids and other foraminifers include textulariids, Spandelina sp., Geinitzina sp., Textrataais spp., Staffella sp., Pseudoschwagerina uddeni (Beede and Knicker), Para- 

 fusulina schuchertil Dunbar and Skinner, P. 

attenuata'i Dunbar and Skinner, and P. spp. 

(USGS 14454, F 9827; field label C 25 C). The 

fusulinids are exceedingly abundant, but tlieir 

tests are commonly abraded or broken, after 

lithification but before incorporation in the sediment. Hueco and Bone Spring fusulinids have 

been mixed by redoposition, the specis of Pseudoschwagerina representing the former, and the 

two species of Parafusulina representing the 

latter____________ _ . 215

17. Limestone, dolomitic, massive 45

16. Slope, with limestone float blocks that contain

Leptodus and other fossils of Bone Spring aspect 50

15. Limestone, dolomitic; forms slopes and ledges; 

contains poorly preserved fusulinids as well as 

larger fossils ____ __ 150

14. Limestone, dolomitic, massive; forms a cliff 30

13. Limestone, dolomitic, gray; forms ledges on slope;

contains silicified fossils of Bone Spring aspect- 30

12. Slope ; no exposure_ 45

11. Limestone, massive, lenticular, reefy; in part brecciated ; contains a few silicified fossils_ 20

10. Limestone, thin-bedded; contains nodules of gray

chert_____________ _ .. 5
STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 147

Bone Spring Limestone Continued Feet 

9. Limestone, conglomeratic or bioclastic, gray, thinbedded ; forms ledges. Contains cup corals and 

a few silicified brachiopods of Bone Spring aspect, including Enteletes. Fusulinids and other 

foraminifers include textulariids, Geinitsina sp., 

Spandelina sp., Spandelinoides sp., Tetrataxis 

spp., Staff ellal sp., ISchubertella Jcingi Dunbar 

and Skinner, Pseudoschwagerina laxissimal 

(Dunbar and Skinner), Paraschwagerina sp., 

Pseudoschwagerina uddeni (Beede and Knicker), and ISchwagerina c omp act a (White) 

(USGS 14453, F 3806; field label C 25 B). Most 

of the identified species of fusulinids are characteristic of the Hueco, rather than of the Bone 

Spring, but the bioclastic nature of the rocks 

suggests possible redeposition___________ 65 

Unconformity (?). 

Hueco Limestone:

Main body of formation :

8. Limestone, dolomitic, granular, gray-buff, very 

massive; contains molds of very small 

fusulinids______________________ 100 

7. Limestone, dolomitic, gray-buff, massive; 

weathers to fairly smooth surfaces; forms 

cliffs. Contains molds of very small fusulinids in upper half________________ 140 

6. Limestone, marly, and marl; interbedded 

with ledge-making layers of slightly dolomitic 

limestone. Lower part of unit contains a 

small cup coral cf. Caninia sp.; the annelid 

Spirorbis sp.; and the brachiopods Dictyoclostus (n. subgen.) cf. D. hessensis (King), 

D. wolfcampensis (King), Aulostegesl, 

Waagenoconcha n. sp., Linoproductus sp., 

"Marginifera" n. sp. aff. "If." lasallensis 

(Worthen), Composita sp., and Neospirifer 

spp. The same strata contain the fusulinids 

and other foraminifers Climacammina sp., 

Spandelina sp., Geinitsina or Spandelina sp., 

Endothyral sp., Tetrataxis sp., Schubertella 

kingil Dunbar and Skinner, Pseudofusulina 

uddeni? (Dunbar and Skinner), Pseudofusulina sp. confr. P. uddeni (Dunbar and 

Skinner) and Parafusulina aff. P. Unearis 

(Dunbar and Skinner) (USGS 14452, F 9823; 

field label C 25 A). The last species occurs 

in a limestone very different litholigically 

from that containing the other species; field 

relations between the two rock types are 

unknown_______________________. 135 

5. Limestone, thin-bedded; contains many fusulinids, productid brachiopotls, and bellerophontid gastropods________________ 18 

Powwow Member:

4. Sandstone; marly in upper part; some layers 

fine grained and red, others coarse grained 

and yellow; forms a slope___________ 70 

3. Sandstone, red, fine-grained; with a few ledges

of coarse conglomeratic yellow sandstone_ 40 

2. Sandstone, coarse to conglomeratic, yellow; 

mostly poorly exposed on slope, which is 

covered by pebbles weathered from conglomerate______________________ 70

Hueco Limestone Continued

Powwow Member Continued Feet 

1. Conglomerate, sandy; forms ledges at base and 

top. Contains angular to rounded pebbles 

and cobbles, consisting of red sandstone 

from Hazel Formation, but including dolomitic and calcitic limestone, quartz, quartzite, 

and rhyolite____ 68

Angular unconformity.

Red sandstone of Hazel Formation at base of section.

Summary of section 27

Part of Bone Spring Limestone exposed 855

Hueco Limestone:

Main body of formation___ 393 

Powwow Member _ 248

Total Hueco Limestone________ - 641 

SECTION 28. FIKST SECTION SOUTH OF VICTORIO PEAK

The following is a section of the Hueco, Bone Spring, 

and Victorio Peak Limestones, about V/2 miles south of 

Victorio Peak (from the southeastern to northwestern 

parts of sec. 19, Block 43). The section begins on the 

southeast near the northernmost outcrop of red sandstone of the Hazel Formation and extends northwestward across successive ledges and slopes to the summit 

of the peak marked by elevation point 6353. The section was measured by P. B. King and R. E. King in 

1928. Brachiopods in the collections made were identified by R. E. King (1931) and fusulinids by Dunbar 

and Skinner (1937).

Top of peak 6353; no higher beds exposed.

Victorio Peak Limestone: Feet

25. Limestone, light-gray, massive; forms a cliff. 

The unit is approximately equivalent to the 

lower part of the Victorio Peak Limestone on 

nearby Victorio Peak, although its lower part 

appears to interfinger in that direction with 

shale and marl of Bone Spring Limestone__ 130 

Intergradation. 

Bone Spring Limestone:

24. Limestone, gray; forms two thick cliff-making 

units and some minor ledges, separated by 

thinner beds of buff sandy marl. The limestone units wedge out northward into marl not 

far north of peak 6353. Marls north of the 

peak contain the brachiopods Enteletes dum- 

'blei Girty, Chonetes permianus Shumard, Productus ivesi Newberry, P. schucherti King, 

Harginifera cristobalensis Girty, M. manzanica Girty, Aulosteges magnicostatus Girty, Lyttonia nobilis americanus (Girty), Camarophoria venusta Girty, Spirifer (Neospirifer) 

pseudocameratus Girty, and Composita mira 

(Girty) (REK 484)________________ 170

23. Limestone, finely crystalline, gray; weathers

white; in 1-ft beds_________________ 16

22. Marl, buff, sandy____________ __ 50

21. Limestone, dolomitic, finely crystalline, gray; in 

1- to 2-ft beds; contains irregular chert nodules. Weathers to light-gray smooth surfaces 

and forms a receding slope__ 303
148 GEOLOGY OF THE SIE.RRA DIABLO REGION, TEXAS

Bone Spring Limestone Continued Feet

20. Limestone, black, thin-bedded__________ 20

19. Limestone, dolomitic, finely crystalline; in 1- to 

2-ft beds. Weathers to gray-brown granular 

surfaces and forms massive ledges ___ 63

18. Limestone, black, platy; weathers gray; interbedded with drab shale above. A conglomeratic layer in lower part contains Productus 

ivesi Newberry (REK 489)___________ 175

17. Limestone, dolomitic, finely crystalline, gray; 

with faint bedding planes, moderately closely 

spaced; weathers drab gray. Thickens northward along outcrop to as much as 150 ft____ 45

16. Shale, drab; weathers buff; with thin seams of 

shaly sandstone and some beds of fossiliferous 

limestone _________.___________ 54

15. Limestone, finely crystalline; contains siliceous

masses and poorly preserved slicified fossils_ 1

14. Shale, drab; weathers buff; some interbedded 

thin limestone layers. Fossils in the limestone layers, and weathered from the shale, include the fusulinids Parafusulina schucherti 

Dunbar and Skinner and Parafusulina sp., and 

the brachiopods Rhipidomella mesoplatys ~baylorensis King, Enteletes dumblei Girty, Derbya 

nasuta Girty, Chonetes Mplicatus King, Marginifera sublaevis King, H.l whitei King, Prorichthofenia uddeni (Bose), Spirifer marcoui 

infraplicata King, Squamularia guadalupensis 

(Shumard), and Spirifernia laaeal Girty 

(REK 485, D & S 127)______________ 17

13. Limestone, dolomitic, drab to orange-brown;

crowded with fusulinids in upper part____ 75

12. Limestone, dense to granular, gray; weathers 

gray brown; in 2-ft beds, separated by beds of 

shale The limestone beds are crowded with 

fossils, which are silicified on the surface. 

Collections from several beds include the 

brachiopods Rhipidomella hessensis King, 

Enteletes dumblei Girty, E. liumbonis King, 

Streptorhynchus pygmaeum Girty, HeeJcella 

attenuata Girty, Chonetes spinoliratus diabloensis King, Productus dartoni King, P. 

ivesi Newberry, Marginifera sublaevis King, 

Mf whitei King, Strophalosia hystericula 

Girty, Prorichthofenia UJcharewi King, P. 

teguliferoides King (types), Lyttonia noMlis 

americanus (Girty), Pugnoides elegans 

(Girty), Spiriferina angulata King (type), 

Hustedia hessensis King, and Composita suT)- 

tilita (Hall) (REK 47 8,419) __________ 75 

Unconformity (?). 

Hueco Limestone:

Main body of formation:

11. Limestone: dolomitic in part; finely granular; gray-brown; faintly bedded; forms 

10- to 20-ft ledges; contains irregular 

chert masses_________________ 243 

10. Limestone, dolomitic, dense, faintly bedded; 

weathers to a rough surface, containing irregular chert masses____________ 27 

9. Limestone, dense, thin-bedded, gray; weathers light gray; contains spherical to lenticHueco Limestone Continued

Main body of formation Continued Feet 

ular chert masses. Composita and other 

silicified fossils observed 74 

8. Limestone, dense, thin-bedded, gray, cherty;

contains many fusulinids 17 

7. Limestone, finely crystalline, dark gray; 

weathers buff; in 1-ft beds; contains the 

fusulinid Sch^vagerina linearis Dunbar 

and Skinner, and the brachiopods Productus dartoni King (type), Productus semistratus Meek, Linoproductus cor a (d'Orbigny), and Composita mira (Girty) 

(REK 460, D & S 99)____ 27 

Powwow Member:

6. Shale; drab to gray, passing into red below;

much concealed by talus 48 

5. Shale, sandy, maroon-red 27 

4. Sandstone, coarse to conglomeratic, brown- 17 

3. Shale, sandy, maroon-red___ 27 

2. Shale, sandy, brown; interbedded with thin

sandstone layers 4 

1. Sandstone, coarse, conglomeratic, brown; 

contains subangular to rounded pebbles, 

mostly limestone and chert, but with a few 

of quartz, rhyolite, and schist; no pebbles 

of red sandstone from rock beneath 2 

Angular unconformity. 

Red sandstone of Hazel Formation at base of section.

Summary of section 28

Part of Victorio Peak Limestone exposed 130 

Bone Spring Limestone 1, 064 

Hueco Limestone:

Main body of formation 388 

Powwow Member______ 125

Total Hueco Limestone- 513

COLLECTIONS FROM HTTECO AND BONE SPRING LIMESTONES ON VICTORIO FLEXURE WEST OF VICTORIO 

CANYON

No stratigraphio sections were measured of the 

Permian rocks on the Yictorio flexure west of sections 

27 and 28, or west of the front of the Sierra Diablo, but 

fossils were collected at various localities in the Hueco 

Limestone and lower part of the Bone Spring Limestone, which are listed below. The collections were 

made in 1936 and 1938, mainly by J. B. Knight, but in 

part by P. B. King; fusulinids and other foraminifers 

were identified by L. G. Henbest, and larger fossils by 

P. E. Cloud, Jr., and E. L. Yochelson (written commun., 1954,1955).

U8GS 8544 (field laTtel Pb IS). Bone Spring Limestone, 

limestone layers above unit of limestone-pebble conglomerate. 

East side of Victorio Canyon, on end of spur a quarter of a 

mile northwest of BM 6148 (north-central part of sec. 18, Block 

43). Contains the brachiopods Avonia spp., Buxtonia (Kochir 

productus) victorioensis King, Chonetes large sp., Enteletes sp., 

Leptodus sp., orthotetacean indet., Rhipidomella sp., and 

Stenocisma sp.; the pelecypod Acanthopecten sp.; and the gastropods Anomphalus sp., Babylonites sp., and a pleurotamarian. 

A shark's tooth was observed in the field.
STEATIGEAPHIC SECTIONS OF PERMIAN ROCKS 149

USGS 8543, F 2692 (field label Pb 12). Bone Spring Limestone, limestone layers interbedded with unit of limestonepebble conglomerate. West of Victorio Canyon on south side of 

ridge, and three-quarters of a mile north-northeast of Estes 

Place (west-central part of sec. 14, Block 43). Contains the 

fusulinids and other foraminifers Climacammina sp., Spandelinoides sp., Pseudofusulina setum (Dunbar and Skinner) var., 

Parafusulina schucherti Dunber and Skinner, P. imlayi Dunber, 

and P. spp.; the sponges Fissispongia n. sp., Girtyocoelia dunbari R. H. King, Heliospongia voJcesi R. H. King, and Stereodictyum orthoplectum Finks; the coral Lophophyllum sp.; the 

bryozoan Fistulipora sp.; a crinoid calyx; the brachiopods 

Aulostegesl sp., Enteletes cf. E. dumblei Girty, Hustedia sp., 

Isogramma sp., productid indet, Scacchinella sp., and Wellerella 

sp.; a pelecypod with revolving lirae; and the gastropods 

Glabrocingulum sp., "Trachydomia" sp., and "Worthenia" sp.

USGS 8542, F 2713 (field label Pb 11). Bone Spring Limestone, from limestone beds interbedded near top of lowest unit 

of thin-bedded dolomite. West of Victorio Canyon on south side 

of ridge a mile east of Estes Place (center of sec. 17, Block 43). 

Contains the fusulinids and other foraminifers Geinitzina sp., 

Spandelinoides sp., Endothyra sp., a millerellid, Parafusulina 

diabloensis Dunbar and Skinner, and P. imlayi Dunbar var.; 

the corals Cladochonus sp. and Triplophyllum sp.; the bryozoan 

Gystodictya sp.; and the brachiopods Derbyia sp., Entelets cf. 

E. dumblei Girty, Leptodus sp., MeeJcella difficilis Girty, Neospirifer sp., productids indet., "Spiriferina" sp., Streptorhynchus 

sp., and Wellerella sp.

USGS 14435, F 9810 (field label C12) . Hueco Limestone, near 

base, on slope above inlier of Montoya Dolomite. Northwest 

side of Victorio Canyon 1% miles northest of Estes Place (northeastern part of sec. 14, Block 43). Fusulinids and other 

foraminifers occur in a detrital conglomeratic limestone, in 

both the matrix and the pebbles, all the free fusulinid shells in 

the matrix being abraded. Field relations indicate that the 

strata are of Hueco age, and this is confirmed by the fusulinid 

species, but their manner of occurrence indicates that they have 

been redeposited in their present position. The foraminifers 

include Geinitsina sp., Spandelina sp., Endothyra sp., a bradyinid, 

Tetrataxis sp., Staffella sp., Schubertella Tcingil Dunbar and 

Skinner, Parafusulina linearis (Dunbar and Skinner), Pseudofusulina emaciata (Beede), and Pseudoschwagerina beedei Dunbar and Skinner.

USGS 14429, F 9807 (field label C 6) . Hueco Limestone, upper 

part. In Victorio Canyon, a few feet above channel, near junction of a side canyon from southeast, 2 miles east-southeast of 

Estes Place (southwestern part of sec. 16, Block 43). Contains 

the fusulinids and other foraminifers Tetrataxis sp., spanelinids, 

Osawainella! sp., Sohubertella Mngi Dunbar and Skinner, Pseudofusulina aff. P. powwowensis (Dunbar and Skinner), P. sp., 

Schwagerina sp., ParafusuUnal sp.; the sponge Heliospongia 

voJcesi R. H. King; cup corals; rhomboporoid bryozoans; crinoid 

columns and echinoid plates; the brachiopods Chonetes sp., 

Dictyoclostus (n. subgen.) cf. D. hessensis (King), Glossothyris 

sp., and Punctospirifer sp.; and the gastropods "Anomphalus" 

sp., S trap ar ollus (Euomphalus) sp., a bellerophontid, a 

murchisonid, and a pleurotomarian.

USGS 14436, F 9811 (field label C IS). Hueco Limestone, 

upper part, about a quarter of a mile southwest of and upstream from locality C 6, 1% miles southeast of the Estes Place 

(southwest cor. sec. 18, Block 43). All the fusulinid shells in 

this collection are maturely rounded, but are not fragmented, 

and have clearly been transported and redeposited. Field relations indicate that the strata containing them are of Hueco age,

and all the identified species are of Hueco type. Contains the 

fusulinids and other foraminifers Climacammina sp., Staffella 

sp., ScJiubertella Jcingi Dunbar and Skinner, Parafusulina 

linearis (Dunbar and skinner), Pseudofusulina^ sp., Schwagerina bellulal Dunbar and Skinner, and S.I sp.

USGS 8560a, F 2118 (field label Ph 26). -Hueco Limestone, 

three-quarters of a mile southwest of Estes Place (southwestern 

part of sec. 16, Block 43). Contains the fusulinids and other 

foraminifers Geinitzina sp., Tetrataxis sp., Staffella sp., a 

millerellid, Ozawainellal sp., Pseudofusulina aff. P. powwowensis (Dunbar and Skinner), P. sp., and Schwagerinal sp.

USGS 14428, F 9806 (field label C 5) . Hueco Limestone, tilted 

on Victorio flexure. Strike ridge 6 miles west-northwest of 

Estes Place and 2^ miles east of Dagger Tank (northwestern 

part of sec. 3, Block 44). Contains the fusulinids and other 

foraminifers Climacammina sp., a spandelinid, Tetrataxis sp., 

Schubertella"! sp., Pseudofusulina cfr. P. powwowensis (Dunbar 

and Skinner), and P. sp.

SECTION 29. VICTORIO PEAK

The following sections are of the Hueco, Bone Spring, 

and Victorio Peak Limestones on the east slope of 

Victorio Peak west of the West-Pyle Cattle Co. headquarters, or Corn Ranch (west-central part of sec. 6, 

Block 66, Twp. 6, into the southeastern part of sec. 

10, Block 43). Two sections were measured here during the investigation, both of which are given, because 

each contains important collections of identified fossils, and because the two sections have different scopes 

and were measured at somewhat different places, thus 

illustrating the varying stratigraphic features of the 

locality. These and other sections which have been measured here were discussed by Dunbar (1953, p. 802-809).

Section 29a (same as section C of Dunbar, 1953, fig. 

2 and pi. 1A) was measured by P. B. King and R. E. 

King in 1928, and begins nearly due west of the ranch, 

at the foot of the Sierra Diablo escarpment, on the north 

side of a reentrant valley, passes south of a prominent 

limestone lens ("Kfiz lens") at the top of the lower 

cliffs, and extends up an eastern spur of Victorio Peak 

nearly to its summit, or as far as the cliffs of the 

Victorio Peak Limestone could be scaled. Brachiopods 

collected in this section were identified by R. E. King 

(1931) -and fusulinids by Dunbar and Skinner (1937).

Section 29b (same as section B of Dunbar, 1953, fig. 

2 and pi. 1A) was measured by J. Brookes Knight in 

1931, and begins about half a mile north of the first section in the next reentrant valley at the foot of the Sierra 

Diablo escarpment, but converges upward with the first 

section, passing north of the prominent limestone lens 

and ending near the middle of the Bone Spring Limestone, or above its highest abundantly fossiliferous layers. Larger fossils collected in this section were identified by P. E. Cloud, Jr., and E. L. Yochelson and 

fusulinids and other foraminifers by L. G. Henbest 

(written commun., 1955,1954).
150 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Section 29a

Top of Victorio Peak; no higher beds exposed.

Victorio Peak Limestone (type section) : Feet 

31. Rocks similar to unit 30, extending to top of peak,

forming an unscalable cliff; thickness estimated- 200 

30. Limestone, medium-crystalline, light-gray; contains subspherical chert nodules as much as 4 

in. in diameter. Bedding planes are a foot or 

two apart, but the rock is coherent and weathers 

massive, forming remarkably fluted cliffs. Upper 

200 ft is more dolomitic than remainder, and 

weathers buff and pitted. Strata 100 ft above 

base contain the fusulinid ScJiwagerina setum 

Dunbar and Skinner, and the brachiopods 

Waagenoconcha montpelierensis (Girty), Productus ivesi Newberry, Spirifer marcoui infraplicata King, and Spirifer (Neospirifer) pseudocameratus Girty (REK 496, REK 500; D & 

S 132)___________________________ 450 

29. Limestone, medium-crystalline, light-gray, cherty; 

thin bedded but coherent; forms massive outcrops and a bench at top. Contains the brachiopods Heekella difflcilis Girty, Chonetes subliratus Girty, Productus ivesi Newberry, Lyttonia 

nobilis americanus (Girty), Spirifer marcoui infraplicata King, Hustedia meekana (Shumard), 

and Composita mexicana (Hall) (REK 499). 

In 1936 a collection was made from approximately this unit, from cliff falls on the southeast 

side of Victorio Peak; according to Cloud and 

Yochelson it contains a cup coral; rhomboporoid, 

fistuliporoid, and other bryozoans; the brachiopods Avonia sp., Buxtonia (Kochiproductus) 

victorioensis King, Chonetes sp., "Marginifera" 

spp., productid indet, Prorichthofenia sp., RMpidomella sp., and Wellerella cf. W. elegans 

(Girty) ; and the pelecypod Streblopteria sp. 

(USGS 8545; field label Pb 14)__________ 150

Intergradation.

Bone Spring Limestone:

28. Limestone, dark-gray to black; in 6-in to 1-f t beds;

contains small chert nodules____________ 33 

27. Limestone, fine-grained, gray; in 1- to 2-ft beds; 

contains small subspherical chert nodules and a 

few fossils________________________ 55

26. Limestone, black, dense, platy; in moderately 

thick beds; contains thin wavy laminae; forms 

steep slope below Victorio Peak__________ 247

25. Limestone, black, dense; platy to papery, fissile; 

weathers buff or brown. Top of unit forms summit of an outer spur of Victorio Peak______ 154

24. Limestone, black, dense, platy; weathers buff; in 

10- to 20-ft units; interbedded with chert in 1- 

to 3-ft beds; and gray fossiliferous limestone_ 71

23. Limestone, gray; contains abundant silicified fossils, mostly massive bryozo>ans although some 

beds are crowded with fusulinids. Contains the 

fusilinids Parafusulina schucherti Dunbar and 

Skinner, and Parafitsulina sp., and the brachiopod Productus ivesi Newberry (REK 477, D & S 

131) _______________.____________ 25

Bone Spring Limestone Continued Feet 

22. Limestone, fine-grained, white; with indistinct bedding; forms a cliff that rims the outer spurs of 

Victorio Peak_____________ ___ 100 

21. Covered, except for a few ledges of fossiliferous

limestone like those beneath 50 

20. Limestone, fine-grained, gray; forms a ledge; contains abundant silicified fossils. These include 

the fusulinid Parafusulina diabloensis Dunbar 

and Skinner, and the brachiopods Enteletes 

dumblei Girty, Meekella attenuata Girty, 

Derbya nasuta Girty, Glionetes Mplicatus King, 

C. spinoliratus diabloensis King, Productus ivesi 

Newberry, Marginifera sutlaevis King, M.I 

wliitei King, Prorichtliofenia teguliferoides King, 

Lyttonia noMlis americanus (Girty), Spiriferina 

angulata King, and Hustedia hessensis King 

(REK 476, D & S 130) ; massive bryozoans 

also observed 5 

19. Limestone, black, siliceous, thin-bedded to platy; 

with some interbedded 6-in to 2-ft layers of gray 

granular fossiliferous limestone. These contain 

fusulinids; massive bryozoans; crinoid stems, 

the brachiopods Marginifera, Pugnax, and various productids; and the gastropod Platyceras___ 66 

18. Limestone; in 1-ft ledges; separated by platy 

black siliceous limestone; forms slopes. The 

ledges contain the fusulinids Parafusulina 

diabloensis Dunbar and Skinner and a slender 

species of Parafusulina; and the brachiopods 

Prorichthofenia teguliferoides King, and Pugnoides elegans (Girty) (REK 475, D & S 129) 67 

17. Limestone, fine-grained; in 2- to 6-ft beds; gray, 

weathering light gray and to a rough surface. 

Contains silicifled fossils, including, fusulinids, 

cup corals, and Hustedia-_____ 22 

16. Limestone, black, siliceous, thin-bedded. Contains 

Hustedia Jiessensis King and Composita subtilita (Hall) (REK 474) ; productids also observed_ 73 

Unconformity ( ?). 

Hueco Limestone:

Main body of formation :

15. Limestone lens or reef (termed "Kfiz lens" 

by Dunbar, 1953, p. 802, and "Huecoan bioherm" by Stehli, 1954, p. 282), which forms 

prominent cliff about a quarter of a mile in 

length, at top of lower bench of eastern spur 

of Victorio Peak. Section crosses south edge 

of lens, which tapers southward, and thickens northward to more than 150 ft, the overlying beds through unit 18 wedging out 

against it. Consists of dense faintly bedded 

limestone, weathering to light-gray rough 

surfaces, containing some small chert 

masses. Abundant cup corals, massive 

bryozoans, Hustedia, and a large Omplialotrochus observed-- 115 

14. Limestone, dense, gray, thin-bedded; with 

shaly partings; bedding surfaces somewhat 

wavy; some layers contain much chert. 

Contains the fusulinids Triticites victorioensis Dunbar and Skinner and Schwagerina laxissima Dunbar and Skinner; and
STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 151

Section 29a Continued

Hueco Limestone Continued

Main body of formation Continued Feet 

the brachiopods Productus ivesi Newberry 

Buxtonia peruviana (d'Orbigny), and 

Avonia loulei (Kozlowski) (REK 472, D & 

S 100) ________________________ 44 

13. Limestone, dense, light-gray; in 1- to 3-ft 

beds; contains small subspherical chert nodules ; forms a massive cliff. Contains slender fusulinids as much as half an inch in 

length, and the brachiopods Chonetes subliratus Girty, Productus ivesi Newberry, and 

Linoproductus cora (d'Orbiguy) (REK 

471)__________________________ 50 

12. Limestone, thin-bedded to platy, dark-gray;

weathers pale buff ___ 4 

11. Limestone, finely crystalline, gray nodular; 

contains numerous fossils that appear in 

cross section ; a Chonetes observed in float 25 

Powwow Member:

10. Sandstone, shaly, poorly consolidated, buff;

partly covered by wash from above___ 16 

9. Sandstone, calcareous, medium-grained; in 

part cross bedded; contains rounded limestone pebbles; forms two ledges. Imprints 

of long, slender fusulinids observed on bedding surfaces._ _ 22 

8. Shale, reddish, sandy, poorly exposed _ 33 

7. Conglomerate, red to buff; formed of pebbles of red sandstone, limestone, and chert, 

in a coarse sandstone matrix; grades upward into coarse red sandstone____ 17 

6. Shale, sandy, maroon-red, poorly exposed- 13 

5. Limestone, dense, splintery, brown_____ 1 

4. Covered ______________ ______ 6 

3. Limestone, dense, splintery, brown 2 

2. Covered_____________________ 7 

1. Sandstone, gray, quartzitic__ _ 5 

Base of exposure at edge of alluvial fan; probably near 

base of Hueco Limestone and Powwow Member.

Section 29b

Bone Spring Limestone:

19. Limestone, black, uufossiliferous; extends up 

spur to base of Victorio Peak Limestone; not 

measured. (See section 29a)___________ (?)

18. Limestone, black, siliceous, thin-bedded; with interbedded 1-ft ledges of dark-gray bioclastic fossiliferous limestone. These contain the fusulinids Ozawainella sp., Staff'ella! sp., Parafusulina imlayi Dunbar, P. aff P. bosei Dunbar and 

Skinner, and Parafusulinal sp.; the sponges 

Fissipongia n. sp., Lyssacina incertae sedis, and 

spicules; a cup coral; the bryozoans Fenestella 

sp., Fistulipora sp., Septopora sp., and Striatopora sp.; the brachiopods Avonia sp., Buxtonia 

(Kochiprodiictus) victorioensis King, Chonetes 

consanguineus Girty, C. (Chonetinella) victorianus (Girty), Crtirithyris sp., Derbyia sp., Enteletes sp., Hustedia mormoni (Marcou), H. sp., 

Leptodus sp., "Marginifera" cf. "H." walcottiBone Spring Limestone Continued Feet 

etna (Girty), "H." (KoslowsUa) aff. "If." (K.) 

wabashensis (Norwood and Pratten), "H." sp., 

MeeJcella sp., productids indet., Rhipidomella 

sp., ScaccJiinella sp., Spiriferina sp., and Wetterella sp.; the pelecypod Acanthopecten sp.; and 

the gastropods Apachella sp., Euconispira pulcJira Batten, Grlabrocingulum sp., Platyceras sp., 

and Shewdagoniat sp. (USGS 8561, F 2710; field 

label Pb 7)______________________ 115

17. Limestone, dark-gray; in 1- to 2-ft beds; interbedded with thin-bedded siliceous black limestone___ ____________________ 35

16. Limestone, gray, massive; forms a ledge; contains silicified fossils. The limestone is bioclastic, consisting of fragments of calcareous 

fossil debris of sand to pebble size, with some 

larger angular limestone cobbles, all variably 

silicified. Contains the fusulinids and other 

foraminifers Climaeammina sp., Oeinitsina sp., 

Spandelina sp., Tetrataxis spp., Ozawainella sp., 

*Schubertella kingi Dunbar and Skinner, Boultonia aff. B. rawi Lee, "iSch-wagerina pseudoregularis Dunbar and Skinner, ?$. gumblei Dunbar 

and Skinner, *Pseudoschwagerina gerontica 

Dunbar and Skinner var., *P. texanal Duubar 

Skinner, Parafusulina diabloensis Dunbar and 

Skinner, *P. linearis Dunbar and Skinner, and 

var., P. schucherti Dunbar and Skinner and P. 

spp. (F 2716; field label Pb 6). The fusulinids 

are preserved partly as whole shells, partly as 

fragments and detritus with varying degrees of 

rounding. They represent a depositional aggregate in which forms characteristic of the Hueco 

(marked by asterisk) have been reworked and 

mixed with those characteristic of the Bone 

Spring. Unit 16 also contains the sponge Heliospongia voJcesi R. H. King; the corals Cladochonus sp., Lonsdaleial sp., and Triplophyllum sp.; 

the bryozoans Chainodictyat sp., Cystodictya sp., 

Domoporal sp., Fistulipora sp., Septopora sp., 

and Striatopora sp.; the brachiopods Chonetes 

(Chonetinella) victorianus (Girty), Enteletes 

cf. E. dumblei Girty, Hustedia mormoni (Marcou), "Marginifera" cf. "If." sublaevis King in 

part, and "H." (KosloivsMa) cf. "H." capaci 

(d'Orbigny) ; the gastropods Babylonites sp. 

and Straparollus (Euomphalus) glabribasis 

Yochelson; an annelidlike Spirorbis; and solenoporoid and other algae (USGS 8562, field label 

Pb 6)___________________________ 15

15. Limestone, gray; in 1- to 2-ft beds; contains silicified fossils; interbedded with thin-bedded black 

limestone and cherty shale______ ___ 30

14. Limestone, massive, gray, bioclastic; with a few 

embedded angular limestone cobbles; contains 

silicified fossils of Bone Spring aspect_____ 15

13. Limestone, gray, fossiliferous; in very irregular 1- 

to 2-ft beds, interbedded with thin-bedded black 

limestone and cherty shale ___ 18 

Unconformity (?).
152 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Hueco Limestone:

Main body of formation: Feet

12. Northern edge of limestone lens or reef (unit 

15 of section 29a) ; massive limestone with 

embedded angular fragments of fossiliferous 

limestone. Contains abraded and rounded 

fragments of fusulinid shells, probably including Parafusulina linearis Dunbar and 

Skinner, Pseudofusulina powwowensis Dunbar and Skinner, tSchwagerina Kellula Dunbar and Skinner, and Pseudoschwagerina sp. 

(F 2706, filed label Ph 10)__________ 7

11. Limestone, fine-grained, dark-gray; contains 

black chert nodules; in 1-ft beds; with marl 

partings. Contains the fusulinids and other 

foraminifers Geinitzina sp., Schubertella 

kingi Dunbar and Skinner, Parafusulina, 

linearis (Dunbar and Skinner) var., Pseudofusulina franklinensis (Dunbar and Skinner), and var.; the cup coral Lophophyllum 

sp.; an orthoceratid cephalopod; the gastropod Omphalotrochus sp.; and the brachiopods Avonia (n. subgen.) cf. A. boulei 

(Kozlowski), Chonetes sp., Dictyoclosfus (n. 

subgen.) cf. D. hessensis (King), "Marginifera" sp,. a productid, Neospirifer sp., and 

Rhipidomella sp. (USGS 8556, F. 2721; field 

label Ph 9)___________________ 37

10. Limestone, dolomitic, cherty, light-gray; forms 

a massive ledge. Near top, contains the 

fusulinids Schubertella kingi Dunbar and 

Skinner, Pseudoschwagerina'? laxissima 

(Dunbar and Skinner), and Schwagerina 

belluto Dunbar and Skinner (F 2687; field 

label Ph 8; identified by C. O. Dunbar, 1953, 

p. 804)_______________________ 32 

9. Limestone, very dark gray, cherty; in 2- to 3-f t 

beds, with marl partings. Contains the 

fusulinids Triticites victorioen$is Dunbar 

and Skinner, Pseudoschwagerinal laxissima 

(Dunbar and Skinner), Pseudofusulina 

franklinensis (Dunbar and Skinner), and P. 

texana Dunbar and Skinner (F 2715; field 

label Ph 7; identified by C. O. Dunbar, 1953, 

p. 804) ; the coral Lophophyllum sp.; the 

bryozoans Cystodictya sp. and Goniocladia 

sp.; the pelecypods Aviculopecten1! sp., Aviculopinnal sp., and Oonocardium sp.; and 

the brachiopods Buxtonia (Kochiproductus) 

victorioensis King, Chonetes cf. O. consanguineus Girty, Composita sp., Derbyia sp., 

Dictyoclostus (Chaoiella) aff. D. oolimensis 

(d'Orbigny), Enteletes aff. E. wordensis 

King, Hustedia sp., Linoproductus large n. 

sp., "Marginifera" cf. "M" wabashensis 

(Norwood and Pratten, "M." sp., Neospirifer 

sp., Rhipidomella sp., Spirifer sp., "Spiriferina" sp., and Waagenoconcha sp. (USGS 

8555; field label Ph 7)____________ 30 

8. Limestone, very dark gray, cherty; in 2- to 

3-ft beds. Contains few larger fossils, but 

fusulinids and other foraminifers are abundant, including Climacammina sp., Endothyra 

sp., Geinitzina sp., Parafusulina linearis

Hueco Limestone Continued

Main body of formation Continued Feet 

(Dunbar and Skinner), P. sp., Pseudoschwagerina'i laxissima (Dunbar and Skinner), 

P. beedei Dunbar and Skinner, Schwagerina 

"bellulal Dunbar and Skinner, ?/8. Ttellula 

Dunbar and Skinner, S. knighti Dunbar and 

Skinner, Spandelina sp., and Tetrataxis sp. 

(F. 2707; field label Ph 6)__________ 33 

7. Limestone, dark-gray, massive, cherty; forms 

a strong ledge. Contains the foraminifers 

Geinitzina sp., juvenaria of fusulinids, and 

a fragment of a larger fusulinid; a lonsdaleoid coral cf. Waagenophyllum texanum 

Heritsch; and the gastropod Omphalotrochus sp. (USGS 8554, F 2689; field label 

Ph 5)_______________-___ __ 30 

Powwow Member:

6. Limestone, marly, black; interbedded with 

shale. This unit, and the one next beneath, 

contain Parafusulina ("Schwagerina") linearis (Dunbar and Skinner) (F 2700; field 

label Ph 4; identified by C. O. Dunbar, 1953, 

p. 804) ; the coral Syringopora sp.; the pelecypod Edmondia sp; and the brachiopods 

Chonetes n. sp.?, and Linoproductus cf. L. 

cora (d'Orbigny) (USGS 8553; field label 

Ph 4)________________________ 15 

5. Sandstone, calcareous, yellow, fossiliferous;

with interbedded marl; forms a ledge_____ 15

4. Sandstone, yellow; forms a ledge _ ___ 6 

3. Marl, gray, and interbedded yellow sandstone;

unfossiliferous_________ _______ 35 

2. Sandstone and siltstone, poorly consolidated_ 55 

1. Conglomerate, yellow; contains limestone pebbles ; forms a ledge________________ 8

Base of exposure at edge of alluvial fan; probably near 

base of Hueco Limestone and Powwow Member.

Summary of section 29

Section 29a:

Part of Victorio Peak Limestone exposed_______ 800 

Bone Spring Limestone_ _ ____ __ 968

Hueco Limestone:

Main body of fonnation_______________ 238

Part of Powwow Member exposed______ 122

Part of Hueco Limestone exposed ___ 360 

Section 29b:

Part of Bone Spring Limestone measured _____ 228 

Hueco Limestone:

Main body of formation____________ 169 

Part of Powwow Member exposed______ 134

Part of Hueco Limestone exposed- 303

SECTION 30. VICTORIO CANYON

The following is a section of the Hueco and Bone 

Spring Limestones at the portal of Victorio Canyon, beginning at its channel and proceeding south, up a spur 

of Victorio Peak to top of outer bench, beyond which 

beds were not measured (south-central part of sec. 3, 

Block 66, Twp. 6, into northeastern part of sec. 1, Block
STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 153

43). The section was measured by J. Brookes Knight 

in 1936. Larger fossils were identified by P. E. Cloud, 

Jr., and E. L. Yochelson and fusulinids and other 

foraminifers by L. G. Henbest (written commun., 1954, 

1955). Earlier collections from the same locality have 

been identified by E. E. King (1931), and Dunbar and 

Skinner (1937) (EEK 459, 470; D & S 101, 102, 103), 

but their lists are not reproduced here.

Top of outer bench on north spur of Victorio Peak; higher

beds, mainly black limestone, not measured. 

Bone Spring Limestone: Feet 

7. Limestone, dolomitic; in 3- to 4-ft ledges, with a 

pebbly layer 10 ft below top. Contains poorly 

preserved fossils resembling those beneath. Long, 

slender fusuilinids abundant at top_________ 85 

6. Limestone, slightly dolomitic, light-gray; in 2-ft 

beds. The rock is abundantly fossiliferous, bioclastic, and in part contains limestone pebbles. 

The pebbles contain a staffellid, abundant Schu- 

'bertella, Jcingi Dunbar and Skinner, Parafusulina 

or Pseudofusulina sp., and Pseudofusulina powwowensis"! (Dunbar and Skinner) var., which are 

fusulinids of Hueco type. The matrix contains 

the fusulinids and other foraminifers Qeinitzina 

sp., Tetrataxis sp., Quinquelooulinal sp., Ozaivainellal sp., Staffella sp., *Schwagerina aff. S. 

bellula Dunbar and Skinner, *Pseudofusulina'i 

laxissima (Dunbar and Skinner) or P. powwowensis (Dunbar and Skinner) var., ISchwagerina 

gumblei Dunbar and Skinner, IParafmulina 

diabloensis Dunbar and Skinner, and P. schuoherti Dunbar and Skinner; the fusulinids are 

largely of Bone Spring type, with the exception 

of those marked by an asterisk, which are of 

Hueco type (F 2723; field label Pb 8). Reworking and mixing of fusulinids and other foraminifers from different stratigraphic levels is indicated. Larger fossils include Lonsdaleiat sp., and 

other cup corals; the bryozoans Fenestella sp., 

Fistulipora sp., Polypora sp., and Rhombopora 

sp.; crinoid stems; the brachiopods Ghonetes 

(ChonetineUa) victorianus Girty, C. large sp., 

Enteletes sp., Hustedia hessensis King, "Marginifera" (KozlowsJcia) cf. "M" capaci (d'Orbigny), 

MeeJcella sp., and Streptorhynchus sp.; and the 

gastropods Apachella sp., Euconispira pulchra 

Batten, and Straparollus (Euomphalus) glabribasis Yochelson (USGS 8539; field label Pb 8)_ 27 

Unconformity (?). 

Hueco Limestone:

Main body of formation:

5. Limestone, slightly dolomitic, dark-gray, 

massive; forms cliffs. Fossils scarce and 

poorly preserved________________ 72

4. Limestone, cherty; forms a slope. Contains 

the fusuilinids and other foraminifers Glimacammina sp., Geinitzina sp., Spandelinoides 1! 

isp., Endothyra sp., Staffella sp., Ozawainella 

sp., Schubertella Jcingi Dunbar and Skinner, 

Triticitesl spp., Pseudoschwagerina texana 

Dunbar and Skinner, Pseudofusulina huecoensis Dunbar and Skinner, Parafusulina

Main body of formation Continued Feet 

Hueco Limestone Continued

linearis (Dunbar and Skinner), and Parafusulina slender sp. (F. 2717; field label 

Ph 12)______________________ 5

3. Limestone, slightly dolomitic, dark-gray, 

cherty, massive; forms cliffs; some beds 

brecciated. Contains larger fossils like those 

in unit beneath, such as productids and 

bellerophontids, but few or no fusulinids 130 

Powwow Member:

2. Limestone, sandy and marly, black; interbedded with shale; both very fossiliferous. 

Contains the fusulinids and other foraminifers Spandelinoidest sp., Osawainella spp., 

Schu'bertella sp., Schioagerina bellulal Dunbar and Skinner, Pseudofusulina powwowensis (Dunbar and Skinner), and Parafusulina 

linearis (Dunbar and Skinner) var.; the 

bryozoan Stenopora sp.; the brachiopods 

Avonia (n. subgen.) cf. A. boulei (Kozlowski), A. sp., Buxtonia (KooMproductus) victorioensis King, Ghonetes n. sp., Gomposita 

sp., Grurithyris sp., Derbyia sp., Dictyoclostus wolfcampensis (King), Linoproductus 

cf. L. oora (d'Orbigny), "Marginifera" aff. 

"M." lasallensis (Worthen), and Squamularia sp.; the pelecypods Allorisma sp., Aviculopectenl sp., Aviculopinna sp., a myalinid, "Nucula" sp., a parallelodontid, and 

Pseudomonotis sp.; and the gastropods bellerophontid indet., "Donaldina" gp., Euconispira cf. E. missouriensis (Shumard), a 

murchisonid, Naticopsis sp., and a pseudozygopleuroid (USGS 8557, F 2694; field label 

Ph 11)________________________ 45

1. Sandstone, red and brown; with seams of conglomerate in upper part; unfossiliferous _ 30 

Base of exposure at level of channel of Victorio Canyon; 

probably near base of Hueco Limestone and Powwow 

Member.

Summary of section 30

Part of Bone Spring Limestone measured _ __ 112

Hueco Limestone:

Main body of formation -____________ 207 

Part of Powwow Member exposed________ 75

Part of Hueco Limestone exposed_______ ___ 282

SECTION 31. NORTH OF VICTORIO CANYON

The following is a section of the Hueco, Bone Spring, 

and Victorio Peak Limestones, beginning at the foot 

of the Sierra Diablo escarpment 2 miles north of the 

portal of Victorio Canyon, and extending westward to 

a promontory of the Victorio Peak Limestone at the 

top of the escarpment (northwest cor. sec. 2, Block 66, 

Twp. 6, across the northern part of sec. 22, Block 42). 

The section was measured in 1936, the lower part 

(through unit 11) being hand leveled and described in 

detail by J. Brookes Knight, and the higher strata 

covered in less detail by observations of P. B. King,
154 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

with thicknesses estimated. Larger fossils were identified by P. E. Cloud, Jr., and E. L. Yochelsoii and 

fusulinids and other foraminifers by L. G. Henbest 

(written commun., 1954, 1955).

Crest of Sierra Diablo escarpment; no higher beds exposed. 

Victorio Peak Limestone: Feet

IS. Limestone, fine-grained; oolitic in part; light- to 

dark-gray; thin- to medium-bedded, with some 

thicker beds at top. Some interbedded layers 

are marly or slightly sandy, very cherty, and 

weather buff. Fossils moderately abundant in 

some layers. A mile to the south of end of 

section were collected a sponge; the bryozoan 

Phyllopora sp.; the echinoderm "Echinocrinus" 

sp.; the brachiopod Buxtonia (Kochiproductus) 

sp.; the gastropods bellerophontid indet., Callistomarial sp., Meekospira sp., loxonematid indet., Stegocoelia"? sp., and Warthia cf. W. waageni Yochel&on; an ammonite; and the scaphopod Plagioglypta sp. (USGS 8546; field label 

Pb 15)_________________________ 250

17. Limestone, gray, massive; with widely spaced 

faint bedding planes, with low original dip. 

The unit forms sheer unscalable walls, recessed 

into embayments, shelters, and caves, and in 

places with pinnacles standing in front, separated from the rest by weathering along joints__ 250

16. Limestone, medium-grained, gray; in 1- to 2-ft 

beds, some crowded with fusulinids; forms 

slopes and small ledges. Unit is transitional 

both vertically and laterally, from gray limestone facies of Victorio Peak into black limestone fades of Bone Spring; both it and units 

14 and 15 beneath merge into typical cliff-making Victorio Peak Limestone on first spur north 

of Victorio Canyon_________________ 100 

Intergradation. 

Bone Spring Limestone:

15. Limestone, black; in 6- to 18-in. beds______ 340

14. Limestone, gray, granular; contains silicified fossils ; forms a ledge. Merges with basal part of 

Victorio Peak Limestone to the south, but 

wedges out to north_________________ 10

13. Limestone, black. In lower three-quarters is very 

thin bedded or platy, with closely spaced light 

and dark laminae. In upper quarter the beds 

are thicker, weather light gray, and contain 

much chert. Bedding slopes irregularly at low 

angles, probably due to original dip of deposit_ 395

12. Irregular cliff; on line of section formed of thinbedded black limestone, with some thicker beds 

near top; farther south includes massive reefy 

limestone beds ___________________ 50

11. Limestone, black to dark-gray, fine grained; in 1- 

to 2-ft beds; contains silicified fossils and bands 

and lenses of brown chert; interbedded toward 

top with thinner bedded black limestone. This 

unit, and that next beneath, contains the 

fusulinids Schubertella kingi Dunbar and Skinner var., Psetidofusulina setum (Dunbar and 

Skinner), Parafusulina fountaini Dunbar and

Bone Spring Limestone Continued Feet 

Skinner var., and P. ? spp.; the coral Lonsdaleia"i sp.; the bryozoan Fistulipora sp.; a 

platycerid gastropod; and the brachiopods 

Heekella sp., Avonia sp., Prorichthofenia sp., a 

productid, Hustedia sp., and Enteletes cf. E. 

dumWei Girty (USGS 8540, F 2705; field label 

Pb 9) _________________ __ 1^2 

10. Slope, with a reefy ledge of brecciated limestone 

at top, containing silicified fossils of Bone 

Spring type, including large fusulinids 33 

Conformity (?). 

Hueco Limestone:

Main body of formation:

9. Limestone, dolomitic, gray, massive; with 

irregular wavy bedding in lower half; 

forms a cliff. Contains a few silicified 

fossils___________ 25 

8. Limestone, dolomitic, fine-grained, gray, thinbedded ; contains black chert nodules 10 

7. Limestone, dolomitic, gray, massive; almost 

without bedding; forms a cliff. Contains 

poorly preserved silicified fossils- 28 

6. Limestone, dolomitic, thin-bedded, cherty. 

Contains the fusulinids and other foraminifers Climacammina spp., Tetrataxis sp., 

Schubertella kingi Dunbar and Skinner, 

Pseudofusulina powwowensisl (Dunbar and 

Skinner), Pseudoschwagerina beedei Dunbar and Skinner, and ScJiwagerina sp. (F 

2702; field label Ph 23)____________ 10 

5. Limestone, dolomitic, thin-bedded, cherty;

forms a slope_________ _ __ 10 

4. Limestone, dolomitic, very cherty; forms a

ledge________________________ 10 

3. Limestone, partly dolomitic, partly calcitic, 

gray; in 1- to 2-ft beds, with marl partings; 

forms a slope. Contains the fusulinids 

ScJmbertella kingi Dunbar and Skinner, 

PseudoscJiwaperinal laxissima (Dunbar and 

Skinner), P. sp., Pseudofusulina sp., Parafusulina linearis (Dunbar and Skinner) (F 

2708; field label Ph 22) ; corals, Composite/,, 

and small productids observed________ 48 

2. Limestone, dolomitic; forms upper part of 

lower cliff. The rock is bioclastic, fragmental, and contains many silicified fossils. 

Fusulinids are preserved as abraded to entire shells. These and other foraminifers 

include a bradyinid, Staffella sp., Triticites 

aff. T. subventricosus Dunbar and Skinner, 

Pseudofusulina powwoicensisl (Dunbar and 

Skinner), ScJiwagerina bellula'i Dunbar and 

Skinner, SI Jiessensis (Dunbar and Skinner), and Parafusulina linearis (Dunbar 

and Skinner) var. (F 2722; field label Ph 

21) ; crinoid columns and corals observed_ 20 

1. Limestone, calcitic, fine-grained, nearly black; 

with marly partings. Contains the bryozoan 

Stenopora sp.; and the brachipods Chonetes 

sp., Buaetonia (KocMproductus) victorloensis King, Linoproductus cf. L. cora (d'Orbigny), and a productid; fusulinids were not
STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS

Hueco Limestone Continued Feet 

Main body of formation Continued

seen in place, but a float block contains 

Schubertella! sp., and Parafmulina, linearis 

(Dunbar and Skinner) USGS 8558, F 2699; 

field label Ph 20)_______________ 25 

Base of section at edge of alluvial fan; no lower beds 

exposed.

Summary of section 31

Part of Victorio Peak Limestone exposed_______ 600

Bone Spring Limestone_____________________ 950

Part of Hueco Limestone exposed_______________ 186

SECTION 32. MARBLE CANYON

The following is a section of the Hueco, Bone Spring, 

and Victorio Peak Limestones on the ridge south of 

Marble Canyon, beginning near the base of the Sierra 

Diablo escarpment half a mile south of portal of the 

canyon and 3 miles southwest of old Figure Two Ranch 

headquarters, and ending on a projecting angle of the 

crest of the escarpment half a mile east of Chambers triangular station (across the northern part of sec. 21, 

Block 66, Twp. 5). A section was measured here by 

P. B. King and R E. King in 1928, but few significant 

fossil collections were made. The lower part of the section was again measured by J. Brookes Knight in 1931, 

from the base of the escarpment to the top of the outer 

bench (through unit 46). The section given here is that 

of Knight, but the higher part has been added from the 

section of King and King, and from observations which 

were made along the crest of the escarpment, in 1938 

and earlier. Larger fossils were identified by P. E. 

Cloud, Jr., and E. L. Yochelson (written commun., 

1954), and fusulmids were identified by C. O. Dunbar 

and J.W. Skinner (1937).

A suite of fossil collections from nearby, on the ridge 

north of Marble Canyon, was made by G. B. Richardson and G. H. Girty in 1907, and identifications by 

Girty were partly reported in the Van Horn folio 

(Richardson, 1914, p. 5; USGS 7165, 7l65a, 7168a to 

7168h; field locality 85). However, the ridge north of 

the canyon lies in a dolomitic reef f acies of the Permian rocks and yielded few fossils except in the Hueco 

Limestone near the base and the Victorio Peak Limestone near the top; Girty observed a resemblance between the facies of the latter and that of the much 

younger Capitan Limestone.

Top of escarpment; no higher beds exposed.

Victorio Peak Limestone:

50. Limestone, gray; in beds a few feet thick, parts 

of which have low original dips; forms ledges 

and slopes at top of escarpment. Some interbedded marl; platy, siliceous brown limestone; 

and slightly sandy cherty buff limestone. Fossils are moderately abundant in places and are 

partly silicified. From several places along the

757-108 «5 11

Victorio Peak Limestone Continued

rim of the escarpment northwest of upper end 

of section, near head of Marble Canyon, were 

collected the sponges Actinocoelia meandrina 

Finks, Defordia densa Finks and Strioderma 

coscinum Finks; crinoid stems; the braehiopods Buxtonia (Kochiproductus) victorioensis 

King, Neospirifer sp., and a large productid 

(USGS 7011, 14444; field label C 19)_____ 

49. Limestone, light-gray to white, granular or crystalline; in thick beds, with some thinner 

beds; forms a sheer unscalable cliff that rims 

the Sierra Diablo escarpment. Contains sparse 

brown chert nodules. In 1928, at head of ridge 

south of Marble Canyon, was collected the 

brachiopod Buxtonia victorioensus King 

(type) (REK 498)_______________ 

Intergradation. 

Bone Spring Limestone:

48. Limestone, black; in 2- to 8-in. beds; irregularly 

bedded, with partings of shale and chert; 

forms a cliff _______ ______ 

47. Limestone, black, thinly laminated, platy; interbedded below with siliceous brown shale. 

Forms a long slope between upper cliffs and 

lower bench of Sierra Diablo escarpment. 

Thickness measured on ridge south of Marble 

Canyon intrusive, where there is a low original 

dip toward south, away from reef masses 

north of Marble Canyon _ 

46. Limestone, dolomitic, gray; without bedding; 

lenticular; passes laterally into thinner bedded 

black limestone. Parts are brecciated, the 

fragments including not only gray limestone, 

but black limestone and chert. Forms crest 

of outer bench of escarpment. Abundantly 

fossiliferous; contains large Parafusulina sp.; 

sponge spicules; the bryozoan Fistulipora sp.; 

the brachiopods Meekella sp., Leptodus sp., 

Prorichthofenia sp., a productid, Hustedia 

mormoni (Marcou), Squamularia sp., Enteletes sp., and Dielasma sp.; and a triolobite 

(USGS 7010, D & S 134; field label 21 K)__ 

45. Limestone, black, platy, shaly; with thin chert 

beds; weathers yellow brown and forms a 

slope_________________________

44. Limestone, dolomitic, coarsely crystalline, gray; 

forms ledges on slope. Partly silicified and 

poorly preserved fusulinids, crinoid columns, 

and echinoid spines observed________________

43. Limestone, black, thin-bedded, shaly___________

42. Limestone, dolomitic, coarsely to finely crystalline, gray; in 2-ft beds. Contains irregularly 

silicified areas; poorly preserved fusulinids 

and crinoid columns observed ___________

41. Limestone, dark-gray to black, thin-bedded; with 

chert bands; weathers brown to light gray; 

forms a slope _ ___________________

40. Limestone, dolomitic, crystalline, light-gray; 

weathers deeply pitted; forms ledges on slope. 

Abundant fusulinid molds observed, some filled 

by calcite___________________._

155

Feet

250

250

1T5

695

27

55

25

3

45

45
156 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Bone Spring Limestone Continued Feet 

39. Limestone, dolomitic, gray; forms a ledge; top 

and base is massive, but middle is thinly 

bedded. Contains poorly preserved fusulinids 

(D & S 133; field label 21 J) __________ 10 

38. Limestone, black, thin-bedded, poorly exposed; 

forms a slope, with a few ledges of gray 

cherty limestone______________ 27 

37. Limestone, dolomitic, massive, brecciated, silicified; forms a rounded ledge. Contains poorly 

preserved fusulinids (D & S 111; field label 

21 I) ; a sponge, crinoid columns, and a large 

spiriferoid brachiopod observed 30 

36. Limestone, coarsely crystalline, light-gray; in 

2- to 3-f t ledges; contains chert lenses ; interbedded with thinner bedded more compact 

limestone. Contains poorly preserved, silicified fusulinids (D & S 110; field label 21 H) ; 

crinoid columns observed_____ 66 

35. Limestone, dolomitic; forms a slope 5 

34. Limestone, dolomitic, light-gray, massive; forms

a ledge_ _ 18 

33. Slope; underlying beds concealed 8 

32. Limestone, dolomitic, light-gray_ _ 3 

31. Limestone, dolomitic, dark-gray, thin-bedded;

contains small chert nodules and a few fossils- 25 

Conformity (?). 

Hueco Limestone:

Main body of formation:

30. Limestone, dolomitic, thinly and evenly 

bedded; lower part dark gray, upper part 

light gray to pinkish; contains large chert 

nodules in lower part, and some fusulinid 

molds. Forms sheer massive cliffs_ 175 

29. Limestone, dolomitic, thin-bedded; forms a 

slope; contains scattered large chert nodules, and near the middle a few calcitized 

fusulinids_ _______. _ 40 

28. Limestone, dolomitic, light-gray, massive. 

At top, contains the fusulinids Schubertella kingi Dunbar and Skinner and 

Schwagerina emaciata (Beede) (D & S 

109; field label 21 G) ____________ 15 

27. Limestone, dolomitic, thin-bedded; contains

a few chert nodules_ _____ 10 

26. Limestone, dolomitic, massive; forms a cliff,

containing chert nodules in lower half_ 35 

25. Limestone, calcitic, thin-bedded. Contains 

the fusulinids Schubertella Jcingi Dunbar 

and Skinner and Schwagerina emaciata 

(Beede) (D & S 108; field label 21 F). A 

later collection at about the same level 

contains the brachiopods Derftyia sp. and 

Linoproductus sp. (USGS 8551; field label 

Ph 2)_____________________ 3 

24. Limestone, massive______________ 4 

23. Limestone, marly. Contains the fusulinids 

Bchubertella kingi Dunbar and Skinner 

and Schwagerina emaciata (Beede) (D & 

S 107; field label 21 E) __________ 4 

22. Limestone, dolomitic, massive________ 10

Hueco Limestone Continued

Main body of formation Continued

21. Limestone, dark-gray, irregularly bedded. 

Contains the fusulinids Schubertella 

kingi Dunbar and Skinner, Schwagerina, 

emaciata (Beede), and Triticities powwowensis (Dunbar and Skinner) (D & S 

106; field label 21 D)__________________

20. Limestone, dark-gray, massive; contains 'a 

few fusulinids ___________________

19. Limestone, gray, irregularly bedded; contains many fusulinids- _____________

18. Slope; underlying beds concealed .

17. Limestone, light-gray, irregularly bedded;

contains a few silicified fossils__________

16. Slope; underlying beds concealed _ 

15. Limestone, granular, gray; contains silicified fossil fragments____________

Powwow Member:

14. Limestone, marly, irregularly bedded;

forms a slope. Contains the fusulinids

Schubertella Tcingi Dunbar and Skinner

and Schwagerina emaciata (Beede) (D

& S 105; field label 21 B) ; other poorly

preserved fossils observed _

13. Marl: poorly exposed _ _

12. Limestone, granular, gray. Fusulinids not

observed, but contains fragments of other

fossils ..______________________

11. Limestone, marly, nodular. Contains the 

fusulinids Staffella sp. and Schwagerina 

emaciata (Beede) (D & S 104; field 

label 21 A)____________________________

10. Slope; underlying beds concealed-________

9. Limestone, pinkish-gray, unfossiliferous__ 

8. Sandstone, arkosic, yellow; poorly exposed_____________________ 

7. Conglomerate, arkosic, red; contains pebbles of igneous rocks__________________

6 Slope; underlying beds concealed-_________

5. Conglomerate, arkosic, red _

4. Sandstone, arkosic, poorly consolidated,

red____________________________________

3. Slope; underlying beds concealed__________

2. Conglomerate, arkosic _ ___ _ 

1. Covered; at nearby localities base of Powwow Member is a conglomerate, containing pebbles of chert and red sandstone_ 

Angular unconformity.

Pennsylvanian rocks at base of section. (See section 

12.)

Summary of section 32

Part of Victorio Peake Limestone exposed-___________

Bone Spring Limestone _ 

Hueco Limestone:

Main body of formation______________ 357 

Powwow Member_________________ 100

Total Hueco Limestone __________________

Feet

16

6

4

18

5

14

3

8

3

12

5

10

10

10

5

5

500

1,270

457

FOSSIL COLLECTIONS FROM HUECO LIMESTONE NEAR 

MARBLE CANYON

An outcrop of marl and marly limestone forms a conspicuous bluff just above the channel on the north side of
STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 157

the portal of Marble Canyon (approx. units 11 to 14 of 

section 32) (east-central part of sec. 20, Block 66, Twp. 

5). Collections have been made here by various geologists at different times, including G. B. Richardson and 

G. H. Girty, E. E. King, J. W. Skinner, and J. Brookes 

Knight. The following fossils have been identified:

REK 456, D & S 113, 114. Collected by B. E. King and J. 

W. Skinner, and identified by B. E. King (1931) and by Dunbar 

and Skinner (1937) : The fusulinids Schubertella kingi Dunbar 

and Skinner, PseudoscJiwagerina uddeni (Beede and Knicker), 

P. texana Dunbar and Skinner, Schwagerina huecoensis Dunbar 

and Skinner, and $. knighti Dunbar and Skinner; and the 

brachiopods Orthotichia Joozlowskii King, Chonetes permianus"! 

Shumard, Isogramma millepunctata (Meek and Worthen), 

Productus semistriatus Meek, P. wolf camp ensis King, Linoproductus cora (d'Orbigny), Marginifera dugoutensis"! King, 

and Composita subtilita angusta King.

USaS 7050, 8550, F 27181) (field labels 22, Ph 1) . Collected 

by J. Brookes Knight in 1931 and 1936; identified by L. G. Henbest, P. E. Cloud, Jr., and E. L. Yochelson (written commun., 

1955, 1954) : The fusulinids and other foraminifers Climacammina sp., textulariids, Geinitzina sp., Endothyra sp., a bradyinid, 

Staffella lacunosal Dunbar and Skinner, Ozawainella huecoensis'! Dunbar and Skinner, Schubertella Jcingi Dunbar and Skinner, Pseudofusulina huecoensis Dunbar and Skinner, and var., 

P. powwowensis (Dunbar and Skinner), Schwagerina knighti 

Dunbar and Skinner, Paraschwagerina gigantea (White), Pseudoschwagerina uddeni (Beede and Knicker), and P. teaana var. 

ultima Dunbar and Skinner; the coral Lophophyllum sp.; the 

bryozoans Fenestella spp., Fistulipora sp., and Septopora sp., 

ecinoid plates and a crinoid calyx; the brachiopods Chonetes 

sp., Cleiothyridina sp,,, Composita sp., Crurithyris sp., Dictyoclostus (Chaoiella) aff. D. boliviensis (d'Orbigny), D. (n. subgen.) cf. D. hessensis (King), D. wolfcampensis (King), Isogramma sp., "Marginifera" (Kozlowskia) capaci (d'Orbigny), 

Schizophoria sp., and Squamularia sp.; the pelecypods Aviculopecten? sp. and Septimyalina sp.; the gastropods Amphiscapha 

cf. A. muricata (Knight), a bellerophontid, Naticopsis sp., Omphalotrochus obtusispira (Shumard), and Pharkidonotus sp.; 

an orthoceratid cephalopod; and a trilobite.

SECTION 88. MINE CANYON

The following is a section of the Hueco Limestone 

on the north side of the portal of Mine Canyon, beginning about 1% miles west-southwest of old Figure Two 

Ranch headquarters, above outcrops of lower fossiliferous shale of Pennsylvanian age and proceeding to the 

top of the outer bench of Sierra Diablo escarpment 

(southeastern part of sec. 15, Block 66, Twp. 5). The 

section was measured by J. Brookes Knight in 1931, 

but some additional fossil collections were made in 1936. 

Fusulinids were identified by C. O. Dunbar and J. W. 

Skinner (1937) and larger fossils by P. E. Cloud, Jr., 

and E. L. Yochelson (written commun., 1954).

Bone Spring Limestone:

Feet

22. Dolomitic facies overlying top of section, not traversed (?) 

Conformity (?).

Hueco Limestone: Feet 

Main body of formation:

21. Limestone, dolomitic, light-gray, thinly and 

and evenly bedded; contains abundant fusulinid molds; forms almost unscalable cliffs; 

thickness estimated _ 200

20. Limestone, dolomitic, light-gray; contains 

small calcitized fusulinids; forms a massive 

bench______________.________ 38

19. Limestone, dolomitic, dark-gray to black; contains large spherical chert nodules; forms 

a slope below cliffs. Contains the fusulinids Schubertella Jcingi Dunbar and Skinner, Triticites powwowensis Dunbar and 

Skinner, Pseudoschwagerina beedei Dunbar 

and Skinner, and Schwagerina emaciata 

(Beede) (D & S 121; field label 13 F) ___ 46

18. Limestone, dolomitic, massive-_ 50

17. Limestone, dolomitic, light-gray, massive. 

Contains the fusulinids Schubertella Jcingi 

Dunbar and Skinner, Schwagerina emaciata 

(Beede), and S. huecoensis Dunbar and 

Skinner (D & S 120; field label 13 B) ; other 

silicified fossils observed___ _____ 55

16. Limestone, thin-bedded; forms a slope. Contains the fusulinids Schubertella Jcingi Dunbar and Skinner, Schwagerina emaciata 

(Beede), and Pseudoschwagerina sp. (D. & 

S 119; field label 13 D) ____________ 25

15. Limestone, gray, massive; forms lowest ledge, 

irregularly bedded in lower part; contains 

large round chert nodules and silicified fossil fragments- 43

14. Limestone, fine-grained; gray below and black 

toward top; contains many large chert nodules. Contains unidentifiable fusulinids; 

the coral Chaetetes sp.; echinoid spines; and 

the brachiopods Dictyoclostus (Chaoiella) 

aff. D. boliviensis (d'Orbigny), D. cf. D. 

hessensis (King), productid indet., Neospirifer sp., and Hustedia sp. (USGS 7001, 

D & S 118; field label 13 C) ; bryozoans observed___ _____ __ _ 33

13. Limestone, coarse-grained, gray; with many 

chert nodules. Contains unidentifiable 

fusulinids; sponge spicules; the corals Clisiophyllum sp. and Lophophyllum sp.; the bryozoans Anisotrypa sp., Cystidictya sp., Fistulipora sp., Polypora sp., Septopora sp., and 

Stenopora sp.; echinoid spines and crinoid 

columns; the brachiopods Cleiothyridina 

cf. D. hessensis (King), D. (Chaoiella) aff. 

cf. D. wolfcampensis (King), D. (n. subgen.) 

cf. D. hessensis (King), D. (Chaoiella) aff. 

D. boliviensis (d'Orbigny), Dielasma sp., 

Hustedia sp., "Marginifera" (Kozlowskia) 

cf. "M. (K.) wabashensis (Norwood and 

Pratten), Rhipidomella sp., and Squamularia sp., the pelecypod Cypricardina sp.; 

and the gastropod Platyceras sp. (USGS 

D & S 117; field label 13 B) __ 17
158 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Hueco Limestone Continued

Powwow Member: Feet 

12. Limestone, marly; poorly exposed on slope;

contains abundant large bryozoans_____ 22 

11. Limestone, granular, gray. Contains the f usulinids Schubertella kingi Dunbar and Skinner, Schwagerina huecoensis Dunbar and 

Skinner, and S. emaciata (Beede) ; the 

sponge Stereodictyum orthoplectum Finks; 

the coral Campophyllum sp.; the bryozoans 

Anisotrypa sp., Cystidictya sp., Fistulipora 

sp., Meekopora sp., Septopora sp., and Btenopora sp.; echinoid spines and plates, crinoid 

columns and a calyx; the brachiopods Buxtonia (Kochiproductus) victorioensis 

(King), C omposita sp., Dictyoclostus 

(Chaoiella) aff. D. boliviensis (d'Orbigny), 

D. cf. D. Jiessensis (King), D. cf. D. wolfcampensis (King), D. sp., Enteletes aff. E. 

wordensis King, Hustedia sp., Linoproductus 

sp., "Harginifera" (Kozlowskia) cf. "If." 

(K.) wabashensis (Norwood and Pratten), 

productid indet., Rhipidomelfa sp., Rhynchopora sp., Schizophoria sp., and Squamularia 

sp.; the pelecypod Aviculopectenl sp.; the 

gastropods Omphalotrochus obtu&ispira 

(Shumard), Naticopsis sp., and a loxonematacean; and a trilobite (USGS 7001a, 

7004, 8552, D & S 116 field labels 13 A, 

Ph 3)______________________ 3 

10. Limestone, marly, thin-bedded, poorly exposed. Contains the fusulinids Schubertella 

kingi Dunbar and Skinner, Schwagerina 

huecoensis Dunbar and Skinner, 8. emaciata 

(Beede), S. nelsoni Dunbar and Skinner, 

and Pseudoschwagerina Tteedei Dunbar and 

Skinner (D & S 115; field label 13 AA)__ 45 

9. Shale and sandstone, arkosic, red_______ 3 

8. Sandstone, arkosic, brown___ _ _ 10 

7. Slope; beds concealed-__________ ___ 15

6. Sandstone, arkosic; contains small pebbles_ 3 

5. Shale, arkosic, red________________ 20 

4. Conglomerate, arkosic, red; contains small

limestone pebbles_______ __ ___ 13

3. Shale, sandy; gray at base; poorly exposed_ 25 

2. Sandstone, arkosic, red; conglomeratic at

base_______________________ 25 

1. Conglomerate, arkosic, massive; composed of

pebbles of limestone and igneous rocks___ 4 

Angular unconformity.

Shale of Pennsylvanian age at base of section, poorly exposed in upper part.

Summary of section 33

Hueco Limestone:

Main body of formation_______________ 507 

Powwow Member______ ___________ 188

Total Hueco Limestone ______________ 695

SECTION 34. SOUTH OF BLACK JOHN CANYON

The following is a section of the Hueco Limestone 

half a mile south of Black John Canyon, on the divide 

between the canyon and drainage to the southeast, up the

main outer bench of Sierra Diablo escarpment, northeast 

of which rocks are downfaulted (east-central part of 

sec. 13, Block 66, Twp. 5). The section given here is 

based on detailed measurement of the lower beds 

(through unit 11) by J. Brookes Knight in 1931, with 

higher beds added from a more generalized section by 

P. B. King and K. E. King in 1928. Fusulinids collected by Knight were identified by Dunbar and Skinner 

(1937) and a small lot of brachiopods by P. E. Cloud, 

Jr., and E. L. Yochelson (written commun., 1954).

Section 34a is included to illustrate variation in thickness of Hueco Limestone. It was measured in 1928 by 

P. B. King and E. E. King on a flat-topped outlier in the 

downfaulted area, about half a mile northeast of the 

main section (north-central part of sec. 12, Block 66, 

Twp. 5).

Bone Spring Limestone: Feet 

13. Shale, siliceous, brown; interbedded with granular 

light-gray dolomitic limestone; forms top of 

outer bench. These and higher beds were not 

measured, as they form edge of a reef mass 

with original dips toward northeast, which extends up to Victorio Peak Limestone_ __ (?) 

Conformity (?). 

Hueco Limestone:

Main body of formation:

12. Limestone, dolomitic, finely crystalline, gray; 

weathers dirty gray and pitted; in 6-in to 

1-ft beds, but forms massive cliffs. Contains 

some subspherical chert nodules. Thickness estimated_________ _ _ 750

11. Limestone, light-gray; contains small fusulinids_______________________ 8 

10. Limestone, thin-bedded_________ _ 12

9. Limestone, marly; forms a slope between cliffs. 

Contains the fusulinids Pseudoschwagerina 

uddeni (Beede and Knicker), P. texana 

Dunbar and Skinner, and Schwagerina 

huecoensis Dunbar and Skinner (D & S 122; 

field label 16 A)________________ 3 

8. Limestone, dolomitic; forms a cliff______ 17 

7. Limestone, dolomitic, gray, massive; contains 

unidentified fusulinids (D & S 123; field 

label 16 B) ____________________ 18 

Powwow Member:

6. Limestone, thin-bedded. Contains unidentified fusulinids and the brachiopods Linoproductus"! (cf. Cancrinella) sp., L. sp., and 

Composita sp. (USGS 7056, D & S 124; field 

label 16 C) : bellerophontid gastropods 

observed_____ _ _ _______ 15

5. Limestone, forming scattered ledges on slope,

with fossils in float-__ _________ 20

4. Slope, covered by talus_ _ _______ 50

(Trachyte sill about 10 ft thick)

3. Slope, covered by talus___ _________ 70 

2. Conglomerate, arkosic _ _ _ _ 20 

1. Conglomerate; composed of limestone pebbles- 10 

Angular unconformity. 

Beds of Devonian age at base of section.
STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 159

Section 34a

Top of outlier; no higher beds exposed.

Bone Spring Limestone: Feet 

4. Shale, siliceous, brown; capped by a 4-ft bed of

dolomitic limestone, containing bryozoans____ 44 

Conformity (?). 

Hueco Limestone:

Main body of formation:

3. Limestone, dolomitic; forms a slope______ 80 

2. Limestone, dolomitic, finely crystalline, lightgray ; weathers dirty gray or pitted; forms 

ledges and cliffs. Contains some small subspherical chert nodules as much as 10 in. in 

diameter, and fusulinid molds; near middle 

was collected Composita mexicana (Hall) 

(REK 462). About 125 ft below top is a thin 

trachyte sill____________________ 355 

Powwow Member:

1. Slope; underlying beds concealed________ 55 

Angular unconformity.

Fusselman and Montoya Dolomites at base of section. 

(See section 9.)

Summary of section 34 

Main section:

Hueco Limestone:

Main body of formation_____________ 808 

Powwow Member________________ 180

Total Hueco Limestone____________________ 993

Section 34a:

Hueco Limestone:

Main body of formation_______________ 435 

Powwow Member___________________ 55

Total Hueco Limestone________________ 490

SECTION 33. Bia.CK JOHN CANYON

The following is a section of parts of the Hueco and 

Bone Spring Limestones on the west side of the south 

fork of Black John Canyon, about a mile south of 

Apache Spring (center of east line of sec. 14, Block 66, 

Twp. 5); a pair of minor faults displaces the Hueco and 

Bone Spring immediately to the northeast. The section combines observations and measurements by J. 

Brookes Knight and P. B. King in 1931. A fusulinid 

from the collections was identified by C. O. Dunbar and 

J. W. Skinner (1937) and the ostracodes by I. G. Sohn 

(written commun., 1960). The rest of the fossils were 

identified by P. E. Cloud, Jr., and E. L. Yochelson 

(written commun., 1954).

Higher beds on slope not measured.

Bone Spring Limestone: Feet 

11. Limestone, black, thin-bedded; forms a slope. 

The brachiopods Chonetes and Marginifera, 

pelecypods, and possible algae observed___ 50 

10. Limestone, dark-gray, granular; partly silicified 

on surface; contains layers of subangular limestone cobbles of different texture from matrix. 

Forms several ledges, but is lenticular, wedging 

out into black limestone northeastward. Contains fusulinids, a sponge, and crinoid stems

Bone Spring Limestone Continued Feet 

(USGS 7055a; field label 20 A) ; bryozoans, and 

productid, spiriferoid, and rhynchonellid 

^brachiopods observed. _ _ _ 20

9. Limestone, black, thin-bedded to platy; with 

interbedded thin layers of granular fossiliferous limestone_______________ 25

8. Molluscan ledge. Limestone, dark-gray, coarsegrained, bioclastic; contains a rich fauna dominated by mollusks, partly silicified. Forms a 

lens several hundred feet long which tapers into 

black platy limestone. Contains the fusulinid 

Parafusulina dlabloensis Dunbar 'and Skinner; 

the sponges Anthracosycon uniforme Finks and 

Stioderma coscinum Finks; cup and tabulate 

corals including Aulopora sp., Cladochonus sp. 

and Lonsdaleial sp. ; echinoid spines and 

crinoid columns; the bryozoans Acanthocladia 

sp., Septopora sp., and Striatopora sp.; the 

brachiopods Chonetes sp., Leptodus sp., and 

various productids; the pelecypods Anthraconeilo sp., Astartella nasuta Girty, A sp., 

"Cypricardinia" sp., Nucula sp., nuculoid 

indet., Nuculana sp., Parallelodon spp., Pleurophorus sp., Pterial sp., and Streblopteria sp.; 

the gastropods Anomphalus sp., Apachella sp., 

Babylonites sp., Bellerophon deflectus Chronic, 

B. sp., bellerophontid indet., Cinclidonema sp., 

Discotropis girtyi Yochelson, Donaldina"! sp., 

JHuphemites sp., Glabrocingulum sp., Glyptospira sp., Knightites (Restispira) sp., cf. Loxonema sp., Naticopsis sp., Orthonema sp., 

Peruvispira sp., pleurotomarian indet., pseudozygopleuran indet., Shewdagonial sp., sublitid 

indet., Warthia waageni Yochelson, and "Worthenia" sp.; orthoceratid and nautiloid cephalopods; the scaphopods "Laevidentalium" sp., 

and Plagioglypta sp.; the chiton "Gryphochiton" sp.; the pteropod Hyolithes sp.; the ostracodes Bairdia sp., Bairdiocypris"! sp., Healdia 

sp., Hollinella sp. or spp., Kellettina sp., and 

RoundyeHa"! sp.; and the trilobite Anisopyge 

sp. (USGS 6938, 7055, D & S 135; field label 20)_ 5

7. Limestone, black; wtih some thin beds of granular limestone _ __ 10

6. Limestone, granular, gray, massive; wedges out

northeastward- _ 25

5. Limestone, black, platy; weathers gray brown;

forms a slope 50

4. Limestone, bioclastic; partly silicified on surface; 

contains abundant crinoid columns, a few fusulinids, and limestone pebbles of possible organic 

origin; forms ledges; interbedded with black 

platy limestone ___ 75

3. Limestone, black, thin-bedded to platy; interbedded wtih siliceous shale______________ 10

2. Limestone, dolomitic, bioclastic; of irregular texture ; contains abundant crinoid columns and 

a few fusulinids. Forms thick beds and ledges 10 

Conformity(?). 

Hueco Limestone:

1. Limestone, dolomitic, thinly and regularly bedded; 

contains fusulinids. Forms steep cliffs, extending to canyon bottom. Thickness estimated 500
160 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Base of section, no lower beds exposed.

Summary of section 35 Feet

Part of Bone Spring Limestone measured__ _ 280 

Part of Hueco Limestone exposed _ _ 500

SECTION 36. APACHE PEAK

The following is a section of the Hueco, Bone Spring, 

and Victorio Peak Limestones on the north spur of 

Apache Peak, beginning on the south side of portal of 

Apache Canyon and extending to summit of peak 

(southeastern part of sec. 5, Block 66, Twp. 5, into 

northeastern part of sec. 1, Block 42). A section was 

measured on the spur by P. B. King and K. E. King 

in 1928, and was remeasured along the same course by 

P. B. King in 1931. The section given here is that of 

1931, but some data have been added from the earlier 

section, including the fossil collection of unit 18, whose 

brachiopods were identified by K. E. King (1931). 

Thickness of the Bone Spring Limestone represents 

vertical distances obtained by hand leveling, and is not 

corrected for an original dip to northeast, off a reef mass 

to the southwest.

Top of peak; no higher beds exposed.

Victorio Peak Limestone: Feet

25. Limestone, light-gray, thick-bedded; contains chert 

lenses. Some granular layers on this peak and 

on the outlier to south, contain large productids, 

Leptodus, Marginifera, and gastropods. Limestone of Apache Peak stands about 300 ft lower 

than main body of Victorio Peak Limestone on 

crest of escarpment 1% miles to south, but intervening outliers demonstrate its continuity and 

indicate an original dip to northeast_______ 50 

Intergradation. 

Bone Spring Limestone:

24. Limestone, black, thin-bedded; forms a slope__ 60

23. Limestone, black; contains long lenses of black 

and brown chert, and some beds of dark-gray 

granular limestone; forms a ledge_________ 50

22. Limestone, black, slabby; weathers white_____ 50

21. Limestone, dark-gray, granular, fossiliferous; in

6-in. beds________________________ 6

20. Shale, siliceous; interbedded with platy black 

limestone; weathers gray or yellow. Has an 

original dip of about 5° northeastward_____ 372

19. Shale, siliceous, platy or stony, brown_______ 75

18. Limestone, dark-gray, granular; contains silicified 

fossils. At about this level were collected the 

brachiopods Chonetes permianus Shumard and 

Composita subtilita (Hall), and various gastropods (REK 483) ____________________ 3

17. Shale, siliceous; with interbedded platy black

limestone________________________ 10

16. Limestone, dark-gray, granular, cherty; in 1-ft

beds; weathers light gray or white. ___ 37

15. Shale, siliceous; interbedded with dense platy

13. Shale, siliceous____________________ 10 

tains abundant silicified fossils__________ 10

14. Limestone, dark-gray, granular; in 2-ft beds; conblack limestone; weathers yellow _____ 48

Bone Spring Limestone Continued Feet 

12. Limestone, dolomitic, thin-bedded; contains many 

limestone pebbles and a few poorly preserved 

fossils. Contains a 3-ft igneous sill in upper 

part_____________________________ 50

11. Slope; underlying beds concealed 13 

10. Limestone, gray, granular, fossiliferous 2 

9. Marl, forming a slope _ 8 

8. Limestone, dolomitic; in 2- to 3-ft beds; weathers 

drab gray and jagged. Contains numerous 

silicified crinoid columns, and other fossils 16 

7. Shale, siliceous, brown; and platy black limestone 33 

Unconformity (?). 

Hueco Limestone:

Main body of formation:

6. Limestone, dolomitic, thin-bedded; in part very

cherty 37 

5. Limestone, dolomitic, thick-bedded; forms

ledges _________________ 26

4. Limestone dolomitic, thin-bedded; forms ledges

separated by slopes_ 20 

3. Limestone, dolomitic, massive; weathers drab 

gray and to a rough surface; forms prominent ledges____ _ _ 32 

2. Limestone, dolomitic, gray; forms thin ledges 32 

Powwow Member:

1. Conglomerate, bluff; formed of limestone pebbles in a marl matrix; poorly exposed in 

most places- 48 

Angular unconformity. 

Fusselman Dolomite at base of section.

Summary of section 36

Part of Victorio Peak Limestone exposed 50 

Bone Spring Limestone_______ 853

Hueco Limestone:

Main body of formation_______________ 147

Powwow Member-_ _ 48

Total Hueco Limestone______ _ 195

FOSSIL. COLJjECTTONS FROM VICTORIO PEAK IJCMBSTONE IN NORTHEASTERN SIERRA DIABIX>

Fossils were collected from the Victorio Peak Limestone in the northeastern Sierra Diablo, near the rim of 

the escarpment, at various localities between Victorio 

and Apache Canyons, or near the upper ends of sections 

31, 32, and 36, some of which have been listed in the 

sections. All collections are from the upper beds of 

the Victorio Peak Limestone exposed at their locality, 

500 feet or more above the base of the formation, but are 

not necessarily near the stratigraphic top of the formation. Collections 7006 and 7011 were made by P. B. 

King in 1931; collection 8546 (Pb 15) was made by 

P. B. King and J. Brookes Knight in 1936; the rest 

were made by Knight in 1938. Fusulinids and other 

foraminifers were identified by L. G. Henbest, and 

larger fossils by P. E. Cloud, Jr., and E. L. Yochelson 

(written commun., 1955,1954).
STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 161

USGS 8546 (field label PI 15) . Crest of Sierra Diablo escarpment north of portal of Victorio Canyon. (See unit 18, section

31. p. 154.)

USGS 7011, 14444 (field label C 19). Crest of Sierra Diablo 

escarpment near head of Marble Canyon. (See unit 50, section

32. p. 155.)

USGS 7006. Crest of Sierra Diablo escarpment at head of 

Black John Canyon, from half a mile north of North Diablo 

triangulation station, for half a mile northwestward (northern 

part of sec. 5, Block 42). Contains undetermined fusulinids 

and sponges; crinoid stems; the bryozoans Fistulipora sp., 

Rhombopora sp., and Septopora sp.; the brachiopods Avonia sp., 

Chonetes sp., Derbyia sp., Enteletes sp., Hustedia sp., Leptodus 

sp., Heekella sp., Neospirifer sp., productid indet., Rhipidomella 

sp., "Spirifer" sp., and Stenocisma cf. S. inequalis (Girty) ; the 

the pelecypods Acanthopecten sp., parallelodontid iudet., and 

Streblopteria sp.; and a tooth of Helodus or Orodus type.

U8G8 14470, F 98S7 (field label C 29) . Crest of Sierra Diablo 

escarpment, near preceding and farther northwest, about a mile 

north of North Diablo triangulation station (northwest cor. 

Sec. 5, Block 42). Contains much abraded shells of at least 

two species of Parafusulina; the sponges Actinocoelia meandrina Finks and Defordia densa Finks; cup coralsi and crinoid 

stems; fenestrate and fistuliporoid bryozoans; the brachiopods 

Avonia sp., Buxtonia (Eochiproductus) sp., Chonetes sp., Composita sp., Dictyoclostiis (Chaoiella) quadalupensis (Girty), 

Dielasma sp., Enteletes dumblei Girty, Hustedia mormoni (Marcou), Leptodus sp., "Marginifera" spp., Meeketta? or Geyerellal 

sp., Noespirifer sp., Rhipidomella sp., Rhynchopora sp., Stenocisma cf. S. inequalis (Girty), Streptorhynchus sp., and Wellerella cf. W. elegans (Girty) ; gastroix>ds, including Babylonites; 

and the trilobite Anisopyge? sp.

USGS 14445, F 9818 (field label C 20). South rim of Apache 

Canyon 3 miles west of North Diablo triangulation station and 

2 miles northeast of Slaughter Ranch (center of sec. 20, Block 

32). Contains the dasycladacean green alga Macroporella sp.; 

poorly preserved fusulinids or bryozoans; and the brachiopods 

"Spirifer" sp., and Enteletes sp.

USGS 14448, F 9820 (field label C 22), and USGS 14449, F 

9821 (field label C 28). Two collections about half a mile apart, 

on north slope of first valley south of Apache Canyon, 2 miles 

west-southwest of North Diablo triangulation station and 2 miles 

northeast of Slaughter Ranch (central part of sec. 8, Block 42). 

Contains the fusulinids and other foraminifers Climacammina 

sp., Gemitsina sp., Spandelinoides sp., *Tetrataxis sp., Endothyra sp., *Schubertella Jcingi Dunbar and Skinner var., *Parafusulinal aff. P. bosei var. attenuata Dunbar and Skinner, P. schuoherti Dunbar and Skinner, P. diabloensis Dunbar and Skinner, 

and Pseudofusulina setuml (Dunbar and Skinner). (Asterisks 

indicate forms which occur in both collections.)

FOSSIL COLLECTIONS FROM BONE SPRING LIMESTONE 

NORTHWEST OF PORTAL OF APACHE CANYON

Fossils were collected in the lower part of the Bone 

Spring Limestone at several levels a mile west-northwest of the portal of Apache Canyon, above the outer 

bench of the Sierra Diablo escarpment (northeastern 

part of sec. 6, Block 66, Twp. 5). No section was measured, but the collections are listed below in stratigraphic 

order. The collections were made by J. Brookes Knight 

in 1936; fusulinids and other foraminifers were identified by L. G. Henbest, and larger fossils by P. E. Cloud,

Jr., and E. L. Yochelson (written commun., 1955,1954). 

Some cephalopods have been identified by A. K. Miller 

and W. M. Furnish (Miller and Furnish, 1940a; Miller,

19-15).

USGS 144489, F 9814 (field label C 16). Molluscan ledge in 

lower part of Bone Spring Limestone, about 100 ft above base. 

Fossils occur in a lens of bioclastic limestone, lying in platy 

black limestone, or in much the same association as those of the 

molluscan ledge in Black John Canyon (unit 8, section 35), and 

show a similar diversity.

Includes poorly preserved fusulinids; several genera of 

sponges; the bryozoan Septopora sp.; echinoid spines; the 

brachiopods Composita small sp., Isogramma sp., and productids 

indet.; the pelecypods Astartella sp., myalinids indet., nuculoid 

indet., Nuculana spp., Paleoneilo sp., Parallelodon sp., pectenoid 

indet., Permophorus sp., Pteriat sp., and others; the gastropods 

Anomphalus sp., Apachella sp., Bellerophon sp., Donaldina"! sp., 

Euphemites cf. E. imperator Yochelson, E. sp., Enightites (Retispira) sp., murchisonid indet., Naticopsis sp., Peruvispira sp., 

Pharkidonotus sp., pseudozygopleuran indet., Stegocoeliaf sp., 

"Strobeus" sp., sublitid indet., "Trachydomia" sp., Warthia 

waageni Yochelson, and "Worthenia" sp.; the nautiloids Hichelinoceras spp., Mooreoceras sp., Pseudorthoceras sp., Metacoceras 

mammiferum Miller, M. megapora Miller, If. spp., and Cooperocerasl sp. (Miller, 1945, p. 282-283) ; the ammonite Propinacoceras knighti Miller and Furnish (holotype) (Miller and Furnish, 1940a, p. 42-44) ; the scaphopod Plagioglypta sp.; and the 

trilobite Anisopyge sp.

USGS 14443, F 9817 (field label C 18 a). Bone Spring Limestone, 50 ft above base. Except for a single brachiopod, Rhipidomella sp., collection consists of fusulinids and other foraminifers, which include Climacammina sp., Geinitzina sp., Endothyra 

sp., Tetrataxis sp., *Parafusulina linearis"! (Dunbar and Skinner) and var., *?P. gracilitatis (Dunbar and Skinner), *Pseudofusulina powwowensis (Dunbar and Skinner), *Pseudoschwagerina teseanal Dunbar and Skinner, *Schwagerina bellula Dunbar and Skinner var., and Parafusulina? spp. Of the fusulinids 

in this collection, only the last are of Bone Spring type, the 

remainder, marked by asterisks, being of Hueco type. The two 

types have a different lithic appearance, and the association 

suggests redeposition of fusulinids from several stratigraphic 

levels.

USGS 14442, F 9816 (field label C 18 B) Bone Spring Limestone, near base. Dolomite, crowded with poorly preserved 

fusulinids, which include Parafusulina linearis? (Dunbar and 

Skinner), Pseudofusulina powwowensis (Dunbar and Skinner), 

and Pseudoschwagerina texana Dunbar and Skinner. These 

are all of Hueco type, and there is no evidence in the sample 

for or against the possibility of their redeposition in Bone 

Spring beds.

U8G814441, F 9815 (field label C 18 A) . Basal Bone Spring 

Limestone or topmost Hueco Limestone, apparently somewhat 

lower stratigraphically than preceding. Sample is a fragment 

of limestone crowded with fusulinids and other foraminifers, 

which show two different associations.

One group occurs in pebbles in the limestone and includes 

Gemitsina sp., Spandelinal sp., Schubertella kingi Dunbar and 

Skinner, Parafusulina linearis? (Dunbar and Skinner), Pseudofusulina powwowensis (Dunbar and Skinner), and Schwagerina 

aff. S. bellula Dunbar and Skinner. All these fusulinids are of 

Hueco type.

The matrix contains Parafusulina diabloensis Dunbar and 

Skinner and a very slender species of Parafusulina?. The first
162 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

is definitely of Bone Spring type, but the affinities of the second 

are uncertain.

The occurrence of Parafusulina diabloensis in the matrix 

suggests strongly that the rock containing it is part of the Bone 

Spring Limestone, and that the fusulinids of Hueco type in the 

pebbles have been redeposited.

SECTION 37. FIRST SECTION IN APACHE CANYON

The following is the northeasternmost of five sections 

of the Hueco, Bone Spring, and Yictorio Peak Limestones in the Apache Canyon. The section is on the 

northwest wall of the canyon, on a spur extending eastsoutheast from the peak marked by elevation point 5741, 

beginning at the channel of the canyon and proceeding 

to the summit of the peak (across southern part of sec. 6, 

Block 66, Twp. 5). The section was measured by J. 

Brookes Knight in 1938; fusulinids and other foraminifers were identified by L. G. Henbest, and larger fossils 

by P. E. Cloud, Jr., and E. L. Yochelson (written 

commun., 1955,1954).

Top of peak; no higher beds exposed.

Victorio Peak Limestone: Feet

28. Limestone, granular, light-gray; in 1-ft. beds; 

contains some chert. Contains the sponge 

Jereina cylindrica Finks; a cup coral; the 

braehiopods Dictyoclostus (Chaoiella) 

guadalupensis (Girty), Enteletes sp., "Marffinifera" sp., and Rhipidomella sp; and the 

gastropods Discotropis cf. D. girtyi Yochelson, Euphemites exquisitus Yochelson, and 

Knightites (Retispira) sp. (USGS 14461; 

field label C 27 D)______________ 100

27. Limestone, granular, gray; in 1- to 2-ft beds; 

upper half forms a cliff and lower half a 

slope; poorly preserved fossils observed. 

Base lies at about same altitude as base of 

main body of Victorio Peak Limestone half 

a mile to southwest, but is stratigraphically 

higher, the lower beds of Victorio Peak 

Limestone wedging out into black limestone 

facies of Bone Spring northeastward, with 

original dip ________ 110

Intergradation.

Bone Spring Limestone:

26. Limestone, black to dark-gray, platy_____ 160

25. Limestone, gray, granular; forms a ledge___ 3

24. Limestone, dark-gray, siliceous, platy; with a 

few 6-in. to 1-ft. beds. Beds have an original dip northeastward, in places as steep as 

25°__________________________ 370

23. Limestone, dark-gray, shaly, very thin bedded,

yellow; with original dips as steep as 25°_ 50

22. Limestone, gray, granular, bioclastic, brecciated; forms a reef like lenticular ledge. 

Abundantly fossiliferous; contains corals, 

massive bryozoans, and the brachiopods 

Avonia and Dictyoclostus_________________ 5

21. Limestone, dark-gray, siliceous, platy; a few 

ledges of gray granular limestone in lower 

part, in one of which a well-preserved gastropod was observed______________ 55

Bone Spring Limestone Continued Feet 

20. Limestone, gray, oolitic; contains siliceous 

masses; forms a massive reeflike, lenticular 

ledge. Large fusulinids observed 5 

19. Limestone, dark-gray, siliceous, platy; weathers brown and forms a slope. Poorly preserved bellerophontid gastropods observed- 50 

18. Limestone, shaly, buff; splits into paper-thin 

sheets; passes upward into dark-gray platy 

siliceous limestone, with some interbedded 

layers of granular limestone. Unit has irregular dips. A ledge near middle contains 

the brachiopod Lissochonetes sp. (USGS 

14460; field label C 27 B) ; sponge spicules 

and euomphalid gastropods observed 40 

17. Limestone, dark-gray, siliceous, platy 25 

16. Limestone, dark-gray, siliceous, platy; weathers yellow; a thin bed of gray granular 

limestone at top, contains silicified fossils 27 

15. Limestone, gray, granular; forms ledges and 

contains silicified fossils of Bone Spring 

type; interbedded with dark-gray siliceous 

thin-bedded limestone; weathers yellow 8 

14. Limestone, dolomitic, finely conglomeratic; 

forms a ledge. Contains the brachiopod 

Marginiferat sp., and the fusulinids and 

other foraminifers Geinitsina sp., Schwagerinal franMinensis Dunbar and Skinner, 

8. gumWei Dunbar and Skinner, Parafusulina aff. P. lineata Dunbar and Skinner, P. 

sohucherti Dunbar and Skinner, and P. spp. 

(USGS 14447, F 9819; field label C 21 A)__ 3 

13. Limestone, dolomitic; weathers craggy and 

and forms a slope. Silicified crinoid columns observed 8 

Unconformity. 

Hueco Limestone: 

Division B:

12. Limestone, dolomitic, light-gray; forms a

ledge . 3 

11. Limestone, dolomitic; weathers craggy

and forms a slope_ 12 

10. Limestone, calcitic or only slightly dolomitic, gray, thin-bedded; weathers 

light gray and to a smooth surface; 

forms upper part of lower bench in 

canyon. Contains abundant molds of 

small fusulinids; a collection 30 ft below 

the top includes Schubertella kingi Dunbar and Skinner, Schwagerina bellula"! 

Dunbar and Skinner, and Pseudofusulina sp. (F 9826; field label C 27 "special 

collection")_______._________ 142 

Division A:

9. Limestone, dolomitic, massive; weathers 

craggy; contains abundant molds of 

small fusulinids______ __ _ 205 

8. Limestone, dolomitic, thick-bedded; contains much chert in topmost ledge; forms 

a slope_______ _ _ 38 

7. Limestone, dolomitic, massive; weathers 

craggy; contains small cherty masses. 

Contains abundant molds of small fusulinids and some crinoid columns _ __ 25
STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 163

Hueco Limestone Continued 

Division A Continued

6. Limestone, dolomitic, thick-bedded to massive ; forms ledges; does not weather so 

craggy as adjacent units; chert absent 

in this and units beneath______________

5. Limestone, dolomitic, thin-bedded; forms 

aslope _____ ___________

4. Limestone, dolomitic, massive; weathers

craggy _ __ __ ___

3. Limestone, dolomitic, gray-brown; does not

weather so craggy as adjacent units____

2. Limestone, dolomitic, massive; weathers 

craggy; forms ledges. Contains molds 

of small fusulinids; extends down to 

channel of Apache Canyon_____________

1. Strata not exposed on line of section; 

thickness to base of Hueco Limestone 

probably______________________________

Angular unconformity.

Fusselman Dolomite, exposed beneath Hueco Limestone a quarter of a mile to northeast.

Summary of section 37

Part of Victorio Peak Limestone exposed____________

Bone Spring Limestone____________________________

Hueco Limestone:

Division B__________________ 157 

Division A___________________ 431-i61

Feet

48

40

15

10

30

20-50

210

809

Total Hueco Limestone_____________ 588-618 

SECTION 38. SECOND SECTION IN APACHE CANYON

The following is a section of the Hueco, Bone Spring, 

and Victorio Peak Limestones on the northwest wall of 

Apache Canyon, three-quarters of a mile southwest of 

section 37, from the channel of the canyon, up a spur 

to the rim at a point half a mile southwest of Elusive 

triangulation station (west-central part of sec. 2, 

Block 42, to center of sec. 1, Block 32). The section 

was measured by J. Brookes Knight in 1938; fusulinids 

and other foraminifers were identified by L. G. Henbest ; a few larger fossils were identified by P. E. Cloud, 

Jr., and E. L. Yochelson (written commun., 1955, 

1954).

Rim of canyon; no higher beds exposed.

Victorio Peak Limestone: Feet 

33. Limestone, light-gray, granular, thick-bedded to 

massive; forms ledges and cliffs. Strata dip 

northeastward and lower part intertongues with 

black limestone beds of Bone Spring. Contains 

three species of Pseudofusulina or Parafusulina, 

or both, apparently of Bone Spring type (F 9836; 

field label O 28 I)__________________ 150 

Intergradation. 

Bone Spring Limestone:

32. Limestone, dark-gray, compact; in 1- to 2-ft beds; 

forms a slope and contains some chert and a 

few fossils______________________ 60 

31. Limestone, gray, compact; forms a cliff. Contains 

abraded and broken fusulinid shells, which include IParafusulina diabloensis Dunbar and 

757-108 65 12

Bone Spring Limestone Continued Feet 

Skinner, and other parafusulinids of Bone Spring 

type (F 9835; field label C 28 H)_________ 50

30. Limestone, gray, fine-grained to compact; in 1- 

to 2-ft beds; contains many silicified fossils of 

Bone Spring aspect___________________ 100

29. Limestone, dark-gray to black; in 6-in to 1-ft beds_ 55

28. Limestone, dark-gray to black; interbedded with 

layers of gray granular limestone that contains 

silicified fossils____________________ 100

27. Limestone, dark-gray to black; in 1- to 2-ft beds; 

some lenses of granular limestone near base, 

which contain bryozoans_ __ 85

26. Limestone, dark-gray to black, thinly laminated; 

in 6-in to 1-ft beds; weathers buff and forms a 

slope. Contains a well-preserved sponge (USGS 

14467; field label C 28 G). This unit, and next 

two above, have an original dip of 12° to the 

northeast________________ __ 95

25. Limestone, gray, granular, reefy; contains abundant bryozoans, sponges, and other fossils 35

24. Limestone, gray to light-gray; weathers buff or 

brown; platy or thinly laminated, in 6-in to 1- 

ft beds. Near middle is a 6-ft bed of more granular limestone. Beds of unit have irregular 

original dips____ _ _ __ 110

23. Limestone, black, thinly laminated, thin-bedded 15

22. Limestone, light-gray, weathers buff; siliceous,

platy. Has steep irregular original dips __ 25

21. Limestone, granular, massive, lenticular and reefy;

contains sponges _ _ _ 15

20. Limestone, gray to dark-gray, siliceous, platy;

forms a slope_ __ _ _ _ 12

19. Limestone, granular, massive, reefy and lenticular- &

18. Limestone, dark-gray, thin-bedded_ 7

17. Limestone, light-gray; brecciated in part; very 

massive, but reefy and lenticular; contains silicified fossils______________________ 60

16. Limestone, marly; forms slopes with interbedded 

ledge-making dark-gray limestone. Contains 

abundant silicified fossils of Bone Spring type, 

including the brachiopod Hustedia sp., as well 

as the fusulinids and other foraminifers Geinitsina sp., Endothyra sp., Quinqueloculina sp., Ozawainella sp., Staffellal sp., Schwagerina gumbeli 

Dunbar and Skinner, Parafusulina diabloensis 

Dunbar and Skinner, P. fountains Dunbar and 

Skinner, and P. imUyil Dunbar (USGS 14466, F 

9834; field label C 28 F)______________ 30

15. Limestone, dolomitic; contains the fusulinids and 

other foraminifers Tetrataseis sp., Parafusulina 

scJiucherti Dunbar and Skinner, and P. fountaini 

Dunbar and Skinner (F 9833; field label C 28 

E) ; echinoderm fragments observed _ 7

14. Limestone, dolomitic; weathers craggy; contains

poorly preserved large fusulinids- 10 

Unconformity. 

Hueco Limestone:

Division C:

13. Limestone, dolomitic, dark-gray (weathers 

brown and craggy), very massive. Contains 

abundant molds of small fusulinids and 

poorly preserved Omphalotrochus. Unconformable surface at top of unit slopes north-
164 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Hueco Limestone Continued

Division C Continued Feet 

eastward and cuts out this unit on next 

ridge to northeast________________ 40 

Division B:

12. Limestone, light-gray; in 2-ft beds; interbedded with thinner layers of white dolomitic 

limestone. Near top it contains the fusulinids Parafusulina linearis (Dunbar and 

Skinner), and Pseudoschwagerinal lawissima (Dunbar and Skinner), and P. sp. (F 

9832; field label C 28 D) ____________ 45 

11. Limestone, light-gray, finely granular, 

massive. Contains many fusulinids and 

other foraminifers, whose shells are variably abraded; these include Climacammina 

sp., Staffella sp., Schiibertella Mngi Dunbar 

and Skinner, Pseudofusulina emaciatal 

(Beede), P. gracilitatisl (Dunbar and Skinner) var., P. powwowensis (Dunbar and 

Skinner), and Parafusulina linearis (Dunbar and Skinner) var. (F 9831; field label 

C 28 C)______________________ 10 

10. Dolomite, white, porcelaneous, splintery___ 5 

9. Limestone, light-gray, massive; contains many 

fusulinids, and other fossils, poorly preserved______________________ 30 

8. Limestone, dolomitic, gray _________ 5

7. Limestone, light-gray; in 2-ft beds; contains 

the fusulinids and other foraminifers 

Qeinitsina sp., Schubertella Mngi Dunbar 

and Skinner var., Parafusulina linearis 

(Dunbar and Skinner), and Pseudoschwagerina teacana Dunbar and Skinner (F. 

9830; field label C 28 B) ; other fossils are 

poorly preserved _______________ 25

6. Limestone, light-gray; in 2-ft beds ____ 32 

5. Limestone, light-gray; interbedded with white 

dolomitic limestone that contains fusulinid 

molds ____. ____ __________ 35

4. Limestone, gray; contains at the base the fusulinids and other foraminifers Spandelinoides 

sp., Endothyra sp., Scliubertella Mngi Dunbar and Skinner, Triticites ventricosust 

(Meek and Hayden) var., T. sp., and Pheudofusulina"! sp. (F 3805; field label C 28 

A) _________..________________ 30 

Division A:

3. Limestone, slightly dolomitic, light-gray; in 8- 

to 18-in. beds; interbedded with thin-bedded 

white dolomitic limestone_____________ 35 

2. Limestone, dolomitic, dark-gray, thin-bedded;

contains fusulinid molds in part_________ 17 

1. Limestone, dolomitic, dark gray; weathers 

brown ; in 4- to 6-ft beds; contains many molds 

of small fusulinids_________________ 120 

Alluvium of floor of Apache Canyon at base of section; 

lower beds concealed. In the field it was estimated that 

the lowest exposed beds are 300-400 ft above base of 

Hueco, as exposed in northeastern part of canyon.

Summary of section 38

Part of Victorio Peak Limestone exposed_______ 150 

Bone Spring Limestone____ _ _ _ 879

Summary of section 38 Continued

Hueco Limestone: Feet 

Division C_____________ - 40 

Division B____________ - 217 

Part of division A exposed-_ 172

Part of Hueco Limestone exposed 429

SECTION 39. THIRD SECTION IN APACHE CANYON

The following is a section of the Hueco, Bone Spring, 

and Victorio Peak Limestones on the northwest wall of 

Apache Canyon, a mile southwest of section 38, from the 

channel of the canyon to the rim at a point 1% miles 

south of Elusive triangulation station (across southwestern part of sec. 10, Block 32). The section was 

measured by J. Brookes Knight in 1938; fusulinids and 

other foraminifers were identified by L. G. Henbest 

(written common. 1955).

Rim of canyon ; no higher beds exposed.

Vietorio Peak Limestone: Feet

31. Limestone, dolomitie, fine-grained, light-gray; 

weathers yellow; in massive beds, containing 

fusulinid molds as much as three-quarters of an 

inch in length_____________________ 20

30. Limestone, dolomitic, light-brown; in massive

beds, containing molds of large fusulinids___ 105

29. Limestone, somewhat dolomitic, crystalline, lightgray ; forms a massive cliff. Contains the fusulinids and other foraminifers Climacammina sp., 

Geinitswa sp., Schubertella Mngi Dunbar and 

Skinner var., Parafusulina linearis (Dunbar and 

Skinner) var., P. cfr. P. dialloensis Dunbar and 

Skinner or Pseudofusulina, and IP. fountaini 

Dunbar and Skinner var. (F 9825; field label C 

26 C) ; cross sections of brachiopods observed_ 105

28. Limestone, dolomitic, light-gray; forms ledges; 

interbedded with marl. Molds of fusulinids and 

a fenestellid bryozoan observed__________ 25

27. Limestone, dolomitic, fine-grained, light-gray;

forms a massive ledge________________ 15 

Conformity. 

Bone Spring Limestone:

26. Limestone, dolomitic, saccharoidal, brown; weathers dark gray; contains small fusulinid molds. 

Forms a set of very massive dark ledges, as 

viewed from a distance, which contrast with the 

lighter colored ledges above____________ 168

25. Dolomite, white, porcelaneous____________ 1

24. Limestone, dolomitic, fine-grained; in 3-ft beds;

contains poorly preserved silicified fossils____ 20

23. Limestone, dolomitic, cherty, marly; weathers yellow ; contains large fusulinid molds___,___ 25

22. Limestone, dolomitic, light-gray; contains large 

fusulinids. Weathers craggy and forms massive ledges______________________ 30

21. Limestone, somewhat dolomitic, light-gray, compact; interbedded with pink chert. Contains 

the fusulinids and other foraminifers Bradyinal 

sp., Geinitzinal sp., and Parafusulina linearis 

(Dunbar and Skinner) var. (F 9824; field label 

C 26 B) ; a cup coral, crinoid columns, and a 

Hustedia observed 27
STEATIGRAPHIC SECTIONS OF PERMIAN ROCKS 165

Unconformity. 

Hueco Limestone:

Division C: Feet 

20. Limestone, dolomitic, thin-bedded; forms conspicuous light-gray outcrops; contains molds 

of small fusulinids_______________ 45 

19. Limestone, dolomitic, dark-gray, thick-bedded; a few layers full of small fusulinid 

molds _______._________ 85

18. Limestone, dolomitic; forms ledges that are 

conspicuously light gray, with a few layers 

full of small fusulinid molds_________ 37 

17. Limestone, dolomitic, dark-gray, thin-bedded; 

weathers to a rough surface; a few layers 

full of fusulinid molds _____ 65

16. Dolomite, white, porcelaneous _ 3 

15. Limestone, dolomitic, dark-gray; weathers

craggy; contains small fusulinid molds___ 10 

14. Dolomite, white, porcelaneous ______ 1

13. Limestone, dolomitic, light-gray; weathers 

craggy; contains some small fusulinid 

molds; forms top of a bench_________ 90 

12. Limestone, dolomitic, dark-gray; forms massive ledges _________________ 30

11. Limestone, dolomite, light-gray; in 1- to 4-ft 

beds, some of which contain molds of small 

fusulinids____.________________ 30 

10. Limestone, dolomitic; contains fusulinid

molds and forms a slope____________ 3

Division B:

9. Limestone, in alternating thin and thick beds_ 22

8. Limestone,, dark-gray. Contains the fusulinids

and other foraminifers Climacammlna, sp.,

Spandelina sp., Geintzina sp., a bradyinid,

Tetratatvis sp., Schu'bertella kingil Dunbar

and Skinner, Pseudofusulina emaciata

(Beede), and Pseudoschwagerina cf. P.

leedei Dunbar and Skinner (F 9828; field

label O 26 A)__________________ 5

7. Limestone,, gray; in beds as much as 6 ft thick.

Forms top of a bench______________ 130 

6. Limestone, light- to dark-gray; mostly in 1-ft 

beds, with some 3-ft beds. In lower 50 ft 

are some interbedded 5-ft beds of dolomitic 

limestone that contains the fusulinids and 

other foraminifers Spandelina sp., Geinitzina 

sp., Tetrataaeis sp., textulariids, Schubertella 

kingi Dunbar and Skinner, and Triticites 

spp. (F 9829; field label C 26 AA). These 

dolomitic beds are probably equivalent to 

upper part of division A farther northeast 

in Apache Canyon _______________ 170 

Division A:

5. Limestone, dark-gray; forms a ledge_____ 2 

4. Slope; underlying beds concealed_______ 3 

3. Limestone, dolomitic, light-gray, massive; contains molds of small fusulinids________ 8 

2. Slope; underlying beds concealed_______ 10 

1. Limestone, dark-gray; in massive ledge___ 5 

Base of section in channel of Apache Canyon; no lower 

beds exposed.

Summary of section 39

Part of Victorio Peak Limestone exposed_________ 270 

Bone Spring Limestone____________________ 271

Summary of section 39 Continued

Hueco Limestone: Feet

Division C________________________ 399

Division B________________________ 327

Part of division A exposed- _ 28

Part of Hueco Limestone exposed- ___ 754

SECTION 40. FOURTH SUCTION IN APACHE CANYON

The following is a section of the Hueco, Bone Spring, 

and Victorio Peak Limestones on the south wall of 

Apache Canyon 2 miles southwest of section 39, from 

the floor of the canyon to the elevation point 5841 on the 

rim (north half of east line of sec. 18, Block 32). The 

section was measured by J. Brookes Knight in 1931; no 

fossils were collected, although they were observed and 

recorded in the field.

Rim of canyon; no higher beds exposed.

Victorio Peak Limestone: Feet 

10. Limestone, dolomitic; forms thinner ledges than

below which alternate with slopes to top 100 

9. Limestone, dolomitic, evenly bedded; forms a

cliff _________________________- 60 

Conformity. 

Bone Spring Limestone:

8. Limestone, dolomitic, thin- to thick-bedded; forms

ledges ___ ____ ___ 200 

Unconformity. 

Hueco Limestone: 

Division C:

7. Limestone, dolomitic, gray; forms ledges on 

slope, but passes into a massive cliff on next 

spur to west 50 

6. Limestone, dolomitic, light-gray; in 1 to 5-ft

ledges; contains traces of fossils 80 

5. Limestone, dolomitic, gray, massive; forms 

cliffs; contains a few fossils, including large 

productid brachiopods and a large euomphalid gastropod- _ 75 

Division B:

4. Limestone, light-gray, thin- to thick-bedded 78 

3. Limestone, light-gray; forms a massive ledge; 

contains a large Meekella, productid brachiopods, and a large euomphalid gastropod- 5 

2. Limestone, light-gray, thin- to thick-bedded.

Fusulinids observed in float_ - 205 

1. Limestone, light-gray, thin- to thick-bedded. 

Many silicified shells of Composita observed 

on weathered surfaces 25 

Alluvium of floor of Apache Canyon at base of section; 

no lower beds exposed.

Summary of section 40

Part of Victorio Peak Limestone exposed_ 160 

Bone Spring Limestone 200 

Hueco Limestone:

Division C______ _ 205 

Part of division B exposed_______ 313

Part of Hueco Limestone exposed __ 518
166 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

SECTION 41. APACHE TANK

The following is a section of the Hueco, Bone Spring, 

and Victorio Peak Limestones on the southwest wall of 

Apache Canyon above Apache Tank, up to summit 

marked by elevation point 5690, iy2 miles northwest of 

section 40 (northeastern part of sec. 14, Block 32). The 

section was measured by J. Brookes Knight in 1931, but 

additional observations and collections were made in 

1938. Fusulinids were identified by L. G. Henbest, and 

larger fossils by P. E. Cloud, Jr., and E. L. Yo'chelson 

(written commun., 1955,1954).

Rim of canyon; no higher beds exposed.

Victorio Peak Limestone: Feet 

11. Limestone, dolomitic, in 2- to 3-ft ledges; forms 

a slope. A large euomphalid gastropod observed- _ 110 

10. Limestone, dolomitic, light-gray; with ramifying 

siliceous masses in top beds. Forms a massive cliff______________________ 60 

Conformity. 

Bone Spring Limestone:

9. Limestone, dolomitic; in 1- to 8-f t beds; thicker beds 

are granular and weather jagged, thinner ones 

dense. Contains a myalinid pelecypod (USGS 

7007a; field label 29 B) ; poorly preserved large 

euomphalid gastropod observed 165 

8. Limestone, dolomitic, light-gray, splintery; lower 

beds porcelaneous, higher ones granular and 

weather jagged___________________ 18 

7. Limestone, gray and yellow; interbedded with

marl __________________________ 22 

6. Marl, gray, yellow, and pink _ _ _ 18 

5. Conglomerate, formed of limestone pebbles and 

cobbles, standing in massive ledges, with intervening slopes _ _ __________ 36 

Unconformity. 

Hueco Limestone: 

Division C:

4. Limestone, dolomitic, thin-bedded; poorly exposed on slope_________________ 52 

3. Limestone, dolomitic, thin-bedded. In 1931, 

about 30 ft from base, was collected the fusulinid Triticites (=Pseudofusulina) powwowensis Dunbar and Skinner (D and S 

125; field label 29 A). In 1938, from same 

general level, were collected Scliubertellal 

sp., Pseudofusulina aff. P. uddeni (Dunbar 

and Skinner), and Schwagerina hessensisl 

Dunbar and Skinner (F 9805; field label 

C 4) _ _____________ 105 

2. Limestone, dolomitic, poorly bedded, massive. 

Contains fusulinids; the corals Syringopora 

sp., and Lonsdaleia sp.; the brachiopods Dictyoclostus sp. and Composita sp.; and the 

gastropod Omphalotrochus obtusispira (Shumard) (USGS 7007; field label 29 AA)__ 60 

1. Limestone, dolomitic, dark-gray; forms

ledges _________ H 

Base of section in stream channel; no lower beds exposed.

Summary of section 41 Feet

Part of Victorio Peak Limestone exposed 170

Bone Spring Limestone 259

Part of Hueco Limestone (division C) exposed 228

SECTION 42. SIERRA PRIETA

The following is a section of the Hueco and Victorio 

Peak Limestones exposed on the south side of Sierra 

Prieta, which form the roof rocks of the Sierra Prieta 

intrusive. The Hueco Limestone was measured from 

the intrusive contact three-quarters of a mile northwest of Black Mountain Tank, across a high conical 

hill and lower hills to the south, to the alluvial valley 

near the tank (eastern part of sec. 47, block N). The 

Victorio Peak Limestone was measured on the low scarp 

south of the alluvial valley (northeastern part of sec. 

50, block N). The section was measured by J. Brookes 

Knight in 1938; fusulinids and other foraminifers were 

identified by L. G. Henbest (written commun. 1955); 

other fossils were observed in the field, but were not 

collected.

Top of scarp; no higher beds exposed.

Victorio Peak Limestone: Feet

22. Limestone, dark-gray, dolomitic; weathers 

craggy; interbedded with white or light-gray 

porcelaneous dolomite- 50

21. Limestone, dolomitic, light-gray, massive- _ 10

20. Limestone, dolomitic, light-gray; weathers brown 

and craggy; interbedded with compact buff 

thin-bedded dolomitic limestone; a poorly preserved bellerophontid gastropod observed _ 20

19. Slope on north face of scarp; underlying beds concealed; probably thin-bedded dolomitic limestone ________-_____-_ _ _- 35

18. Alluvial valley 900 ft broad; underlying beds 

concealed; probably thin-bedded or marly dolomitic limestone______________ _- 150 

Unconformity. 

Hueco Limestone:

17. Limestone, dolomitic, dark blue-gray; weathers

craggy 10

16. Limestone, dolomitic, white or light-gray, porcelaneous ; some dark-gray craggy dolomitic limestone ; mostly poorly exposed, but forms ledges 

in part________________________ 45

15. Swale; underlying beds concealed_________ 15

14. Limestone, dolomitic, light-gray splintery; interbedded darker craggy-surfaced dolomitic limestone, with a few 1-ft beds of white porcelaneous dolomitic limestone. Both light-gray 

and dark-gray dolomitic limestone beds contains numerous molds of small fusulinids-__ 30

13. Limestone, dolomitic, dark-gray__________ 5

12. Limestone, dolomitic light-gray; with a 1-ft bed

of white porcelaneous dolomitic at base___ 15

11. Limes-tone, dolomitic, lightrgray, partly splintery,

partly craggy _ __ __ _ __ 100

10. Limestone, dolomitic, light-gray, splintery____ 40 

9. Limestone, dolomitic, dark-gray; weathers to 

smooth light-gray surfaces; forms 1- to 2-ft 

beds _________________________ 25
STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 167

Hueco Limestone Continued Feet

8. Limestone, dolomitic; in alternating dark-gray 

and light-gray layers; weathers craggy. Top 

bed contains large pseudoschwagerinids which 

were unidentifiable in the laboratory (F 9839; 

field label 0 31 B)___________ 15

7. Limestone, dolomitic, dark-gray to black; weathers craggy and forms a conspicuous ledge 17

6. Limestone, dolomitic, dark-gray; weathers 

craggy; interbedded with light-gray dolomitic 

limestone. Contains many molds of small 

fusulinids _______________ ______ 13

5. Limestone, dolomitic, dark-gray; forms a massive 

ledge. Contains Climacammina 2 sp., G-einitzina sp., Spandelina sp., and Schwagerina aff. 

8. hawJcinsi Dunbar and Skinner (F 9838; field 

label C 31 A)_____________________ 12

4. Limestone, dolomitic, dark-gray; forms a massive

ledge ________________ _ 8

3. Limestone, dolomitic, dark blue-gray; parts more 

calcitic than others. Beds near middle form 

a hogback ridge. A bellerophontid observed 50

2. Limestone, dolomitic, dark blue-gray; weathers 

blue; probably slightly altered by intrusive; in 

1- to 2-ft beds. Poorly preserved staffellid foraminifers and an Omphalotrochus observed_ 100

1. Contact rocks next to intrusive: Limestone, dolomitic, gray or brown, mannorized and bleached; 

weathers yellow; alternating with bluish thinbedded baked and silicified limestone, probably 

originally argillaceous. Crinoid columns observed in top layer _______________ 47 

Intrusive contact at base of section; igneous rock of 

Sierra Prieta intrusive beneath.

Summary of section 42

Part of Victorio Peak Limestone exposed_________ 265 

Part of Hueco Limestone exposed______________ 547

SECTION 43. SOUTH MESA

The following is a section of the Bone Spring Limestone, Victorio Peak Limestone, Cutoff Shale, sandstone 

tongue of Cherry Canyon Formation, and Goat Seep 

Limestone, at the north end of the Sierra Diablo, from 

south of Babb Canyon and the Babb flexure, to the top 

of South Mesa. The section is in two parts:

Section 43a was measured by P. B. King and R. E. 

King in 1928, and covers the Bone Spring Limestone 

and Victorio Peak Limestone, which are exposed at the 

east end of the cuesta that borders Babb Canyon on 

the south, beginning in a reentrant valley a mile south 

of the portal of the canyon (mainly in western part of 

sec. 29 Block 67, Twp. 4). A small collection made in 

1936 has been inserted at its appropriate position; identifications were made by P. E. Cloud, Jr., and E. L. 

Yochelson (written commun., 1954).

Section 43b covers the upper part of the Victorio 

Peak Limestone, and the higher formations, and is tied 

to section 43a by the occurrence in both of the distinctive middle division of the Victorio Peak Limestone.

The section extends up the east face of South Mesa at 

about midlength, or nearly due west of the old Babb 

Kanch (along eastern half of center line of sec. 18, 

Block 67, Twp. 4). Sections were measured here by P. 

B. King and K. E. King in 1928, and by J. Brookes 

Knight in 1936. Fusulinids collected in 1928 were identified by C. O. Dunbar and J. W. Skinner (1937), and 

the brachiopods by R. E. King (1931). Fusulinids and 

other foraminifers collected in 1936 were identified by 

L. G. Henbest, and larger fossils by P. E. Cloud, Jr., 

and E. L. Yochelson (written commun., 1955, 1954). 

The section given below combines the field observations of 1928 and 1936 and includes both sets of fossil 

identifications.

Section 43b

Top of South Mesa; no higher beds exposed 

Goat Seep Limestone: Feet 

24. Limestone, dolomitic, light-gray to pink; 

weathers brown and to rough surface; in 

thin to thick irregular beds. Contains 

rounded chert nodules, geodes, and silicified fossils. The latter include poorly preserved fusulinids; the sponges Actinocoelia 

meandrina Finks, A. ? sp., and Stioderma coscinum Finks; a cup coral; the bryozoan 

"Acanthocladia" sp.; the pelecypod "Aviculopecten" sp. indet.; the gastropod Platyceras sp. indet.; and the brachiopods Chonetes (Chonetinella) sp., "Harpinifera" sp. 

aff. M. occidentalis Schwellwein or M. walcottiana (Girty), "M." sp., Dictyoclostus 

(Chaoiella) cf. D. guadalupensis (Girty), 

Leptodus cf. L. americanus Girty, Composita 

sp., Neospirifer sp., Stenocisma n. sp., Hustedia cf. H. mormoni (Marcou), Wellerella 

cf. W. elegwns (Girty), Enteletes spp., Rhynchoporal sp., Dielasma sp., and a phricodothyrinid (USGS 8548, F 2688; field label 

Pd 1) ______________________ 200 

Conformity. 

Sandstone tongue of Cherry Canyon Formation:

23. Sandstone, fine-grained to silty, buff; weathers brown; mostly thin bedded, but with 

thicker layers toward base- _______ 150 

22. Sandstone, medium-grained, dolomitic; weathers brown; forms a massive bed. Contains 

poorly preserved fusulinids. Thickness variable ; lies with irregular contact on underlying shale and limestone, of which it contains chips and pebbles _ ____ 5-40 

Unconformity. 

Cutoff Shale:

21. Shale, fine-grained, sandy____________ 22 

20. Limestone, laminated, sandy__________ 5 

19. Limestone, gray to black, fine-grained, platy to 

medium-bedded; some platy fine-grained 

sandstone. A Squamularia observed. Forms 

a bench___ ________________ 139 

18. Shale, siliceous and sandy, buff_________ 11 

17. Limestone, dense, platy, buff and gray____ 8
168 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Cutoff Shale Continued Feet 

16. Slope; underlying beds concealed_______ 11 

15. Limestone, gray, dense, platy___________ 18 

14. Shale, siliceous; interbedded with platy gray

limestone __________ ____ 33 

13. Limestone, dense, gray, -thinly laminated. 

Contains Composita mira (Girty) (REK 

506) ; poorly preserved brachiopods and a 

possible ammonite observed_ ____ _ 15 

12. Limestone, thin-bedded, dark-gray, and siliceous shale, poorly exposed______ 13 

Conformity.

Victorio Peak Limestone: 

Upper division:

11. Limestone, dolomitic, dark-gray; forms 

massive ledges; interbedded with 

thinner bedded limestone. Collection 

of 1928 contains the fusulinid 

Schwagerina setuml Dunbar and Skinner, and the brachiopods Productus dartoni sullivanensis King, Productus ivesi 

Newberry, Lyttonia nobilte americamis 

(Girty), Spirifer (Neospirifer) pseudocameratus Girty, and Squamularia 

quadalupensis (Shumard) (D&S 

137, REK 493). In 1936 collections 

were made near top of unit (USGS 

8535, F 2698; field label Pb 2) and near 

middle of unit (USGS 8534, F 2691; 

field label Pb 1). These contain the 

fusulinids and other foraminifers Geinitzina sp., Endathyra sp., a schubertellid or millerellid, Parafusulina 

baJceri Dunbar and Skinner var., P. 

fountaini Dunbar and Skinner, and 

Pseudofusulina setum (Dunbar and 

Skinner) ; lophophyllid corals; the bryozoans "Batostomella," sp., a fistuliporoid, and "Stenopora" sp.; the gastropod Edbylonites sp.; and the brachiopods Buxtonia (Kochiprodttctus) cf. B. 

victorioensis King, Chonetes (Chonetinella) spp., Composita sp., "Dictyoclostus" aff. D. semistriatus (Meek), Hustedia sp., Leptodus sp., "Marginifera" 

spp., Neospirifer cf. N. pseudocameratus 

(Girty), Rhipidomella sp., "Spirifer" 

sp., and Squamularia sp 65 

Middle division:

10. Limestone, dolomitic, white or light-gray;

forms a slope_ ___ 15 

9. Limestone, dolomitic, dark-gray; forms a

massive ledge _ 5 

8. Limestone, dolomitic, white or light-gray;

forms a slope__ ___ 10 

7. Limestone, dark-gray; forms a massive

ledge_______ _______ 3 

6. Limestone, dolomitic, white or light-gray; 

forms a slope; slender fusulinids observed______ _ 38 

5. Limestone, dolomitic, dark-gray; contains calcite vugs; forms a prominent 

ledge _______ 3

Victorio Peak Limestone Continued Feet 

Middle division Continued

4. Limestone, dolomitic, dense, white or lightgray ; in 1- to 2-ft beds. Contains irregular specks of crystalline calcite. Forms 

a slope with thin ledges 45 

Lower division:

3. Limestone, dolomitic, dark-gray; forms

ledges_____ . 23 

2. Limestone, dolomitic, light-gray; weathers 

pitted; forms a massive ledge; contains 

small crinoid columns 8 

1. Limestone, medium-bedded; poorly exposed at base of slope- _ 33 

Base of section covered by alluvium; no lower beds exposed.

Section 43a

Top of cuesta; higher beds exposed north of Babb canyon (see section 43b).

Victorio Peak Limestone: 

Upper division:

7. Limestone, dark-gray, thick-bedded; forms

dip slope of cuesta 50 

Middle division:

6. Limestone, dolomitic, light-gray, thin-bedded; with partings of marly sandstone. 

Weathers white and forms a conspicuous 

light-colored band on hillsides_.____ 34 

Lower division:

5. Limestone, gray, thick-bedded; interbedded 

with layers of light-gray dolomitic limestone in upper part; includes lower part 

of middle division as distinguished in 

section 42b__________________ 260 

4. Limestone, dolomitic, gray; weathers drab 

gray or gray brown; in 1- to 2-ft beds; 

forms thick ledges and cliffs-______ 300 

3. Sandstone, fine-grained, brown________ 12 

2. Limestone, finely crystalline, dark-gray; 

weathers light gray; in 1- to 10-ft beds; 

forms ledges and cliffs. Contains irregular chert nodules_______________ 250 

Break in section. (Across reentrant valley a mile south 

of portal of Babb Canyon; a fault of small displacement follows the valley, and some of lower part of 

Victorio Peak Limestone may be cut out along it; 

basal Victorio Peak overlies the Bone Spring Limestone south of the valley.) 

Bone Spring Limestone:

1. Limestone, black to dark-gray, weathers drab 

gray; fine grained; in 3- to 6-in. beds; in 

part with brown chert bands, and with marl 

partings. Some beds contain silicified fossils. In 1936 were collected the brachiopods 

Chonetes sp., Avonia sp., Busetonial cf. B. 

(Kochiproductus) sp., and the gastropod 

Anomphalus"! sp. (USGS 8538; field label 

Pb5). Thickness about____________ 500 

Base of section covered by alluvium.

Summary of section 43

Part of Goat Seep Limestone exposed__________ 200 

Sandstone tongue of Cherry Canyon Formation___ 155-190 

Cutoff Shale_________________________ 275
STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 169

Summary of section 43 Continued

Victorio Peak Limestone:

Upper division (in section 43b)________ 65 

Middle division (in section 43b)_______ 119

Lower division (approx., in section 43a) __ 822

Total Victorio Peak LimestonePart of Bone Spring Limestone exposed.

Feet

1,006

500

FOSSIL COLLECTIONS FROM VICTORIO PEAK 

STONE SOUTHEAST OF SOUTH MESA

Southeast of South Mesa, foothills fringing the 

northeast-facing escarpment of the Sierra Diablo consist of Victorio Peak Limestone that has been downfaulted and tilted. Collections were made from it by 

R. E. King in 1928, and by J. Brookes Knight in 1936. 

Brachiopods in the first collections were identified by 

R. E. King (1931). Fusulinids and other foraminifers 

in the second were identified by L. G. Henbest, and 

larger fossils by P. E. Cloud, Jr., and E. L. Yochelson 

(written commun., 1955,1954).

USGS 8536 (field label PI 3). Victorio Peak Limestone. 

Hogback ridge at foot of Sierra Diablo escarpment, 3 miles 

southeast of South Mesa, southwest side near west end (northeastern part of sec. 5 Block 31). Contains the brachiopods 

Meekella sp., ProricMofenia sp., Buxtonial cf. (Kochiproductus) 

sp., and "Spirifer" sp.

USGS 8537, F 2709 (field label Pb 4). Victorio Peak Limestone. Near foot of northeast slope of hogback ridge, about 

half a mile east of its western end (northeastern part of sec. 4, 

Block 31). Contains the fusulinids and other foraminifers 

Geinitzinal sp., Pseudofusulina setum (Dunbar and Skinner) 

and Pseudofusulina or Parafusulina sp.; the brachiopods 

Chonetes sp., Buxtonia (Kochiproductus) ? sp., "Marginifera" 

sp., Avonia small sp., Enteletest sp. and Rhipidomella sp.; the 

pelecypod lAstartella sp.; Meekospira sp. and other gastropods; 

and the scaphopod Plagioglypta sp.

USGS 8541 (field label Pb 10). Victorio Peak Limestone, 

float on alluvial fan below and north of locality Pb. 4. Contains 

Buxtonia (Kochiproductus) cf. B. victorioensis King.

REK 494- Victorio Peak Limestone, at approximately the 

same locality as Pb 4. Contains the brachiopods Productus 

schucherti King, Marginifera manzanica Girty, M. reticulata 

angusta King, Martinia rhomboidalis Girty, and Composita 

subtilita (Hall).

REK 495. Victorio Peak Limestone at east end of hogback 

ridge, about half a mile east of locality Pb 4 and REK 494 

(northwestern part of sec. 3, Block 31). Contains the brachiopods Chonetes permianus Shumard and Productus ivesi Newberry.

USGS 8547 (field label Pb 17). -Victorio Peak Limestone. 

Ridge of downfaulted rocks 1% miles northwest of portal of 

Apache Canyon, and about 4 miles southeast of preceding localities (southeast part of sec. 43, Block 66, Twp. 4). Contains 

Enteletes cf. E. dumblei Girty.

FOSSIL COLLECTIONS FROM GOAT SEEP LIMESTONE 

NORTH OF SOUTH MESA

The Goat Seep Limestone is preserved in a series of 

mesalike outliers for about 10 miles north of South

Mesa, beyond the map area. (See King, P. B., 1949.) 

Collections were made in these outliers by R. E. King 

in 1928, and by J. Brookes Knight in 1936. Brachiopods in the 1928 collections were identified by R. E. 

King (1931); fusulinids and other foraminifers in the 

1936 collections were identified by L. G. Henbest, and 

larger fossils by P. E. Cloud, Jr., and E. L. Yochelson 

(written commun., 1955,1954).

REK 504, D & S 139. Goat Seep Limestone at east end of 

North Mesa (north of present map area, western part of sec. 

40, Block 67, Twp. 3). Includes unidentified fusulinids and 

the brachiopods Enteletes wordensis King, Meekella skenoides 

Girty, Linoproductus waagenianus (Girty), Avonia signata 

(Girty), Marginifera opima (Girty), Aulosteges guadalupensis 

Shumard, A. tuberculatus King, Lyttonia nobilis americanus 

(Girty), Camarophoria venusta Girty, Spirifer (Neospirifer) 

pseudocameratus Girty, Hustedia meekana (Shumard), and 

Composita emarginata afflnis Girty.

USGS 8549 (field label Pd 2). Goat Seep Limestone, near 

base. Same locality as REK 504. Contains a polyporoid bryozoan and the brachiopods Linoproductus'} sp., Marginifera aff. 

M. lasallensis? (Meek and Worthen), if.? sp., "Pustula" sp., 

Dictyoclostus (Chaoiella) cf. D. guadalupensis (Girty), Stenocisma sp., Composita sp., and Wellerella sp.; fusulinids observed 

in field, but not reported on.

F 2697 (field label Pd 3). Goat Seep Limestone, from float 

near Dos Alamos Hills (sec. 17, Block 67, Twp. 3). A porous 

coquina, crowded with large very slender fusulinids that are 

probably Parafusulina maleyl var. referta Dunbar and Skinner.

SECTION 44. HIGH POINT OF DELAWARE MOUNTAINS

The following is a section of the Bone Spring Limestone and Brushy Canyon Formation on a promontory 

of Delaware Mountains near the northeast corner of 

the map area. The section begins at the fault at the 

west base of the mountains, on a salient 3 miles northnorthwest of Cone triangulation station, and proceeds 

eastward to the summit of a mesalike outlier at the crest 

(center of sec. 4 to center of sec. 3, Block 65, Twp. 4). 

The section was measured by R. E. King in 1928; fusulinids were identified by C. O. Dunbar and J. W. Skinner (1937), and brachiopods by R. E. King (1931). 

This section is the same as section 49 of King (1948, pi. 

8).

Summit of outlier; no higher beds exposed. 

Brushy Canyon Formation:

Main body of formation: feet 

13. Sandstone, coarse, light-buff; in thick beds, 

interbedded with thinner bedded finer 

grained sandstone; some bedding surfaces 

show molds of large parafusulinids__ 205 

Pipeline shale member:

12. Shale, sandy, dark-gray, thinly laminated_ 33 

Conformity (?). 

Bone Spring Limestone:

11. Limestone, black, dense; in 2- to 6-in. beds; 

forms a prominent cliff. A few poorly preserved fossils observed_______ _____ 264
170 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Bone Spring Limestone Continued Feet 

10. Shale, sandy, thinly laminated, gray; weathers 

yellow brown. The shale contains concretions 

of black granular limestone a foot or two broad 

and a foot thick, also some interbedded 3- to 

6-in. layers of black limestone_ _____ 82

9. Limestone, black, dense, thinly laminated; 

forms a cliff; contains spherical concretions 

3-in. to 1-ft across________________ 115

8. Limestone, black, dense; sandy in part; thinbedded to papery _ _____ ______ 126

7. Limestone, black, sandy; in 8-in. to 1-ft beds_ 18

6. Limestone, black, unevenly bedded; contains 

irregular masses of chert and siliceous limestone. Some beds very fossiliferous_____ 93

5. Limestone, black; very thinly and evenly 

bedded, with a few thicker bedded fossiliferous layers. Forms a well-defined ledge. 

Contains the fusulinid Parafusulina sp., and 

the brachiopods Meekella attenuata Girty, 

Productus leonardensis King, Productus occidentalis Newberry, Productus sp., Striatifera 

pinnaformis (Girty), Prorichthofenia likharewi King, Pugnoides bidentatus (Girty), 

Pugnoides texanusl (Shumard), Spirifer 

(Neospirifer) mexicanus latus King, Ambocoelia guadalupensis Girty, and Hustedia meekana (Shumard) (REK 491 D & S 153)____ 77

4. Limestone, black, platy or papery; with some

layers of granular chert____________ 132

3. Limestone, black; in 1- to 6-in. beds; contains 

many thick chert layers and granular siliceous 

layers __ _ ______ 72

2. Limestone, black; in beds half an inch to 5 in. 

thick, but somewhat irregularly bedded, with 

interbedded chert layers as much as 3 in. 

thick, and lenses of fossil breccia that contain 

whole shells of brachiopods. These include 

Meekella attenuata Girty, Chonetes permianus Shumard, lAnoproductus waagenianus 

(Girty), and Ambocoelia guadalupensis Girty 

(REK 490)______________________ 258

1. Limestone, black; in even beds half an inch to

an inch thick, with a few chert bands_____ 308 

Base of section at fault at foot of escarpment; no lower 

beds exposed.

Summary of section 44

Brushy Canyon Formation:

Part of main body of formation exposed___ 205 

Pipeline Shale Member_____________ 33

Part of Brushy Canyon Formation exposed__ 238 

Part of Bone Spring Limestone exposed_________ 1,545

STRATIGRAPHIC SECTIONS AND FOSSIL COLLECTIONS 

OF CRETACEOUS ROCKS

Sections 45-54, which follow, were measured in the 

southern and western parts of the Sierra Diablo during the present investigation. Some of these are 

plotted graphically on plate 13 where, to complete the 

stratigraphic picture, four other sections to the south 

and west have been included; these were measured by

other geologists and are described in their publications. 

The locations of these four sections are as follows:

(A) Devil Ridge above Devil Ridge thrust. Section of Yucca 

Formation, Bluff Mesa Formation, Cox Sandstone, and Finlay 

Limestone, measured by J. Fred Smith, Jr. (1940, p. 625-628, 

sec. 3). Measured south westward across Front Ridge and 

Devil Ridge at a locality about Sy2 miles west of the edge of 

the present report area and 5 miles south of town of Sierra 

Blanca, in northwestern part of Block 69%.

(B) Southwest of Eagle Flat below Devil Ridge thrust. 

Section of Washita Group measured by J. Fred Smith, Jr. 

(1940, p. 628-629, sec. 5). Measured south westward across low 

ridges south of Bola siding, in southwestern part of present 

report area, in sec. 46, Block 69, Twp. 8, and sec. 3, Block 69, 

Twp. 9. A section of the overlying Eagle Ford Formation is 

given in the original publication, but is not plotted on plate 13.

(C) Spar Valley, below Devil Ridge thrust. Section of Yucca 

Formation, Bluff Mesa Formation, Cox Sandstone, Finlay Limestone, and Washita Group, measured by Elliot Gillerman (1953, 

p. 19-29, sees. 2, 4, 5, and 6). As plotted on plate 13, the section combines various partial sections measured in the vicinity 

of Spar Valley on the east side of the Eagle Mountains about 

5 miles south of southern edge of present report area. To complete the sequence, the basal Cretaceous beds exposed near Eagle 

Spring just south of the present report area have been plotted 

from descriptions by Gillerman.

(D) Flat Mesa, north of Sierra Blanca. Section of Cox Sandstone, Finlay Limestone, Kiamichi Formation, and basal part 

of Washita Group, described by W.S. Adkins (1932, p. 352) and 

measured by P. B. King (unpub. field notes, 1930). Measured 

across north end of Flat Mesa about 6 miles north-northwest of 

town of Sierra Blanca, near the center of the east line of Block 

71, Twp. 7.

SECTION 45. EAGUS F!LAT

The following is a section of parts of the Campagrande Limestone and Cox Sandstone on a mesa 1% 

miles east of Eagle Flat section house (sec. 8, Block 68 

Twp. 8). The section was measured by P. B. King and 

J. Brookes Knight in 1931. Fossils were observed in 

the field, and a few were collected in 1938, which proved 

to be unidentifiable.

Top of mesa ; no higher beds preserved. 

Cox Sandstone :

5. Sandstone, massive, sugary, light-brown: forms 

remnant on top of mesa at west end 

Campagrande Limestone :

4. Limestone, marly; contains Exogyra and Tri~

Feet

25

10

3. Nodosaria bed." Limestone, massive, sandy, 

dark-gray, evenly bedded. Shells of the medium-sized foraminifer Haplostiche ("Nodosaria") occur on weathered surfaces, and many 

unidentifiable shells appear in cross section, 

probably mainly oysters (USGS 17828; field 

label K 10) _______ __ 

2. Limestone, nodular, light-gray; interbedded with 

marl; in part conglomeratic 

1. "Cap ledge." Limestone, massive, light-gray; at 

base of slope _ 

25

30

10
STRATIGRAPHIC SECTIONS OF CRETACEOUS ROCKS 171

Base of section covered by alluvium.

Summary of section 45

Part of Cox Sandstone exposed _______

Part of Campagrande Limestone exposedFeet 

25

75

SECTION 46. STREERTTWITZ

The following is a section of part of the Campagrande Limestone in the Streeruwitz Hills, 4^/2 miles 

northwest of Eagle Flat section house (northwestern 

part of sec. 22, Block 57). The section was measured by J. Brookes Knight in 1931. The top unit of 

this section appears to be the basal unit of section 45, 

and the two sections combined give an approximate total 

thickness of the Campagrande Limestone in the district 

of 205 ft; however, units of the lower part of the Campagrande in nearby sections in the Streeruwitz Hills are 

much thinner than in section 46, due to overlap on an 

eroded topography of Hueco Limestone and Precambrian rocks.

Top of section; no higher beds preserved. 

Campagrande Limestone:

3. "Cap ledge." Limestone, massive, dark- to lightgray ; nodular in upper part; contains chert pebbles in lower 4 ft_____________________________

2. Conglomerate, mainly limestone pebbles, but includes some chert pebbles, in a limestone matrix 

that is red below, grayer above______________

1. Conglomerate, red; contains pebbles and cobbles 

of limestone and chert from Allamoore Formation ________________________________________

Unconformity.

Hueco Limestone at base of section.

Summary of section 46

Part of Campagrande Limestone exposed_______________

Feet

55

80

140

SECTION 47. DOME PEAK

The following is a section of the Campagrande Limestone and Cox Sandstone on Dome Peak (summit 5485). 

The section was measured by P. B. King and J. Brookes 

Knight in 1931. The Campagrande Limestone was 

measured a mile south of the peak on the west side of 

the ridge, southwest from the road from Sierra Blanca 

to the Keen Ranch (east-central part of sec. 28, Block 

51). Two sections of the Cox Sandstone were measured, one on the west slope (northeastern part of sec. 

21, Block 51), the other on the south slope (west half of 

sec. 22, Block 51); descriptions of units in the two sections have been combined in the text, and thicknesses 

averaged. No fossils were collected, but they were observed in parts of the Campagrande Limestone.

Top of Dome Peak; no higher beds preserved.

Cox Sandstone:

37. Sandstone, massive, brown____________________

36. Sandstone, shaly, buff_________________________

35. Sandstone, massive, sugary, crossbedded; forms

rimrock at top of Dome Peak__________ 36 

34. Sandstone, friable; forms a slope_________ 25

Feet

8

12

Cox Sandstone Continued Feet 

33. Sandstone, massive, brown; crossbedded in part; 

forms ledges, with a 10-ft bed of marly limestone in lower part 82 

32. Sandstone, friable; forms a slope____ 15

31. Sandstone, massive, brown; with many pebbly

seams; forms prominent ledges 19 

30. On west slope of Dome Peak; red sandy shale 

interbedded with gray marly limestone; on 

south slope; represented by a 4-ft layer of conglomerate, formed of limestone fragments 25 

29. Sandstone, white or buff, pebbly; forms a slope; 

contains small pebbles and ferruginous 

nodules __ 21 

28. Sandstone, friable, crossbedded, white 16 

27. Sandstone, massive, brown 5 

26. Sandstone, friable; forms a slope 8 

25. Sandstone, massive, brown; with pebbly seams; 

passes at top into a conglomerate of chert and 

quartz pebbles 5 

24. Sandstone, friable; forms a slope- 6 

23. Sandstone, massive, brown- ____ 22

22. Sandstone, shaly, red; with thin beds of coarser 

sandstone; forms a succession of benches and 

slopes ________ 40 

21. Sandstone, slabby or shaly, white or red; forms 

slopes, with several ledges of massive brown 

pebbly sandstone in upper part 25 

20. Sandstone, massive, brown, pebbly 10 

19. Sandstone, marly, red; forms a slope- 8 

18. Sandstone, massive sugary brown; contains wellrounded chert and quartz pebbles; in part 

crossbedded. Small spherical limonite nodules 

occur on weathered surfaces. Forms prominent ledge, which breaks out into cubical 

blocks ______________________ 18 

17. Marl and shale, poorly consolidated, gray or 

purple; at top, a conglomerate of rounded chert 

pebbles in a yellow marl matrix. In most 

places, poorly exposed on slope and covered by 

blocks from bed above______ _ 100

16. Limestone, marly, gray; interbedded with purple

shale ________________________ 43 

15. Marl, gray; forms a slope, with a 2-ft ledge of

gray limestone at top_ _ 12 

14. Sandstone, brown, shaly; with a 2-ft ledge of red

limestone at top____ ___ __________ 12

13. Sandstone, thin-bedded, slabby; with small-scale

crossbedding ___ _ _ _ 10 

12. Sandstone, massive, sugary, brown; crossbedded

in part-_ _ _ _ _ _ __ __ 16 

Campagrande Limestone:

11. Marl, sandy; forms a slope____________ 5 

10. Limestone rusty-brown; in 2-ft beds_______ 7 

9. Marl, nodular, blue-gray to brown________ 5 

8. Limestone, light-gray to gray-brown; with marl

partings __ _______ _______________ 9

7. Marl and thin layers of nodular limestone____ 16 

6. Limestone, dark blue-gray; contains oysters and

rudistids in upper part______________ 6 

5. Shale and marl with beds of brown dense nodular limestone____________________ 16
172 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Campagrande Limestone Continued Feet 

4. "Nodosaria bed." Limestone, dark-gray or graybrown, sandy; in 1- to 2-f t beds; contains fragments of oysters and echinoids 16 

3. Marl, nodular limestone, and conglomerate 22 

2. "Cap ledge." Limestone, massive, nodular lightgray ; contains chert pebbles at base 8

I. Conglomerate, composed of pebbles of Hueco 

Limestone, in a sandy or marly limestone 

matrix __________________ _ _ 9 

Unconformity.

Hueco Limestone at base of section; about a mile to the 

southeast the Hueco is truncated and the Campagrande 

Limestone lies directly on red sandstone of the Hazel 

Formation.

Summary of section 47

Part of Cox Sandstone exposed_______________ 599 

Total Campagrande Limestone________________ 119

SECTION 48. HOCK CRUSHER

The following is a section of the Campagrande Limestone and Cox Sandstone on the north slope of the high 

knob northeast of the Gifford-Hill rock crusher, on the 

opposite side of the Texas and Pacific Railway (summit 

5188; north half of sec. 26, Block 67, Twp. 8). The 

section was measured by P. B. King in 1936, but the 

sequence here had been described previously by Richardson (1914, p. 6). No fossils were recorded by King, 

but Richardson observed gastropods, oysters, and an 

Exogyra in the Campagrande Limestone.

Top of knob 5188; no higher beds preserved.

Cox Sandstone: Feet 

13. Sandstone, massive, pebbly, crossbedded_____ 10 

12. Sandstone, fine-grained, thin-bedded; forms a

slope__________________________ 65

II. Sandstone, massive, crossbedded; very pebbly

at top__ _____________________ 70 

10. Sandstone, fine-grained, thin-bedded, poorly exposed; with a massive sandstone ledge 15 ft 

above base _____________________ 59 

9. Sandstone, massive, brown, coarse-grained; in 

2- to 10-ft beds, which form prominent ledges 

and break out in rectangular blocks. Contains 

dispersed quartz and chert pebbles in places, 

and some layers are crossbedded. Weathered 

surfaces are dark-brown and quartzitic____ 95 

8. Sandstone, fine-grained, thin-bedded, shaly, gray 

or red. Upper part poorly exposed and much 

covered by float from above. A bed of massive 

sandstone may occur near middle, but it is represented only by loose blocks that might have 

slumped from above_________________ 112 

Campagrande Limestone:

7. Limestone, buff, dense; with conchoidal fracture;

forms a prominent ledge_______________ 4 

6. Shale, reddish, poorly exposed____________ 17 

5. Limestone, gray, granular; contains limestone

pebbles________________________ j 

4. Shale, reddish, poorly exposed____________ 13 

3. Limestone, brown, sandy and pebbly; forms a

ledge ____________________ 4

Campagrande Limestone Continued Feet 

2. Shale, reddish, sandy, poorly exposed 18 

1. Conglomerate, formed of pebbles as much as an 

inch in diameter of quartz, chert, and limestone, 

in a coarse sandstone matrix, with thin beds of 

calcareous sandstone at top 6 

Unconformity. 

Hueco Limestone at base of section.

Summary of section 48

Part of Cox Sandstone exposed- 411 

Total Campagrande Limestone 63

SECTION 49. COX MOUNTAIN

The following is a section of the Campagrande Limestone, Cox Sandstone, Finlay Limestone, and Kiamichi 

Formation on Cox Mountain (sees. 19 and 20, Block 

45%. The Cox Sandstone was measured on the north 

face of the mountain, west of a prominent reentrant, 

the Finlay and Kiamichi at various favorable places 

on the summit of the mountain. The whole section was 

originally measured by P. B. King and R. E. King in 

1928; the Finlay and Kiamichi were measured again 

in more detail by J. Brookes Knight in 1938; the text 

given below contains data from both sections. Fossils 

from the Kiamichi Formation that were collected in 

1938 were identified by R. W. Imlay (written commun., 

1940), and his determinations are given in the text. 

Fossils collected in 1928 were examined by W. S. Adkins (1932, p. 353), who reported virtually the same 

assemblage, which he regarded as of Kiamichi age 

(see table 11, p. 87).

Tertiary: Feet 

18. Basalt, vesicular; forms three remnants on top of 

mountain; at base, a conglomerate of limestone 

cobbles a few feet thick, partly derived from 

Cretaceous rocks, partly from earlier rocks 30

Unconformity.

Kiamichi Formation:

17. Shale, brown, sandy. Contains Oxytropidoceras 

acuticarinatum (Shumard), O. Iravoense 

Bose, Natica! sp., Trigonia emoryi Conrad, 

Exogyra texana Roemer, GrypJiaea navia Hall, 

G. cf. O. corrugata Gabb, Pecten (Neithea) 

subalpinus Bose, and Protocardia texana (Conrad) (USGS 17838, 17280; field labels K 3 G, 

K 2) ; horn corals and colonial corals observed. 

According to Imlay, correlation with the Kiamichi is signified by the Gryphaea navia; the 

species of Oxytropidoceras range through beds 

of late Fredericksburg age 15 

16. Sandstone, brown; forms a ledge 3 

15. Marl, yellowish, sandy. A collection from this 

unit, and unit 13 below, contains Oxytropidoceras cf. 0. supani (Lasswitz), Nerineal sp., Tylostoma sp., Natica"! sp., Pecten (Neithea) sp., 

Exogyra texana Roemer, and Enallaster teasanus (Roemer) (USGS 17857; field label K 2 

EF). According to Imlay, occurrence of an 

ammonite like Oxytropidoceras supani indicates 

a late Fredericksburg age, but not necessarily 

a Kiamichi age 8
STRATIGRAPHIC SECTIONS OF CRETACEOUS ROCKS 173

Kiamichi Formation Continued Feet 

14. Sandstone, yellow; contains oysters 2 

13. Limestone, blue-gray, marly; contains abundant 

fossils, such as Pecten, Exogyra, oysters, and 

Turritella'i _____________________ 15 

12. Marl and limestone, forming a slope, containing

Lunatial sp. (USGA 17836; field label KID) 15 

11. Limestone, brown; forms a prominent ledge; 

cross sectiions of shells are visible, possibly 

rudistids _ -_____ ____ 5 

10. Limestone, marly; forms a slope 6 

Finlay Limestone:

9. Limestone, massive, gray; forms 1- to 3-ft ledges ; 

contains obscure rudistids, chamids, and other 

fossils. This, and lower beds of the formation 

are reported to contain the chamid Toucasia sp., 

and the other mollusks Protocardia filosa Conrad 

and Tylostoma sp., (DeFord and Brand, 1958, 

fig. 11, p. 23)_ ________________ _ 10 

8. Marl, forming a slope__________________ 5 

7. Limestone, gray; forms a ledge___________ 2 

6. Limestone, gray, nodular, marly, sandy in part; 

contains gastropod steinkerns, oysters, and many 

other poorly preserved fossils____________ 28 

5. Sandstone, yellow-brown, ripple-marked______ 3 

4. Limestone, gray, marly_________..______ 8 

Cox Sandstone:

3. Sandstone and clay, poorly exposed_________ 16 

2. Sandstone, coarse, yellow-brown; weathers brown; 

in 5-ft beds that break out into great cubical 

blocks. Many layers are crossbedded on a large 

scale, and some bedding surfaces are ripple 

marked. Some layers are conglomeratic, containing quartz 'and chert pebbles as much as 1% 

in. across. Weathered surfaces are dotted with 

ferruginous pellets. Some purplish shaly sandstone is interbedded, but is mostly obscured by 

float from the more massive layers. About 10 ft 

of nodular limestone, with 15 ft of shale beneath 

is reported 225 ft below the top (DeFord and 

Brand, 19561, p. 23, fig. 11), but was not recorded 

in 1928__________________________ 390

Campagrande Limestone:

1. Limestone, thin-bedded, conglomeratic, white; with 

yellow and pink mottling; passes into a more 

massive ledge at top________________ 20

Unconformity.

Hueco Limestone at base of section.

Summary of section 49

Part of Kiamichi Formation exposed____________ 69 

Total Finlay Limestone_____________________ 56 

Total Cox Sandstone_______________________ 406 

Total Campagrande Limestone_______________ 20

SECTION 50. BLACK KNOBS

The following is a section of the Campagrande 

Limestone and Cox Sandstone on Black Knobs, 5!/£ 

miles east of Cox Mountain (summit 5480, west-central 

part of sec. 15, Block 44). The section was measured 

by P. B. King and K. E. King in 1928. 

Top of knobs; no higher beds preserved.

Cox Sandstone: Feet 

7. Sandstone, medium-grained, crossbedded, bluff;

contains small limonite nodules___ 20 

6. Shale, sandy, buff and purple_____ 15 

5. Sandstone, coarse-grained, massive 20 

4. Sanstone, buff, shaly___ _____ _ 13 

3. Sandstone, medium- to coarse-grained, pink; 

weathers purple in places, in others to a brown 

crust. Texture uneven, in part contains seams 

of well-rounded chert and quartz pebbles as 

much as an inch in diameter, in part crossbedded____________________ _ 20 

Campagrande Limestone:

2. Limestone, massive, lumpy and nodular, lightgray ; weathers pale brown and forms a prominent ledge. In places weathered surface contains irregular limonite veinlets 19 

1. Limestone, sandy and marly, white or buff; with 

some harder reddish dolomitic layers and a few 

beds of sandstone _ _ 40 

Unconformity. 

Hueco Limestone at base of section.

Summary of section 50

Part of Cox Sandstone exposed 88 

Total Campagrande Limestone- 59

SECTION 51. ROBERTS MESA

The following is a section of the Finlay Limestone 

at the east end of Roberts Mesa (east-central part of 

Sec. 10, Block 39). The section was measured in 1936 

by J. Brookes Knight. Fossils were identified by K. W.

Imlay (written cominun., 1940).

Top of mesa ; no higher beds preserved.

Finlay Limestone: Feet

1. Limestone, marly; contains rudistids_ _ 10

6. Limestone, massive; contains rudistids; forms a

ledge at rim of mesa 3

5. Marl, sandy_ ___ 12

4. Sandstone, massive, coarse-grained, crossbedded, 

ripple-marked; contains silicified wood. (This 

unit is separately shown on geologic map.) 8

3. Marl, light-gray, fossiliferous. Contains Natical 

cf. N.l pedarnates Roemer, Tylostoma sp., 

Exogyra texana Roemer, Lima sp., Protocardia 

cf. P. texana (Conrad), and Homomya sp. 

(USGS 17844; field label K 9). According to 

Imlay, these fossils are probably of Fredericksburg age 20

2. Shale, sandy, with a 2-ft bed of yellow fine-grained

sandstone at top 15

1. Limestone, containing abundant poorly preserved 

oyster shells, including Ostrea cf. O. crenulimargo Roemer (USGS 17843; field label K 8) 3 

Base of section covered by alluvium.

Summary of section 51

Part of Finlay Limestone exposed _____ _ 71 

SECTION 52. NORTON MESA

The following is a section of the Finlay Limestone 

on the northeast side of Norton Mesa (southeastern part 

of sec. 16, Block 34). The section was measured by
174 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

P. B. King in 1936, and fossils were collected in 1938, 

which have been identified by R. W. Imlay (written 

commun., 1940).

Top of Mesa; no higher beds preserved.

Finlay Limestone: Feet 

12. Sandstone, brown, platy 1 

11. Marl _______________ 2 

10. Limestone, gray; contains rudistids; forms rim

of mesa_ _ 3 

9. Marl, and nodular limestone, containing Exogyra 

cf. E. texana Roemer, Pecten (Neithea) cf. P. 

occidentalis Conrad, and Natica! sp. (USGS 

17281; field label K 2)______________ 15 

8. Sandstone, medium-grained, brown, partly laminated, partly crossbedded; forms a prominent 

ledge on slope of mesa. (This unit is separately shown on geologic map.)_________ 5 

7. Marl, sandy______________________ 15 

6. Sandstone, medium-grained, brown; forms a

ledge___ _ _ _ _ _ _ ___ ___ 4 

5. Marl, sandy, buff; contains limestone lumps and 

interbedded layers of sandstone and nodular 

limestone. At west end of mesa contains Anchura! sp., Natica! cf. N. incisa Giebel, AmpulUna! sp., Cardita sp., Protocardia cf. P. texana 

(Conrad), Homomya! cf. H.t alta Roemer, 

Exogyra texana Roemer, and Enallaster cf. E. 

texanus (Roemer) (USGS 17900; field label K 

12). According to Imlay, these fossils are probably of Fredericksburg age____________ 19 

4. Sandstone, calcareous, buff; forms a ledge____ 1 

3. Marl, soft, sandy, buff ______________ 10 

2. Sandstone, fine-grained, brown; forms a ledge

Oryphaea and Alectryonia observed______ 4 

1. Marl __________________________ 3 

Base of section covered by alluvium.

Summary of section 52

Part of Finlay Limestone exposed______________ 82

COLUECTIONS FROM FINIiAY UEMESTONE AND KIAMICHI FORMATION WEST OF ROBERTS MESA AND 

NORTON MESA

The following three collections amplify the faunas 

of the Finlay and Kiamichi Formations. They were 

collected in the plateau country west of Roberts and 

Norton Mesas, in the Triple Hill quadrangle a short 

distance beyond the west edge of the report area. The 

first was collected during the present investigation, the 

second and third during the investigation of C. C. 

Albritton, Jr., and J. F. Smith, Jr., (1965); all were 

identified by R. W. Imlay.

Finlay Limestone (USGS 17899, field label K 11.) Fossiliferous marl underlying capping 6-ft limestone ledge. Three 

miles southwest of Roberts Ranch and half a mile west of 

road to Sierra Blanca (sec. 19, Block 38). -Collected by P. B. 

King and J. Brookes Knight in 1938 and identified by R. W. 

Imlay (written commun., 1940). Contains Anchura! sp., 

Tylostoma sp., Nerita sp., Exogyra texana Roemer, Protocardia 

texana (Conrad) Lima! sp., and Enallaster cf. bravoensis BSse. 

According to Imlay, these fossils are probably of Fredericksburg age.

Finlay Limestone. From strata 54-82 ft below Kiamichi (?) 

Formation. Northeastern part of Triple Hill quadrangle, west 

of Norton Mesa (Block 35). Collected by J. F. Smith, Jr., and 

identified by R. W. Imlay (written commun., 1950). Contains 

Exogyra texana Roemer, Trigonia sp., Protocardia texana 

Conrad, P. multisriata Shumard P, sp., Cardium! cf. C.! subcongestum Bose, Cypremeria sp., Pecten (Neithea) occidentalis 

Conrad, Brachydontes sp., Modiolus concentrice-costellatus 

(Roemer), Sphaera cf. S. roblesi (Bose), Tapes! sp., Neritina! 

cf. N.! elpasensis Stanton Tylostoma sp., Gyrodes! sp., Aporrhais! sp., Monodonta! sp., Cerithium! cf. C.! pecosense Stanton, and Turritella seriatim-granulata Roemer.

Kiamichi ( ?) Formation. From 34-ft unit of sandstone overlying top limestone layer of Finlay Limestone. Northeastern 

part of Triple Hill quadrangle, west of Norton Mesa (Block 

35). Collected by J. F. Smith, Jr., and identified by R. W. 

Imlay (written commun., 1948). Contains Turritella seratimgranulata Roemer, Cerithium! sp., Ostrea sp., Pecten (Neithea) 

sp., Pecten (Syncyclonema) sp., Nucula sp., Nuculana! sp., 

Cardium cf. C. congestum Conrad, C.! sp., Trigonia emoryi 

Conrad, Protocardia sp., and Engonoceras cf. E. peirdenale 

(VonBuch).

SECTION 63. EASTERN SIERRA PREETA

The following is a section of the Campagrande Limestone, Cox Sandstone, and Washita Group on the east 

slope of the southeast prong of Sierra Prieta about due 

east of Black triangulation station (west-central part 

of sec. 21, Block 68, Twp. 4). A section was measured 

here by P. B. King and R. E. King in 1928, and again 

in more detail by J. Brookes Knight in 1938; the section 

given here is that by Knight. Fossils collected by 

Knight were identified by R. W. Imlay (written 

commun., 1940).

Sill of igneous rock at top of mountain.

Intrusive contact

Washita Group: Feet

38. Sandstone, marly, pink________________ 8

37. Marl, gray; partly covered by float of igneous 

rock. Contains Cardita sp., Cyprimeria sp., 

Pecten (Neithea) sp., Alectryonia qtiadriplicata 

(Shumard), A. cf. A. subovata Shumard, Gryphaea washitaensis Hill, Kingena! sp., Nautilus! sp., Enallaster bravoensis BSse, and 

Hemiaster n. sp. (USGS 17914; field label K 14 

K). According to Imlay, these fossils do not 

afford a definite correlation, but the presence 

of Alectryonia quadriplicata suggests an age 

not younger than lower Mainstreet_______ 65

36. Sandstone, brown__________________ 2

35. Marl, yellow; mostly covered by float of igneous 

rock. Contains many Gryphaea washitaensis 

Hill (USGS 17913; field label K 14 J)_____ 22

34. Covered by float of igneous rock; some intermingled float of brown shale___________ 10

33. Marl, pink; mostly covered by float of igneous 

rock. Contains Kingena! sp. (USGS 17912; 

field label K 14) __________________ 10

32. Limestone, marly; packed with shells of Gryphaea 

washitaensis Hill and Pecten (Neithea) texanus Roemer (U SG S17911; field label K14 H) _ 15
STRATIGRAPHIC SECTIONS OF CRETACEOUS ROCKS 175

Washita Group Continued Feet 

31. Marl, with a profusion of shells. Contains Anchura'i sp., Tylostomal sp., Turritella sp., Lima 

wacoensis (Roemer), Pecten (Neithea) subalpinus Bose, Gryphaea washitaensis Hill, Enallaster cf. E. texanus (Roemer), Tetragramma 

cf. T. taffl (Cragin), and Pseudopyrina clarki 

(Bose) (USGS 17910; field label K 14 G). 

According to Imlay, correlation with Fort 

Worth or Denton is indicated by Pseudopyrina 

clarki ______________________________ 27

30. Marl; white; with numerous fossils. Contains 

Pecten (Neithea) subalpina Bose, Pholadomya 

cf. P. sanctisabae Roemer, Gryphaea washitaensis Hill, Cyprimeria cf. C. crassa Meek, C, cf. C. 

texana (Roemer), C. sp., Alectryonia aff. A. 

carinata (Larmarck), Pinna sp., Lima wacoensis (Roemer), L. sp., Cercomya sp., Isocardita 

cf. I. medialis (Conrad), Tapes ? cf. T.I vibrayeana d'OrMgny, Enallaster texanus (Bose), 

Phymosoma cf. P. texanum (Roemer), Pseudopyrina cf. P. inaudita (Bose), Dumblea symmetrica Cragin, Holaster simplex Shumard, 

Holectypus limitus Bose, Engonoceras sp., Mortoniceras wintoni (Adkins), Prohysteroceras"! 

sp., Cymatoceras texanum (Shumard), Tylostoma cf. harrisi Whitney, Tylostoma sp., and 

Amauropsisl sp. (USGS 17909; field label K 14 

F). According to Imlay, a correlation with the 

Denton or Weno is indicated. Pervinqueria 

wintoni lias been recorded from the Weno and 

Pawpaw, Dumblea symmetrica ranges as high 

as the Weno; Holectypus limitus has been recorded from Fort Worth to Mainstreet; Pseudopyrina inaudita is known from Fort Worth to 

Denton ________________________ 25 

29. Limestone, containing Gryphaea; forms a ledge_ 1 

28. Marl, gray. Contains abundant Gryphaea corrugata Say and G. aff. G. washitaensis Hill, as 

well as Natica sp., Tylostoma cf. T. harrisi 

Whitney, and Turritella sp. (USGS 17906; field 

label K 14 E2) ____________________ 32 

27. Sandstone, red-brown, platy; interbedded with 

clay and marl toward top. Contains Trigonia 

cf. T. emoryi Conrad, Lima sp., and Gryphaea 

corrugata Say var. (USGS 17907; field label 

K 14 E)________________________ 40 

26. Poorly exposed; one outcrop of yellow clay__ 12 

25. Sandstone, yellow-brown, slabby. Contains Gryphaea corrugata Say (USGS 17906; field label 

K 14 D)________________________ 5 

24. Clay, gypsiferous, yellow______________ 12 

23. Slope, covered by float of igneous rock_____ 25 

22. Marl, yellow, sandy; much concealed by float of 

igneous rock. Contains Pervinqueria cf. P. 

kiliani (Lasewitz), P. sp. indet., Hamitesl sp., 

Pecten (Neithea) sp., and Kingenal sp. (USGS 

17905; field, label K14 C). According to Imlay, 

a Duck Creek or Fort Worth age is suggested 

by Pervinqueria cf. P. kiliani________________ 15

21. Marl, gray, abundantly fossiliferous. Contains 

Cymatorceras texanum (Shumard), Eopachydiscus brazoense (Shumard), E.I sp. juv., 

Mortoniceras cf. M. leonensis (Conrad), M. sp.,

Washita Group Continued Feet 

Idiohamites cf. /. fremonti Marcous, /. cf. /. 

comanchensis (Adkins and Winton), Anchura 

sp., Cercomya sp., Pholadomya cf. P. shattucki 

Bose, Eomomya cf. E. ligeriensis (d'Orbigny), 

Trigonia sp., Inoceramus cf. I. comancheamts 

Cragin, Lima leonensis Conrad, L. sp., Pinna 

sp., Ostrea sp., Alectryonia aff. A. carinata 

(Lamarck), Pecten (Neithea) subalpinus Bose, 

Tapes'! cf. T. chilhuahuensis Bose, Kingenal 

cf. K.I leonensis (Conrad), Enallaster texanus 

(Roemer), Pliotoxaster whitei (Clark), Pseudopyrina parryi (Hall), Dumbleal sp., and 

Phymosa cf. P. mexicana Bose (USGS 17904; 

field label K 14 B). According to Imlay, correlation with the Duck Creek is shown by 

Eopachydiscus brazoense, Idiohamites cf. fremonti, I. cf. 7. comanchensis, and Inoceramus 

comancheanus _____________ ___ 30

Cox Sandstone:

20. Sandstone, platy, mottled purple, red and white; 

bedding surfaces show sun cracks and fucoidal 

markings_______..____ __ 10

19. Sandstone, fine-grained, massive, crossbedded, 

light buff; weathers lumpy. Contains a silicified log________________________ 36 

18. Sandstone, coarse-grained, very massive, crossbedded, light-brown 10 

17. Sandstone, friable, ocherous 18 

16. Sandstone, very massive, crossbedded, lightbrown 8 

15. Sandstone, friable, yellow; mostly covered by

float from unit above- 15 

14. Sandstone, slabby, brown _ 2 

13. Sandstone, friable, marly, yellow; with a thicker

ledge near base_ 15 

12. Sandstone, yellow; contains nodules of possible

algal origin 15 

Campagrande Limestone:

11. Clay, white___________ __ 2 

10. Shale, sandy, ocherous; contains unidentifiable 

oysters and other pelecypods (USGS 17903; 

field label K 14 A) ______ _____ 5 

9. Sandstone, argillaceous, chalky, white 2 

8. Clay ocherous 7 

7. Limestone, mottled, yellow; forms a ledge. Contains nodules of posssible algal origin 2 

6. Marl, ocherous; contains nodules of possible

algal origin _ 5 

5. Marl, white. ___ 5 

4. Limestone, forming a ledge 2 

3. Marl, gravelly, gray- 8 

2. Limestone, gray, lumpy; forms a massive ledge;

contains obscure fossils 7 

1. Limestone, light-gray to purple; weathers to 

rounded lumps. Contains algal nodules and 

poorly preserved gastropod molds 35 

Unconformity. 

Victorio Peak Limestone at base of section.

Summary of section 53

Part of Washita Group exposed________ 356

Total Cox Sandstone- _ 129

Total Campagrande Limestone 80
176 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

OTHER FOSSIL COLLECTIONS FROM WASHITA GROUP 

IN EASTERN SIERRA PRIETA

The following three collections of fossils were made 

from the Washita Group of the eastern part of the 

Sierra Prieta, and supplement the data given in section 53.

USGS 17915 (field label K 15 C). Washita Group, 25 ft 

above top of Cox Sandstone, a quarter of a mile south of the line 

of section 53 (southwestern part of sec. 20, Block 68, Twp. 4). 

Collected by J. B. Knight in 1938 and identified by E. W. Imlay 

(written commun., 1940). Contains Eopachydiscus lacvicaniculatum (Roemer), E. brazoense (Shumard), Pervinqueria 

trinodosa (Bb'se), P. Jciliani (Lasswitz), and P. n. sp. According to Imlay, a Duck Creek age is indicated by Eopachydiscus 

brazoense; the listed species of Pervinqueria are recorded from 

both the Duck Creek and Fort Worth Formations.

USGS 17901 and 18091 (field label K 13). Washita Group, 

first 25 ft of beds above Cox Sandstone, west side of southeast 

prong of Sierra Prieta, southwest of Black triangulation station 

(center of sec. 19, Block 68, Twp. 4). Collected by J. Brookes 

Knight in 1938, and identified by E. W. Imlay (written commun., 1940). Contains Eopachydiscus brasoense (Shumard), 

Cymatoceras texanum (Shumard), (7.? sp., Pervinqueria sp., 

P. cf. P. Jciliani (Lasswitz), Montoniceras cf. M. leonensis (Conrad), Pleurotomaria sp., Alectryonia quadriplicata (Shumard), 

A. aff. A. carinata (Lamarck), Astartel sp., Gryphaea cf., Cf. 

washitaensis Hill, Lima sp., Pholadomya cf. P. shattucJci Bose, 

Homomya aff. H. Ligeriensis (d' Orbiguy), Pecten (Neithea) 

subalpinus Bose, Trigonia sp., Spondylus sp,. Kingena cf., K. leonensis (Conrad) K. cf. K. ivacoensis (Eoemer), K. spp., Enallaster texanus (Eoemer), Pliotoxaster whitei (Clark), Holectypus sp., Pseudopyrina parryi (Hall), and Phymosoma cf. 

P. mexicanum Bb'se.

The first two and the fourth of the ammonites listed above 

are of exceptionally large size and are represented only by 

fragments, some of which are several feet across.

According to Imlay, these fossils indicate a Duck Creek or 

Fort Worth age. The large Eopachydiscus indicates a Duck 

Creek age. Ammonites similar to or identical with Pervinqueria 

kiliani and with Mortoniceras leonensis occur in both the Duck 

Creek and Fort Worth Formations. Phymosoma mexicanum 

has been recorded only from the Fort Worth and Denton 

Formations.

USGS17902 (field label K13 A). Same locality as preceding, 

higher beds of Washita Group. Collected by J. Brookes Knight 

in 1938 and identified by E. W. Imlay (written commun., 1940). 

Contains Pervinqueria, cf. P. trinodosa Bose, Gryphaea washitaensis Hill, Enallaster sp., Macraster sp., and Kingenal sp.

SECTION 54. WESTERN SIERRA PRIETA

The following is a section of the Campagrande Limestone, Cox Sandstone, and Washita Group at the western end of Sierra Prieta ("at northwest corner of Black 

Mountain or Sierra Prieta"), probably below the western angle of the igneous sill (summit 5110, northwestern 

part of sec. 27, block N). The section was measured 

by J. W. Beede and W. S. Adkins in 1921, and has been 

published by Adkins (1932, p. 354). The text given

here has been edited to agree with the styling of the 

other sections of this report, and additional data on 

fossils have been added from notes furnished by Adkins 

(oral commun., 1930). A section was also measured by 

P. B. King and E. E. King in 1928 at a locality about 

three-quarters of a mile farther south, but is less 

complete.

Sill of igneous rock at top of mountain. 

Intrusive contact.

Washita Group: pee^ 

14. Limestone, light-gray; largely a shell coquina. 

Contains Macraster sp., echinoid fragments, 

Prohysteroceras whitei (Bb'se), and Pervinqueria trinodosa (Bose). The two ammonites 

indicate a correlation with Bose's unit 5 of the 

Cerro de Muleros section, which may be of Fort 

Worth or Denton age__ ____ 50

13. Marl, calcareous, with thin seams of gray nodular 

limestone. Contains Dumblea symmetrica 

Cragin, Enallaster bravoensis (Bb'se), Diplopodia sp., Phymosa sp., Pyrina sp. (abundant) 

Salenia sp., Gryphaea washitaensis Hill, and 

Pecten n. sp. This distinctive assemblage is 

like one at a similar level in the Washita Group 

at Cerro de Muleros, and may be equivalent 

to the Denton _ 40 

12. Marl, brown, and interbedded flaggy limestone 40 

11. Marl and limestone _ 22 

10. Limestone, yellow-brown, platy 1 

9. Marl, yellow-brown; contains Pecten subalpinus

Bb'se and Gryphaea sp_ 11 

8. Conglomerate, massive; composed of heterogeneous rounded pebbles as much as 5 mm in diameter, in a calcareous matrix _ _ 1 

7. Marl, yellow-brown. Contains Eopachydiscus 

brazoense (Shumard), Pervinqueria nodosa 

(Bose), P. trinodosa (Bb'se), P. spp., Mortoniceros leonensis (Conrad), and Idiohamites spp., 

which are typical Duck Creek fossils___ _ 10 

Cox Sandstone:

6. Sandstone, fossiliferous in part_________ 95 

5. Sandstone, thin-bedded, crossbedded, brown;

forms a bluff___________ ___ 26 

4. Sandstone, crossbedded, brown; massive above, 

nodular below. Top beds contain abundant 

Exogyra texana Eoemer, Alectryonia carinata 

(Lamarck) (casts and molds), Pecten sp., 

Limal sp., Plagiostomal sp., and gastropods; 

this is a Fredericksburg fauna 40 

3. Sandstone, crossbedded, nodular, brown. Contains irregular sandy inclusions as much as 

a foot long____ ______ _ _ 8

2. Sandstone, massive, yellow 20 

Campagrande Limestone:

1. Limestone, called Hueco limestone in published 

section, but probably Campagrande; thickness 

not stated (?) 

Base of section concealed by alluvium.

Summary of section 54

Part of Washita Group exposed- ___ ____ 175 

Total Cox Sandstone_____________________ 189 

Part of Campagrande Limestone exposed (?)
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Stevenson, F. V., 19451, Devonian of New Mexico: Jour. Geology, 

v. 53, p. 217-245.

Streeruwitz, W. H. von, 1890, Geology of trans-Pecos Texas: 

Texas Geol. Survey, 1st Ann. Rept. (1889), p. 219-235.

 1891, Report on the geology and mineral resources of 

trans-Pecos Texas: Texas Geol. Survey 2d Ann. Rept. 

(1890), p. 665-713.

 1892, Trans-Pecos Texas: Texas Geol. Survey, 3d Ann. 

Rept. (1891), p. 383-389.

 1893, Trans-Pecos Texas: Texas Geol. Survey, 4th Ann.

Rept. (1892), p. 141-175. 

Thompson, M. L., 1942, Pennsylvanian system in New Mexico:

New Mexico Bur. Mines and Mineral Resources Bull. 17,

92 p. 

Twiss, P. C., 1959, Geology of Van Horn Mountains, Texas:

Texas Univ. Bur. Econ. Geology Geol. Quad. Map 23. 

Warner, L. A., Holser, W. T.( Wilmarth, V. R., and Cameron,

E. N., 1959, Occurrence of nonpegmatite beryllium in the

United States: U.S. Geol. Survey Prof. Paper 318, 198 p. 

Warren, W. C., 1955, Introduction to field trip, in Permian field

conference, Guadalupe Mountain, October 21-22, 1955: Soc.

Econ. Paleontologists and Mineralogists, Permian Basin

Sec. Guidebook, p. 11-14.

Winterer, E. L., and Murphy, M. A., 1960, Silurian reef complex and associated facies, central Nevada: Jour. Geology,

v. 68, p. 117-139. 

Yochelson, E. L., 1956, Permian Gastropoda of the southwestern

United States; [Pt.] 1, Euomphalacea, Trochonematacea,

Pseudophoracea, Anomphalacea, Craspedostomatacea, and

Platyceratacea: Am. Mus. Nat. History Bull., v. 110, p.

179-275. 

 1960, Permian Gastropoda of the southwestern United

States; 3, Bellerophontacea and Patellacea; Am. Mus.

Nat. History Bull., v. 119, p. 209-293. 

Yochelson, E. L., and Bridge, Josiah, 1957, The Lower Ordovician gastropod Ceratopea: U.S. Geol. Survey Prof. Paper

294, p. 281-304.

INDEX

[Italic numbers indicate major references]

A Page

Abrigo Limestone of Middle and Late Cambrian age--. 32 

Acknowledgments_ 3 

Adkins, W. S., fossils identified by . 88,8Q 

section measured by- 176 

Agricultural areas... 17,121 

Aleman Cherty Member of Montoya Dolomite___-_-_____-___- 35, 56 

fossils.....- 38,37,185,128-131

in Caballo Mountains of New Mexico _ SB, 56 

Alkali flats, Salt Basin....__._______ 15,97

Allamoore Formation. . 16,25,29 

Bean Hills . ___._ 108 

fossils__ _ ......_...___ %

jasperoid. SB 

limestone beds_ . ..... 2S

marble_ _ ...._ __ 180

minerals in veins... 119 

phyllite___..- ....__..._ 84, 101,119

rock alteration_. ..._..._ 85,101,119 

stratigraphic relations.....__ ___ SB

structure_ ... __ 101 

talc in phyllite units .. __ 24,110 

Tumbledown Mountain... 23, 25, 108 

volcanic rocks.. . . ...._ 84,28

Alluvial deposits, older. ......_...___ 98

younger. .. .. 98,99

Alluvial fans._.__ ..___ 15,97,98,109, 110 

Alluvial slopes. IS, IS 

Analyses, hornfels, Bone Spring Limestone_ 93 

hornfels, Powwow Member of Hueco

Limestone .. ..__ 98 

marble and limestone from Hueco Limestone. _ 9S, 95 

Annotated bibliography __ 5 

Anticlines.. . . ..__ 101,105 

Apache Canyon. - ___ IS, 15,61, 111, 160 

Hueco Limestone . . ... 49, 50,54 

northern marginal belt of Bone Spring

Limestone- ... __ 64

stratigraphic sections. .._...___ 168

Apache Mountains ... 117

faults . .-. . _.... 107

wells drilled for oil - . __ S5,122

Apache Peak, reef mass on __ ____ 65

stratigraphic section ... _ 160

Apache Spring, Fusselman Dolomite. _ S8

stratigraphic section . ___ 1S2

Apache Tank, Bone Spring Limestone....... 4

stratigraphic section ... 166

Arizona.. . . . 31,82,118

Colina Limestone of Naco Group.- 57

Arkansas, Atoka Formation. . 45

Black Rock Formation.. . 33

Atoka Formation in eastern Oklahoma and

western Arkansas__ 45

B

Babb Canyon .. 63

Babb flexure... ... 14,.61, 73,77, 82, 106, 107, 109

Barnes, V. E., quoted .. 31,34

section measured by -. 124

Barnett Shaleage- .

lithology and thickness, 

regional features ..... 

stratigraphic relations.. 

stratigraphic section 

Page

41

41

f1 f«?«? J^-J-jl OO

41

42

41

Basin and Range province_ 11,99,107, 118 

Bass Canyon, stratigraphic section... 136 

Bat Cave, stratigraphic section - 145 

Bat Cave fault_-_____..._ 112 

Bat Cave Formation in Caballo Mountains of

New Mexico_ S4 

Bat guano, nitrate ___ . . 121 

Baylor Mountains......___ 15, 30,104,107,109, 110

beds of Devonian age_ 40 

beds of Middle(?) Ordovician age. . 54 

Bone Spring Limestone___ 61,66,72,139-141 

Cretaceous outliers_________ - 85 

El Paso Limestone__________ 58,53,110 

escarpment-. ......_..... ...... IS, 34,38

fault block. __......._____ 13, 111, US

Fusselman Dolomite_ 58 

Hueco Limestone___.......... 49, 50,52,110

joints __....__._______... 116

Montoya Dolomite 35, SS 

Permian rocks __.... __ 46, US

stratigraphic sections.. .. 187,128,129,1S8, HI 

Victorio Peak Limestone_ 73,74 

Beach Mountain_ ... . 14, 

15,28, 29, SO, 105, 107,119, US, 124 

El Paso Limestone__________ S8,SS,S4 

faults . .-. Ill, US 

Hueco Limestone_._.-. -.-__ 49,52 

joints-. . 116 

Montoya Dolomite_ - 35,86 

Permian rocks.. ___.. ..__ 46 

stratigraphic sections___ __ 123-127, W 

Bean Hills. - _-_-___ 14, 16,101,102 

AUamoore Formation._ . 102 

talc mined from phyllite units. . 24,120 

Campagrande Limestone. 83 

Beds of Devonian age, distribution and thickness. S9 

fossils-.._ .. . . 40 

lithology..- . - 40

regional relations_ 40 

stratigraphic relations..._ . 40 

stratigraphic sections_ . 129 

Beds of Middle(?) Ordovician age..__ 84 

fossils .. _...__...__. 34,129 

stratigraphic section __________ 129, ISO 

BedsofPennsylvanianage.. 42 

age. - 43 

distribution-... 43 

fossils - - - 48,134

local features 43 

regional relations..... 4$

stratigraphic relations. __ . . 43

stratigraphic section. 184

Beede, J. W., section measured by. -.... 176

Bend Formation_ 

Berdan, Jean, fossils identified by _ . 

Beryllium ......_ ......... .

Black John Canyon, beds of Devonian age 

molluscan ledges. .

stratigraphic section.. .

stratigraphic section, south of... - 

Black Knobs, Cretaceous rocks.._.. . .

stratigraphic section.. . . 

Black Rock Formation of Arkansas. .. . 

Blackshaft mine_.._ _ . 

Bleaching, red sandstone of Hazel FormationPage

42, 43

133

159

158

82, 83

173

33

119

27,

103

sandstone of the Van Horn Sandstone... - 

Bliss Sandstone £0,30,34

calcareous division . SO 

distribution.... SO

fossils . 30, 31,123,124,187,128

main body of formation... SO 

regional relations.._ 31 

stratigraphic relations.--.-. SI 

stratigraphic sections-. _ 183,184,127,128 

thickness.- ..... SO

Block faulting, Cenozoic time. - 99,104

of Sierra Diablo. - 94

Bluff Mesa Formation- 81,82

fossils._____________ ___ 83

Bolsa Quartzite of Middle Cambrian age 51

Bone Canyon. __ 60

Bone Spring Limestone 14, 60, 90,92, 93

Apache Tank... 64

Baylor Mountains.. ........ 61,66,72,139-141

correlation of faunas....._ 78

Delaware Mountains... 60 

faunal assemblages.-. . 66 

fossils. 49,6S, 1S8-141,146-15S, 169-164,166,167-170 

fossils and correlation... 66 

Guadalupe Mountains .... 60

lithology and fades 81

molluscan ledges... 63,66,67,72

northern marginal belt_.. 64

outcrop 81

reefs and banks... 61,63,64,65

Sierra Diablo escarpment 81

southern marginal belt .. 65

stratigraphic relations__ 72

stratigraphic sections 1S8-141,146-160,168-170

Brand, J. P., fossils identified by. 87

Branson, C. C., section measured by. 129,130

Bridge, Josiah, fossils identified by.. 124,125

sections measured by 123,132

Brucite. - - 121

Brushy Canyon Formation. 78 

Pipeline Shale Member..... 79

stratigraphic section 169 

Buda Limestone in foothills of Eagle Mountains .. 88

Cable Canyon(?) Sandstone Member of Montoya Dolomite- . 34,56

181
182 INDEX

Page

Caballo Mountains of New Mexico, subdivisions of El Paso Limestone.. . 34 

subdivisions of Montoya Dolomite ..-. 35,36 

Caballos Novaculite of Marathon region_ 41 

California, faults...... . . 118

Camp Creek Shale Member of Pueblo Formation..___.. . 56 

Campagrande Limestone_________ 81,82, S3 

BeanHills._______________... 83 

Cox Mountain_ 83 

Finlay Mountains_ _.___._ 83,84 

fossils. .__ 84,170-172,176

Sierra Diablo Foothills . - . 83 

Sierra Prieta.._____._______..... 83

stratigraphic sections. _____ 170-173,175 

western Sierra Diablo - __---- --- 83

Campo Grande Arroyo in Finlay Mountains.. 83 

Canutillo Formation, in Franklin Mountains. 40,41 

Capitan Limestone___ . ________ 155 

Carlsbad Limestone of Guadalupe Mountains. 74 

Carrizo Mountain Formation. _._..._..19,114 

igneousrocks intrusive into.... tt, 25, SB, 101, ISO

metamorphie features_ ._._ 21 

sequence in Carrizo Mountains._____ gO,lgl 

stratigraphic relations_.. . ... & 

Carrizo Mountains.__... 14,23,28,^00,101,*^, 138 

crushed stone______________.. ISO 

Hueco Limestone-. ..... 49, 52

Pennianrocks ... .. 46 

vein deposits of metallic sulflde minerals_ 119 

Carrizo Spring fault_____________ 103, 113 

Cave Peak, beryllium_.__________ ISO 

igneousrocks______________ 65,90,91 

Cherry Canyon Formation, typical, of Delaware Mountains_________ 79 

Cherry Canyon Formation sandstone tongue. 79,

167 

fossils..... . ...._.____ 167

stratigraphie section- ________ 167 

Chihuahua tectonic belt.. _____ 106, 107, 115 

Circle Ranch fault zone___-________ 112 

Cisco Group of central Texas_________ 56 

Climate.. ._______...._.___.. is, 16

Cloud, P. E., Jr., quoted. --_____ 31,34,63 

section measured by...__________ 124 

Colina Limestone of Naco Group in southern

Arizona__ ________ 57 

Comanche Series.__ ....____... 81

Conglomerate, Hazel Formation __.... SB

Van Horn Formation- ___- _____ 28

Cooper, Q. H., fossils identified by_____ 129

Copper, production___ ...____ 17,119

Cornudas Mountains_ ..______ 81,96

Cox Mountain, Campagrande Limestone_.. 83

Cox Sandstone.._ .._________ 84

Finlay Limestone..._ ________ 88

flow of vesicular basalt . _________ 96

Kiamichi Formation..___________ 87

stratigraphic section __.. l?g

Cox Mountain fault... ___ 32, 112 

Cox Sandstone.... ... .__ 81,84,95

Finlay Mountains.. ________ 84 

fossils and age.. . _________ 86 

outlying areas. .._______._ 85 

Sierra Diablo foothills and Cox Mountain. 84 

Sierra Prieta-.._______________ 85 

southwest of Eagle Flat... ________ 84 

stratigraphic sections. ........_ 170-176

Cretaceous System___..._________ 80

Cretaceous rocks... ______________ 80

angular discordance with older rocks.... 81,105

mineral deposits in Eagle and Quitman

Mountains..__ ._____ 119 

stratigraphic sections and fossil collections.. 170 

stratigraphy......_..._________ 80

Crushed stone. ___-_________ .. 120 

Cutoff Mountain.__ ___.. __.._. 74

Page

Cutoff Shale.--.... ... 81,74,79

age 78

"Dos Alamos gypsum member" 77 

fossils...... . 78,167

Guadalupe Mountains..... 74

lithologic features...-- 77 

stratigraphie relations.... 78

stratigraphic section 167 

Cutter Formation of Montoya Dolomite. 35, 38,37

D 

Dallas fault 29, 103, 114

Dallas mine_________ . -- 119 

Davis Mountains__ 122 

Delaware basin. 46,61,99,104, 106, 122

Delaware Mountains. 14,46, 78,98, 169

Bone Spring Limestone .. . 60, 73,169 

Brushy Canyon Formation_ 78,79, 169 

faults... _ 107,110

wells drilled for oil - -- 35

Permian rocks_______ -_ 46,60, 169

stratigraphic section- 189

Dell City.______ 17

Devil Ridge thrust fault 82,86,106

Devonian, beds of Devonian age . 39 

regional relations... 40 

Diabase, dikes and sills... 96 

Diablo Plateau IS, 14,83,85,94,96, 99,106 

Diablo platform....._ . . 48, 99

Dikes.___________________ 90,9g,94 

Dome Peak, stratigraphic section 171 

"Dos Alamos gypsum member" of Cutoff

Shale. . 77 

Drainage of region.. 14,15,121 

Drake, D. A., fossils identified by.. 134,136 

Dunbar, C. O., fossils identified by. - 134, 

147,149,152,153,155,157-159,167,169 

Dunean, Helen, fossils identified by .. 58,

59,68,76,80,133 

Dunes- . . 16,98

E

Eagle Flat, ground water in unconsolidated

depositsof Cenozoicage 121, \

intermontane plain. 13, 14, 16,22, <

stratigraphic sections. 141,170

Eagle Ford Formation. 88

Eagle Mountains-___ - 20,106,119

Early Mesozoic age, structures of 105

Early Tertiary age, structures of 106

East Baylor fault... . 107, 110, 114

East Diablo fault-. 107, 109, 111, US, 113

Economic geology.. 118

Edwards Limestone 81,86

El Paso Limestone.. Sg, 123

age.__._____ ' S3

Baylor Mountains_ 32, S3, 127

Beach Mountain. . 32,33,124

distribution and thickness_ 32

fossils ____ Sg, S3,12S-128,128-1SO

regional relations . 34

stratigraphic relations..-. S3

stratigraphic sections. 123,125, 127-182

subdivisions_.... 52

Elgin Limestone Member of Maquoketa

shale of Iowa_ 37 

Ellenburger Group of central Texas.... SI, S3,84, 123 

Eureka prospect.. 103,119

Fanglomerate along edges of Salt Basin-- 15, 98, 110 

Fault, Bat Cave-_ lit 

Canizo Spring.__ _ 103, 113 

Cox Mountain-.-.. lit 

Dallas 29, 103, 114 

Devil Ridge thrust- - - 106

Fault Continued

East Baylor.. 107, 110 

East Diablo-_ _ 107, 109, 111, lit, 113; 

Grapevine..__- __ - 29,102,103,113 

Hillside.-.___ . 105,114,117

North Baylor __ - . 107,109- 

North Diablo- ._ 107,111,112

Red Hills thrust . ... lOff

Sheep Peak._ - lit 

South Diablo-___- 105, 106, lit

Streeruwitz thrust - 22,23,25,27, 100- 

Sulphur Creek... 105,lit, 114

West Wylie.. - - 110 

Fault blocks .- _- IS, 19,32,35, 39, 41, US, 116. 

Faults-_........ IS, 14,96,103,105,107,112, 159,169

Apache Mountains. 107 

Baylor Mountains.-.- - 111,113' 

Beach Mountain.-. . 111,118 

bordering the mountains... 107 

Delaware Mountains. 107,110> 

on east side of Salt Basin 110 

Precambrian age.. 117 

Red Tank Canyon.. . 113- 

with strike-slip displacement . 10% 

Faults and related structures within the

mountains- 111 

Faunal assemblages, Bone Spring Limestone. 66~ 

Figure Two Ranch, water wells... m, Itt 

Fillman, Louise, quoted 42 

Finks, R. M., fossils identified by.... 58,59,68,76,80'

Finlay Limestone. - 85, 87

age. - 8&

Cox Mountain-. . 8ff

Finlay Mountains. 85

fossils ___. - 86,173,174

local features... 86

Norton Mesa. 8ff

Roberts Mesa.. . . 8ff

stratigraphic sections 173~

Finlay Mountains, Campagrande Limestone. 83,84

Cox Sandstone.. 84

Finlay Limestone_ 85

Flexures-._____ ___- IS, 105,113,116, 117

Flower, R. H., quoted 32

Fossils, Aleman Cherty Member of Montoya

Dolomite__ -__ 36, 87,125,128-lSt 

Allamoore Formation. -. 24 

Barnett Shale . - . 41,133

beds of Devonian age 40 

bedsof Middle (?) Ordovicianage. . 34,129 

bedsofPennsylvanianage . 48,184 

Bliss Sandstone 30, SI, 123,124,1*7,128 

Bluff Mesa Formation 83 

Bone Spring Limestone .. 49,63,138- 

141,146-156,159-164, 166, 167-170 

Brushy Canyon Formation- . 79, 169 

Campagrande Limestone. _ 84, 170-172,175 

Cox Sandstone.. 85 

Cutoff Shale...-._____ _ . 78,167 

El Paso Limestone_ __ St, S3,123-128,128-1SO 

Finlay Limestone. _ . 86,173,174 

Fusselman Dolomite 39 

Goat Seep Limestone. 49, SO, 167 

Hueco Limestone - - 48, 

50,52,54, 55, 68,135-159,162-167 

Kiamichi Formation - . 87,172 

Permian rocks . 4,17,49,134-170

Victorio Peak Limestone . .. 49,73,74,

76,136,150,154,155,160-164,166,168

Yucca Formation_ 82

Washita Group - 88,174

Fractures and fracture zones, Hazel Formation. 27,

103,119

Franklin Mountains, Bliss Sandstone. SO, 31 

Canutillo Formation 40,41 

El Paso Limestone_._ 32,34 

Fusselman Dolomite_ 38,39 

Montoya Dolomite. 35,37 

Paleozoic formations 5
INDEX 183

"Pug*

Furnish, W. M., fossils identified by . 42,70,161

quoted.. 42

FusselmanDolomite.....__ ...... 35, 36,38,105

distribution-_ . 38 

fossilsandage SS 

litbology - - 38

regional relations 39 

stratigraphie relations__.. 39 

stratigrap hie sections... 125,128,129,131 

thickness.. - - 38

G

Geography... . 11

human... - 16

Gifford-Hill rock crusher, ............ 114,120,172

Gillerman, Elliot, section measured by.. 170 

Gilliam Limestone of the Glass Mountains.... 74

Girty, G. H., fossils identified by.. . 134,136,138

Glen Kose Formation in central Texas_.. 81, 83

Goat Seep Limestone.. . 79

age ... - 80

fossils....__ .. ..._.... 49,80,169

Guadalupe Mountains. __ __ . 79,80 

lithologic features- . 79 

stratigraphic relations.... 80

stratigraphic section 167 

Gordon, Mackenzie, Jr., fossils identified

by .-____..__-__ 41-43,133,134 

quoted..__ ... ..... ____.__ 42,45

German Formation of central Texas. ... 31,33,34 

Grape Creek Limestone Member of Clyde

Formation__... ___ . 57 

Grapevine fault .- .. _. $9,102,103,113 

Grayson Formation in fDothills of Eagle

Mountains..... 88

Grayton Lake, alkali flat 97,99 

Greenstone, Intrusive into Carrizo Mountain

Formation__... ..___._ 22,03 

Ground water.... _. _________ 16, 121

quality. 181 

Guadalupe Mountains__.... ........... 14,96

Bone Spring Limestone_-_ .-... 60 

Cenozoic block faulting..-. 104 

Cutoff Shale....- 74

Goat Seep Limestone_ ... 79,80 

Joints-___....__-_______._ 107

Permian rocks_ __ ___ 48, 60

Victorio Peak Limestone__ - 73

Guadalupe Series... __.-. 14, 48,72,78, 79,82,105

Gulf Series..._.____..__....__._ 8/,88

Gypsiferous clay, hills 15,97

H

Hackberry Creek. - 14, IB, 18,98, 102,110

Hass, W. H., fossils identified by.-.-_ _ 40

quoted_ ... . 40

Hawkins Tank, stratigraphic section-.. .. 30, ISO

Hazel Formation.. . .... 25,100

conglomerate- . . 16,25,108

fracture zones . . 103,119

joints... .... . .. . lie

red sandstone -. ----- 14, 16, 25, 28,109,112

rock alteration . 27

stratigrapbic relations.... .._. . 27

structure.-. .... .-_ ._ 101

Hazel fracture zone. . . ..... . 103

Hazel mine .. 119

stratigraphic section .. . 144

Helms Formation._ .... _ . 41,42

Henbest, L. G., fossils identified by__ 56,

58, 67, 76, 80, 136, 142, 145, 146, 148,

149, 153, 154, 157, 160-164, 166, 167,

169.

quoted . 64 

Hess Limestone of the Glas;3 Mountains.. 72,74 

Hills of gypsiferous clay .. 97 

Hillside fault. 14, 52, 105,114, W

Page

History..... _ . 16 

Hollingsworth, K. V., fossils identified by. 134 

Honeycut Formation of central Texas.... 33,34 

Hornfels, chemical analyses and mineralogy. 92,93 

Hot Wells, Southern Pacific railroad well_ - - - 15,

99, 122

Howe, H. J., fossils identified by_ 128 

sections measured by__ - 128 

Hueco Limestone _ 5, IS, 49, 

65,90,92,93,95,101, 106, 109, 111, 127 

Apache Canyon. --__ 49,50,54 

Baylor Mountains____ ...._ 49,50, 52,110 

Beach Mountain_ 49 

central Sierra Diablo_ 54 

fossils. . 49,50,52,54, 55, 56,135-159,162-167 

fossils and correlation_ - ... 55 

Hueco Mountains.. 49 

inclusions in Sierra Prieta intrusive_ 95 

lithology and subdivisions.. ___ - 50 

marble and altered limestone.. .__ 95, 121 

outcrop_ . 49 

Powwow Member__________ 50, 

52,53,54,92,114,115, 117, 136-139 

regional relations of fauna. . 55 

stratigraphic relations__ 57 

stratigraphic sections____ ___- 135-145, 

147-148,150-160,162-167

subdivisions In Apache Canyon area.. . 54 

thickness. . . 50 

Wylie Mountains....-.-. .._ 49,50 

Hueco Mountains, beds of Devonian age_ 40,41 

Bliss Sandstone.... .... 31 

El Paso Limestone_.... ...._ 34 

Hueco Limestone 49 

Magdalena Limestone.. - - 46 

Montoya Dolomite_.... 37 

Human geography 16

Igneous rocks_ _ ... 22,25,89,92 

intrusive Into Carrizo Mountain formation.- - 88,86

outlying 92 

Sierra Prieta.. ...._ ___ - _ 95

Imlay, R. W., fossils identified by. ._ 86-89,

172-174,176

IndiansinTrans-Peco Texas_______ IS

Indio Mountains. . ... 106

Investigations, present_.. 2

previous_ 4

related,__ _ 4

Jasperoid, Allamoore Formation_ S5

Jefferson City Formation of Missouri_.. 33

Joints...._.__..____ __ 95, 103, 111, 116

Baylor Mountains.... 116

Beach Mountain_ _ 116

Guadalupe Mountains.._ - 107

Sierra Diablo fault block.._ - 116

Kelley, V. C., quoted___ 32

Kiamichi Formation.._ .. 85,87 

Cox Mountain - 87,172 

stratigraphic section.. 172

King, P. B., sections measured by. 123, 

124, 127, 128, 130, 131, 134, 136, 138, 

144, 147, 149, 153, 155, 157, 159, 160, 

166, 167, 170-174, 176.

King, R.E., fossils identified by_ - 56, 

134, 136, 138, 147, 149, 153, 157, 160, 

167, 169.

sectionsmeasuredby-..-. - 128, 

134, 136, 138, 147, 149, 155, 157, 160, 

166, 167, 169, 172-174, 176.

Knight, J. Brookes, sections measured by- 123, 

124,127-129,132-134,136,138,141-146, 

149,153,155,157-159,162-166,170-174.

L Page

Landslides-.....__ _ 41,43,97 

Late Cretaceous age, structures of... ..- 106 

Late Tertiaryage, structuresof. 107 

Lee, D. E., quoted . 95,96 

Leonard Series.... ._ 48, 49, 61, 78,105,106 

of the Glass Mountains.-- 66,72 

in West Texas region_ . 72 

Llano uplift of central Texas___ 34,38,41,45 

Lobo Flats district, ground water.. _ 15,17, 121,122 

Lone Mountain Formation, Nev._ ... 39 

Love Hogback_ _ 82 

Lowland areas.. . 14 

Luedere Limestone, central Texas 57

M

McAdoo Ranch, stratigraphic section_.. - 143 

Magdalena Limestone.. ____ 42,46 

Mainstreet Formation, north-central Texas... 88 

Malone Mountain _ 106 

Marble ___ 95, 120 

analyses. . 93, 95,121 

Marble Canyon.... 43,45,46,54,61,63,109

fossil collections from Hueco Limestone

near. ....___ 156

stratigraphic sections_ ..____ 134,156 

Marble Canyon-Mine Canyon intrusive complex. .. 112 

Marble Canyon stock___.____ 65,90, 92, 93,121 

petrology . 90 

Marvin-Judson prospect . ..____ 119 

Metarhyolite, intrusive into Carriao Mountain Formation. ____ 22, 

25,28,101,105,114,115,120 

klippen of Streerawitz thrust sheet___ 100,101 

Middle Mesa.... .... _____ 79,80,109

Middle Ordovician Simpson Group __.. 18t

Miller, A. K., fossils identified by. ____ 42,70,161

Millican Hills. r . __ 14, / 0,22,100,/Of,//9

conglomerate of Hazel Formation......

talc._. 

Mine Canyon.... . 43,46,48,64,61, M, 65

stratigraphic sections... ... /33, 157

Mine Canyon stock 90,91,92,120

rock units __ 91,120

Mines, Blackshaft- . ___ 102, 119

Dallas.. .._._ 119

Hazel . 17, 102,103,113, 119

Mohawk_ ..... 119

Pecos . .. 103,109,113,119

St. Elmo- ...... 102,119

Saneho Panza. 102, 119

Missions founded by Franciscan monks... 16

Mississippian, stratigraphy. .. 41

Missouri, Roubidoux Formation.. 33

Montoya Dolomite . 33,35,38,113,114

age. 57

AlemanCherty Member_ ... 35,35

Cable Canyon (?) Sandstone Member. 34, 36

Cutter Formation__ 36, S7

fossils...-._ . 36,37,126,129-138

Hueco Mountains...- 37

regional relations . 37

stratigraphic relations__ S6

stratigraphic sections... 124, 125,128-133

Upham Member___.... . 36, 125

Mountain areas.... /3

Murata, K. J., analyst-_ . 24,74,83,90,92,93,95 

Murray fracture zone of the Pacific Ocean

basin. - . 118

N

Nevada, Lone Mountain and Roberts Mountains Formations.- 39 

Pogonip Group 35
184 INDEX

New Mexico, Aleman Formation of Montoya

Dolomite __ SB,S6

Bat Cave Formation of ElPaso Limestone. S4 

Bliss Sandstone- 31, S2 

Cable Canyon Sandstone of Montoya

Dolomite ___-_ _._ SB, SB

Cutter Formation of Montoya Dolomite S5

Fusselman Dolomite S9

Onate formation. 40

Pennsylvanian rocks 45

Percha Shale___ 40

Sierrite Limestone of El Paso Limestone Sj.

Up ham Dolomite of Montoya Dolomite 35

Nitrate prospect HI

North Baylor fault.. - 107,^09

North Diablo fault zone. 107, 111, 112

North Mesa...__ 77,78, 79,80, 109

Norton Mesa, Finlay Limestone - 86 

stratigraphic section. 17S

Ochoa Series- 48

Old Circle Ranch, stratigraphic section 144

Ofiate formation of New Mexico 40

Oil possibilities - - - in

Oklahoma, Simpson Group. 35

Ordovician, stratigraphy... SO

Ozark uplift in Missouri_ 33

Pacific Ocean basin, fracture zones . 118 

Paleozoic rocks... 17 

Paluxy Sandstone.- . 81 

Patterson Hills ...... ... 107

Pecosfracture zone... 103 

Peneplain, pre-Cretaceous. 82 

Pennsylvanian, stratigraphy . 4% 

Percha Shale, N. Mex~ 40 

Permian, stratigraphy 46 

Permian age, structures of.... . 105,117

Permian rocks, fossils._ 17,49,134-170

paleontologic data 49

stratigraphie classification.. 48

stratigraphic sections. 134-170

thickness... 17

Phyllite, Allamoore Formation..-.. ££,101

Pipeline Shale Member of Brushy Canyon

Formation.-... 79

Pogonip Group of Nevada 35

Powwow Member of Hueco Limestone 50,

53,54,92,114,115,117

fossils-........- __ 50,52,54,55,136-137,

14$-14S, 145,151-153,156,158 

Threemile Mountain. 50,52 

Victorio Peak... ..... 54

Precambrian and Precambrlan(?) rocks,

structure_ .. ....___ 100

Precambrian rocks_.. ...._ 17,19, 100

vein deposits of copper and silver .._.. 119 

Precambrian(?) rocks.__ ......___ 19

Precambrian surface, structure_ ___ 103 

Pre-Permian Paleozoic rocks, structure.. 17,^04 

Pump Station Hills, red rhyolite porphyry... 28

Q

Quaternary age, structures-.... ___ 107

unconsolidated deposits_ 96

Quitman Mountains...- 106,115,119

R

Railroads, construction ._.-...___ 16 

Rainfall- - ... ... __ IS

Rancheria Formation.._. . ___ 42 

Ransome, F. L., quoted._.-_-______ 118 

Red Hills thrust fault. ____________ 106 

Red sandstone, Hazel Formation_____

Page

Red Tank Canyon______ ... 53,85 

faults-...... . ___.__. 113

Red Valley___ __-_.... _ 14,87,29

folds....--_. . __..._...... 103

joints ... . 118 

Red Wash...... ..............__.... 15,98,99

Reef and bank deposits in Bone Spring Limestone______________ 61,64,65 

Regional metamorphism of sedimentary rocks

of Carrizo Mountain Formation.. SS 

Relief. - IS, 14,104,103

Rhyolite intrusive into Carrizo Mountain

Formation.... _ Si

Rhyolite porphyry and breccia, Mine Canyon stock 91 

Roberts Mesa, Finlay Limestone. 86 

stratigraphic section.... 17S

Roberts Mountains Formation, Nev..... - 39

Rock formations--...__ 17 

Ross, C. S., quoted-. 95 

Roubidoux Formation of Missouri_. _ 33

St. Peter Sandstone of the northern interior

region. - 34 

Salt Basin.-. - 13, 14, 46,48,73, 107,109, 111, 113 

alkali flats. ... _ 15,97 

deposits of fanglomerate along edges.. 98 

deposits of floor...__ . 97 

faults 110,117

ground water in unconsolidated deposits of

Cenozoic age___ - lit

interior drainage____-_ ^4.15

Salt lakes. - 15, 97

Sancho Panza mine__. 119 

Sandstone, Hazel Formation__ 26 

Van Horn Formation. __ £8,29 

Sandstone tongue of Cherry Canyon Formation-.. __.__ 79,167 

Settlements, early.._____ . 16 

Seven Rivers Limestone of Guadalupe age 74 

Sierra Blanca___.__ __ 115 

yield of wells. _____________ 122 

Sierra Diablo, description.... IS

northern part, faults and related structures_______.__._ 111 

southern part, faults and related structures. US 

Sierra Diablo escarpment__...- IS, 

25, 26, 27, 28, 29, 43, 46, 50, 54, 61, 

73, 83, 84, 102, 106, 107, 110, 143, 

144, 145, 146, 153, 155, 157, 169. 

Sierra Diablo fault block, joints.... 116

Sierra Prieta ..... ........ ... ... 13,81,88

Campagrande Limestone. 83

Cox Sandstone...____.- 85

Hueco Limestone______-__ 55

igneous rocks...____________ 94,95,166

marble.________________... 95

stratigraphic sections. 166,174

Washita Group_______________ 87

Sierra Prieta intrusive, structure...___... 95

Sierrite Limestone, N. Mex__ 34

Sheep Peak, fossil collections from Hueco

Limestone._____ 146 

Sheep Peak fault..______________ 113 

Sills_ __ 20,22,23,90, 92,94,95, 96,97,112 

Silver, Caswell, quoted____...__ 32 

Silver, discovery_______._ 17 

production________________- 17,119 

Silurian, stratigraphy_____.... 38

Simpson Group of Middle Ordovician__ 34,35, Hi 

Sixmile Mountain, stratigraphic section_ 1SS 

Skinner, J. W., fossils identified by__ 134, 

147, 149, 153, 155, 157-159, 167, 169 

Slaughter Ranch well.____________ 122 

Smith, J. Fred, Jr., sections measured by__ 170 

Smithwick Shale of Llano uplift in central

Texas____.____ 45

Sohn, I. G., fossils identified by... 70,159 

South Diablo fault.. . 105,106,112 

South Mesa _. 77,78,79,80,109 

stratigraphic section_.-.___.____ 167 

Southern Pacific railroad..___________ 16 

Stehli, F. G., quoted_ -__ ....._ 72 

Stratigraphic classification of Permian rocks.- 48 

Stratigraphic nomenclature of Precambrian

rocks, development_______ SO 

Stratigraphy....________________ 17 

Streerawitz Hills.-_-_-_....__ 14, 16,101, 102 

Campagrande Limestone . ___ 85 

Hazel Formation____________.. 26,102 

Hueco Limestone.__...__ _ 49,50,52 

stratigraphic sections. __________ 142,171 

talc mined from phyllite units of Allamoore Formation.. __ 24,120 

Tertiary intrusive rock__.... __. 96 

Streerawitz thrust fault- __- 22,23,25,27, 100,101 

Structural features_______ ___ 100 

Sulphur Creek,....-________ 15,16,98, 99,110 

Sulphur Creek fault.___________ 105,^0,114 

Surface of pre-Cretaceous rocks _ __. 81

Talc, to phyllite units of Allamoore Formation. .__ ____

production__ _ _ ___ 17, 120 

Tanyard Formation in central Texas_____ 31, 34 

Tectonic history___ -...__ iOO 

Tectonics_ ___ 99

regional interpretations and synthesis__ 117 

Tertiary rocks__________________ 17 

Texas and Pacific Railway__ 14,16,19,22,114, ISO 

Texas Construction Materials Co_ ___ 1S1 

Texas lineament ______ ___ 115, 118 

Threemile Mountain, Hueco Limestone___ 50,5a

stratigraphic section___.-._...___ 136

Threemile Mountain area, fossils. ______ 138

Topography________... _._____ 13,99

Torbet, ground water____...________ 122

Trans-Pecos Texas.-._____.______ 4,5,

16, 31, 34, 39, 40, 41, 42, 45, 49, 61, 80,

87, 96, 103, 104, 107, 117, 118, 119

Transverse Ranges, Calif. __. 118

Travis Peak Formation of central Texas___ 81,82

Tumbledown Mountain_________ 29,133,124

Allamoore Formation__ .. 23, 25, 10S

faulting ___ -. . __- 103 

Tungsten__ __. ISO 

Turquoise in copper prospects __. 1S1

Unconformities, angular. .. 17,53,99 

Unconformity between beds of Pennsylvanian age and Hueco Limestone. 43, 

99, 104

Bliss and Van Horn Sandstones 29,30,99 

Hazel Formation and Van Horn Sandstone S7 

Hueco Limestone and Bone Spring Limestone______ _ 5S,53,60 

Leonard and Guadalupe Series...--__ 78 

Unconsolidated deposits of Quaternary age... 96 

Upham Member of Montoya Dolomite_... 36, 125 

fossils... - 36,37

N. Mex.. 35

Van Horn. _ _ 13,15, 16

ground water. 1S1,122

Van Horn dome 104

Van Horn Mountains__ __. 20,21
INDEX 185

Page

Van Horn quadrangle.. ...... ___._ S

Van Horn Sandstone. .. 14, SB, 27,110,114 

age .. 29 

bleached.. .._ . . 89 

conglomerate . 28 

joints - .. .__... 115,116 

sandstone__.... ... _ . 28, S9 

stratigraphic relations . 89 

structure .. 103

Vein deposits containing metallic sulfide minerals, in Precambrian rocks_.... 119

Veins, Allamoore Formation.. ____ _ 23 

calcite, in Hueco Limestone 113 

Carrizo Mountain Formation__... 23

Victorio Canyon......... ... IS, 15,54, 105,109, 111

Cretaceous rocks .. 82 

Montoya Dolomite. .. SB, SB, 105 

stratigraphic sections. .. . 158 

vesicular basalt_ .. . 96

Victorio flexure- ... IS, 49,50,54,61,

63,65, 66, 73, &?, 82,86, 106, 107, 110,112

fault along_._ __.......___ _ 105

Victorio Peak........ ...... 46,7S,152

Hueco Limestone____.....____-_ 49,50

Powwow Member..__.....___...... 54

Page

Victorio Peak Limestone..__ 14, 61, 65, 72,107,109 

Baylor Mountains__ . __. 73,74

fossils 49,73,

74,76,1S5,150,154,155,160-164,166,168

Guadalupe Mountains.._ ... 7S

joints_ __ __ __... 112

northeastern calcitic facies.__ ____ 7S

southwestern dolomitic fades ... 74

stratigraphic relations__-__ __ 74

stratigraphic sections .. 1S5,

147,140,150,154-156,160,162-169

Wylie Mountains-_ . .. 73,74

Volcanic rocks, Allamoore Formation....__. i4

basaltic, of Tertiary age 96

W 

Washita Group. ....... 81,87.95,97

fossils....__ _______..____ 88,174 

Sierra Prieta. ________.____ 87, 176 

southwest of Eagle Flat 87 

stratigraphic sections. 174-178

Wells. . .. 14, SV, 111, 121,122

West & Armour, 1 Davis Investment

et al _________...___ 97 

Van Horn, yield.________.____ 181 

Wildhorse Valley irrigation district.__- 97

Weno Formation, north-central Texas. .. 87

Page

West Texas basin..... 34,38,39,41,42,45,122 

West Wylie fault___.___._._____ 110 

Wichita Group of central Texas. ___.__ 56 

Wichita paleoplain of Hill___._______ 81 

Wildhorse Creek.. . . 15,98,121 

Wildhorse Valley, irrigation district_ 15,17,97, 121 

Wolfcamp Series_______-___ 48,49, 55, 105 

Woodford Chert of Late Devonian and Early

Mississippianage. _ .. 41

Word Formation of Glass Mountains____ 80

Wylie Mountains___________... 20,61, 110

Hueco Limestone 49,50,52

stratigraphic section . ... 134

Victorio Peak Limestone.. _______ 7S, 74

Yates Ranch, stratigraphic section 183 

Yearwood Formation of the Apache Mountains.__-_____ ______ 83,84 

Yoehelson, E. L., fossils identified by..... 41,43,58, 

59, 70, 76, 80, 133, 134, 136, 138, 140- 

142,146,148,149, 153-155,157-163,166, 

167,169.

quoted__._... . 45,63,72

Yucca Formation. 81,88

fossils . 82