Mesozoic Stratigraphy of 

the Santa Rita Mountains, 

Southeast of Tucson, 

Arizona

GEOLOGICAL SURVEY PROFESSIONAL PAPER 658-C
Mesozoic Stratigraphy of 

the Santa Rita Mountains, 

Southeast of Tucson, 

Arizona

By HARALD DREWES

MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

GEOLOGICAL SURVEY PROFESSIONAL PAPER 6S8-C

A description of seven thick sequences of volcanic 

and sedimentary rocks and an interpretation of 

the sporadically active continental environments 

in which they were deposited

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1971
UNITED STATES DEPARTMENT OF THE INTERIOR

GEOLOGICAL SURVEY 

William T. Pecora, Director

Library of Congress catalog-card No. 70-6095,55

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

Washington, D.C. 20402 - Price $1.50 (paper cover)
CONTENTS

Abstract-__________________________________________

Introduction. ______________________________________

Geologic setting.___________________________________

Sub-Triassic unconformity.__________________________

Triassic and Early Jurassic stratigraphy.______________

Mount Wrightson Formation_____________________

Distribution___ ___________________________

Lithology and petrography___________________

Lower member_________________________

Middle member._______________________

Upper member.________________________

Chemistry.________________________________

Age and correlation.________________________

Environment of deposition. __ _________ _______

Gardner Canyon Formation_____ _________________

Distribution ________________________________

Lithology and petrography___________________

Siltstone member-______________--___---

Mudstone member._____________________

Age and correlation.________________________

Environment of deposition.__________________

Canelo Hills (?) Volcanics_____________---_-_---

Sub-Cretaceous unconformity._______________-___----

Cretaceous stratigraphy_____________________________

Pre-Bisbee rocks________________________________

Temporal Formation._______________________

Distribution...., _______________________

Basal unconformity._______________.----

Lithology and petrography...____---.----

Lower member._____________--_.---

Middle member.___________________

Lower and middle members undividedUpper member. _____________-__--_-

Age and correlation.____________________

Environment of deposition _______________

Bathtub Formation.________________________

Distribution. _ __ _ _______________________

Lithology and petrography_______-_-----_

Lower member.____________________

Middle member.___________________

Upper member_____________-___--_-

Age and correlation. _____________ _______

Environment of deposition.._____________

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42

43

43

Creataceous stratigraphy Continued Page

Bisbee Group__________________________________ C 43

Glance Conglomerate.______________________ 44

Distribution ____________________________ 44

Lithology-________________-__-----____- 46

Environment of deposition_______________ 47

Willow Canyon Formation___________________ 47

Distribution_ _________________________ 47

Lithology._ ____________________________ 48

Fauna and age_________________________ 49

Environment of deposition_______________ 50

Apache Canyon Formation_________________ 50

Distribution- ___________________________ 50

Lithology-_____________________________ 50

Fauna_________________________________ 51

Environment of deposition.._____________ 51

Shellenberger Canyon Formation.____________ 51

Turney Ranch Formation__________________ 52

Distribution.. _ ________________________ 52

Lithology._ ____-_-_______________--_--- 52

Environment of deposition.._____________ 53

Post-Bisbee rocks__ ______--_____________--_-_-_- 55

Fort Crittenden Formation._________________ 55

Distribution, _ __________________________ 57

Lithology _________________-_____--__--- 57

Shale member,_____________________ 57

Lower red conglomerate member______ 59

Brown conglomerate member_______ 60

Upper red conglomerate member.____ 62

Rhyolitic tuff member.______________ 62

Fauna and age_________________________ 63

Correlation______ _ ______________________ 64

Environment of deposition.______________ 64

Salero Formation.__________________________ 65

Distribution_ _________________________ 65

Basal unconformity.____________________ 65

Lithology and petrography________-_-__-- 66

Lower member.____________________ 66

Exotic-block member______________ 67

Welded-tuff member._______________ 70

Arkose member_____________________ 71

Upper member,____________________ 73

Age and correlation.______________--_--_ 74

Environment of deposition and origin_____- 75

References cited-___________________________________ 77

Index____________________________________ 79

m
IV CONTENTS

ILLUSTRATIONS

Page 

FIGURE 1. Index map showing location of the Sahuarita and Mount Wrightson quadrangles and the Santa Rita

Mountains. __________________________________________________________________________________ 2

2. Index map of the Santa Rita Mountains----------------------------------------------------------- 3

3. Geologic map showing the distribution of the main body of the Mount Wrightson Formation,-___________ 8

4. Photograph of a specimen of augite andesite of the lower member of the Mount Wrightson Formation-__ 9

5. Photomicrographs of augite andesite from the lower member of the Mount Wrightson Formation_________ 9

6. Photograph of a specimen of layered rhyolitic lava flow from the middle member of the Mount Wrightson

Formation.____-_______----___---____---_--------__-------_______--__________________________ 10

7. Photograph of a specimen of rhyolitic welded tuff from the middle member of the Mount Wrightson

Formation._ _ ________________-__----____________-____________________________--_-_---___---- 10

8. Photomicrographs of latitic flow from the middle member of the Mount Wrightson Formation._________ 11

9. Photomicrographs of a tuffaeeous sandstone intercalated in the middle member of the Mount Wrightson

Formation.__________________________________________________________________________________ 12

10. Photomicrographs of a typical eolian sandstone intercalated in the upper member of the Mount Wrightson

Formation.____________________________________________________________________________________ 14

11. Geologic map of the Gardner Canyon-Cave Creek area__________________-_-__-______-------------- 18

12-15. Photographs:

12. Typical outcrop of the mudstone member of the Gardner Canyon Formation.__________________ 21

13. Small limestone pockets and blebs in the mudstone member of the Gardner Canyon Formation. __ 22

14. Crudely developed limestone nodules in red mudstone of the mudstone member of the Gardner

Canyon Formation.___-__________-__-____________-________-_____-_-__--_-_------------ 23

15. Specimen of a dacite flow(?) associated with the mudstone member of the Gardner Canyon

Formation_-________-__-_--_--____-_____________-____-____-___-------_-------------- 24

16. Photomicrograph of a dacitic flow(?) intercalated in the mudstone member of the Gardner Canyon

Formation.__________________________________________________________________________________ 24

17. Photograph showing typical terrain underlain by the Temporal Formation.________________---_-------- 27

18. Geologic map of the Temporal Gulch area.__________________________-__--------------------------- 28

19. Stratigraphic and facies diagram of the Temporal Formation.____________________---__--------------- 29

20. Photograph showing andesitic sandstone of the middle member of the Temporal Formation-___.___------ 30

21. Photomicrograph of augite andesite of the lower and middle members of the Temporal Formation.-______ 32

22. Photomicrographs of rhyodaeite of the upper member of the Temporal Formation._______--_----------- 34

23. Stratigraphic and facies diagram of the Bathtub Formation_________---__._-------------------------- 37

24. Photograph of a specimen of strongly flow-laminated intensely indurated welded tuff from the northern unit

of the middle member of the Bathtub Formation._ _________________.______-----__---------------- 38

25. Photograph of a specimen of less strongly welded tuff from the northern lens of the middle member of the

Bathtub Formation-___-______________-___________________________________-------------------- 38

26. Photomicrographs of same welded tuff shown in figure 25_ __-__-___--------_------------------------- ^9

27. Photomicrograph of porphyritic andesite from the southern part of a flow of the -middle member of the

Bathtub Formation___-________________________________________________-_----_---------------- 41

28. Map showing distribution of rocks of the Bisbee Group_________-_-__-__-------_------------------- 45

29. Photomicrograph of an arkose from the red beds of the Willow Canyon Formation in the Box Canyon area. 49

30. Photograph of crossbedded arkose of the Apache Canyon Formation-________________----------------- 51

31. Photograph of outcrops of slightly hornfelsed mudstone and siltstone of the Apache Canyon Formation

along Agua Caliente Canyon._______________________________..____________---------------------- ^1

32. Measured Stratigraphic section of the Turney Ranch Formation.______-___-__-_----_----------------- 54

33. Photograph showing typical sandstone beds of the lower part of the Turney Ranch Formation- - _____-_----- 55

34. Geologic map of part of the Adobe and Hog Canyons area, showing the relations between the members of the

Fort Crittenden Formation_________________________________________________------.------------- 56

35. Measured Stratigraphic section of part of the Fort Crittenden Formation.______.__-___---------------- 58

36. Photograph showing typical outcrop of the clam-siltstone unit of the shale member of the Fort Crittenden

Formation__ _ _______________________________________________-__-_-____---_----------------- 59

37. Photograph showing typical beds of the lower red conglomerate member of the Fort Crittenden Formation-- 60

38. Section showing structure along line A-A'- __________-___________---_--_---_----------------------- ^1

39. Photomicrograph of a fairly unaltered specimen of a dacite flow of the lower member of the Salero Formation. 67

40. Photomicrographs of a daeitic fragment of the matrix to the exotic blocks, exotic-block member of the

Salero Formation.________--_-__________________________________________-___------------------ 68

41. Photomicrographs of the pulverized component to the exotic blocks, exotic-block member of the Salero

Formation-______-______-_________________________________________--___-____---_------------- 69

42. Photograph of hand specimen of fairly unaltered rhyodaeite of the wslded-tuff member of the Salero Formation. -----_____________________________________________________________________---_---------- 71

43. Photomicrograph of rhyodaeite from the welded-tuff member of the Salero Formation.__________-------- 71
Page 

TABLE 1. Summary of the Mesozoic stratigraphy of the Santa Rita Mountains._____--___-_____-__-___--________ 4

2. Modal, chemical, and spectrographic analyses and norms of volcanic rocks from the Mount Wrightson Formation. _____________________________________________________________________________________ 15

3. Comparison of average analyses of the volcanics of the Mount Wrightson Formation with average analyses of

Nockolds____________________________________________________________________________________ 16

4. Modes of three volcanic rocks of the Temporal Formation____________________________________________ 31

5. Chemical and spectrographic analyses and calculated norms of a specimen of andesite from: the Temporal

Formation.__________________________________________________________________________________ 32

6. Modal, chemical, and spectrographic analyses and norms of dacifcic to andesitic rocks of the middle and

upper members of the Bathtub Formation _______________________________________________________ 41

7. Chemical and spectrographic analyses and norms of members of the Salero Formation___________________ 72

8. Modal analyses of rhyodacite from the welded-tuff member of the Salero Formation____________________ 72
MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

MESOZOIC STRATIGRAPHY OF THE SANTA RITA 

MOUNTAINS, SOUTHEAST OF TUCSON, ARIZONA

By HARALD DREWES

ABSTRACT

The Santa Rita Mountains, Ariz., consist of complexly deformed sedimentary, volcanic, and intrusive rocks of Precambrian through Ceiiozoic ages. The Mesozoic rocks comprise 12 

formations, have a cumulative thickness of more than 30,000 

feet, and represent parts of at least the Triassic and Cretaceous 

Periods. These rocks were almost all deposited subaerially, 

many of them in basins associated with block faulting or volcanisni or both, but others were deposited in a more gently 

downwarped basin. The rocks of the Late Cretaceous show signs 

of increasing erogenic activity, and the deposition sequence 

described here ends at the close of that period with the intrusion of large plutons. Fossils from two of the formations 

and isotopic dates from six of them augment the geologic field 

relations to provide a framework for the interpretation of the 

geologic development of the area through the Mesozoic.

The Triassic rocks consist of the Mount Wrightson and Gardner Canyon Formations, and the Triassic and Jurassic rocks 

are represented by the Canelo Hills (?) Volcanics. These formations are dominantly composed of rhyolitic to andesitic volcanics and of red beds, arkose, and sandstone. Of minor abundance, but of major importance in deciphering the geologic 

history, are the intercalated cobble conglomerates, eolian sandstones, and pillow lavas of the Mount Wrightson and the coaly 

limestone of the Gardner Canyon.

During the Early Cretaceous, the Temporal and Bathtub 

Formations, the Glance Conglomerate, and the Willow Canyon, 

Apache Canyon, Shellenberger Canyon, and Turney Ranch 

Formations were deposited. The first two of these formations 

are mixed volcano-clastic rocks, whose coarse conglomerate 

wedges and whose basal unconformity indicate a locally rugged 

relief. The other formations of Early Cretaceous age, all part 

of the Bisbee Group, are strongly arkosic and typically are increasingly finer grained upsectioii, thus indicating a waning 

local relief. A little marine limestone is intercalated near the 

middle of the group.

During the Late Cretaceous, the Fort Crittenden and Salero 

Formations were deposited; black shaly rocks were deposited 

first, followed by intertonguing drab-colored arkoses and red 

volcanic conglomerate and siltstone, and then by a complex 

sequence of volcanic rocks. Of special significance in these 

rocks is the evidence of the close association of volcanic and 

tectonic events with succeeding plutonic events, all of which 

record the first part of the Laramide orogeny.

INTRODUCTION

Volcanic and sedimentary rocks of Mesozoic age 

underlie much of the Santa Rita Mountains and comprise a composite stratigraphic sequence more than 

30,000 feet thick. The Santa Rita Mountains are the 

first range of mountains southeast of Tucson; they extend more than 25 miles southward from Pantano 

Wash, site of the main railroad and the highway east 

of Tucson, to Sonoita Creek, about 12 miles from the 

Mexican border (figs. 1, 2). The mountains commonly 

reach elevations of 6,000 to 7,000 feet; the high point 

is Mount Wrightson, whose elevation is 9,453 feet. The 

broad valley to the east is at an elevation of about 

4,500 feet, whereas that to the west is at an elevation of 

only 3,000 feet, The mountains thus are sufficiently high 

to support extensive largely scrubby forests, which contrast markedly with the grasslands to the east and the 

Sonoran Desert vegetation to the west. The mountains 

are also sufficiently rugged to provide good exposures 

which have helped in unraveling the stratigraphy of 

the Mesozoic rocks.

Mesozoic strata are divided into 14 formationalrank units, of which five are combined to form one 

group. The names, relations, thicknesses, and lithologies of these units are listed in table 1. The table does 

not emphasize, however, that the thicknesses of the 

individual formations, which range from 600 to 8,500 

feet, are highly variable and that commonly only 2,- 

000-10,000 feet of beds is present at any one place. Most 

geologic relations shown in the table are demonstrable 

in the Santa Rita Mountains, but a few of them are 

demonstrable in adjacent ranges, especially the Empire 

Mountains and the Canelo Hills, both to the east. Nevertheless, the Santa Rita Mountains apparently provide the most complete Mesozoic geologic record in 

southeastern Arizona.

01
C2 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

110°00'

 MOUNTAINS

MUSTANG

MOUNTAINS

^- OLJAD

PYEATT

RANCH

ORT

HUACHUCA 

QUAD Fort /QUAJD

uachuc i . . .Vista

CONTOUR INTERVAL 1000 FEET 

DATUM IS MEAN SEA LEVEL

FIGURE 1. Location of the Sahuarita and Mount Wrightson quadrangles and the Santa Rita Mountains, southeastern Arizona. 

The geology of the other outlined quadrangles is described in collateral reports. Areas covered by geologic maps in this 

report: 1, figure 34; 2, figure 11; 3, figure 28; and 4, figure 18. Area 5 is Salero area. Contour interval 1,000 feet. Datum 

is mean sea level.

The relative completeness of the Mesozoic record in 

these mountains adds considerably to the geologic history of the region. Some of the more important contributions concern the environments of deposition and 

the record of tectonic activity during the Mesozoic 

Era. These contributions may be useful in stimulating 

the exploration for deposits of copper, lead, zinc, and 

silver, which were emplaced chiefly during the Laramide orogeny (the erogenic period at the close of the 

Mesozoic). An improved knowledge of the Mesozoic 

stratigraphy should aid in delimiting potential host 

rocks of the mineralization. Similarly, knowledge of 

the deformation that occurred earlier during the Mesozoic should help in deciphering the structural complexities of the Laramide and the related problems of 

structural control.

This report describes the stratigraphy and petrography of the Mesozoic strata and interprets the depositional environments of the strata. Eocks older and 

younger than Mesozoic and the Mesozoic intrusive 

rocks are planned to be described in separate reports 

and are mentioned here only to provide a framework 

for the description of the Mesozoic layered units. Likewise, the structure of the Santa Eita Mountains will 

be described and interpreted in a separate report. Geologic maps of the Mount Wrightson and Sahuarita 

quadrangles (Drewes, 1971a, b), covering the area of 

this report, will prove helpful in understanding much 

of the material herein. Other brief reports on economic 

and tectonic topics are also available (Drewes, 1967, 

1968,1970; Simons and others, 1966).
SANTA RITA MOUNTAINS C3

TO TUCSON

SAHUARITA QUADRANGLE EMPIRE MOUNTAINS= 

QUADRANGLE (10

Corona de 

Tucson

Hf

. , - MOUNT WRIGHTSQN/6QUADRANGLE ELGIN QUAD.RANQL&i

FIGURE 2. The Santa Bita Mountains showing places discussed in text. Areas covered by geologic mapsi 

in this report: 1, figure 34; 2, figure 11; S, figure 28; and 4, figure 18. Area 5 is Salero area.

404-482 O - 71 - 2
C4 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

TABLE 1. Summary of the Mesozoic stratigraphy of the Santa Rita Mountains

[m.y., million years]

Age

Paleocene(?)

Late 

Cretaceous

Early 

Cretaceous

Early Jurassic 

and 

Late Triassic

Triassic

Permian

Group

S&+

«£&""

Formation

Gringo Gulch Volcanics

Salero Formation

Fort Crittenden Formation

Bathtub Formation

Temporal Formation

 Unconformity (major granite intrusion) 

CaneloHills(?) Volcanics

Gardner Canyon Formation

Mount Wrightson Formation

Eainvalley Formation

Thickness 

(feet)

5,000±

4, 200-5, 800+

1, 500+ 

1,600+ 

1, 500-2, 000 

2, 200+ 

0-1, 500+

1, 500-2, 300

1, 000-2, 000

600+

1, 000+

8, 500±

Subdivisions

Khyolitic tuff member. ... 

Upper red conglomerate 

member. 

Brown conglomerate 

member. 

Lower red conglomerate 

member.

Description

Ehyolitic volcanics and clastic rocks.

Sedimentary and volcanic rocks; 2,500± ft. 

Arkose and conglomerate largely fades of welded-tuff 

member; 500± ft. 

Ehyodacite welded tuff; 1,200+ ft. 72.5± 2.2 m.y. 

Dacitic volcanics containing large exotic blocks; 1,000± 

ft. 

Dacitic volcanics; 400+ ft.

Tuff intercalated in upper red conglomerate; 0-650 ft. 

Volcanic conglomerate to siltstone; 1,400+ ft.

Arkosic conglomerate to siltstone; 2,000+ ft. 

Volcanic conglomerate to siltstone; 800-1,200 ft. 

Fossiliferous shale, and sandstone; 4-550+ ft.

Sandstone and red siltstone. 

Siltstone and arkose. 

Arkose, siltstone, and limestone lenses. 

Arkose and conglomerate. 

Limestone-and-granite cobble conglomerate.

Dacite volcanics and tuffaceous sandstone; 0-1,500 ft. 

Khyolite to andesite volcanics; 800-1, 500 ft. 

Conglomerate and volcanic sandstone; 700± ft.

Conglomerate and rhyolite volcanics; 600-1,000 ft. 

Ehyolite to latite volcanics and conglomerate; 100-400 

ft. 

Ehyolitic to dacitic volcanics and fanglomerate; 203- 

1,300 ft.

Arkose, tuffaceous sandstone, tuff, and conglomerate. 

173±7 m.y.

Red mudstone, dacite volcanics and conglomerate. 

192±20 m.y. 

Red siltstone and chert pebble conglomerate.

Eolian sandstone, andesitic to rhyodacitic volcanics; 

2,000+ ft. 

Rhyolitic to latitic volcanics, trace of clastic rocks; 

5,000± ft. 220±30 m.y. 

Dacitic to andesitic volcanics, and sandstone; 1,500+ ft.

Marine limestone, dolomite, and sandstone.

The geologic investigation of the Santa Kita Mountains is part of a larger program of the U.S. Geological 

Survey to establish the regional setting of mineralization in the ranges between Tucson and Bisbee. Many 

geologists are involved in the program, and most of the 

neldwork has been completed. Cooper (1970) has 

mapped the Sierrita Mountains, Finnell (1970) the 

Empire Mountains, Creasey (1967) the Whetstone 

Mountains, R. B. Raup the Canelo Hills, F. S. Simons 

the Patagonia Mountains, P. T. Hayes the Huachuca 

Mountains, Raup the Mustang Mountains (see Hayes 

and Raup, 1968, for the geologic map of the Huachuca 

and Mustang Mountains), and Hayes and Landis 

(1961, 1964) the Mule Mountains/ This collateral 

work has provided abundant data which support interpretations of the geology of the Santa Rita Mountains 

given here and also some data which restrict those 

interpretations. Thus, for example, the divisions of the 

Mesozoic rocks presented in this report have been 

found practical over a broader region than that covered 

in this report alone. Nevertheless, some interpretations 

on correlation and environments of deposition included

here are only permissive interpretations and therefore 

are my sole responsibility. Where my colleagues prefer 

an alternative explanation or wish to avoid one favored 

here, they will do so in other chapters of this professional paper. Inasmuch as not all the other areas contain significant amounts of Mesozoic strata, not all the 

above-mentioned geologists have contributed directly 

to this professional-paper series; however, all of them 

have been intimately involved with the growth and development of the ideas of the authors of this series and 

with the editing of the maps and reports.

GEOLOGIC SETTING

The geologic events of the Paleozoic Era that led 

up to the deposition of the oldest Mesozoic rocks in 

southeastern Arizona are relatively well established; 

however, the record of still earlier events remains fairly 

fragmentary. In brief, the pre-Mesozoic geologic history involves five major episodes: (1) a period of early 

Precambrian sedimentation, (2) orogeny with attendant metamorphism and batholithic intrusion of at 

least one age, (3) further sedimentation, largely of
SANTA RITA MOUNTAINS C5

clastic rocks, during late Precambrian time, (4) an 

episode of diabase intrusion and minor uplift, and (5) 

deposition during Paleozoic time, largely of marine 

carbonate rocks.

The oldest known rock unit in southeastern Arizona 

is the Pinal Schist, which includes some slate, metavolcanics, gneiss, and migmatite. The Pinal in this part 

of Arizona is exposed in the Little Dragoon Mountains, 

where Cooper and Silver (1964, p. 11-23) described it 

in considerable detail as a sequence at least 20,000 feet 

thick of metamorphosed conglomerate, sandstone, siltstoiie, and shale, and lava flows of rhyolite and basalt. 

They further described the major aspect of this 

sequence as a "cyclic graywacke-slate lithology * * *" 

which contains "graded bedding, the intercalated lava 

flows, and abundant volcanic debris." L. T. Silver (oral 

commun., 1968) dated a rhyolite flow as 1,715 ±10 m.y. 

(million years), using the uranium-lead isotopic 

method on a suite of zircon samples. Cooper and Silver 

(1964) interpreted the thickness and lithology of the 

Pinal Schist as indicative of geosynclinal deposits. 

Some aspects of the geosyncliiie were reviewed by 

Anderson (1951, p. 1345).

In the Santa Rita Mountains, schist and gneiss that 

are correlated with the Pinal Schist form inclusions, 

roof pendants, and possible remnants of wallrock 

within large granitic plutons. Only very rarely were 

they the source rocks of detritus incorporated in the 

coarser clastic formations of Mesozoic age. The Precambrian rock that was exposed to erosion during the 

Mesozoic was largely of the granitic varieties.

Many of the ranges of southeastern Arizona in which 

the Pinal is exposed also contain extensive masses 

some probably of batholithic proportions of coarsegrained or porphyritic alkali granite, quartz monzonite, 

and granodiorite. These masses usually contain assorted 

small bodies of aplitic rock, fine-grained quartz monzonite, pegmatite, and lamprophyre. The batholiths and 

stocks intrude the Pinal and commonly metamorphose 

the schist along their contacts. Several of these granitic 

masses have been isotopically dated using the uraniumlead, lead-alpha, and rubidium-strontium methods, 

separately or together. Three of the dates fall in the 

range 1,410 to 1,655 m.y., three other dates are later 

in the Precambrian, and one is post-Cambrian. The 

youngest date clemonstrably reflects a younger recrystallization event; the other relatively young dates 

are believed to be minimum dates, caused by loss of 

radiogenic daughter products. It seems likely that 

southeastern Arizona contains intrusives that are representative of both the older (1,650-1,700 m.y.) and the 

younger (1,430-1,460 m.y.) magmatic episodes that 

were described by Silver (1969). Locally, the plutonic

rocks were modified by later thermal events, such as 

the Laramide orogeny.

In the Santa Rita Mountains, much of the basement 

rock is a coarse-grained porphyritic granodiorite and 

quartz monzonite of the l,450-m.y.-old type. One sample 

of this rock yielded a Precambrian date by rubidiumstrontium and lead-alpha methods, but another sample 

dated by the potassium-argon method records only a 

Laramide thermal event (Drewes, 1968, p. C5).

In the mountain ranges east of Tucson, rocks of the 

Apache Group of late Precambrian age uiiconformably 

overlie the Pinal Schist and various granitic masses. 

The stratigraphic sequence of this group is probably 

most complete in the Little Dragoon Mountains, where 

the units were described in detail by Cooper and Silver 

(1964, p. 36-41). But, even there, the upper two of 

the six formations that make up the Apache Group to 

the north are absent, and it is doubtful whether as 

many as four formations of this group are present 

anywhere between Tucson and the Little Dragoon 

Mountains. However, all these areas contain some diabasic intrusive bodies which are associated with remnants of the Apache Group. The absence of the Apache 

Group from the central and southern parts of southeastern Arizona and the absence of the upper third of 

that group from the northern part indicate that these 

areas either remained sufficiently high so as not to 

receive sediments during all of Apache time or more 

likely were uplifted so that the top of the Apache deposits was eroded. None of these rocks are present in 

the Santa Rita Mountains.

In Paleozoic time, shallow marine deposits were 

spread uniformly across all of southeastern Arizona, 

where they locally lie with minor angular discordance 

on rocks of late Precambrian age. Initially they formed 

a composite sheet about 6,000 feet thick; the oldest 

rocks are the Middle Cambrian Bolsa Quartzite, and 

the youngest are the Permian Rainvalley Formation. 

Sedimentation during the Paleozoic was interrupted 

probably several times; the longest of the hiatuses 

represents at least part of Ordovician time and all of 

Silurian time. Rocks of late Paleozoic age comprise, in 

rising order, the Earp Formation Colina Limestone, 

Epitaph Dolomite, Scherrer Formation, Concha Limestone, and Rainvalley Formation. The Rainvalley Formation and commonly also other Permian rocks, which 

are typical widespread marine units, are absent from 

southeastern Arizona east of the San Pedro River. 

Apparently, the Mesozoic rocks near the Santa Rita 

Mountains preserved the Permian rocks from subsequent erosion. Thus, the absence of Permian rocks to 

the east could be due to the lack of deposition of Mesozoic rocks there. During Rainvalley time, sometime
C6 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

near the middle of the Permian, southeastern Arizona 

was uplifted, the sea receded, and a continental environment was established. The epeirogenic movements associated with this major marine regression continued, 

perhaps with increased intensity, into the Triassic and 

set the stage for the volcanic and stratigraphic events 

in the Santa Rita Mountains, of prime interest in this 

report.

SUB-TRIASSIC UNCONFORMITY

Regionally, the Triassic strata are inferred to be 

separated from the underlying Paleozoic beds by an 

unconformity. Both the configuration and the precise 

age of this unconformity remain conjectural because the 

unconformity is so poorly exposed and because the 

Triassic rocks are relatively poorly dated. The contact 

between the Rainvalley Formation and the oldest Triassic unit, the Mount Wrightson Formation, is nowhere 

actually exposed owing to the abundance of faults and 

intrusive rocks. Nevertheless, the change from a major 

marine sequence to a continental one implies a crustal 

movement most consistent with existence of a widespread unconformity.

In the Santa Rita Mountains, for example, the base 

of the oldest Triassic rocks is concealed by a string of 

plutons. Despite this, an unconformity is inferred at 

the base of the Mount Wrightson because these volcanics contain some lenses of conglomerate whose clasts 

were derived from pre-Mesozoic rocks. In the Gardner 

Canyon area (fig. 11), the Triassic Gardner Canyon 

Formation overlies the Permian Rainvalley Formation, 

either with disconformity or with minor angular unconformity; and nearby it lies unconformably upon 

the Epitaph Formation. However, even these contacts 

are poorly exposed, because the siltstone at the base of 

the Gardner Canyon Formation is so weak that it is 

usually covered by colluvium.

The precise age range of the sub-Triassic hiatus 

remains problematic because of the lack of precise 

dating of the adjacent formations. The fauna of the 

Rainvalley is like that of the underlying Concha Limestone and is devoid of the most diagnostic Permian 

fossils, the fusulinids. Thus, Bryant and McClymonds 

(1961, p. 1333) initially dated the Rainvalley as Guadalupe(?), and Bryant (1968, p. 42) later stated that it 

may be late Leonard but more probably is early Guadalupe in age. The overlying Mount Wrightson Formation is unfossiliferous, but a lava flow from the middle 

member was isotopically dated by T. W. Stern by the 

lead-alpha method as 220±30 m.y. (in Drewes, 1968, 

p. C7). Even if that date is fairly accurate, there is 

several thousand feet of rock beneath the dated horizon 

whose age can only be estimated. The oldest exposed

part of the formation could be as old as Late Permian 

or as young as Triassic. Because the latter age is 

believed to be the more reasonable one, the duration of 

time represented by the sub-Triassic unconformity is 

probably 30 m.y.

The character of the sub-Triassic contact must at 

present be inferred from the geologic history of the 

region around the Santa Rita Mountains, only a local 

part of which will be discussed in this report. The 

remainder will be discussed in the collateral reports 

previously mentioned. In brief, I believe that after the 

general uplift that led to the marine regression, uplift 

increased and block faults developed concurrently with 

the oldest Triassic volcanism. The base of the oldest 

Triassic rocks of the region is inferred to lie over a 

gentle angular unconformity or possibly even a disconformity. This unconformity is also believed to merge 

with the larger unconformity, which in Gardner Canyon separates the younger Triassic rocks from the Rainvalley and Epitaph Formations. Farther east, the same 

unconformity separates still younger Mesozoic rocks 

from the Rainvalley (Hayes and Raup, 1968), and elsewhere it commonly separates Cretaceous rocks from 

Pennsylvanian or Permian rocks.

TRIASSIC AND EARLY JURASSIC STRATIGRAPHY

Most rocks of Triassic and Early Jurassic age are 

volcanic, and lesser amounts are sedimentary red beds. 

These rocks constitute, in ascending order, the Mount 

Wrightson Formation and Gardner Canyon Formation 

of Triassic age and the Canelo Hills (?) Volcanics of 

Triassic and Jurassic age. These formations have in 

common a predominance of volcanic elements over 

sedimentary ones. They also form relatively thick deposits of limited extent, which suggests that they 

accumulated in deep local basins rather than in broad 

depressions. The combination of abundant volcanism 

and local deep basins of deposition suggests a blockfaulted structural environment. A similar inference of 

lower Mesozoic block-faulted terrane is obtained from 

the structure of the Santa Rita Mountains, which is 

described in a companion paper (Drewes, unpub. 

data). The deposition of Triassic and Jurassic rock in 

this area ended with the emplacement of a large granitic stock into rocks as young as Triassic and was followed by uplift and erosion. The resulting hiatus is the 

most significant one in the Mesozoic record.

MOUNT WRIGHTSON FORMATION

A sequence dominantly of volcanic rocks and subordinately of sedimentary rocks, at least 8,500 feet 

thick, underlies the crest of the high, central part 

of the Santa Rita Mountains. These rocks were con-
SANTA RITA MOUNTAINS C7

sidered Tertiary by Schrader (1915, pi. 2) and Cretaceous by W. R. Jones, C. G. Bowles, and D. C. Hedlund, as reported by Wilson, Moore, and O'Haire 

(1960), but they were assigned a Triassic age by 

Drewes (1966) and were named the Mount Wrightson 

Formation by Drewes (1968, p. C6). The formation is 

divided informally into upper, middle, and lower members, which are distinguished by general lithologic differences, the chief one being a restriction of most of the 

andesitic rocks to the upper and lower members.

DISTRIBUTION

The Mount Wrightson Formation is exposed mainly 

in the Mount Wrightson quadrangle (Drewes, 197la) 

but extends slightly northward into the Sahuarita 

quadrangle (Drewes, 197lb). The largest of three general outcrop areas of the formation is shown in figure 

3. The rocks in this area form a simple homoclinal 

structural block, which has provided most of the 

information about the stratigraphic succession and 

facies variation. The formation is also exposed in two 

outlying structural blocks, the one about 6 miles west 

of the central part of the range, and the other 2 miles 

northwest of Patagonia.

The lower member underlies a discontinuous band 

along the west side of the main outcrop area and is 

accessible along Mansfield Canyon, the uppermost 

reaches of Temporal Gulch, and near Bog Spring. 

Probably most or all of the inclusions of altered volcanic rocks in the intrusive complex west of the main 

outcrop area are of the lower member.

The middle member of the formation underlies most 

of the main outcrop area and makes an unbroken belt 

extending from near Mansfield Canyon, across Mount 

Wrightson, to the mouth of Florida Canyon. It also 

underlies an accessible low hill just north of the mouth 

of that canyon and just north of the north edge of the 

area of figure 3, as well as the two outlying structural 

blocks. Rocks of the middle member, in small fault 

slices, also appear west of Elephant Head (Drewes, 

19Tla) and as exotic blocks in the Salero Formation 

(Drewes, 1968; Simons and others, 1966).

The upper member is restricted to the area near 

Gardner and Sawmill Canyons (fig. 3), an area only 

3 miles long. A sliver of this member lies along the 

fault, which bounds the east margin of the main mass 

of the upper member but which lies east of the area of 

figure 3. Several other slices, either of this member or 

possibly of the middle member, also appear along the 

northeast side of the Sawmill Canyon fault zone, which 

adjoins the wedge of the Paleozoic sedimentary rock 

that is shown in figure 3.

LITHOLOGY AND PETROGRAPHY

LOWER MEMBER

Rocks of the lower member of the Mount Wrightson 

Formation are at least 1,500 feet thick, and their base 

is intruded by plutonic rocks. Most of the rocks of the 

lower member are dacitic or andesitic volcanics, but 

they also include a small amount of latite or rhyolite 

volcanic rocks and sedimentary rocks. The dacitic to 

andesitic rocks usually are medium-gray aphanitic or 

very finely porphyritic lava flows, in which individual 

flows are only rarely recognizable. In the upper reaches 

of Temporal Gulch, a more coarsely porphyritic andesite, resembling some rocks locally referred to as "turkey track porphyry," overlies finer grained rocks. One 

of these porphyries, in which the phenocrysts are fairly 

small, is shown in figure 4. Vesicles and amygdules 

appear in scattered outcrops west of Mount Wrightson 

and in Mansfield Canyon. Near Dripping Spring to 

the south, the member contains two lenses of tuffaceous 

fanglomerate or block breccia, which contain clasts of 

dacitic or other felsitic material that are probably of 

local origin. Lenses of quartz sandstone or quartzite, 

generally about 20 feet thick and a few hundred yards 

long, are scattered throughout the member, and near 

Bog Spring several tongues of sandstone thicken northward and join to make a single body several hundred 

feet thick.

In outcrop, the volcanics of the lower member are 

invariably slightly altered to moderately intensely 

altered and contain abundant epidote, chlorite, and 

clay minerals. The intensity of alteration increases 

westward toward the plutonic rocks that intrude the 

volcanics. A faintly gneissic foliation is superposed on 

the sandstone and the volcanics near Bog Spring, and 

west and south of Dripping Spring a hackly fractured 

homfels forms the lowest rocks. Elsewhere alo'ng the 

contact with the plutonic rocks, the volcanics have been 

changed to a closely fractured sugary-textured massive 

rock.

Under the microscope, most of the rocks in the lower 

member are seen to retain vestiges of their original 

texture and mineralogy, although quantitative measurements are difficult to make and are thus of limited 

value. Phenocrysts range in abundance from 20 to 50 

percent and appear in a felty- or trachytic-textured 

groundmass of feldspar laths (fig. 5) and interstitial 

material which is commonly obscured by alteration. In 

a few thin sections, the interstitial material consists of 

abundant ferromagnesian minerals. Plagioclase is 

abundant but is almost always albitized; the few unalbitized remnants are of sodic labradorite. Phenocrysts of clinopyroxene and pseudomorphs of uralite, 

chlorite, and epidote after pyroxene are present in
C8 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

110°50'

EXPLANATION

Sedimentary and volcanic rocks

Intrusive rocks

Include plutons of Paleocene diorite and 

quartz monzonite, Jurassic granite,and 

Triassic monzonite

Mount Wrightson Formation 

"fiwu, upper member: andesite and rhyolite

q, quartz sandstone

"fiwm, middle member: rhyolite and quartz 

latite

q, quartz sandstone and quartzite

t, tuffaceous conglomerate

c, conglomerate 

"fiwl, lower member: andesite and rhyolite

q, quartzite

c, conglomerate

Gneiss and quartz monzonite

Contact

Fault

30

Strike and dip of beds

oooo

Pillow lava

Reference section

2 MILES

FIGURES. Distribution of the main body of the Mount Wrightson Formation. NOTE. More recent data indicate that the diorite 

and quartz monzooite plutons are Cretaceous in age, not Paleocene.
SANTA RITA MOUNTAINS C9

FIGURE 4. Specimen of an augite andesite of the lower member 

of the Mount Wrightson Formation, obtained from the upper 

reaches of Temporal Gulch.

many of the rocks, in some pseudomorphs after 

amphibole, and in a few possible pseudomorphs after 

olivine. Titaniferous magnetite and apatite are the 

usual accessory minerals. Secondary minerals include, 

in addition to those already mentioned, sericite, kaolinite, quartz, and schorlite tourmaline.

The chemistry of the rocks of the lower member 

(table 2) is discussed in the section "Chemistry" 

(p. CIS).

MIDDLE MEMBER

The middle member of the Mount Wrightson Formation consists of a sequence about 5,000 feet thick of 

chiefly rhyolitic and latitic rock but includes about 5 

percent of dacitic rock and less than 1 percent of sandstone, quartzite, and conglomerate. No sharp contact 

with the rocks of the lower member has been seen 

because commonly the change from the more andesitic

FIGURE 5. Photomicrographs of augite andesite (fig. 4) from the lower member of the Mount Wrightson Formation. Left, 

plane-polarized light; right, crossed nicols. Phenocrysts: twinned augite (A), containing patches of chlorite alteration (C), 

and a uralitized hornblende(?) (H) reaction rim; altered plagioclase (P) ; and magnetite (M).
CIO MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

rocks below to the more rhyolitic ones above lies beneath 

an apron of talus or colluvium. The volcanics of the 

middle member are typically pale red and grayish red, 

but some tend toward pale reddish purple, pale reddish brown, or light brownish gray. Bocks of this 

member are usually highly resistant to weathering and 

thus underlie extensive cliffs and prominent ridges, 

such as the high crest of the Santa Rita Mountains.

Lava flows are the dominant type of rock in the 

central part of the main outcrop area; their textural 

variety is large, but their phenocryst variety is small. 

Many flows are conspicuously layered (fig. 6), and 

laminae less than one-quarter of an inch thick are especially characteristic of this member and are preserved 

even in some strongly altered rocks. However, nonlaminated flows are also present, particularly low in 

the member west and north of Mount Wrightson. In 

places, individual flows appear to be about 100-300 

feet thick. Locally, parts of the flows are vuggy or contain spherical lithophysaelike structures 14-! inch 

across.

The volcanic facies changes away from the central 

part of the main outcrop area. Welded tuff is more 

dominant to the north than lava flows, and some welded 

tuff also appears in a smaller outcrop area on the 

western flank of the range (fig. T). This welded tuff 

is strongly lamellar, but the laminae seem to consist 

largely of lenticular crushed pumice fragments rather 

than of unbroken layers like those in the lava flows. 

(Compare figs. 7 and 6.) The middle member contains 

much flow breccia and some tuff breccia which is the 

most plentiful to the south, between the upper reaches 

of Temporal Gulch and Mansfield Canyon. These 

rocks are commonly very light gray. Sheets of flow 

breccias alternate with nonbrecciated flows, and in 

some places the nonbrecciated flows appear to grade 

laterally into brecciated ones. However, small amounts 

of tuff breccia and flow breccia are scattered throughout the middle member, and several small pipelike 

bodies of volcanic breccia are exposed in the member 

along the crest of the mountains near Mount Wrightson.

Under the microscope, rock texture and composition 

are seen to be those of normal rhyolitic or latitic volcanics. The fine laminae of the flows show up as alternating zones of finely crystalline and more coarsely 

crystalline material, as alined crystal laths, and as thin 

iron oxide layers and trains of iron oxide specks (fig. 

8). Phenocrysts of albitized plagioclase constitute as 

much as 25 percent of the rock, and phenocrysts and 

xenocrysts of quartz constitute 2-5 percent. Potassium 

feldspar, in several thin sections demonstrably sanidine, is commonly present in subordinate amounts. The 

feldspar phenocrysts of most rocks are less than 5 mm

FIGURE 6. Specimen of layered rhyolitic lava flow from the 

middle member of the Mount Wrightson Formation, obtained 

from 2 miles northeast of Mount Wrightson. Each unit in scale 

on right is 0.05 cm.

FIGURE 7. Specimen of rhyolitic welded tuff from the middle 

member of the Mount Wrightson Formation, obtained from 

the west flank of the Santa Rita Mountains about 5 miles 

east of Amado.
SANTA RITA MOUNTAINS Cll

FIGURE 8. Photomicrographs of a latitic flow (fig. 6) from the middle member of the Mount Wrightson Formation, showing 

flow laminations gently inclined toward the left and a quartz veinlet steeply inclined toward the left. Left, under 

plane-polarized light; alined black specks and bands of iron oxide mark the flow laminations, some of which are crinkled. 

Right, under crossed nicols, variations in the grain size emphasize the laminations. Phenocrysts of feldspar (F) and 

magnetite (M).

(millimeters) long, but in a few rocks they are 2-3 cm 

(centimeters) long and thus resemble those of the 

much younger "turkey track" porphyries of the region. 

About half the thin sections contain a few percent, at 

most, of chlorite pseudomorphic after biotite, and a 

very few contain traces of uralite or chlorite pseudomorphic after amphibole and possibly after pyroxene. 

Accessory titaniferous magnetite, apatite, and zircon 

are usually present. Altered devitrified glass is present 

in many thin sections; probably most of the rocks were 

once glassy. Petrographic and X-ray detraction analyses indicate that kaoliiiite, epidote, chlorite, minerals of 

the group illite-sericite, and some uralite are the common alteration minerals and that montmorillonite is 

sparse.

Chemical descriptions (table 2) are presented in the 

section on "Chemistry", which covers discussion on all 

members of the formation.

Lenses of sandstone and quartzite, similar to those in 

the lower member, are widely scattered throughout the

middle member of the Mount Wrightson Formation. 

Altogether, about 30 lenticular bodies are sufficiently 

large to be shown for the Mount Wrightson on the 

geologic maps of the Mount Wrightson and Sahuarita 

quadrangles. They are intercalated in the volcanics of 

the middle member, where they weather to form small 

ledges of pale-yellowish-brown slabby-weathering rock. 

A large sweeping type of crossbedding is always present in the lenses, and the grains are well sorted, commonly subrounded, and 0.2-0.5 mm in diameter. Quartz 

makes up 70-80 percent of most sandstone lenses, and 

clay minerals or sericite derived from the clay makes 

up most of the remainder. Some lenses, however, contain considerable amounts of pumiceous shards, as 

shown in figure 9. Traces of tourmaline, zircon, leucoxene, plagioclase, orthoclase, microcline, and possibly monazite and epidote are found. Tourmaline, apatite, and rutile are included in some of the quartz 

grains. Although the rocks contain the same assemblage 

of alteration minerals as do the adjacent volcanics, the

404-482 O - 71 - 3
C12 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

V''-"'^ "t % "'.' f ."'" '.^itKf^ *4<(:,""*"*;? - ^ f? ".-1; "'^&* - ->~: ;*

FIGURE 9. Photomicrographs of a tuffaceous1 sandstone intercalated in the middle member of the Mount Wrightson Formation, 

obtained from about 1 mile north of Mansfield Canyon and 1% miles west of Temporal Gulch. Left, under crossed nicols, 

shows sorting and degree of roundness of quartz grains. Bight, under plane-polarized light, shows pumiceous shards.

occurrence of some clastic tourmaline, of possible clastic epidote, and also of tourmaline in quartz suggests 

that some of the source rocks of the sandstone had 

already been metamorphosed before the deposition of 

the Mount Wrightson Formation. Most likely, these 

tourmaline-bearing quartz grains were derived from a 

Precambrian source, because by Triassic time the Precambrian rocks were typically metamorphosed, whereas 

the Paleozoic rocks were not.

Several conglomerate lenses are also intercalated in 

the middle member of the Mount Wrightson Formation. One lens, exposed just north of the upper reaches 

of Temporal Gulch, contains abundant cobbles of a 

very coarsely porphyroblastic coarse-grained quartz 

monzonite or granodiorite, aplite, and fine-grained 

aplitic quartz monzonite, an assemblage resembling 

only the Precambrian rocks of this region and especially typical of the Continental Granodiorite in the 

northern part of the mountains. Another lens 1 mile 

north of Mount Wrightson contains another type of

granitic rock, also probably derived from a Precambrian source rock, along with abundant volcanic fragments that could have been derived from the nearby 

flows of the older portions of the Mount Wrightson 

Formation. Detrital microcline in the sandstone and 

quartzite must likewise have come from Precambrian 

rock, because the other plutonic rocks of the nearby 

area are virtually free of microcline. A conglomerate 

lens on the north side of Mansfield Canyon contains 

about 30 percent shards of very delicate finely vesicular 

devitrified volcanic glass, in addition to the more usual 

volcanic detritus; it also contains some wTell-rounded 

and well-sorted grains of quartz, microcline, zircon, 

and possibly orthoclase. The source of the coarse volcanic fragments was probably very local. The source 

of the delicate pumiceous shards, even though different 

from the source of the coarse volcanic fragments, was 

probably also local, because the shards wTould have 

been destroyed by extensive transportation or by transportation with coarse detritus. The quartz grains, how-
SANTA RITA MOUNTAINS CIS

ever, have had a history of extensive abrasion and 

may have come a great distance.

UPPER MEMBER

The upper member of the Mount Wrightson Formation is at least 2,000 feet thick and is about 50 percent 

sandstone, 40 percent dacitic and aiidesitic volcanics, 

and 10 percent rhyodacitic volcanics. Flows of dacitic 

to andesitic rock of the upper member intertongue with 

the more rhyolitic rocks at the top of the middle member; so the contact between these members was arbitrarily placed at the base of a sandstone-rich part of 

the sequence. This contact lies slightly above the zone 

at which rhyolitic rocks begin to be subordinate to 

andesitic rocks.

Sandstone in the upper member of the Mount 

Wrightson Formation forms fewer but much thicker 

lenses as much as 800 feet thick 'than sandstone in 

the lower and middle members. It forms small cliffs 

and gentle slopes on which bare rock is exposed over 

large areas, giving these slopes a moderate-oraiigepink to grayish-oraiige-piiik color. Large sweeping 

crossbedding, whose f oreset beds commonly slope southeastward (R. F. Wilson, oral commuii., 1968) is conspicuous, and the quartz grains are frosted, well 

rounded, and well sorted. Photomicrographs of typical 

sandstone of this member are shown in figure 10. The 

rock closely resembles some of the eolian sandstones of 

the Colorado Plateau and may even be contemporaneous with some of them.

In hand specimen, the volcanic rocks of the upper 

member of the Mount Wrightson Formation are seen 

to be very much like those of the other members. They 

are largely lava flows but include some agglomerate. 

The rhyodacite flows intertongue with the dacitic and 

andesitic flows and seem to be more abundant northward. Pillow lava appears in the canyon bottom half a 

mile east of Sawmill Spring and high in the unnamed 

canyon south of that spring (fig. 3). Individual pillows 

are as much as 3 feet across and are set in a sandstone 

or limy siltstoiie matrix. Pillows typically are sheathed 

in red oxidized aiidesite and contain annular zones of 

vesicles or amygdules of zeolite and epidote. Other 

dacitic and andesitic rocks of this member are also 

amygdaloidal or vesicular, and some of the rhyodacite 

is welded tuff. However, in this member too, individual 

flow units are difficult to detect because the pervasive 

mild alteration has left much of the rock too fractured 

and friable to produce many large outcrops.

Little more can be seen in thin sections of these rocks 

than in thin sections of the other volcanics of the formation. Pheiiocrysts commonly form 30-45 percent of 

the rock. Plagioclase is invariably albitized, and a

little quartz and kaolinized potassium feldspar is present in many rocks. Most rocks contain chloritized biotite, and a few also contain replaced amphibole and 

pyroxene. Accessory minerals are magnetite, apatite, 

and zircon; secondary epidote, sericite, chlorite, and 

clay minerals are moderately abundant. On the basis 

of their modes alone, the volcanics of the upper member range in composition from rhyodacitic to andesitic 

rocks; too much of the groundmass is obscured to make 

more specific determinations.

CHEMISTRY

Modal, chemical, and spectrographic analyses and 

calculated norms of volcanic rocks of the upper member, as well as those of the other members, are presented 

in table 2. Study of these analyses suggests that at 

least some of the rocks are more intensely altered than 

is indicated by thin sections; most likely, selective addition or removal of material has occurred, as well as 

recoiistitution of minerals. For instance, the chemical 

analyses show that specimens 3 and 5 contain nearly 80 

percent silica, which seems high even for rocks in 

which some deuteric silica was deposited in vugs. Specimens 3, 5, and 8 are unusually low in CaO, whereas 

the K2O content of at least specimens 7 and 8 is high 

in comparison to the common values of rhyodacites and 

even of the alkali rhyolites reported by Nockolds (table 

3). Thus there is evidence of metasomatic changes from 

both chemistry and petrography. As a consequence, 

the calculated norms have limited significance. The 

appearance of normative magnesite in specimens 8 and 

10, for example, and the appearance of "normative 

phosphate" in specimens 3, 4, 5, and 9 (footnote 3, table 

2) are abnormalities in the rock chemistry indicative of 

cation transfer, not merely mineral reconstitution. Apparently some of the rocks have been silicified, potash 

nietasomatized, and leached of lime.

Although the limitations implied by local metasomatism must be kept in mind, it is useful, nevertheless, 

to compare the chemical analyses of the Mount Wrightson volcanics (table 3, this report) with those tabulated 

by Nockolds (1954). The average composition of the 

lower member resembles that of Nockolds' average 

andesite, whereas that of the average upper member 

has affinities with both Nockolds' average rhyodacite 

and his average peralkaliiie trachyte. The average 

chemical composition of the middle member resembles 

most nearly Xockolds' alkali rhyolite, atlhough the fit 

is poorer than it was \v ith the other members. In each 

analysis, contents of SiO2 , A12O3 , total FeO, MgO, and 

TiO2 of the Mount Wrightson volcanics compare most 

closely with Nockolds' values, whereas contents of CaO, 

Na2O, K2O, and P2O5 compare least favorably; and
C14 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

K^^> '4 .^ 'a v- £ ' ^^ff^v^ , : "'.-' !i *«* »> -'»--4--' ' * * 4"s --4 y W »*.'' ^ * *" ' >^ >- « ^V' '<«i.** «.-" .%feH^^:;..en^^^i^,^i^; ' ^- -^

^ ' xi^ M^'^^^^^-^*^^^^. - l--^

t^-' , r**-. iV * %My-';- ; ^..'" * l^-^^^lr «' *^ V:^ '' "^ ^

!' ->.. I'^Vir - '< " V*fe'^5V f-,'*- >. it'i*,/V>«^;ViiJv- VS?1^ - '^' ,-i .^'t'

FIGURE 10. Photomicrographs of a typical eolian sandstone intercalated in the upper member of the Mount Wrightson Formation, obtained from 1 mile southeast of Sawmill Spring on Cave Creek. Left, plane-polarized light, shows quartz as nearly 

white grains and potassium feldspar as light-gray grains. Right, under crossed nicols, shows a single striped plagioclase grain.

that disparity is greatest, percentagewise , in the rhyolitic rocks. The amount of alteration, however, is not 

so great as to affect the broadly inclusive rock names 

that have been assigned to the volcanics.

AGE AND CORRELATION

From geologic evidence, the Mount Wrightson Formation is dated as pre-Late Triassic and post-Early 

Permian, but because the volcanics were deposited in a 

continental environment much more typical of the 

Mesozoic than the Paleozoic Era, a Triassic age is favored. In the Patagonia Mountains, the Mount Wrightson Formation is demonstrably younger than Early 

Permian, because it lies unconformably on the marine 

Concha Limestone of Early Permian age (Leonard 

provincial series of West Texas). The marine Bainvalley Formation, which conformably overlies the 

Concha, is also present in the Santa Eita and Patagonia 

Mountains but is not in contact with the Mount 

Wrightson Formation; presumably, the Mount Wrightson overlies the Rainvalley Formation, as well as the 

Concha. The Mount Wrightson Formation is also older 

than Late Triassic, because it is intruded by plutons as 

old as 184±20 m.y., and detritus of the formation is 

incorporated in the Gardner Canyon Formation, dated 

by T. W. Stern as 192+20 m.y. (Drewes, 1968, p. CTC8).

The age of the Mount Wrightson is determined 

directly by isotopic methods. A zircon concentrate from 

a welded tuff (specimen 7, table 2), which was collected 

from near the middle of the middle member within the 

type area, was dat ed as 220 ±30 m.y. by T. W. Stern 

(in Drewes, 1968, p. C7) by means of the lead-alpha 

method. This age is probably reliable because it fits the 

geologic relations and the other isotopic ages well. At 

least some of the Mount Wrightson Formation is of 

Triassic age and possibly even of Early Triassic age.

A zircon concentrate from specimen 8 (table 2) was 

dated by T. W. Stern (written commun., 1966) as 

60 ± 10 m.y. This specimen almost certainly came from 

the middle member of the Mount Wrightson Forma-
SANTA RITA MOUNTAINS C15

tion, but inasmuch as it came from a highly weathered 

outcrop on a pediment rather than from a blasted outcrop on a steep mountain slope, R. F. Marvin suggested 

(oral commun., 1968) that it may have lost lead owing 

to weathering. To the skeptical, neither age may be acceptable, but inasmuch as most of the 25 available ages

are internally consistent and fit the geologic picture 

developed independently of the isotopic dating, the 

220-m.y. age seems credible to me.

Rocks whose composition, appearance, and age are 

similar to those of the Mount Wrightson Formation 

appear in two mountain ranges bordering the Santa

TABLE 2. Modal, chemical, and spectrographic analyses and norms of volcanic rocks from the

Mount Wrightson Formation

Stratigraphic position. .............

Specimen No...- ..-.-.---.--.-...

Field No... ........................

Lower member

1

63D141

2

63D179

3

62D114

4

62D126

Middle member

5 6

63D153 63D226

Upper member

7

65D794

8

65D751

9

62D67

10

62D57

Modal analyses (percent)

Quartz- __ _ ___

Plagioclase__ _ ___ __ .

Potassium feldspar. __

Biotite_ _ __ ___ _ _.

Amphibole.. _ _ _ ...

Pyroxene _ _ __

Olivine(?)_-___________._.

Magnetite __ __ .

Apatite _ __ _ __

Sphene __ __ _ _ _ .

Zircon _

Groundmass_ _ _

Total.... __________

0

60. 9

0

0

28. 1

1. 0

0

10. 0

0

0

0

0

100. 0

1. 6

81. 9

0

.7

5. 6

2. 8

3.3

3. 6

0. 6

0

0

0

100. 1

0

. 9

. 2

. 3

0

0

0

0

0

0

0

98. 6

100. 0

0. 8

3. 0

. 4

. 4

. 2

0

0

. 1

0

0

. 1

95. 1

100. 1

20. 2 2. 0

2. 0 3. 5

3. 5 10. 5

1.0 .3

. 1 0

0 0

0 0

.3 .5

0 . 1

0 0

0 . 1

72. 8 83. 0

99. 9 100. 0

1. 8

5.4

11. 6

. 4

0

. 1

0

. 1

. 1

0

. 1

80. 3

99. 9

5. 8

2. 3

8.6

1. 0

0

0

0

1. 3

. 1

0

. 1

80. 8

100. 0

7.9

14. 0

7.0

. 2

. 3

0

0

. 5

. 1

0

. 1

69. 9

100. 0

8.6

18. 1

5. 6

2. 2

.7

0

0

1.3

. 3

. 1

. 1

63. 1

100. 1

Chemical analyses (percent) 1

SiO2 ._. __________________

A12O3 _________________

Fe2O3 __-____-________._.

FeO____________________

MgO______ ____ __

CaO____

Na_O__________ __________

K2O____________________.

H2O-__________________.

H2 0 + __________________.

Ti02._ __________________

P205 ___________________.

MnO________________ __.

C02 _____. ______________

Total (rounded)

49. 9

16. 7

8.0

4. 8

4. 4

6. 6

2. 7

2.2

. 15

1. 9

1. 5

. 60

.28

. 11

100. 00

55. 2

15. 1

5. 1

4. 0

3.7

4. 7

3. 3

3. 1

. 14

2. 3

1. 4

.75

. 18

. 46

99. 00

79.7

11. 4

.36

. 14

. 1

. 30

3. 8

2.7

. 14

. 58

. 08

. 28

. 02

. 05

100. 00

72. 5

14. 0

1.2

. 04

. 1

. 55

2. 1

6. 5

. 31

1. 1

. 24

.45

. 24

. 14

99. 00

79.7 _________

11.3 _________

.59 _________

. 24 _________

. 1 ________

. 20 _________

. 23 _________

4.8 _________

. 25 _________

1.7 -_---_---

. 12 _________

. 26 _-____---

. 00 _________

. 05 _________

100. 00 _________

71. 6

15. 0

1. 2

. 26

. 1

. 42

2. 6

7.6

. 15

.45

. 17

. 02

. 21

. 08

100. 00

71.5

14.7

1. 6

. 08

. 2

. 08

2. 0

8. 3

. 22

. 73

. 42

. 04

. 02

. 11

100. 00

67. 7

15. 3

3.3

. 10

. 1

. 48

4. 2

6. 2

. 38

. 82

.71

. 50

. 00

. 09

100. 00

63. 9

15. 9

3. 6

. 28

. 1

1. 5

4. 8

5. 9

. 08

. 92

.77

. 50

. 13

. 68

99. 00

Sera-quantitative spe trographic analyses -

B.

Ba________ _ _

Be__________________ __.

Ce_

Co__________________ __.

Cr______._ ___ _ _

Cu________________._ __

Ga_ ____ _ __

La_ ____ ____ _ _ _ Mo_______ ___

Nb._____ _ _ _

Ni____________ ___ _ _

Pb_

Sc_

Sr_____________________.

V____ _

Y_ _

Yb______

Zr.____. ________ _

._ 0

. 1

. 0001

__ . 01

. _ .007

._ . 0005

._ . 005

._ . 002

._ . 01

__ . 0003

_. 0

__ 0

__ . 002

. 03

._ . 07

__ . 03

__ . 003

__ . 0003

. 015

0

. 1

. 0001

. 03

. 005

. 002

. 05

. 002

. 01

0

0

. 01

. 0015

. 03

. 07

. 02

. 005

. 0005

. 02

<. 003

.07

. 0002

0

0

0

. 002

. 0015

0

0

0

. 003

0

0

. 005

0

0

0

. 007

0. 01

. 07

. 00015

. 01

0

0

. 00015

. 00015

. 01

. 0003

. 0005

0

. 003

. 005

. 005

0

. 005

. 0005

.03

0.01 __--__---

1 _ _ -

. 0002 _________

0 _________

0 _________

0 _________

. 0007 __-_-__--

. 0015 _________

0 _________

0 __-____--

0 ___-__--_

0 ____-_---

.002 _-__-__-

.03 _________

.07 __-_----_

.03 _________

.003 _________

. 0003 _________

.015 _________

0. 003

. 05

. 0001

0

. 0003

0

. 0003

. 001

. 005

0

0

0

. 007

. 0003

. 01

. 0007

. 002

. 0002

. 02

0

. 1

0

. 02

. 0003

0

. 001

. 001

. 005

. 0003

. 001

0

. 002

. 0007

. 005

. 003

. 003

. 0003

. 07

0

. 15

. 0001

.02

0

0

. 00015

. 001

. 01

0

. 0003

0

. 002

. 0015

. 01

. 005

. 003

. 0003

. 03

0

. 15

. 00015

. 02

0

. 0003

. 0007

. 0015

. 01

0

. 0003

0

. 003

. 001

. 03

. 005

. 003

. 0003

. 02

See footnotes at end of table.
C16 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

TABLE 2. Modal, chemical, and, spectroffraphic analyses and norms of volcanic rocks from the 

Mount Wrightson Formation Continued

Stratigraphic position- Lower member Middle member Upper member

Field No.... .-............. ... 63D141 63D179

g 4

62D126

5

63 D 153

6

63D226

7

65D794

8

65D751

9

62D67

10

62D57

Norms (percent) 3

c

or____ __

ab_____

(

en _ ___ __ _

fs__. _________

wo _ __ __

hyfen __ _

\fs____________

mt_ _ _ _ _ __

hm _ _ ___ _ __

il ______________

ru___ ____

ap __

cc____ ___ ___

mg4 ___ _ ___ _

_________ 7.

0

_________ 13.

_________ 22.

_________ 26.

_________ 10.

_________ 11.

_________ 0

2.

_________ 0

_________ 1.

_________ 0

221

021

883

994

418

009

492

557

240

618

853

423

250

11. 467

. 635

18. 423

28. 084

15. 598

0

0

0

9. 268

1. 161

7.437

0

2. 674

0

1. 786

1. 052

0

47 094

1. 999

16. 043

32. 332

. 654

0

0

0

. 250

0

. 286

. 165

. 153

0

. 190

. 114

0

35. 180

3. 220

38. 732

17. 918

. 872

0

0

0

. 251

0

. 218

1. 059

. 460

0

. 358

. 321

0

60

5

28

1

0

0

0

0

0

0

096 _____

636 _____

555 _____

959 _____

352 _____

251 _____

429 _____

298 _____

229 _____

119 _____

114 _____

____ 26.656

____ 1.969

____ 44.973

____ 22. 031

____ 1. 449

____ 0

____ 0

____ 0

. 249

____ 0

1. 032

____ .490

. 323

____ 0

. 047

____ . 182

0

27. 926

2.426

49. 046

16. 923

0

0

0

0

. 296

0

0

1. 600

. 211

. 309

. 095

. 049

. 169

19. 125

1. 382

36. 810

35. 707

. 836

0

0

0

. 250

0

0

3. 315

. 212

. 602

. 357

. 206

0

13. 406

1. 633

3. 195

41. 001

0

0

0

0

. 206

0

0

3. 634

. 878

. 315

1. 195

1. 516

. 038

Total____________ 97.98 97. 59 99. 28 98. 59 98.04 _._____ 99.40 99. 05 98. 80 99. 02

1 Rapid rock analyses determined by means of methods described by Ward, Lakin, Canney, and others (1963), supplemented by atomic absorption methods. 

Analysts: P. L. D. Elmore, Samuel Botts, Lowell Artis, Gillison Chloe, II. Smith, and John Glenn.

2 Results are reported in percent to the nearest number in the series 1, 0.7, 0.5, 0.3, 0.2, 0.15, 0.1, and so on. which represent approximate midpoints of group data on a geometric scale. The assigned group for semiquantitative results includes the quantitative value about 30 percent of the time. Elements looked for but not found: Ag, As, Au, 

Bi, Cd, Eu, Ge, Hf, Hg, In, Li, Nd, Pd, Pr, Pt, Re, Sb, Sm, Sii, Ta, Te, Th, Tl, U, W, and Zn. Analysts: W. B. Crandell and J. L. Harris.

3 The chemical analyses of specimens 3, 4, 5, and 9 show a P2Os content that is so high relative to that of CaO that not all of it can be accommodated by normative apatite. Inasmuch as the reported values of these oxides are all low, amounts of PjCH of 0.35 percent (specimen 3), 0.2 percent (specimen 4), 0,3 percent (specimen 5), and 0.25 percent (specimen 9) are arbitrarily subtracted from the reported values; the subtracted values may be considered normative PzOs. The norms thus obtained are only slightly 

modified because the amounts of P2Os subtracted are sniall. In the rocks, small amounts of an undetected secondary mineral, such as wavellite or variscite, may be present.

4 Normative magnesite.

SPECIMEN DESCRIPTIONS

Altered andesite from upper flow of lower member, trachytic groundmass; NWMNW1^ sec. 33, T. 20 S., R. 15 E., unsurveyed.

Altered andesite from flow near top of lower member, ophitic groundmass; NEJiNW1^ sec. 4, T. 21 S., R. 15 E.

Altered rhyolite fragment of an autoclastic flow breccia from upper third of middle member, cryptocrystalline groundmass; SWJ^SWM sec. 21, T. 20 S., R. 15 E.,

unsurveyed.

Altered rhyolitic specimen from flow in lower third of middle member, groundmass layered, possibly vesicular; SE^SEVi sec. 29, T. 20 S., R. 15 E., unsurveyed. 

Altered rhyolite from friable laminated flow containing quartz pods and veinlets and lithic fragments; SWJ^SWJ^ sec. 3, T. 21 S., R. 15 E. 

Altered rhyodacitic vitrophyre from laminated and vesicular flow in unknown position in middle member; SWJ^SE^ sec. 35, T. 22 S., R. 15 E. 

Altered rhyodacitic vitrophyre from welded tuff from low in middle third of middle member; SEJ^SWk sec. 7, T. 20 S., R. 15 E., unsurveyed. 

Altered rhyolitic specimen from a strongly laminated probably vitric flow probably from middle member; NWJ4NWJ4 sec. 13, T. 20 S., R. 13 E. 

Altered dacitic specimen from flow, cryptocrystalline groundmass, from high in upper member; NWMNW'4 sec. 3, T. 20 S., R. 15 E., unsurveyed. 

Altered dacitic specimen from a flow with an hyalopilitic groundmass from high in upper member; NEMNW^ sec. 10, T. 20 S., R. 15 E., unsurveyed.

TABLE 3. Comparison of average analyses of the volcanics of the 

Mount Wrightson Formation with average analyses of Nockolds (1954, tables 1,2,3, 6)

NockAverage Nock- Average Nock- Nock- Average olds'

lower olds' middle old's olds' upper peralkamember andesite member alkali rhyoda- member line 

rhyolite cite trachyte

SlOz.. .....

AljOs-- -~-

FeO. .........

MgO. ......

CaO.....-.-.

NaiO. ....... .

KjO.. ...... ._

HjO-......__

H20+. ...,_..

Ti02._...-..._

Pj05 -------

MnO. ........

CO2 ._ ........

Total 

(rounded) .

52 6

15 9

6.5

4.4

4.1

5.7 3 n

2.6

.15 ..

2

1

1.4

.68

.23

.28 .-

100.00 -.

M 9n

17. '7

3 48

5 49

7 Q9

1.11

1 31

9ft

.15

75.9

12 9

9

1 3

.19ft

9 n

.23 --

1.0

22

.07

' 09

100.00 -.

74.57

10 EQ

1 O

1 02

.11

d

4 MO

.17

.07

.05

15 39 15 2

2 14 35

2 23 19

1 57 1

4. 13 4. 5

........ .23 ...

.66 .74

.17 .50

.07 .07

........ .38 .-.

17 99

1 SI

AK.

1 58

6 no

c on

CO

59

12

10.

Rita Mountains; these three mountain ranges are alined 

north west-southeast. In the southeastern part of the 

Sierrita Mountains, the Oxframe Formation of Lootens 

(1965) lies 12 miles to the northwest of the nearest

exposures of the Mount Wrightson Formation. Similar 

rocks underlie part of the Flux Canyon area in the 

north end of the Patagonia Mountains. (See southeast 

corner of Mount Wrightson topographic quadrangle 

map, U.S. Geological Survey, 1958; and Drewes, 

1971a). In the Sierrita Mountains area, some volcanics 

have been recognized by J. R. Cooper (oral commun., 

1963) and in the Patagonia Mountains by F. S. Simons 

(oral commun., 1968) as possibly early Mesozoic. My 

impression is that the lithologies of rhyodacitic to 

latitic flows and tuff breccias that contain intercalated 

quartzite lenses are sufficiently distinctive and unique to 

be correlated with the Mount Wrightson Formation. 

However, all the Mesozoic volcanics are considerably 

altered, and some of them change f acies rapidly within 

each area; therefore, applying one formation name to 

these rocks in both areas may be undesirable, despite 

the correlation suggested here. More detailed work on 

this problem is not apt to lead to the resolution of the 

problem because neither fossils nor unaltered minerals
SANTA RITA MOUNTAINS C17

suitable for direct isotopic dating, other than zircon, 

are likely to be obtained from these formations.

ENVIRONMENT OF DEPOSITION

The Mount Wrightson Formation is a continental 

sequence that was deposited almost entirely subaerially; it is the oldest continental sequence deposited 

after the final regression of the Paleozoic seas. Not 

only had the region around the Santa Rita Mountains 

emerged from the sea, but locally the relief was considerable, because some of the detrital components in 

the formation were derived from a Precambrian source 

rock which had been deeply buried beneath Paleozoic 

sediments. The northwestward alinement of faults and 

plutonic bodies of Mesozoic age indicates that a strong 

structural grain had already been established in the 

region. Block faulting is believed to have uplifted parts 

of the region sufficiently to enable erosion to remove the 

Paleozoic cover. The linear distribution of the bodies of 

Triassic volcanics is inferred to reflect an initial restriction of the thicker parts of the volcanic field to 

structural troughs between the postulated block-faulted 

ranges.

The lenses of sandstone and quartzite intercalated in 

the volcanics are probably eolian deposits. The strong 

resemblance of these deposits to some of the Triassic 

eolian deposits of the Colorado Plateau region may not 

be accidental; the well-sorted and rounded crossbedded 

sandstones of the two regions are partly contemporary, 

and their direction of deposition, to the southeast, also 

is alike. Furthermore, Hayes, Simons, and Raup (1965, 

p. M8) suggested that the source of the volcanic material in the fluviatile Upper Triassic Chinle Formation 

of northeastern Arizona may have been in southeastern 

Arizona. Although the intercalated eolian sandstone 

indicates at least a moderately arid climate, the pillow 

lavas were formed in some local ponds, and, conceivably, some streams could have flowed northward out 

of the region toward northeastern Arizona.

In the central part of the Mount Wrightson Formation of the Santa Rita Mountains, lava flows are 

strongly dominant over pyroclastic rocks, whereas 

pyroclastic rocks are more abundant to the northwest 

and southeast. This suggests that the volcanics of the 

Mount Wrightson area may have been deposited close 

to their volcanic vents.

GARDNER CANYON FORMATION

The Gardner Canyon Formation consists of a redbed sequence at least 1,000 feet thick that underlies 

several small areas in the northern part of the Santa 

Rita Mountains. These rocks have been considered to 

be part of a Cretaceous sequence since the orginal

mapping by Schrader (1915, pi. 2) but, as a result of 

more detailed study, they are now believed to be Triassic (Drewes, 1968, p. C7). In its type area near 

Gardner Canyon and Cave Creek, the formation consists of an underlying siltstone member and an overlying mudstone member, but this division is not recognized farther north wThere faulting and metamorphism 

are more intense.

DISTRIBUTION

The Gardner Canyon Formation underlies several 

small areas near the Cave Creek-Sawmill Canyon area 

(fig. 11) and several near Sycamore Canyon (Drewes, 

197lb). The combined extent of these areas is less than 

2 square miles. In the type area, the red beds form 

essentially three belts of outcrops, all lying within the 

Sawmill Canyon fault zone. The rocks of the three 

belts are progressively more broken up by the faults 

toward the northeast; details of their stratigraphy and 

facies thus come largely from the southwestern and 

central belts of red beds.

The southwestern belt of red beds extends from the 

gravel cover just south of Gardner Canyon northwestward about 21/2 miles. A fault bounds the northeastern 

edge of the belt and the northern half of its southwestern edge. Along the southern half of the southwestern 

edge east of Onyx Cave, however, the red beds rest 

unconformably on the Rainvalley Formation. Excellent exposures of the formation occur along the bottoms 

of Gardner Canyon, Cave Creek, and Sawmill Canyon, 

where these valleys cut across the red-bed belt, and also 

in the low hills midway between Cave Creek and Sawmill Canyon (fig. 11). Basically, this belt of red beds 

forms a northeastward-dipping structural wedge which 

contains fairly open folds to the south and tighter 

folds, as well as faults, to the northwest. Several small 

slivers of red beds closely associated the main southwestern belt of red beds have been faulted into the 

Permian limestone along the southwestern edge of 

the Sawmill Canyon fault zone for example, northwest of Onyx Cave.

The central belt of red beds lies between Cave of 

the Bells on the northwest and the eastern part of 

Cave Creek on the southeast. The contacts of the red 

beds of this outcrop belt are also largely faulted, but 

near the southwestern edge of the belt the red beds also 

lie unconformably on Permian rocks, here the Epitaph 

Dolomite. Basically, the rocks of this belt form another 

northeastward-dipping homoclinal structural block 

that is only moderately tightly folded toward the east. 

However, toward the northwestern end of this belt, 

where faulting was more intense, the red beds are
CIS MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

110°45'

1000 2000 3000 FEET

broken into several small slivers which are wedged 

between structural blocks of Paleozoic rock.

The red beds of the most fragmented northeastern 

outcrop belt follow the structural pattern of the other 

two belts. Several small fault slices of red beds lie 

between blocks of Paleozoic and Cretaceous rocks 

northwest and north of Gardner Kanch. Most contacts 

are faults, but the red beds of the largest structural

slice, which are largely covered by gravel, dip homoclinally northeastward and appear to lie unconformably on the Epitaph Dolomite.

Several deposits of red beds and associated phyllite, 

arkose, conglomerate, and tufiaceous sandstone believed 

to be part of the Gardner Canyon Formation occur in 

several areas along Sycamore Canyon near the north 

end of the mountains. The largest of these deposits lies
SANTA RITA MOUNTAINS C19

EXPLANATION

Piedmont and terrace deposits

Include sandstone, siltstone, and

Contact

Dotted where concealed

Fault

Dotted where concealed. Most faults in 

pre-Triassic rocks are omitted

c

A A /-d 

Breccia

c, channel deposit 

d, clastic dike

Anticline

Mudstone member

"fcgm, red mudstone; includes some conglomeratic siltstone beds near conglomerate 

(c)

c, conglomerate; includes some sandstone 

beds

v, volcanics; largely dacitic tuff and 

flows; may include some shallow intrusive bodies

b, breccia of volcanic rocks in red mudstone

Siltstone member 

Grayish-red siltstone; one limestone marker

bed forms top of member 

a, another limestone marker bed; lies near

the top of the member

Syncline

80 30 | 

Inclined Vertical Overturned 

Strike and dip of beds

.,.192 my

Collection site of radiometrically dated 

rock and age, in million years

A 

Collection site of plant fossils

Sedimentary rocks

Undifferentiated limestone, dolomite, and 

quartzite; commonly severely faulted

FIGXJEE 11. Gardner Canyon-Cave Creek area, showing the distribution and subdivisions of the Gardner Canyon Formation.

to the south of Johnson Ranch, near the mouth of the 

canyon, where it forms the basal part of a synclinally 

folded thrust plate. The southeast end of the klippe is 

faulted, and the rocks there are poorly exposed. Metasedimentary rocks that possibly are correlative with 

the Gardner Canyon Formation also crop out half a 

mile west to southwest of the ranch. A third body of 

phyllitic red beds that is believed to be Gardner Canyon Formation crops out a mile northeast of the ranch. 

It forms a separate thrust plate of steeply northeastward-dipping rock that overlies a plate of Permian 

rocks and underlies a plate of Glance Conglomerate.

Finally, along the road near the head of Wasp Canyon (Drewes, 197lb), about midway between the two 

main groups of outcrops of the Gardner Canyon Formation, a thin sheet of red beds is in thrust contact

with a plate of Permian rocks below and a plate of 

Glance Conglomerate above. Although the rocks of this 

sheet are not metamorphosed, the exposed sequence is 

sufficiently small and undiagnostic that it cannot be 

distinguished with certainty from some beds of the 

Bisbee Group; only by association with the structure 

northeast of Johnson Eanch does the correlation of 

these red beds with the Gardner Canyon become reasonable.

LITHOLOGY AND PETROGRAPHY

SILTSTONE MEMBER

The siltstone member is about 200 feet thick and is 

typically a grayish-red massive or faintly bedded siltstone. Its basal contact, an unconformity, is exposed 

only locally near the mouth of the Sawmill Canyon in

404-482 O - 71 - 4
C20 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

the Mount Wrightson quadrangle, about 2,000 feet west 

of Gardner Eanch where the basal siltstone is draped 

around blocks of dolomite of the Permian Epitaph 

Dolomite. The siltstone member contrasts subtly with 

the upper member in that the siltstone member is 

coarser grained and more resistant to weathering; it 

also contains two limestone marker beds. The top of the 

upper marker bed is taken as the top of the member; 

this position coincides roughly with the top of the zone 

of gradual upward transition from siltstone to mudstone.

The siltstone is fairly uniform in composition, but 

locally it does vary in color and grain size. The chief 

variant is a rock along the lower mile of Sawmill Canyon that is a light-gray to pale-yellowish-brown finegrained sandstone. At the base of the member (fig. 11) 

there are two lenses of quartzite breccia, each about 10 

feet thick and 50 feet long. These lenses fill channels 

perhaps two sections of the same channel cut into the 

underlying Permian rocks. The quartzite blocks were 

probably derived from the Scherrer Formation, which 

locally had been eroded before Gardner Canyon time. 

In a few places, the lower part of the siltstone member 

also contains small cobbles of light-gray finely crystalline limestone, which probably are stray clasts derived 

from the Paleozoic terrane on which and against which 

the siltstone was deposited. Elsewhere the member also 

contains nodules and pods of limy siltstone at least 

1 inch long, like those that occur in other red-bed units 

of Mesozoic age.

In thin section a fine-grained sandstone of this member is seen to consist largely of poorly sorted angular 

grains about 1 mm in diameter. Modal analysis of the 

sandstone is as follows:

Mineral

Quartz. _______

Plagioclase_ ____

Rock fragments

Percentage

20

20

20

10

20

10

1

1

________________________

Clay minerals ___________________________

Iron oxides ____________________________

Calcite cement. _________________________

Muscovite- _ _ _________________________

Chert grains.- __ ______________________ Trace

Magnetite. _____________________________ Trace

Zircon, _ _____________________________ Trace

Apatite inclusion. ______________________ Trace

Tourmaline_ ___________________________ Trace

The lower limestone marker bed is generally about 5 

feet thick, and it commonly is composed of a lower, 

slightly reddish light-gray silty limestone and an upper, light-gray crystalline limestone. Both limestones 

resemble some of the underlying Paleozoic rocks. Bedding is indistinct or absent, and the dominant sedimentary feature is usually a bouldery or hummocky 

surface on the reddish light-gray limestone. Some zones 

of limestone sedimentary breccia, conglomerate, or pods 

occur in a red silty and limy matrix. Small chert chips 

are scattered through this limestone. South of Cave 

Creek, the lower limestone marker bed is entirely reddish gray but is distinctly of a shade lighter than that 

of the upper member.

The upper limestone marker bed lies 10-50 feet above 

the lower one and is typically about 10 feet thick, although locally it is twice that thick. This limestone is 

distinguishable from the lower limestone marker and 

from the Paleozoic limestones by the combination of 

its dark-gray color, its laminations, and its mediumcoarse-grained bioclastic texture. Fresh surfaces have a 

faint fetid odor. In a few places, this dark-gray limestone conformably overlies the hummocky top of a 

lighter gray bed of algal (?) limestone. South of Cave 

Creek, the laminations are inconspicuous but the dark 

color persists. Several samples of these limestones have 

been checked, in vain, for fossil pollen.

MUDSTONE MEMBER

The mudstone member of the Gardner Canyon Formation is at least 1,000 feet thick and conformably 

overlies the siltstone member. The lower 300-400 feet 

consists of moderate-red to pale-reddish-brown massive 

or very poorly bedded mudstone. The basal few tens 

of feet of this unit contains some fine-grained siltstone 

in transition from the underlying member; a few siltstone beds which are intercalated throughout the mudstone, provide indistinct bedding, as shown in figure 

12. A few thin zones in the mudstone contain limy 

pockets or blebs rarely as much as 1 inch across (fig. 

13) and crudely developed limy nodules a few inches 

across (fig. 14). These limy zones are believed to be 

lithified old caliche zones. High in the mudstone unit, 

there are also a few inconspicuous thin beds of arkosic 

sandstone.

About midway between Cave of the Bells and 

Gardner Eanch, and 20 feet above the base of the member, there is a small lens of fossiliferous shale. The lens 

is only 1 foot thick and about 10 feet long; it crops out 

just downslope from an old road grade (fig. 11), which 

locally on the topographic map of the Mount Wrightson quadrangle has been placed too far east. The rock is 

a fetid coaly shale to carbonaceous limestone which 

contains chips of coal and fragments of plants that 

resemble reeds. The material collected at and near the 

surface, however, contained no identifiable material, 

including pollen.

The mudstone member also includes some conglomerate and conglomeratic sandstone, the lowest occurrences
SANTA RITA MOUNTAINS C21

FIGURE 12. Typical outcrop of the mudstone member of the Gardner Canyon Formation, along Cave Creek near Gardner

Ranch. Yucca stalk in center of outcrop is about 10 feet long.

of which are generally 300-400 feet above the base of 

the member. These materials make up about 5 percent 

of the rock of the southwestern structural slice, as much 

as 15 percent of the central slice, but less than 1 percent 

of the northeastern slice (fig. 11). In the southwestern 

structural slice, north of Cave Creek, the lowest conglomerate unit is fairly extensive; but higher ones 

form lenses, commonly 10-20 feet thick and in one 

place more than 100 feet thick, and probably are channel deposits. In the northern part of the central structural slice, conglomeratic sandstone first appears about 

350 feet above the base of the member, but in the southern half of that slice it appears about 100 feet lower. 

In the southern half of the central structural slice, 

pebbles, instead of occurring in lenticular channel 

conglomerates, are more widely scattered, and there are 

only a few distinct conglomerate beds, such as the 

marker bed near Gardner Ranch (fig. 11). The clasts 

of many conglomerates are well-rounded pebbles of 

limestone, chert, and quartzite, all derived from the 

Paleozoic rocks. A few beds also contain pebbles and

small cobbles of subrounded intensely indurated laminated volcanics derived from the Mount Wrightson 

Formation.

Volcano-clastic material makes up some of the coarsegrained beds in the mudstone member. Cobbles and 

blocks of the dacitic volcanics, like those interbedded 

with the red beds, constitute small lenses in the mudstoiie member. These sedimentary volcanic breccias 

usually lie near their sources and wedge out rapidly 

away from the flows. Fairly high in the mudsone member, near the stratigraphic position at which some tuff 

appears, tuffaceous sandstone and conglomerate and 

arkosic sandstone beds are more abundant than the red 

mudstone, and the formation is faintly varicolored 

rather than uniformly red, and the outcrops are larger. 

The few thin conglomerate beds in the northeastern 

structural slice are chert- and quartzite-pebble beds, 

and, as they are associated with a little tuff, they probably belong high in the mudstone member.

A small granite-pebble dike intrudes the lower part 

of the red mudstone about 700 feet east of Onyx Cave.
C22 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

FIGUEE 13. Small limestone pockets and blebs in the mudstone member of the Gardner Canyon Formation, cropping out along

Cave Creek near Gardner Ranch. Bedding dips gently to the left.

Two blocks of Paleozoic limestone, the largest about 

15 feet thick and more than 50 feet long, are intercalated in the red beds of the northeastern structural slice. 

One of them lies near the faulted contact with the 

Paleozoic rocks, and the other is several hundred feet 

higher stratigraphically. These blocks may have 

slumped or slid onto the red mud from an adjacent 

high area before the consolidation of the mud; thus, 

in a modest way, they resemble some of the exotic 

blocks described by Raup (in Simons and others, 1966, 

p. D14-D16) in the red beds in the Canelo Hills 6-10 

miles to the southeast.

Small lenses of faintly purplish gray dacitic porphyry volcanics appear in about a dozen places in the 

middle and upper parts of the mudstone member of 

the Gardner Canyon Formation. The largest body of 

volcanics lies 1,000 feet northeast of Onyx Cave, and 

others are exposed in the canyon bekw Gardner Ranch 

and on a hill between Cave Creek and Gardner Canyon, 

about 2,000 feet southwest of the Gardner Ranch. Most 

of the volcanic bodies are roughly lenticular and lie

parallel to at least the underlying bedding, and surrounding mudstone beds apparently lap against the 

volcanics rather than are truncated by the volcanics. 

Volcanic breccias near some of the volcanic bodies are 

noteworthy in that the volcanic fragments are scattered 

in a red mudstone matrix in such a w^ay that they 

rarely are in contact with each other. Apparently these 

breccias are colluvial rather than fluvial deposits. The 

volcanic breccia in the canyon below Gardner Ranch 

contains abundant fragments of vesicular rock. Very 

light gray tuff overlies a relatively dark gray flow on 

the hill southwest of the ranch, and other small bodies 

of tuff appear north of Cave Creek.

A typical dacitic rock that is associated wT ith the 

mudstone member is shown in figure 15. The abundance of small phenocrysts, and especially of bronzy 

biotite, is a common feature. Likewise, the scarcity or 

absence of quartz distinguishes this rock from the more 

rhyolitic tuff of the overlying Canelo Hills(?) Volcanics.
SANTA RITA MOUNTAINS C23

FIGURE 14. Crudely developed limestone nodules in red mudstone of the mudstone member of the Gardner Canyon Formation,

cropping out along Cave Creek near Gardner Ranch.

Thiii sections available from six volcanic bodies indicate that tuffaceous rocks are the most abundant, because several specimens of rocks not showing a macroscopic fragmental texture do have a very fine grained 

fragmental texture and contain relict shards. Most of 

the tuffs and flows or shallow intrusives are petrographically alike; they are dacitic rocks that contain 

5-20 percent phenocrysts which are commonly %-A mm 

long and are set in a cryptocrystalline matrix. The 

largest crystals always include xenocrystic quartz, 

phenocrystic albitized plagioclase, and altered biotite, 

each constituting 2-3 percent of the rocks. In some 

rocks, the largest crystals also include potassium feldspar and altered amphibole. The relatively dark flow 

rock from the hill southwest of the Gardner Ranch contains a few percent of relict augite(?) in addition to 

the other ferromagnesian minerals. Accessory minerals 

include traces of apatite, magnetite, and zircon, which 

is relatively abundant in two specimens. Alteration 

minerals are abundant; ferromagnesian minerals are 

replaced by sericite and iron oxides, feldspars are 

changed to clay minerals, and a few rocks also contain 

a little chlorite. The intensity of alteration has discouraged extensive petrographic and chemical study of these

rocks; but as a whole, the rocks resemble other volcanics of the Santa Rita Mountains, many of which 

are less altered and are classified as rhyodacites, quartz 

latites, or dacites a large family of rocks here included in the term "dacitic" volcanics (fig. 16).

The volcanics are believed to be nearly contemporaneous with the red beds; they are largely extrusive rocks 

but may include some rocks that intruded the once 

unconsolidated deposits near the surface. This contemporaneity is indicated by the abundance of tuffs and 

especially by the presence in the conglomerates of 

dacitic prophyries identical with those in the adjacent 

volcanics. Although the volcanic breccias also appear 

to have formed at the surface, some of them alternatively may have been formed by an injection of fluid mud 

into the edges of flows or sills. The breccia of vesicular 

dacite near the Gardner Ranch likewise appears to be 

of sedimentary rather than of intrusive origin.

The slightly metamorphosed plate of rocks southeast 

of Johnson Ranch that is assigned to the Gardner Canyon Formation consists of a clastic sequence. Its base is 

faulted, and its top is arbitrarily placed at the top of 

a thin calc-silicate bed. This upper contact with the 

Canelo Hills(?) Volcanics is selected because lime-
C24 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

ft.

2 cm

FIGURE 15. Specimen of a dacitic flow(?) associated with 

the mudstone member of the Gardner Canyon Formation, 

obtained from about 1,000 feet northeast of Onyx Cave in 

the Cave Creek area. A zircon concentrate from this rock 

gives a calculated age of 192 m.y.

stones are known in the Gardner Canyon but not in 

Canelo Hills (?) Volcanics and because the tuff of the 

overlying rocks resembles the rhyolitic tuff in the 

Canelo Hills (?) more than it does the dacitic tuff in 

the Gardner Canyon Formation. The stratigraphic 

sequence on the north limb of the syncline southeast 

of Johnson Ranch is:

Unit Minimum 

thickness 

(feet)

Calc-silicate rock_______________________ 5

Brown hornfelsed siltstone_______________ 60

Blue-gray phyllitic siltstone______________ 40

Brown arkose and conglomerate hornfels_ 70

Blue-gray phyllitic siltstone_ _____________ 100

Arkosic sandstone__ ___________________ 100

Light-gray phyllite____________________ 80

Arkosic sandstone_____________________ 80

Arkosic conglomerate__ ________________ 5

Arkosic sandstone_____________________ 90

Total. 630

Of these units, at least the two phyllitic ones were 

probably red beds, because, despite their dominant 

color, some patches retain a reddish cast. The sequence 

on the south limb is much attenuated, and all but the 

highest units are sheared out. The sequence northeast 

of Johnson Ranch, about 500 feet thick, is largely of 

phyllite, which presumably was also a red-bed unit.

^^ii^f®

,^-v- .

FIGURE 16. Photomicrograph of a dacitic flow(?) (fig. 15) intercalated in the mudstone member of the Gardner Canyon 

Formation. White tabular crystals are altered plagioclase; 

dark-rimmed lozenge-shaped crystal is a pseudomorph of 

chlorite and iron oxide after amphibole; and dark tabular 

crystals are similar pseudomorphs after biotite.

AGE AND CORRELATION

The Gardner Canyon Formation is younger than 

the Mount Wrightson Formation of Triassic age, whose 

pebbles it contains. The Gardner Canyon is believed to 

be equivalent either to the rocks at the base of the type 

Canelo Hills Volcanics of Jurassic and Triassic age or 

to the rocks immediately beneath it. The available fossils are undiagnostic, but the volcanics interbedded in 

the mudstone member northeast of Onyx Cave are 

dated isotopically. A zircon concentrate yielded a leadalpha age calculated at 192 m.y. and presented as 

190 ±20 m.y. by T. W. Stern (Drewes, 1968, p. CT). 

Provisionally, then, this formation is assigned to the 

Triassic.

Rocks of similar lithology have been identified in 

several adjacent ranges. The red beds and conglomerate 

low in the Canelo Hills Volcanics (Feth, 1948; Hayes 

and others, 1965, p. M3), as mapped in the Canelo Hills
SANTA RITA MOUNTAINS 25

and Mustang Mountains (Hayes and Raup, 1968), are 

probably equivalent to the upper part of the Gardner 

Canyon Formation. The slightly metamorphosed red 

beds, conglomerate, arkose, and some rhyodacite volcanics that were mapped by Finnell (1970) in the 

Empire Mountains and similar red beds and volcanics 

of Rodolfo Wash that were mapped by Cooper (1970) 

in the Sierrita Mountains are probably also correlative 

with the Gardner Canyon Formation. The Recreation 

Redbeds of the Tucson Mountains, described by Brown 

(1939) and Kinnison (1958), may be correlative with 

the Gardner Canyon Formation. These relations are 

discussed in greater detail by Hayes and Drewes (1968, 

p. 51-54).

ENVIRONMENT OF DEPOSITION

During Gardner Canyon time, perhaps late in the 

Triassic, the Gardner Canyon area appears to have 

consisted of at least one basin into which detritus from 

the adjacent volcanic, granitic, and limestone hills was 

deposited. The presence of rather fine grained conglomerates and subrounded chert and volcanic pebbles 

suggests that the local relief was IOWT , and possibly 

recycling of detritus produced the roimdness of hard 

rock types that apparently are of local origin. These 

deposits, then, filled their old channels and ultimately 

buried the Paleozoic terrane. Early during Gardner 

Canyon time, the basin was closed at least twice; these 

closures resulted in shallow lakes, whose chief forms 

of life may have been algal. Reeds flourished at least 

locally along the shore. Fluvial silt and mud filled the 

lakes as the center of deposition shifted elsewhere. The 

streams again carried detritus of older rocks from the 

surrounding hills as well as volcanic detritus from a 

new and more local source. At first, the volcanics appear to have been ejected on, and possibly injected into, 

the sediments along the already established Sawmill 

Canyon fault zone; but toward the close of this time, 

the volcanics were spread more widely, and tuffaceous 

components were reworked and incorporated into rocks 

of the upper part of Gardner Canyon Formation.

CANELO HILLS (?) VOLCANICS

Arkose, tuffaceous sandstone, tuff, and conglomerate, 

together more than 600 feet thick, occur in a small 

area near the north end of the Santa Rita Mountains. 

These rocks are mildly metamorphosed and poorly exposed. They form the upper part, of a thrust plate and 

lie with apparent conformity upon rocks which are 

correlated with the Gardner Canyon Formation and 

which make up the lower part of that thrust plate 

(Drewes, 197Ib). The tuffs associated with this sequence are rhyolitic rather than dacitic, and thus they 

are tentatively assigned to the Canelo Hills Volcanics,

which is the next younger formation, rather than to the 

Gardner Canyon itself.

The rocks here considered as possible correlatives of 

the Canelo Hills Volcanics crop out on the low hills 

along the road about ^-l1/^ miles southeast of Johnson 

Ranch near the mouth of Sycamore Canyon. The low 

north-trending spur which reaches the jeep road just 

east of the northernmost group of prospects (Drewes, 

1971b) provides the best local section in this formation. 

These rocks overlie the Gardner Canyon Formation to 

the north and west and are presumed to overlie them 

also to the south. Large remnants of terrace gravel 

cover the central part of the outcrop area. The northwestern part of these rocks clearly forms an asymmetric southeastward-plunging syncline.

The sequence exposed along the north-trending spur, 

in rising order, is composed of about 180 feet of brown 

arkosic conglomerate and sandstone, 15 feet of rhyolitic 

tuff, about 200 feet of volcanic and arkosic conglomerate, 0-15 feet of quartzite, and at least 250 feet of 

arkosic and tuffaceous sandstone. The tuff is a crystallithic tuff that contains fragments of quartz and potassium feldspar and some pseudomorphs after fragments 

of biotite (?) and plagioclase. Quartzose siltstone and 

impure sandstone chips are scattered, together with the 

crystal fragments, in a much-altered cryptocrystalline 

weakly laminated groundmass. The quartzite forms 

beds 4-12 inches thick in which there are some finer 

laminations. The rock is light gray but weathers brownish gray, and it is medium coarse grained.

The age of these rocks is presumed to be Triassic and 

Jurassic by correlation of these rocks with the Canelo 

Hills Volcanics. This age range is sufficiently broad to 

allow for the uncertainties of correlation as well as 

for the uncertainty of age assignment of the type 

Canelo Hills Volcanics. A tuff within them has been 

dated isotopically as 173 ±7 m.y. old by S. C. Creasey 

(in Hayes and others, 1965, p. 1965, p. M7), but the age 

range of the formation is thought to be large. Apparently, the dacitic volcanism that began during 

Gardner Canyon time continued with greater frequency 

and had a more rhyolitic composition from about Late 

Triassic time into the Early Jurassic. This volcanic 

activity may have been an early near-surface magmatic 

phenomenon that culminated with the intrusion of a 

large granite stock during the Jurassic.

SUB-CRETACEOUS UNCONFORMITY

Cretaceous sedimentary and volcanic rocks are separated from Jurassic or older rocks by a major unconformity, along which the relations vary from place to 

place. In a few places, such as along the lower reaches 

of Temporal Gulch (bottom of fig. 18), this uncon-
C26 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

formity is marked by a pronounced angular discordance. Along the middle reaches of Josephine Canyon 

(Drewes, 19Tla) and north of Johnson Spring (fig. 

18), Cretaceous strata lie across truncated coarsegrained Jurassic, Triassic, and Preoambrian plutonic 

rocks. Near the mouth of Mansfield Canyon, Cretaceous 

beds lie with apparent conformity on Triassic beds. 

Thus, both the age of the underlying rock and the 

degree of angularity vary along the unconformity.

The age of the rocks directly above the sub-Cretaceous unconformity also varies from place to place in 

the Santa Rita Mountains. Along the southeast flank of 

the mountains, the oldest Cretaceous rocks overlie the 

niiconformity. In the Box Canyon area, the upper 

Lower Cretaceous rocks occupy this position, whereas 

along the southwestern flank of the mountains the upper Upper Cretaceous rocks are the oldest ones above 

the unconformity. Indeed, from place to place various 

members of this upper Upper Cretaceous formation 

occupy the basal position.

The complex variety of relations along the sub-Cretaceous unconformity suggests that the unconformity is 

composite, in the sense that it is the result of several 

episodes of erosion whose effects are separable in some 

places but are combined in others. The stratigraphic 

record of the Cretaceous rocks also bears out the idea 

that this major unconformity was composite. The pertinent features are the intercalated wedges of coarse 

conglomerate and the minor intraformational unconformities. Because the component parts of the composite unconformity are most intimately associated 

with the rocks that overlie them, they will be described 

with the overlying rocks. The combined records of the 

composite unconformity will demonstrate that the area 

had a rugged relief at recurrent intervals before and 

during the Cretaceous Period.

CRETACEOUS STRATIGRAPHY

The Cretaceous formations, in rising order, are the 

Temporal and Bathtub Formations, the sequence of 

Glance Conglomerate, Willow Canyon, Apache Canyon, Shellenberger Canyon, and Turney Ranch Formations of the Bisbee Group, and the Fort Crittenden and 

Salero Formations.

In contrast to the older Mesozoic deposits of the 

Santa Rita Mountains, these formations, as a whole, 

are doniinantly sedimentary. Volcanic elements are 

most abundant in the oldest and the youngest formations but are virtually absent, except as clasts, from the 

thick units of the middle of the Cretaceous sequence. 

Although the Cretaceous rocks reflect a continental

environment, they were largely deposited in broader, 

shallower basins than were the earlier Mesozoic rocks. 

This contrast in modes of deposition is most pronounced with the brief incursion of an arm of the continental sea during at least part of Apache Canyon 

time.

PRE-BISBEE ROCKS 

TEMPORAL FORMATION

A formation of mixed rhyolitic to andesitic volcanic 

rock and sedimentary rock, 1,000-2,000 feet thick, occurs in a long area low on the east flank of the Santa 

Rita Mountains. These rocks lie with pronounced URconformity upon rock as young as the Squaw Gulch 

Granite, of Jurassic age, and they are unconformably 

overlain by another volcano-sedimentary formation, 

which in turn is overlain by the Bisbee Group, of laite 

Early Cretaceous age. These volcanic and sedimentary 

rocks were mapped as Tertiary aiidesite by Schrader 

(1915, pi. 2) and as Cretaceous andesite by W. R. Jones, 

C. G. Bowles, and D. C. Hedlund, as reported by 

Wilson, Moore, and O'Haire (1960). As the result of 

more recent and more detailed work, their geologic 

relations indicate that they are Early Cretaceous, and 

they were named the Temporal Formation (Drewes, 

1968, p. C8).

DISTRIBUTION

The Temporal Formation forms an outcrop belt 

about 10 miles long that extends from 1 mile west of 

Patagonia northward to Cave Creek. The formation is 

easily accessible along the Temporal Gulch road, near 

the head of the road up Gardner Canyon, and near the 

mouth of Temporal Gulch. It is commonly well exposed 

because of the sparsity of vegetation on the lower part 

of the mountain flank and beause of the moderate dips 

and alternating weak and resistant lithology of the 

rock. As a result, the stratigraphic relations and facies 

variations within the formation are clear and are 

mapped in considerable detail (Drewes, 197la).

The rocks in this outcrop belt form a homoclinal 

sequence, which dips 20°-30° eastward. They are usually unfaulted or only very slightly faulted; however, 

toward both ends of the belt the rocks are more abundantly, but not complexly, faulted.

The Temporal Formation underlies a relatively 

gentle terrain which contains small ridges, knolls, and 

gullies. The more resistant rocks, such as lava flows 

and welded or indurated tuff, form alined ledges and 

steep slopes, whereas many of the less resistant rocks, 

such as the tuffs, are stripped bare of their colluvial 

cover. Figure 17 shows a typical area underlain by the 

Temporal Formation.
SANTA RITA MOUNTAINS C27

FIGURE 17. Typical terrain underlain by the Temporal Formation. View north-northwest from about 1,000 feet east of the 

junction of Mansfield Canyon and Temporal Gulch toward 

Mount Wrightson, the distant skyline peak. The knoll in the 

middle distance, center, is capped by rhyolite tuff of the 

middle member of the Bathtub Formation, dipping east. The

west slope of that knoll and the tuffaceous sandstone in the 

foreground are of the middle member of the Temporal Formation. The two nearly horizontal lines of trees in the foreground lie along normal faults which bound a small horst. 

Slightly mineralized quartz veins, here marked by prospects, 

follow the faults.

BASAL UNCONFORMITY

The unconformity at the base of the Temporal Formation is well exposed and shows a highly varied preTemporal paleotopography. North of Gardner Canyon, 

the Temporal Formation cuts gradually across the underlying rocks of the upper member of the Mount 

Wrightson (Drewes, 197la), which, together with the 

slight divergence of attitudes across the contact, indicates that it is an angular unconformity. From Gardner 

Canyon south to Mansfield Canyon, the two formations 

appear to be conformable, and the sub-Temporal surface is very regular. For the first few^ miles south of 

Mansfield Canyon (upper half of fig. 18), the surface 

is a disconformity. Several small hills and a small 

valley wwe cut on the older rocks and were filled with 

the deposits of the Temporal Formation. In figure 18, 

the marker horizon is seen to lap., against these hills. 

The rocks adjacent to the old surface are virtually 

parallel, although bedding in the nearby part of the

Mount Wrightson Formation is obscure. Locally then, 

the surface is a disconformity. Still farther south, at 

Johnson Spring (lower half of fig. 18) the trace of the 

pre-Temporal surface swings widely to the west into a 

granite terrane and abruptly returns to a position of 

alinement with the trace to the north. The basal rocks 

of the Temporal Formation lap against the underlying 

granite and consist of volcanic rocks and arkosic fanglomerate, which interfinger along the lower marker 

horizon shown in the figure. Just south of Johnson 

Spring, there are remnants of upended Mount Wrightson Formation lying alongside the granite, upon both 

of which the Temporal rocks w^ere deposited with a 

strong angular unconformity.

The sub-Temporal surface is interpreted to be a highly irregular old land surface. Part of it w^as a plain and 

part was hills and valleys. The deepest valley, exposed 

in oblique section near Johnson Spring as a result of 

an eastward tilting of about 30° in post-Temporal time,

404-482 O - 71 - 5
C28 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

EXPLANATION

Undifferentiated younger rocks 

Include intrusive rocks and piedmont gravel

Temporal Formation 

Ktm, middle member 

Ktl, lower member

a, marker horizon at base of conglomerate unit

b, marker horizon; conglomerate facies 

to south and volcanic facies to north

Mount Wrightson Formation

Contact

Fault 

Dotted where concealed

Inclined Vertical 

Strike and dip of beds

H C 

Hill Canyon 

Paleographic features

FIGUKE 18. Temporal Gulch area, showing that part of the sub-Temporal unconformity indicative of a rugged

topography.

was about 800 feet deep. The paleotopography in preTemporal time appears to have been comparable to the 

present topography. Mansfield Canyon is a deep V-- 

shaped valley comparable to the deep paleocanyon, and 

along the flanks of the Santa Kita Mountains there are 

some little-dissected surfaces like the surface recorded 

along the unconformity north of Mansfield Canyon. 

The angular discordance across the unconformity seems 

restricted to the extreme north and south and thus suggests that structural tilting in pre-Temporal time was 

localized.

LITHOLOGY AND PETROGRAPHY

Three stratigraphic subdivisions of the Temporal 

are mapped as upper, middle, and lower members.

These members are separated chiefly by conglomerate 

marker beds. Because of the rapid lateral variation of 

thickness and facies, no more than two of these members are present in any stratigraphic section across the 

formation. At any one given place, the formation as a 

whole typically is 1,000-2,000 feet thick; a composite 

maximum thickness of the individual members, however, is about 3,800 feet. In general, the middle member 

is restricted to the southern half of the outcrop belt 

and the upper member to the northern half. Near the 

center of the belt, both the middle member and the 

lower member are lateral equivalents of a pile of volcanics which remains undivided. Thus, in addition to 

the three members, a unit of lower and middle member 

undivided is also described.
SANTA RITA MOUNTAINS C29

LOWER MEMBER

The lower member of the Temporal Formation is 

recognized over a distance of about 5y2 miles, approximately between the junctions of Mansfield Canyon and 

Gringo Gulch with Temporal Gulch (Drewes, 1971a). 

It is 200-1,300 feet thick, a range of thickness reflecting 

various amounts of fill on the rugged relief of the underlying unconformity. The member has been further 

subdivided into more than a dozen lithologic units 

which intercalate or intertongue with each other (fig. 

19). In general, the member consists, in ascending 

order, of volcanics, epiclastic rocks, and more volcanics.

The basal volcanic unit consists of rhyolitic to dacitic 

pyroclastic rocks. Dacitic volcanic breccia fills the bottom of the paleocanyon near Johnson Spring, rises to 

about 900 feet on the north side of the paleocanyon and 

laps over some of the rocks deposited on the north 

shoulder, and, on the south side of the canyon, beginning 350 feet above the base of unit, intertongues with 

fanglomerate adjacent to the south wall. The dacitic 

breccia is a bluish-gray unbedded rock with fragments 

rarely more than a f ewT inches across that are strongly 

argillized.

A sheet of rhyolitic tuff breccia lies along the base

of the low^er member north of the large paleocanyon 

(fig. 19). Commonly, it is 80-100 feet thick, but locally 

it fills a shallower paleocanyon to a depth of 200 feet. 

A little tuffaceous sandstone, which is too thin to be 

mapped, appears at the base of the formation west of 

the ranch and is the northernmost remnant of this unit. 

Likewise, a thin tongue of rhyolitic tuff, which is interbedded in the fanglomerate along the south wall of 

the large paleocanyon at the stratigraphic level of the 

rhyolite to the north of that canyon, is the southernmost occurrence of this unit. The rhyolitic tuff breccia 

is a very pale orange to grayish-orange poorly indurated or "punky" rock in most places, but over a distance of about half a mile on the north side of the 

paleocanyon it is welded to a light-gray crystal-lithic 

tuff which contains alined porous inclusions commonly 

about i/^-l inch long. Comparison with similar features 

in less altered rocks indicates that the inclusions are 

flattened pumice chips in a welded tuff.

In thin section, lithic f ramments are seen to be about 

as abundant as crystal fragments, which consist of 

quartz, sericite pseudomorphs after biotite, magnetite, 

apatite, and zircon in sufficient abundance to be readily 

concentrated for isotopic dating. An intense clay-minISIORTH SOUTH

Basin(?) EXPLANATION

Volcanic 

breccia

Sandstone

Andesite-dacite

* * » 1

1 ~ 1

'=axnnnx» XXX

Volcanic 

breccia

Tuffaceous 

rock

Flows Welded 

tuff

Member boundary 

Contact

Unconformity

*180

Collection site of isotopically dated specimen 

and age, in million years

FEET

i- 0

L1000

VERTICAL EXAGGERATION 

ABOUT X5

Rhyolite-latite-rhyodacite

2 MILES

Conglomerate-fanglomerate

FIGURE 19, Stratigraphic and facies diagram of the Temporal Formation. Datum is top of Temporal Formation, modified to show 

greatest post-Temporal erosion and volcanic pile of possible late Temporal age.
C30 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

eral alteration has almost obliterated the textural details of a cryptocrystalline groundmass, which seems 

to consist of plagioclase, a potassium feldspar, and 

quartz.

The clastic rocks of the middle units of the lower 

member of the Temporal Formation consist of conglomerate and sandstone, which extend for 4 miles and 

are interrupted only by two small hills on the subTemporal unconformity. To the north where the clastic 

rock is at the base of the formation, it is a dark-reddishbrown polymictic conglomerate which contains boulders 

of porphyritic dacite, andesite, and rhyolite, as well 

as of diorite(?), granite, and aplite; all of these 

boulders could have been derived from within a distance of a few miles to the west. The source of the 

diorite (?) is least certain; it may have been derived 

from the Triassic (?) diorites that appear to the northwest (Drewes, 197la) or from a dioritic rock included 

in, or intruded into, the Squaw Gulch Granite near 

Johnson Spring. The matrix of the conglomerate 

is sandy to the north but more tuffaceous southward; 

about 1 mile south of the ranch, the conglomerate 

grades laterally into a dacitic conglomerate and sandstone facies, which thickens to about 300 feet above 

the welded tuff. On the north flank of the large paleocanyon, these volcanic sediments grade into the top of 

the dacite breccia that fills much of the canyon, and 

they also are correlative with some of the fanglomerate 

tongues that are interbedded with the dacite volcanic 

breccia (fig. 19).

Near the junction of Gringo Gulch and Temporal 

Gulch, fanglomerate is the dominant rock throughout 

the lower member of the Temporal Formation. It 

intertongues with each of the three subdivisions of the 

lower member, and its largest tongues may actually be 

parts of the conglomerate sheets that are mapped as 

separate units in the middle of the lower member and 

at the base of the middle member. Fanglomerate near 

the granite on the south flank of the large paleocanyon 

is a sedimentary breccia of very local origin, because 

most clasts are granite detritus and some are the diorite(?), similar to rock appearing in the adjacent 

Jurassic granite. Farther from the south wall of the 

paleocanyon, arkosic sandstone and gritty conglomerate 

alternate with fanglomerate. Fragments of volcanic 

rocks are admixed in the arkosic fanglomerate of a 

few lenses, especially near the volcanic tongues. South 

of the Gringo Gulch junction, a basal unit of tuffaceous 

sandstone is probably correlative with the clastic rocks 

in the paleocanyon, because the southern end of this 

sandstone lens is conglomeratic.

A rhyolitic tuff 100-600 feet thick forms the upper 

unit of the lower member of the Temporal Formation.

It extends from the mouth of Mansfield Canyon southward almost to the mouth of Gringo Gulch, and in two 

places near the ranch where the underlying unconformity forms ancient hills, the tuff is the only unit of the 

lower member. To the north, the rock is typically a 

poorly indurated, "punky," very pale orange to pinkish-gray or yellowish-gray thickly bedded tuff and 

fine-grained tuff breccia. A more indurated coarsely 

blocky tuff breccia or agglomerate sheet, as much as 

400 feet thick, overlies the tuff to the southeast and is 

the only facies present to the southwest. In the absence 

of petrographic or chemical analyses of these pyroclastic rocks, they are considered to be rhyolitic, in the 

sense that their actual composition probably falls in 

the range of rhyolite-latite-rhyodacite.

MIDDLE MEMBER

The middle member of the Temporal Formation is 

commonly 100-400 feet thick and is almost coextensive 

with the lower member, reaching from half a mile 

north of the mouth of Mansfield Canyon to more than 

half a mile south of the mouth of Gringo Gulch. The 

member is subdivided on the map (Drewes, 197la) and 

in figure 19 into lower clastic units, an upper rhyolitic 

tuff, and, to the south, porphyritic latite flows which 

occur as a lens occupying about the same stratigraphic 

interval as the other units combined.

Most of the conglomerate of the lower clastic units 

is a reddish-brown polymictic cobble conglomerate, 

about 100 feet thick, that closely resembles the conglomerate in the lower member. The clasts of this conglomerate are granite, aplite, porphyritic rhyolite, and 

porphyritic andesite or dacite. However, 1 mile north 

of the ranch, the conglomerate grades laterally into a 

gray monomictic conglomerate and sandstone of andesitic detritus that appears to be derived from the

FIGURE 20. Andesitic sandstone of the middle member of the 

Temporal Formation, exposed along a tributary east of 

Temporal Gulch 1 mile north of the ranch house on that gulch.
SANTA RITA MOUNTAINS C31

volcanics of the undivided lower and middle members 

to the north. Grain size, bedding, and sorting of this 

sandstone, illustrated in figure 20, indicate deposition 

by gently flowing streams. In an area 1^-2 miles south 

of the ranch, andesitic or dacitic clasts become sufficiently abundant so that locally the unit is indistinguishable from the basal unit of th& overlying Bathtub 

Formation.

A second unit of rhyolitic tuff and tuff breccia, as 

much as 250 feet thick, overlies the conglomerate unit 

of the middle member. The tuff and tuff breccia is a 

very pale orange "punky" or poorly indurated, rock 

which contains lithic fragments usually smaller than 

half an inch in diameter. The tuff is thickest near the 

ranch, it thins to about 150 feet toward Mansfield 

Canyon, where it grades into slightly bluish gray tuffaceous sandstone which contains andesitic debris, and 

it wedges out between andesite flows and volcanic breccia. Half a mile south of Mansfield Canyon, the rhyolitic 

tuff fills a channel cut a few tens of feet into the underlying 'andesitic conglomerate, thus indicating that 

minor disconformities are probably common within this 

formation. A mile and a half south of the ranch, the 

tuff breccia also contains andesitic chips and wedges 

out, reappearing only in two small lenses near the 

mouth of Gringo Gulch.

A porphyritic latite lava flow, or flows, make up a 

unit about 1 mile long and 200 feet thick, just north of 

the mouth of Gringo Gulch. The porphyritic latite is 

a medium-dark-gray to brownish-gray blocky-weathering rock that contains small plagioclase phenocrysts. 

In thin section, it is seen to be holocrystalline, with 

strongly alined phenocrysts as much as 3 mm long 

making up about 15 percent of the rock and with 

groundmass laths 0.05-0.1 mm long. The mode of a 

typical specimen of porphyritic latite is given in table 

4, specimen 1. In this rock, plagioclase phenocrysts are 

albitized and are strongly altered to sericite, calcite, 

and clay minerals. Amphibole and possibly biotite appear as anhedral pseudomorphs of chlorite, iron oxides, 

and calcite. The groundmass contains a little interstitial 

quartz and abundant feldspar laths, which have a strong 

kaolinite alteration that suggests the presence of potassium feldspar.

LOWER AND MIDDLE MEMBERS UNDIVIDED 

Near the mouth of Mansfield Canyon, the lower and 

middle members of the Temporal Formation abut medium-gray to dark-gray andesite volcanic breccia and 

flows. The lateral change occurs 11/2 miles farther south 

in the basal unit of the lower member than it does in the 

tuff unit of the middle member. Because the andesite occupies the same stratigraphic interval as the lower and

TABLE 4. Modes of three volcanic rocks of the Temporal Formation

Rock__-_ _________ __-_-___- Latite Andesite Rhyodacite

Specimen No...___ -_____-__---- 1 

Field Na._-______- --------------- 63D205

234 

63D183 66D993 62D19

Quartz.. -. __ _ _ --.. ------- -.

Plagioclase----- ._. __. ____-_-..

Potassium feldspar. .-. - . .--.-_

Amphibole.----------- -- . .

Biotite(?)_._-_. _.___._ __-_.--

Augite(?) .._-__ .__ 

Magnetite..-. - ___ - ___ _-

Apatite _ ...--... . -_ _ .- _ .

Sphene .- __ . - .-.- 

Zircon_--__ ..- -------

Groundmass. ____ ---.__- ..-

-- ____ 0

.. -. 11.8

._-- _ 0 

 ... . 2.3

-- - .3

... . 1.2

-. ....... .3

.1

---__--..- 0

0

- --. 84.0

0

35.8

0 

1.7

1.2

3.2

2.8

.3

0 

0

55.0

0

14.5

0

5.7

0

2.1

2.0

0

.2 

0

75.6

3.1

12.4

7.3 

1.7

.8

0

1.7

.3

.1

Trace

72.6

Total- 100.0 100.0 100.1 100.0

SPECIMEN DESCRIPTIONS

1. Altered latite porphyry from lower quarter of flow (or flows?) of the middle member, hyalopilitic groundmass of laths 0.05-0.1 mm long, containing phenocrysts 

as much as 2 mm long; from half a mile northwest of the mouth of Gringo Gulch 

(NW^NWM sec. 35, T. 21 S., R. 15 E.).

2. Andesite porphyry from possible feeder dike of the volcanics of the lower and 

middle members undivided, hyalopilitic to cryptocrystalline groundmass; 

from lower Mansfield Canyon (SEMSEM sec. 10, T. 21 S., R. 15 E.).

3. Altered andesitic porphyry intrusive into altered latitic(?) tuffs of the middle 

member, hyalopilitic groundmass; from Smith Gulch (NWMNWM sec. 2, T. 22 

S., R. 15 E.).

4. Altered rhyodacite vitrophyre from high in upper member, groundmass an altered 

devitrified glass, phenocrysts as much as 2 mm long; from half a mile southwest 

of Tunnel Spring (SW^NE^ sec. 15, T. 20 S., R. 15 E., unsurve>ed).

middle members, it is considered to be the undivided 

stratigraphic equivalent of those members. Most likely, 

the contact between the andesite breccia and the rocks 

of the divided lower and middle members is largely a 

local unconformity, but the andesitic conglomerate 

facies of the conglomerate unit of the middle member 

may actually grade into the andesitic volcanic breccia 

by way of a zone of tuff breccia that is exposed north 

of the mouth of Mansfield Canyon.

The andesite unit forms a lens 600-700 feet thick and 

3y2 miles long in the upper reaches of Temporal Gulch. 

Its greatest extent appears at a low stratigraphic position, and at Anaconda Spring, three-fourths of a mile 

north of Mansfield Canyon, it makes up the entire 

thickness of the formation. Massive andesite and andesite breccias are about equally abundant. Most of 

the rocks are intensely altered to clay minerals, and 

as a result the structural features of the original 

rock are obliterated; thus, it is not possible to be certain that all the massive andesite is lava. Some remnants of less altered rock, however, do show that flows 

were present, and the widely scattered occurrences of 

these remnants suggest that flows may have been 

abundant. Several bodies of relatively unaltered rock 

cut across other andesite and thus indicate that they 

may be local intrusive bodies, some of which may have 

been pipes for the effusive material. I suspect that some 

of the apparently crosscutting bodies, however, are 

only steep contacts between more intensely and less 

intensely altered andesite. Most of the andesite is 

weakly resistant to erosion and is pale bluish gray 

due to alteration. In some rocks, an original darker 

gray color is preserved, along with amygdaloidal zones.
C32 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

A small irregularly shaped body of augite andesite 

that intrudes (?) altered tuff aceous sandstone of the 

lower member along Smith Gulch (Drewes, 1971a), 

south of Johnson Spring, is probably related to these 

voloanios. Its mode is listed as specimen 3 in table 4.

Under the microscope, the andesite is seen to be 

about half altered granular cryptocrystalline groundmass and half blocky phenocrysts, which are commonly 

less than 2 mm long (fig. 21). The mode of the rock 

that is shown in figure 21 is given in table 4 (specimen 

2); chemical and spectrographic analyses and calculated norms are given in table 5. This rock is nearly 

unaltered and was collected from a body in the SE. 

cor. SE1/4SE14 sec. 10, T. 21 S., R. 15 E., that is probably a local intrusive pod associated with the volcanics.

Plagioclase forms blocky euhedral crystals, which 

are largely altered to sericite and clay minerals but 

which contain some unaltered calcic andesine to sodic

TABLE 5. Chemical and spectrographic analyses and calculated 

norms of a specimen, field No. 6SD18S, of andesite from the 

Temporal Formation

[See specimen 2, table 4, for modes]

Chemical analysis (percent) '

SiO2______

A12O3_____

Fe2O3_____

FeO _ ___

MgO_____

CaO______

Na2O_____

K2O______

__________ 58.3

__________ 17.7

__________ 4.0

__________ 1.9

__________ 2.6

___________ 5.6

4 4

__________ 2.5

H2O-______________

H20+______________

TiO2_.______________

P205__ ________

MnO_______________

CO2

Total __ _

35 

1 1 

80 

35 

12 

18

100.0

Semiquantitative spectrographic analysis 2

Ba ___ _

Be _____

Co_______

Cr_______

Cu______.

Ga_______

La ___

__________ 0. 15

__________ .0001

__________ .0015

. 0007

__________ .0015

_ __ ___ .0015

______ _ _ .007

Nb_________________

Sc_________________

Sr_ _ _ ___________

V

Y__________________

Yb_________________

Zr_________________

0015 

001 

07 

007 

0015 

00015 

015

Norms (percent)

Q-__.._._

or

ab

an

fs __ _

Mfe '

._ __ ___ 9.443

.__ ___ _ 14.788

__ _______ 37.269

_ 21. 183

___ _ __ 1. 154

______ 0

__ ______ 1.336

._ __ _ __ 5.327

. ____ __ 0

mt _ _ __

il ________ __ ___

cc _ _ ___

Total 

(rounded) ___

4.201 

1. 107 

1.521 

.830 

.410

98.57

FIGURE 21. Photomicrograph of augite andesite of the lower 

and middle members undivided, Temporal Formation. Phenocrysts, roughly in decreasing order of abundance: plagioclase, 

chiefly labradorite (P) ; clinopyroxene, probably augite (cp) ; 

chlorite (C) and uralite (U) pseudomorphs after amphibole(?) ; magnetite (M); iron oxide and clay mineral pseudomorph after biotite (B).

1 Rapid rock analysis made by means of methods described by Ward, Lakin, 

Canney, and others (1963), supplemented by atomic absorption methods. P. L. D. 

Elmore, Samuel Botts, Lowell Artis, Gillison Chloe, H. Smith, and John Glenn, 

analysts.

2 Results are reported in percent to the nearest number in the series 1, 0.7, 0.5, 0.3, 

0.2, 0.15, 0.1, and so on, which represent approximate midpoints of interval data on a 

geometric scale. The assigned interval for Semiquantitative results will include the 

quantitative value about 30 percent of the time. Elements looked for but not found: 

Ag, As, Au, B, Bi, Cd, Ce, Ge, Hf, In, Li, Mo, Ni, Pb, Pd, Pt, Re, Sb, Sn, Ta, Te, 

Th, Tl, U, W, and Zn. J. L. Harris and W. B. Crandell, analysts.

labradorite remnants. Most ferromagnesian minerals 

are altered to iron oxide, clay minerals, sericite, calcite, 

and a little quartz, but some augite crystals still contain very pale brown unaltered patches. Amphibole 

is recognizable by the euhedral outlines of its pseudomorphs, and the combination of chlorite and leucoxene 

in other pseudomorphs may have been derived from 

biotite. Quartz veinlets and pods appear with the other 

alteration minerals.

UPPER MEMBER

The upper member of the Temporal Formation appears only in, and north of, the upper reaches of Temporal Gulch, where it overlies the andesite of the undivided lower and middle members. The upper member commonly is 600-1,000 feet thick; it wedges out to 

the south but is almost 2,000 feet thick north of Gardner Canyon near where it is faulted out. It is divided 

into a lower conglomerate unit, small lenses of rhyolite
SANTA RITA MOUNTAINS C33

flows and tuff, and a large overlying tongue of rhyodacite breccia.

The conglomerate unit forms a tongue that is about 

1,000 feet thick north of Gardner Canyon but wedges 

out along the base of the upper member about 1 mile 

south of that canyon (fig. 19). Small lenses of conglomerate lie at or near the base of the upper member 

along the middle fork of Big Casa Blanca Canyon, and 

as much as 400 feet of basal conglomerate reappears 

in the upper reaches of Temporal Gulch, with more 

conglomerate lapping over the thin end of the rhyodacite breccia. In general, the conglomerate is not very 

resistant to weathering and, so, forms gentle slopes, 

which are locally capped by the more strongly indurated rhyodacite breccia. Boulders as much as 3 feet 

in diameter are scattered in the conglomerate, but most 

clasts are cobbles and pebbles; all the detritus is set in 

a gray gritty to silty matrix. Sand lentils and pebble 

beds, although few, are generally available for determination of attitudes. The clasts are subrounded and 

consist of abundant volcanic and plutonic detritus and 

a little reworked sedimentary rock. Of special interest 

are fragments of porphyritic quartz monzonite that 

resembles the Precambrian rock which is exposed a few 

miles north of the conglomerate, a granite that resembles the Jurassic Squaw Gulch Granite, and a diabasic rock a little like some rocks assigned to the Triassic that are exposed to the northwest within a few hundred feet of the conglomerate. Volca-nic clasts consist 

of porphyritic rhyolitic to dacitic rock, as well as a 

"turkey track" type of andesitic rock; these clasts are 

typical of the Mount Wrightson Formation on which 

the conglomerate is deposited. Other clasts, of reddishbrown quartzitic sandstone, were also derived from the 

Mount Wrightson Formation. Sparse clasts of very 

light gray recrystallized limestone, fine-grained gray 

limestone, and light-brownish-gray to purplish-gray 

quartzite probably were derived from Paleozoic rocks.

Rhyolite flows form two thin lenses in the conglomerate unit in the Gardner Canyon area and two 

more in the upper reaches of Temporal Gulch. Each of 

these lenses is 50-100 feet thick, but none is more than 

1 mile long. Rhyolitic tuff is associated with the southernmost lens. The rhyolite is a light-gray to palereddish-gray massive to slightly flow laminated and 

locally flow brecciated rock that contains sparse phenocrysts, chiefly of plagioclase. In some places, it also 

contains vugs.

A sheet of rhyodacite breccia as much as 1,000 feet 

thick overlies the conglomerate unit in Gardner Canyon and intertongues with that conglomerate in the 

upper reaches of Temporal Gulch. The rhyodacite 

breccia forms low cliffs and high spurs above the conglomerate unit, but its resistance to weathering is variable, depending largely on the proportions of resistant 

blocky components to less resistant tuffaceous matrix. 

The included blocks are medium gray, slightly porphyritic, and commonly 1-3 inches across but may be 

as large as 6 inches. Their matrix is finely comminuted 

rhyodacite that has been deuterically(?) altered to a 

"punky" rock rich in clay minerals. Thin beds of volcanic sandstone and volcanic conglomerate are scattered throughout the breccia, and two lenses of tuff 

breccia occur high in the unit between the middle fork 

of Big Casa Blanca Canyon and Gardner Canyon. 

Locally, fragments other than rhyodacite appear in the 

breccia sheet. For instance, along the abandoned ditch 

on the north wall of the north fork of Big Casa Blanca 

Canyon half a mile south of hill 6445 (Drewes, 1971a), 

abundant rhyolite or latite fragments are mixed with 

the rhyodacite. Likewise, half a mile southwest of 

Tunnel Spring in Gardner Canyon, about 10 percent 

of the fragments are volcanics, other than rhyodacite; 

and widely scattered fragments of Precambrian porphyritic quartz monzonite, which must have been derived from the northeast or from depth, also occur 

there.

In thin section, the rhyodacite fragments in the 

breccia sheet are seen to consist of a strongly altered 

vitrophyre containing 25 percent phenocrysts as much 

as 3 mm long (fig. 22). The groundmass is mottled 

light-brown to darker brown devitrified and kaolinized 

glass. The matrix in the southern tongue of this sheet 

contains abundant alined microlites. A mode of rhyodacite vitrophyre is given in table 4, specimen 4.

Quartz forms euhedral to anhedral crystals which 

typically are embayed or rounded owing to partial 

resorption. Plagioclase forms subhedral crystals, which 

in some specimens have the composition of sodic andesine with normally zoned rims of sodic oligoclase but 

which in other rocks are albitized. Amphibole and biotite( ?) are completely altered to chlorite, sericite, iron 

oxide, and clay minerals and are recognizable only by 

their distinctive euhedral crystal forms. Magnetite is 

titaniferous. Zircon is present but is not abundant 

enough to be concentrated for isotopic dating. The 

phenocryst assemblage resembles most closely that of 

the more thoroughly analyzed rhyodacite of the Grosvenor Hills Voloanios of Oligocene age; therefore, despite the relatively dark gray color of the rock, it is 

here called a rhyodacite rather a dacite or andesite.

AGE AND CORRELATION

The Temporal Formation is dated as Early Cretaceous because of its geologic relations to adjacent rocks. 

It demonstrably overlies the Jurassic Squaw Gulch
C34 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

FIGURE 22. Photomicrographs of rhyodacite of the upper member of the Temporal Formation. Left, plane-polarized light; right, 

crossed nicols. Phenocrysts: albitized plagioclase (P) ; quartz (Q) ; iron oxide and mica pseudomorph after biotite (B) ; 

titaniferous magnetite (M) ; and iron oxide and chlorite(?) pseudomorph after amphibole (A).

Granite and underlies the Bathtub Formation, which 

in turn underlies the Glance Conglomerate and other 

formations of the Bisbee Group of known Early Cretaceous age. The Temporal and Bathtub Formations 

could be assigned an age from Late Jurassic to Early 

Cretaceous; however, an Early Cretaceous age is preferred because a greater span of time would have been 

needed to expose and deeply erode the granite before 

Temporal time than would have been needed for deposition and minor erosion between Temporal and Glance 

times.

The welded-tuff lens at the base of the lower member of the Temporal Formation has been isotopically 

dated, but the age is somewhat older than anticipated. 

A zircon concentrate from the welded tuff was dated 

by the lead-alpha method as 180 ±20 m.y. (T. W. Stern, 

written commun., 1966). This age falls at the older 

limit of the available time range of the Temporal as 

determined from geologic evidence and is similar to 

the age of the Squaw Gulch Granite. Because of the 

refractory property of zircon and the presence of the

welded tuff directly upon the granite, the age obtained 

may not date the tuff itself; rather, it seems likely that 

the zircons are xenocrysts picked up by the tuff as it 

flowed over grus-covered granite terrane and thus were 

formed independent of the cooling process of the tuff. 

The sparsity of zircon in all the other volcanic units 

of the Temporal Formation and the intensity of the 

alteration of biotite, amphibole, and other minerals 

may prevent direct dating of the formation.

Rocks of earliest Cretaceous age have not been reported in southeastern Arizona, and rocks having an 

appropriate geologic age range and an appropriate 

lithology to be correlated with the Temporal Formation are scarce. In the Huachuca Mountains, Hayes 

(Hayes and Raup, 1968) mapped a lower part of the 

Glance Conglomerate as containing many lenses of 

andesite breccia. This unit also overlies Jurassic granite. Thus, his lower part of the Glance probably is correlative with an unknown part of the combined Temporal and Bathtub Formations. Gilluly (1956, p. 68- 

70) briefly described pre-Bisbee Cretaceous rocks in the
SANTA RITA MOUNTAINS C35

Dragoon Mountains, still farther east. These, too, are 

chiefly andesitic to rhyolitic volcanic rocks and are 

subordinately tuffaceous sandstone and grit. Pyroclastic rocks are more common than flows. These rocks also 

overlie Jurassic granitic rocks and underlie the Glance 

Conglomerate and, so, are also probably correlative to 

some part of the combined Temporal and Bathtub 

Formations.

ENVIRONMENT OF DEPOSITION

The abundant data available on the facies variations 

and stratigraphic sequence of the Temporal Formation 

provide considerable insight into the environment of 

deposition of the formation. Subaerial conditions are, 

of course, indicated by the sorting and rounding characteristics of the sedimentary units and by their strong 

lenticularity. Furthermore, during Temporal time, the 

area must have had a rugged relief to shed so much 

more conglomerate and fanglomerate than finer 

grained sediments. Finally, the association of rugged 

relief and volcanism suggests a time of tectonic 

activity.

By establishing the source areas of the various clastic components in the conglomerates, the general location of some high areas may be deduced. For instance, 

the more unusual clasts (limestone and quartzite) in 

the conglomerate unit of the upper member could only 

have been derived from within or beyond the Sawmill 

Canyon fault zone (Drewes, unpub. data) a few miles 

to the north or east; likewise, the abundant cobbles of 

porphyritic quartz monzonite of Precambrian age 

could only have come from the northeast, just beyond 

that fault zone, where they are presently exposed and 

lie unconformably beneath sediments of Early Cretaceous age. The southward wedging-out of the conglomerate unit in the upper member of the Temporal Formation further substantiates the proposed northern source 

of the cobbles. A southerly direction of flow is similarly deduced for the rhyodacite breccia, because the 

breccia also wedges out southward and contains scattered fragments of porphyritic quartz monzonite of 

Precambrian age. Very likely, that flow moved down 

the slope of a large fan which had been deposited at 

the foot of an uplifted fault block northeast of the 

Sawmill Canyon fault zone.

Conglomerate units of the lower and middle members of the Temporal Formation also provide some 

clues about their source area and direction of transport. However, the inferred source area of these conglomerates cannot be pinpointed too closely because 

the most common clasts in them are granite and older 

volcajnios. The present distribution of these rocks is 

widespread, and their past distribution could have 

been even more widespread. The rugged canyon

topography that underlies the conglomerate-bearing 

rocks and the coarseness of the conglomerate indicate 

that the source lay nearby; indeed, the arkosic fanglomerate unit rests on its granite source rock. The easterly or westerly trends of the paleocanyons gives us the 

most likely alternative directions of transport of the 

cobbles. A western source area is certainly plausible 

because Jurassic granite is abundantly exposed to the 

west, and the Triassic volcanic host rocks of the granite almost certainly extended over that area, too. However, an alternate eastern source area, along the present 

Sonoita Creek valley, cannot be precluded simply 

because only younger rocks are exposed in the area.

BATHTUB FORMATION

A second sequence of volcanic and sedimentary rocks 

of early Early Cretaceous age, 1,500-2,300 feet thick, 

lies along the east flank of the Santa Rita Mountains. 

This sequence overlies the Temporal Formation with 

minor local disconformity and is overlain with probable unconformity by rocks correlated with the Glance 

Conglomerate of late Early Cretaceous age. It is intruded by dikes and by a plug which, as a result of 

isotopic dating, are assigned to the Paleocene. The 

rocks of this sequence were previously considered as 

Tertiary by Schrader (1915, pi. 2) and as Cretaceous 

by W. R. Jones, C. G. Bowles, and D. C. Hedlund, as 

mapped by Wilson, Moore, and O'Haire (1960). As a 

result of recent mapping, the sequence has been assigned to the Early Cretaceous and named the Bathtub Formation (Drewes, 1968, p. C9).

The disconformity at the base of the Bathtub Formation is not everywhere apparent. However, in the Big 

Casa Blanca Canyon drainage, the lowest unit of the 

Bathtub Formation thickens several hundred feet precisely where the underlying rocks thin a few hundred 

feet. These relations suggest that a broad channel that 

had been cut into the Temporal was filled with the 

basal unit of the Bathtub. A local unconformity is also 

inferred to lie beneath the northern part of the Bathtub because the basal beds there are massive conglomerate; their deposition presumably was accompanied 

by some scouring of underlying rocks. An unconformity may also underlie the southernmost part of the 

formation, because neither the middle nor the upper 

members of the Temporal Formation is present there.

The Bathtub Formation is divided into lower, middle, and upper members, each of which is further subdivided into fairly local lenticular units. The lower 

member consists chiefly of conglomerate and sandstone, 

the middle member of rhyolite pyroclastics to the 

north and andesite flows to the south, and the upper 

member of dacitic volcanic breccia.

404-482 O - 71 - 6
C36 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

DISTRIBUTION

The Bathtub Formation extends from the low hills 

about 1 mile west of Patagonia northward about 10 

miles to Gardner Canyon. The outcrop belt lies along 

the foothills of the mountains, where the local relief 

is ideal to provide abundant outcrops and where vegetation is sparse. The rocks of the belt dip gently to 

moderately steeply eastward, are only slightly faulted, 

and are covered on the east by younger volcanics or by 

gravel. The Bathtub Formation is faulted out at both 

ends of the belt.

The three members are generally not present 

together. The lower member extends from about 1 mile 

north of the southern limit of the formation to near 

the mouth of Mansfield Canyon (Drewes, 1971a). 

After being cut out for almost 3 miles, it reappears 

north of the upper reaches of Adobe Canyon and 

extends to the northern bounding fault. The middle 

member is the most extensive one and is absent only at 

the extreme north. The upper member is the most 

restricted one, occurring only in the basin of Big Casa 

Blanca Canyon, and is scarcely 2 miles long.

No single stratigraphic section is both accessible and 

complete because of the discontinuity of the members 

and their subdivisions. The most complete section 

known extends almost 2 miles northwestward from 

Bath Tub Water in Big Casa Blanca Canyon; however, this section lies far from a road and is largely on 

a dip slope. Therefore, a section just south of the 

ranch in Temporal Gulch (fig. 18) that is less complete 

but more accessible has been selected as the type area. 

The base of the formation and the lower beds in the 

type area are exposed along tributaries to Temporal 

Gulch about 1,000 feet east of the gulch, and the upper 

units occur on the south walls of Temporal Gulch. In 

the type area, the lower member is a gray andesitic 

sandstone and conglomerate, and the middle member 

consists of a sequence of pyroclastic and epiclastic 

rocks, whereas elsewhere the lithologies are different 

and must be individually determined. The conglomerate unit of the lower member is most accessible a 

quarter of a mile southwest of Tunnel Spring. The 

andesite flows that form the southern facies of the 

middle member can best be reached 2 miles northwest 

of Patagonia along lower Gringo Gulch and west of 

the end of the jeep trail. (This trail actually extends 

1 mile farther westward than is shown on the Mount 

Wrightson quadrangle topographic map.) The upper 

member is most accessible along the middle reaches of 

Big Casa Blanca Canyon, northwest of the ranch house 

at the end of the road in that canyon.

LITHOLOGY AND PETROGRAPHY 

LOWER MEMBER

Strongly lenticular conglomerate and sandstone, 

which together have a maximum thickness of about 

700 feet, make up the lower member of the Bathtub 

Formation (fig. 23). To the north, the rocks of the 

lower member consist of polymyctic boulder conglomerate, and to the south they form a monomyctic volcanic conglomerate and sandstone facies. Both facies 

appear about 1 mile north of the ranch house in Temporal Gulch, but the relation between them is obscured 

by local faulting.

The polymyctic boulder conglomerate is a brownishgray massive nearly unsorted rock which is as much as 

600 feet thick near Gardner Canyon but which wedges 

out only 21/2 miles to the south. Its clasts are typically 

subrouiided boulders and cobbles, the largest of which 

are as much as 4 feet in diameter; its matrix is sand 

and grit. Many clasts are of volcanics, which range in 

composition from rhyolite to andesite and which include flow-layered and porphyritic types typical of the 

Mount Wrightson Formation. However, granitic clasts 

that resemble the Squaw Gulch Granite and coarsely 

porphyritic granodiorite clasts that resemble the Precambrian rocks are also common; clasts of limestone 

and marble that are derived from either the normal 

Paleozoic rocks or the recrystallized Paleozoic rocks 

are also present but sparse. Most of these rock types 

could have been derived from a source area to the 

northwest or to the northeast of the conglomerate 

wedge. However, the Precambrian granodiorite boulders must have been derived from the northeast because 

this is the only known nearby place where Precambrian 

granodiorite was exhumed from its cover of preBathtub rocks.

The small lenses of polymictic conglomerate 1 mile 

north of the ranch house are reddish brown and contain abundant subangular pebbles and some cobbles of 

latite or dacite and also some of aplite. This conglomerate is associated with thin units of rhyolitic tuff 

breccia and andesitic breccia too small to be mapped 

at a scale of 1:48,000.

To the south, roughly between the mouths of Mansfield Canyon and Gringo Gulch, a distance of 3V£ miles, 

volcanic conglomerate and sandstone make up another 

lens of the lower member of the Bathtub Formation. 

The central 2 miles of the lens is 500-700 feet thick. 

Locally, to the south, a thin tongue of the top of this 

unit interfingers with the basal part of the overlying 

flows. A small-scale interfingering of rocks of the top 

of the lower member with rocks at the base of the 

middle member may also occur north of the ranch,
SANTA EITA MOUNTAINS C37

NORTH SOUTH

EXPLANATION

_!_!_

 1 ~~

+ + +

+ +

Tuff breccia 

and tuff

Welded 

tuff

Indurated 

tuff

Rhyolite-latite

Sandstone

Member boundary

Dashed where inferred in a faulted area; 

dotted where projected

A > C- SL ----- * # »

Breccia Flows Conglomerate Arkosic 

and sandstone material

Contact 

Dashed where inferred in a faulted area

Unconformity

Dacite-andesite

FEET 

0

L 1000

VERTICAL EXAGGERATION 

ABOUT X5

Polymictic 

conglomerate

FIGURE 23. Stratigraphic and faciesi diagram af the Bathtub Formation. Datum is base of Bathtub Formation, modified to

show pre-Bathtub erosion and pre-Bathtub volcanic pile.

where minor faulting has obscured the stratigraphic 

sequence.

The conglomerate and sandstone of the lower member consist almost wholly of dacitic or andesitic detritus in beds 1-6 inches thick. A few thin beds, however, 

contain some clasts of a dioritic rock, and other beds 

high in the unit contain granitic pebbles. In the type 

area of the Bathtub, the fragments are 2-4 inches 

across; but this size diminishes northward, and the 

proportion of sandy to conglomeratic beds also increases northward. Southward from the type area, 

increasing amounts of arkosic detritus are admixed 

with the volcanic detritus, and the rock resembles a 

gritty to conglomeratic subgraywacke.

Two source areas probably contributed to the southern lens of the lower member. The granitic detritus was 

derived from the Squaw Gulch Granite to the west, and 

likewise the dioritic clasts may have come from rocks 

such as those that are included in the Jurassic Squaw 

Gulch Granite near Johnson Spring. The volcanic detritus is inferred to have come from other nearby areas, 

possibly from the Temporal Formation.

MIDDLE MEMBER

Rhyolite tuff breccia and subordinate tuff, together 

800-1,000 feet thick, make up most of the middle member of the Bathtub Formation. These rhyolitic pyroclastic rocks contain several lenses of tuffaceous sandstone, two larger lenses of welded tuff, and two small 

lenticular rhyolitic flows. A lens of indurated tuff forms 

an additional subdivision south of the ranch, but the 

origin of the induration could either be a metamorphic 

effect of the nearby Paleocene plug or a diagenetic 

effect related to the deposition of the volcanics. Half a 

mile north of the lower reaches of Gringo Gulch, these 

rhyolitic pyroclastic rocks abut against, and interfinger 

slightly with, a unit of dacitic to andesitic flows 1,200- 

1,500 feet thick, which are the southernmost subdivision of the middle member.

The rhyolitic tuff breccia unit is itself a heterogeneous body in which color, sorting, and size of fragments vary laterally and, to some extent, vertically. 

Weathered and fresh rock surfaces typically are very 

pale green to light greenish gray and, less commonly, 

as north of Temporal Gulch, pinkish gray. East of the
C38 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

upper reaches of Temporal Gulch, the pyroclastics are 

subtly varicolored; they occur as alternating units of 

white to light bluish gray and pale yellow to pale 

brown, and one unit is grayish orange. Near the ranch 

in Temporal Gulch, pale-bluish-gray tuff overlies a 

nearly wT hite tuff IOWT in the middle member, and a paleyellowTish-brown tuff overlies the welded tuff high in 

the member. Bedding consists of thin lentils to massive 

sheets about 100 feet thick. Typical beds are 1^-10 feet 

thick and consist of alternating layers of coarse and 

fine fragments. Tuffaceous sandstone lentils are scattered throughout the middle member but usually are too 

small to be used as marker beds. The more massive beds 

contain a faint parting that is parallel to the bedding 

of adjacent less massive units.

The fragments in the tuff breccia are commonly 1-9 

inches across, but in some beds they are as much as 12 

inches across; a fewT blocks are even larger. The coarser 

blocks are most abundant north of Temporal Gulch; 

they also occur in the units that overlie the wTelded tuff 

south of the ranch house in Temporal Gulch. Most 

fragments in the tuff breccia are volcanic debris of 

pumiceous rhyolite and light-gray or reddish-gray 

laminated to unlaminated porphyritic rhyolite or 

rhyodacite. However, half a mile northwest of Bath 

Tub Water in Big Casa Blanca Canyon, the tuff breccia 

high in the middle member is about 10 percent granitic 

chips and orthoclase grit, presumably derived from a 

granite grus.

The pale-bluish-gray tuff is typical of the rhyolitic 

tuff^breccia unit. It contains about 35 percent rhyolitic chips ^-l1/^ inches across. The matrix is finegrained volcanic ash that is indurated and altered to a 

soft punky material. This punky ash weathers readily 

to release the lithic fragments, wThich accumulate on the 

slopes to an extent that is out of proportion to their 

abundance in the parent rock.

Under the microscope, the tuff is seen to consist of 

equally abundant crystal and lithic fragments, wThich 

together make up half the rock and are scattered in a 

cryptocrystalline groundmass rich in argillic alteration 

products. Relict shard textures are only rarely preserved. A mode of tuff breccia specimen 62D28 from 

near the northern end of the outcrop area, contains:

Percent- Mineral age

Quartz_____________________________ __ 3. 5

Plagioclase___________________________ 6. 8

Potassium feldspar__________________ 3. 6

Biotite____________ ________ ______ . 2

Magnetite_____________________ Trace

Apatite __ __________________ Trace

Zircon. ____ ______________________ Trace

Groundmass________________________ _ 63. 2

Lithic fragments______________________ 22. 7

Total___________________ 100. 0

The plagioclase is always albite and probably is 

albitized. Some of the potassium feldspar crystals are 

coarse patch perthite, and in one specimen they are 

microcline, which probably was derived from Precambrian source rock. Most of the visible quartz is fragmental, but a little quartz fills small cavities in the 

groundmass. Other secondary minerals are sericite 

(after biotite and feldspars), clay minerals, calcite, iron 

oxides, and possibly chlorite. Many lithic fragments are 

probably altered devitrified glass.

The welded tuff forms two lenses intercalated in the 

rhyolite tuff breccia at about the same stratigraphic 

position high in the member. The -northernmost lens, 

wThich extends l1/^ miles southward from the upper 

reaches of Little Casa Blanca Canyon, is 300-400 feet 

thick. Zones of unwT elded tuff alternate with the 

welded tuff, thus marking several cooling units in this 

part of the middle member; but most textural details 

are obliterated by pervasive deuteric (?) alteration. The 

welded tuff is a pinkish-gray to pale-red flow-laminated 

rock, along some zones of which lenticules of gray

FIGURE 24. Specimen of strongly flow-laminated intensely 

indurated welded tuff from the northern unit of the middle 

member of the Bathtub Formation.

FIGURE 25. Specimen of less strongly welded tuff from the 

northern lens of the middle member of the Bathtub Formation.
SANTA RITA MOUNTAINS C39

altered and flattened pumiceous fragments are abundant. These fragments reach a size of about i/2 incn by 

2 inches by 8 inches and are elongate in various directions in the bedding plane. The southern lens of welded 

tuff, half a mile southeast of the ranch house in Temporal Gulch, probably represents a single cooling unit 

only and is less than 200 feet thick; it is less conspicuous than an overlying sandstone unit. The lens grades 

upward from a gray indurated tuff at the base to a purplish-gray conchoidally fractured welded tuff which contains lenticules that are presumed to be pumiceous 

chips. The overlying sandstone unit is 5-20 feet thick 

and forms a row of low brownish-black cliffs with 

coarse blocky debris at their base. The grains of the 

sandstone include clastic quartz as well as volcanic 

detritus.

Under the microscope, the welded tuff is seen to be 

flow laminated (fig. 24), as emphasized by strongly 

attenuated lenses of devitrified and oxidized material. 

These attenuated lenses are much larger and better 

preserved than any others seen in the Mount Wrightson

Formation, but the laminated rock in a few areas does 

resemble some of the older rock. Figure 25 illustrates a 

specimen of the welded tuff in which the lenticularity 

of the deformed pumice fragments is not extreme. The 

vitric groundmass still shows shard remnants (fig. 26). 

Lithic fragments or unattenuated pumiceous chips are 

present in one specimen. Apparently these tuffs were 

only locally hot enough during deposition to be welded. 

Phenocrysts are largely fragmental and form 10-20 

percent of the rock. Several specimens have the following modes:

Mineral

Percentage

Northern lens Southern lens

Quartz (phenocrysts)__________________ 0.7 2.7

Quartz (secondary).__ _____ __________ __ 2.1 1.0

Plagioclase-------___-_-___--__--___-__--_-_-_--.__ 5.3 3.8

Potassium feldspar.____________________________ .3 .4

Biotite (or oxybiotite)_ __ __ _____-.______-__ .4 .8

Amphibole-----_-__-_----__-___._.-...-___._..._. Trace Trace

Magnetite__________ __ ____________ _ _ .2 .1

Apatite._______________-_______________.____________ 0 0

Zircon._ _ _______ ________ _ __________ Trace 0

Lithic fragments__.-_-________.____ _________ 0 0

Groundmass_______ ._.__ ____________ 91.0 91.2

0

.5

18.0

0

1.2

0

.5

.1

0

4.8

74.9

Total-___---_--___--_-_-_-___--_--_-_-___.___ 100.0 100.0 100.0

'

fifc^Q^sli-v M"* "&£&F\-*;-\ Wi^'TjW

FIGURE 26. Photomicrograph of same welded tuff shown in figure 25. Left, at X 11.5, showing eutaxitic structure. Phenocrysts : 

albitized plagioclase (P), oxybiotite (ob), titaniferous magnetite (M), secondary quartz (Q), and pumice fragment (pf) ; 

B, area of photomicrograph at right outlined. Right, at X 100, showing relict shards in vitreous groundmass.
C40 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

Most plagioclase is albitized, but one specimen contains a remnant of andesine, which may indicate the 

initial composition. Potassium feldspar is usually too 

intensely kaolinized for specific identification, but the 

feldspar of one specimen may be perthitic orthoclase. 

Biotite or oxybiotite and amphibole appear as pseudomorphs, now of iron oxide, sericite, clay minerals. 

Accessory magnetite is fairly free of titanium, and 

zircon crystals are small and sparse. Alteration minerals comprise iron oxides, sericite, abundant clay minerals, and a little quartz or chalcedony found in small 

cavities and as veinlets.

Two small lenses of rhyolite lava flows, each about 

50-100 feet thick and less than half a mile long, are 

intercalated near the middle of the middle member of 

the Bathtub Formation. The lava commonly crops out 

along low spurs and ledges in the more readily 

weathered tuff breccia and appears as a reddish-gray 

to light-medium-gray sparsely flow brecciated rock.

In thin sections of the flows, phenocrysts, less than 

3 mm long, are seen to be sparsely scattered in a finely 

crystalline to devitrified glassy groundmass, which 

probably consists largely of a mixture of feldspars and 

quartz. A mode of the northern flow is tabulated as 

follows:

PercentMineral age

Quartz phenocrysts-____________________ 0. 2

Quartz, secondary______________________ 2. 4

Plagioclase___________________________ 4. 2

Sanidine (?)_____________________ 3. 1

Oxybiotite_____________________________ . 6

Amphibole(?)__________________________ Trace

Magnetite_ ____________________________ . 4

Zircon_________________________________ . 1

Groundmass___________________________ 89. 0

Total._________________________ 100. 0

Most of the quartz forms anhedral crystals in small 

cavities, possibly as amygdules, but some forms veinlets 

or anhedral phenocrysts. Plagioclase is so severely altered to clay minerals that its composition cannot be determined, but presumably it has been albitized. Some 

of the potassium feldspar has the small ( )2V of sanidine, but most of it is intensely kaolinized and indeterminable. Biotite and amphibole are intensely oxidized 

and sericitized.

The southern part of the middle member of the 

Bathtub Formation consists of andesitic lava flows 

which crop out in low rolling hills that are cut by 

small steep-walled gullies. Individual flows commonly 

weather out to form brownish-gray subdued cliffs and 

alined rubbly outcrops. The margins of flows or materials deposited between the flows form intervening 

small benches. South of lower Gringo Gulch, seven 

individual flows are recognized; these average 175-200

feet in thickness. North of Gringo Gulch, individual 

flows, especially in the lower part of the member, are 

difficult to recognize, perhaps because they coalesce. 

Most tops of the flows are a platy-fractured rock, or 

they contain zones of flow breccia or vesicular and 

amygdular rock. Amygdules of chalcedony, quartz, 

calcite, and epidote(?) are common in the upper few 

tens of feet of most flo\vs; and the top of the uppermost flow contains especially abundant vesicles and 

geodes lined with quartz, calcite, opaline material, and 

hematite. Weathered andesite is brownish gray, but the 

fe\v relatively unweathered rock surfaces are medium 

dark gray to greenish gray, and even the abundant 

feldspar phenocrysts have a greenish tinge and the 

amphibole the dull luster of altered crystals.

In thin section, the andesitic flows (fig. 27) are seen 

to have a strongly felty to intergranular texture in 

which alined phenocrysts 1-4 mm long make up 15-20 

percent of the rock. The finely crystalline groundmass 

is made up of altered equidimensional and lath-shaped 

grains. Modes of two rocks of these flows, specimens 

1 and 3, are given in table 6. Specimen 1 is from one 

of the lower flows and was collected in a narrow part of 

an unnamed tributary that lies about half a mile northwest of the junction of Temporal and Gringo Gulches. 

Specimen 3 is from the upper flow and was collected 

about half a mile southeast of the junction of Temporal 

and Gringo Gulches.

The finely granular groundmass of specimen 3 probably contains 1 2 percent clinopyroxene, and some of 

the pseudomorphic grains of hematite which are reported as magnetite may have been biotite or amphibole. Plagioclase of some specimens is calcic andesine 

or sodic labradorite (An = 47-52), but in others it is 

albitized. Clinopyroxene is very pale brown and has 

a Z/\c of 42° 45°,suitable for augite. Amphibole and 

biotite are altered to chlorite, iron oxide, and clay minerals. Other secondary minerals are epidote, calcite, 

and sericite.

Chemical and spectrographic analyses and calculated 

norms of specimens 1 and 3 are given in table 6. Specimen 1 is an epidotized andesite porphyry with a nearly 

obscured felty groundmass, which was collected from 

the north end of one of the lower flows of the middle 

member of the Bathtub Formation in the NW^NEi/4 

sec. 35, T. 21 S., R. 15 E. Chemically, it most closely 

resembles the average doreite of Nockolds (1954, p. 

1018), having distinct calc-alkali affinities. Specimen 3 

is a vesicular andesite porphyry with a felty to granular groundmass. It was collected near the south end of 

the uppermost flow of the middle member near Gringo 

Gulch, in the NW. cor. SW^4SE^4 sec. 36, T. 21 S., R. 

15 E.
SANTA RITA MOUNTAINS C41

FIGURE 27. Photomicrograph of porphyritic andesite from the 

southern part of a flow (specimen 1, table 6) of the middle 

member of the Bathtub Formation. Phenoerysts: plagioclase 

(P), also dominant in groundmass; chlorite and iron oxide 

pseudomorphs after possible olivine (O) ; clinopyroxene, 

possibly augite (cp) ; magnetite (M) ; and chlorite pseudomorphs after possible amphibole (A).

TABLE 6. Modal, chemical, and spectrographic analyses and 

norms of dacitic to andesitic rocks of the middle and upper 

members of the Bathtub Formation

Specimen No. 

Field No..... 

Member_...

1

63D217 

Middle

2

62D32 

Upper

3

63D223 

Middle

Modal analyses (percent)

Plagioclase_ _

Olivine(?) ___ __ .

Biotite

Magnetite

Apatite.

Zircon

Chlorite 2 - __ _ __ __.

Quartz 3

______ 84.5

______ 7.4

______ .4

.___ _ 0

.-____ 3.4

______ .2

______ 0

______ 0

______ .8

______ 0

32. 1

0

5. 6

0

4. 3

2.5

. 7

. 1

54. 7

0

0

82.9

1 5. 1

i 1. 7(?)

0

7.7

.9

0

0

0

1. 7

Total___________ 100.0 100. 0 100. 0

See footnotes at end of table.

TABLE 6. Modal, chemical, and spectrographic analyses and 

norms of dacitic to andesitic rocks of the middle and upper 

members of the Bathtub Formation Continued

Specimen No____. 

Field No............

Member_______

63D217 

Middle

2

62D32 

Upper

3

63D223 

Middle

Chemical analyses (percent)

SiO2 ________________ 54.2 66.9

A12O3 ______________ 15.3 16.3

Fe2O2 _______-_______ 5.0 3.9

FeO_________________ 2.4 .20

MgO_______________ 5.4 .26

CaO_________________ 5.9 2.0

Na2O_________________ 4.2 4.3

K2O__________ _ _____ 2.6 4.1

H_O-_ ____ - .48 .18

H2O+______________ 2.3 .59

TiO2 ________________ 1.2 .47

P2O5 __________________ .27 .23

MnO__________________ .14 .05

CO2 ___________________ .56 <. 05

Total (rounded) __ __ 100 99

Semiquantitative spectrographic analyses 5

Ba_________________ 0.07 0.1

Be_._________________ 0 .0001

Ce________________ 0 .01

Co__________________ .003 .0005

Cr_________________ .02 .0003

Cu____________________ .005 .001

Ga______________________ .003 .0007

La____________________ .005 .005

Nb______________ _ __ .0015 .002

Ni____________________ .01 0

Pb____________________ .0015 .0005

Sc_________________ .0015 .0003

Sr______________________ .15 .07

V____-_-_______-_____-___- .02 .002

Y__ _ ___ ___ .002 .0015

Yb______________________ 0 .0001

Zr______________________ .015 .007

Norms (percent)

Q__ _ ____________________ 3.334

C-__-_---______----____-_- 0

or________________.________ 15. 361

ab __ ____ _ ______________ 35. 520

an______-_______________-_ 15. 224

fen______________________ 3.153

difs. 

[wo

mthm_

ru_ 

ap 

cc_

0

3.647

10. 291

0

4. 714

1.749

2. 279

0

.639

1. 274

22. 416

1.827

24. 342

36. 557

8. 142

0

0

0

.651

0

0

3.918

.532

. 192

.547

. 114

Total___________ 97. 186 99. 238

1 Reported value may be too low; groundmass contains much obscure granular 

altered material.

2 Of uncertain origin, ingroundmass.

s Filling cavities.

4 Rapid rock analyses determined by methods described by Ward, Lakin, Canney, 

and others (1963), supplemented by atomic a tsorption methods. Analysts: P. L. D. 

Elmore, Samuel Botts, Lowell Artis, Gillison Chloe, H. Smith, John Glenn, and 

D. Taylor.

s Results reported in percent, to the nearest number in the series 1, 0.7, 0.5, 0.3, 

0.2, 0.15, 0.1, and so forth, which represent approximate midpoints of group data on a 

geometric scale. The assigned group for serniquantitative results includes the quantitative value about 30 percent of the time. Elements looked for but not detected: 

Ag, As, Au, B, Bi, Cd, Ge, Hf, Hg, In, Li, Mo, Pd, Pt, Re, Sb, Sn, Ta, Te, Th, Tl, 

U, W, and Zn. Analysts: J. C. Hamilton and J. L. Harris.
C42 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

UPPER MEMBER

In the Big Casa Blanca Canyon area, a sequence as 

much as 1,500 feet thick, chiefly of dacitic volcanics, 

overlies the rhyolite tuff breccia of the middle member 

of the Bathtub Formation with minor unconformity. 

Small lenses of tuffaceous sandstone and of rhyodacitic 

tuff and a lava flow are intercalated in the dacite (fig. 

23). These rocks are provisionally considered to be the 

upper member of the Bathtub Formation (rather than 

a younger formation, such as the Gringo Gulch Volcanics of Paleocene (?) age that lie unconformably 

over the middle member near Patagonia) because to 

the east they are cut by a fault of Laramide age and 

because the small rhyodacitic tuff bodies intercalated in 

the dacitic volcanics resemble the coarser grained yellower tuff breccia of the Bathtub Formation more than 

they resemble the finer grained white to pale-purplishgray tuff of the younger volcanics.

The unconformity between the middle and upper 

members is usually very subtle and is marked only by 

minor discrepancies in attitudes across the contact. 

Along the southern part of the contact however, units 

of the middle member are truncated by the basal unit 

of the upper member. Elsewhere, such as along the 

canyon northwest of Bath Tub Water, a well-exposed 

contact separates apparently disconformable beds of 

the two members.

Tuffaceous sandstone forms a sheet 200 feet thick 

and more than 1 mile long at the base of the upper 

member in the southwest corner of the basin of Big 

Casa Blanca Canyon, precisely where underlying rhyolitic tuff breccia is gently truncated by the basal unconformity. The tuffaceous sandstone consists largely of 

fine-grained light-colored rhyolitic detritus but locally 

includes an admixture of darker dacitic fragments. 

Toward the north, the tuffaceous sandstone body grades 

laterally into dacitic breccia with an increase in the 

darker fragments and a corresponding decrease in the 

light-gray matrix. The tuffaceous sandstone is poorly 

sorted and is generally less indurated than the adjacent 

rocks.

Most volcanics of the upper member are dacitic flow 

breccias, which crop out in a basin that contains many 

broad expanses of bare rock. These outcrops form low 

rounded bosses of medium-dark-gray to slightly brownish gray massive to very thick bedded rock which are 

strewn with blocks weathered from the flow breccia. 

The breccia blocks are angular to subangular and are 

generally about 4 inches across; near the base of the 

member, however, the blocks are less than 2 inches in 

diameter, and at several levels in the central and upper 

parts of the member they are as much as 24 inches 

across. The blocks are set in a matrix of comminuted

and altered dacitic material that weathers readily and 

possibly is tuffaceous. Bodies of fairly unaltered dacitic 

rock, low in the member, may be remnants of flows or 

may mark vents of this volcanic field.

In thin section, blocks from the dacitic breccia are 

seen to be porphyritic and intensely argillized. Phenocrysts are commonly less than 1 mm long and make up 

about 30 percent of the rock; the groundmass is finely 

granular to cryptocrystalline. Plagioclase, which is 

probably albitized, and iron oxide pseudomorphs, 

which have the shape of amphibole and contain 

sparse cores of unaltered green hornblende, each 

make up about a third of the phenocrysts. Pyroxene 

and biotite phenocrysts may also be present but cannot 

be reliably distinguished from other altered ferromagnesian minerals. Accessory magnetite and apatite appear; secondary clay minerals are abundant, and 

epidote and chlorite are also present.

The less altered intrusive(?) rock that is associated 

with the dacitic breccia is texturally much like the 

dacitic breccia blocks; but the plagioclase phenocrysts 

are stubbier, and their size ranges from 2.5 mm to 0.25 

mm, the size of the granular groundmass. A phenocryst 

mode of a specimen of intrusive rock is tabulated as 

follows:

Mineral Percentage

Plagioclase _ __________-____---_------- 74. 5

Pyroxene. _____________________------_- 17. 3

Oxybiotite__ ________ __ - 1. 0

Oxyhornblende- ____--------_----------- 2. 2

Magnetite. __________________-_------_- 4. 6

Zircon _ _ 

Quartz(?)

Total ___________ - 100. 0

The determination of the abundance of combined oxybiotite and oxyhornblende, 3.2 percent, is more reliable 

than the separate counts of the minerals because they 

are so intensely altered to iron oxides as to be nearly 

indistinguishable. Likewise, the reported abundance of 

pyroxene is uncertain because the pyroxene appears 

chiefly as altered granular crystals. Plagioclase forms 

euhedral to subhedral crystals, whose cores are 

calcic labradorite (An = 57-65) and whose rims are 

calcic andesine to sodic labradorite (An =35-50). Most 

pyroxene is anhedral, and all of it is in the groundmass 

and is intensely altered. Oxyhornblende and oxybiotite 

relicts appear in euhetlral to subhedral pseudomorphs of 

iron oxide, calcite, and chlorite. Quartz of possible primary origin makes a few small interstitial patches in the 

groundmass.

A pale-reddish-gray porphyritic rhyolite flow is 

intercalated in the upper part of the upper member of 

the Bathtub Formation. This flow is poorly exposed 

along a row of alined noses and small spurs on the east
SANTA RITA MOUNTAINS C43

wall of the north fork of Big Casa Blanca Canyon. 

Macroscopically, the rhyolite with its small feldspar 

and quartz phenocrysts resembles the lithic fragments in the few lenses of rhyolite tuff intercalated in 

the member, one lens of which overlies the flow itself.

Six lenses of rhyodacitic tuff and tuff breccia are also 

intercalated in the dacitic volcanics of the upper member. Two appear near Bath Tub Water, three lie half 

a mile west of the ranch in Big Casa Blanca Canyon, 

and another lies adjacent to the fault that bounds the 

east edge of the formation. The blocks in the rhyodacitic tuff breccia west of the ranch are as much as 12 

inches across and are so thoroughly altered as to be 

punky almost like pumice but without the abundant 

vesicles of pumice. Some blocks, however, consist of 

slightly less argillized rhyodacitic vitrophyre, which 

contains small phenocrysts of biotite, hornblende, and 

plagioclase; and so, except for its lighter color, the 

rock resembles the dacitic flow breccia. Conceivably, the 

rhyodacitic tuff lenses are alteration lenses rather than 

intercalated depositional units.

A vitrophyric fragment from the uppermost of the 

two intercalated lenses near Bath Tub Water (SW^4- 

SE*4 sec. 26, T. 20 S., R. 15 E., projected) is moded 

and chemically and spectrographically analyzed in 

table 6 (specimen 2). Chemically, this specimen closely 

resembles Nockolds' (1954) rhyodacite. The modal 

plagioclase forms albitized and kaolinized euhedral to 

anhedral grains. Hornblende is pleochroic in bright 

green to pale olive green; and biotite is almost completely altered to granular iron oxide, leucoxene, and 

chloritic or sericitic material, but one biotite crystal 

is still pleochroic in brown. The groundmass glass is 

very pale brown, contains few percent microlites, and 

is only slightly devitrified, which is surprising for a 

rock assigned a Cretaceous age in this region of widespread Laramide alteration.

AGE AND CORRELATION

The Bathtub Formation is unfossiliferous and has 

not been directly dated by isotopic means, but geologically the available age range is limited. The Bathtub 

overlies the Temporal Formation, which in turn overlies the isotopically dated Jurassic Squaw Gulch Granite. The formation is also intruded by dikes and small 

plug which are dated (five determinations on three 

specimens, zircon, hornblende, and biotite) as Paleocene. The youngest age of the formation is geologically 

further restricted because a small part of the formation 

is overlain by conglomerate correlated with the Glance 

Conglomerate of late Early Cretaceous age. Therefore, 

the Bathtub Formation is assigned to the early Early 

Cretaceous.

The Bathtub Formation, either by itself or with the 

underlying Temporal Formation, is probably correlative with the lower part of the Glance Conglomerate, 

as mapped by Hayes in the Huachuca Mountains 

(Hayes and Raup, 1968). This part of the Glance contains large intercalated masses of andesitic volcanics as 

well as exotic blocks, rock types that are absent from 

the type Glance near Bisbee. The Bathtub Formation 

may also be correlative with some or all of the andesite 

volcanics of the Dragoon Mountains, which Gilluly 

(1956, p. 68-70) mapped as post-Jurassic granitic rocks 

and as pre-Bisbee. The widespread occurrence of volcanic clasts in the Glance Conglomerate at the base of 

the Bisbee Group as compared with the reported occurrence of pre-Glance volcanics, suggests that such 

volcanics may have occurred in other local deposits that 

either are covered or have been eroded.

ENVIRONMENT OF DEPOSITION

During Bathtub time, conditions of deposition were 

virtually like those of the immediately preceding time. 

The time between the deposition of the Temporal and 

Bathtub Formations was probably one of renewed uplift on the fault block to the northeast. During early 

Bathtub time, fanglomerate that was shed from this 

block was deposited in the northern part of the outcrop 

area of the formation. Volcanism was renewed during 

middle Bathtub time, involving an andesitic source near 

the south end of the area and a rhyolitic source farther 

north. After a brief period of erosion and local tilting, 

the northern part of the area was again overwhelmed 

by a thick cover of dacitic breccia, whose source probably lay nearby and, in part perhaps, within the area.

BISBEE GROUP

The Bisbee Group, a thick sequence of conglomerate, 

arkose, and red siltstone, crops out in scattered areas 

along the flanks of the central and northern parts of 

the Santa Rita Mountains. Although most commonly 

faulted or intruded, the sequence lies unconformably 

on rocks as young as the Bathtub Formation. The 

sequence is unconformably overlain by rocks as old as 

the Fort Crittenden Formation of Late Cretaceous age. 

In a few places, the sequence contains thin limestone 

beds that have a sparse marine molluscan fauna; thus, 

in many respects the sequence resembles the Bisbee 

Group of the Mule Mountains. The Bisbee Group, with 

which the sequence is correlated, was first described by 

Dumble (1902) and later described in more detail by 

Ransome(1904,p.56).

The Bisbee Group of the Santa Rita Mountains, 

however, shows some differences in lithology with respect to the type Bisbee, so that most of its subdivisions 

are not recognized with confidence. Only the basal
C44 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

Glance Conglomerate persists this far northwest of its 

type area, and it, too, is changed in that it is highly 

lenticular and occupies various stratigraphic horizons, 

but always as a basal sheet or lens. Recent work in the 

Empire Mountains by Tyrrell, (1957) and by 

Schafroth (1965) and current work there by T. L. 

Finnell (oral commun., 1968) have led to establishment 

of other subdivisions of the Bisbee Group which are 

more practical to use in the Santa Rita Mountains. In 

rising sue/cession, the Bisbee Group described here consists of the Glance Conglomerate and the Willow Canyon, Apache Canyon, Shellenberger Canyon, and 

Turney Ranch Formations. The chief distinction between the type Bisbee Group and the Bisbee of the 

Empire, Santa Rita, and surrounding mountains is the 

absence of the Mural Limestone from the northwestern 

part of the area; to the southeast, this limestone forms 

a conspicuous unit in the middle of a thick and uniform 

arkose and siltstone sequence. Because of the absence of 

the Mural from what will here be referred to as the 

northwestern facies of the Bisbee Group, more subtle 

changes in lithology involving the kind and abundance 

of clastic components are the bases of the subdivisions 

used by Tyrrell, Schafroth, and Finnell.

The local thickness of the Bisbee Group is about 

7,500 feet, but this amount is a total of the common 

thicknesses of its component formations rather than 

a measure across a single stratigraphic section. In the 

Santa Rita Mountains, few of the areas that are underlain by the Bisbee contain more than parts of two 

formations; thus, the values for the estimated composite thickness are obtained over a distance of more 

than 10 miles, with no assurance that the individual 

formations are less lenticular than the units within the 

Bathtub and Temporal Formations. Contact metamorphism has also changed the lithology and thickness of 

parts of the Bisbee in several areas and adds to the 

difficulties in estimating a representative composite 

thickness and in establishing a useful local section.

GLANCE CONGLOMERATE

The basal formation of the Bisbee Group is a lenticular conglomerate that was named the Glance Conglomerate by Ransome (1904, p. 56, 57). In the Santa 

Rita Mountains the conglomerate is more lenticular 

than it is in its type area, and it is as much as 1,500 

feet thick, although in most areas it is only a few tens 

to a few hundred feet thick. Where not faulted or 

intruded, the Glance rests unconformably upon either 

the Bathtub Formation or the Precambrian Continental Granodiorite. Because of its intertonguing relations with the overlying rock, some small wedges of

Glance may locally overlie rocks with Willow Canyon 

lithology.

The conglomerate of the Glance is typically a reddish-brown cobble conglomerate whose clasts are detritus of Paleozoic rocks or of Precambrian rocks but 

in places also include detritus of Mesozoic volcanic and 

granitic rocks. The composition of these fragments may 

vary rapidly along strike, so that from one outcrop 

area to the next the lithologies appear unlike. Nevertheless, these changes are believed to reflect lateral facies 

variations rather than vertical stratigraphic changes.

DISTRIBUTION

The Glance Conglomerate has been recognized in a 

few widely separated areas in the Santa Rita Mountains, as shown in figure 28. The southernmost of these 

outcrop areas, A in figure 28, lies near Bathtub along 

the north fork of Big Casa Blanca Canyon (Drewes, 

1971a). There a homoclinally eastward dipping body 

of conglomerate overlies the Bathtub Formation on the 

west and is faulted out against the Fort Crittenden 

Formation on the east. A few miles farther north, two 

small slices of nearly upended Glance are faulted into 

the Sawmill Canyon zone between fault slices of the 

Gardner Canyon and Mount Wrightson Formations on 

the west and a fault slice of Precambrian rock on the 

east. Another small wedge of Glance lies just north of 

the 31° 45' parallel. Its western contact is locally unfaulted, but a large unexposed fault lies virtually parallel to, and closely adjacent to, the contact; its eastern 

contact with Willow Canyon is normal.

In the Box Canyon area (loc. B, fig. 28; see also 

Drewes and Finnell, 1968), several bodies of Glance 

have different clast types and different basal contacts. 

The three westernmost bodies of Glance lie unconformably upon Continental Granodiorite, Bolsa Quartzite, and Abrigo Limestone. These bodies of conglomerate dip moderately steeply southward or southeastward, although the underlying rocks, where bedded, 

are upended. Glance also underlies a larger area, extending from just south of Box Canyon to about 1 

mile north of the canyon, where it dips southeastward 

to eastward and rests unconformably upon the granodiorite on the north but is faulted on the south. This 

mass of Glance is overlain by the Willow Canyon Formation in a normal sequence. Just northeast of locality 

#, the Glance overlies a thrust fault and dips moderately steeply to the west. Six small much-faulted bodies 

of Glance, generalized as two patches in figure 28, 

occur in the Rosemont district, locality E.

In the Sycamore Canyon area, locality C, there are 

also two small bodies of Glance. The southern body 

underlies the Willow Canyon Formation, and both dip
SANTA RITA MOUNTAINS C45

EXPLANATION

£

Includes some older rocks intermittently

Shellenberger Canyon Formation

Other rocks

Include older and younger volcanic, intrusive, and sedimentary rocks

Contact

Fault

Stratigraphic section 

V points up section

QTg

QTg

FIGURE 28. Distribution of rocks of the Bisbee Group in the Santa Rita Mountains. Localities A-H are referred to in the text
C46 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

steeply eastward. The Glance there is thrust upon the 

Pennsylvania!! Horquilla Limestone and is intruded by 

a lower Tertiary quartz monzonite. The northern body 

of Glance forms a gently eastward dipping sheet 

between an underlying thrust plate of nearly upended 

Gardner Canyon Formation and an overlying plate of 

westward-dipping Willow Canyon Formation.

LITHOLOGY

The conglomerate near Bathtub, locality A in figure 

28, is a poorly exposed brownish-gray to greenish-gray 

cobble-and-boulder conglomerate that is poorly bedded 

and poorly indurated. Most of the clasts are subrounded 

to subangular and are 4-6 inches across, but some are 

angular and some are as much as 2 feet across. The 

clasts consist of a heterogeneous assortment of granite, 

limestone, cherty and fossiliferous limestone, flow-laminated volcanics, porphyritic granodiorite, and dioritic 

rocks, but in one zone they consist of angular detritus 

almost wholly made up of laminated volcanics. The 

fossiliferous limestone clasts contain fragments of a 

large gastropod that resembles Omphdlotrochus sp.

The source rocks of the clasts are generally identifiable. The granite closely resembles the Jurassic Squaw 

Gulch Granite, and the granodiorite porphyry is typical of the Precambrian Continental Granodiorite. The 

laminated volcanics were derived from the Mount 

Wrightson Formation. The fossiliferous limestone 

probably is from the Permian Colina Limestone, but 

the other limestones could have come from any of the 

several Permian formations. The dioritic rock was 

eroded either from the Triassic intrusives related to 

the Piper Gulch Monzonite or from the lamprophyres 

in the Precambrian or Jurassic granitic rocks.

The matrix of the conglomerate is a friable tuffaceous sandstone. Some of the friability may, however, be 

a secondary feature, imparted to the rock through deformation during the Laramide orogeny.

The Glance Conglomerate in the Sawmill Canyon 

fault zone consists of a brown pebble-and-cobble conglomerate which is well indurated. It is exposed along 

the jeep track south of the Snyder mine (Drewes, 

197la) but is poorly exposed southeast of the track. 

Most of the subrounded pebbles and cobbles are Paleozoic limestone, dolomite, and quartzite, and some are 

moderate-orange-pink to pale-red siltstone that was 

derived either from the siltstone member of the Triassic Gardner Canyon Formation or from the Pennsylvanian and Permain Earp Formation. The matrix of 

the conglomerate in this area is also sandy, and locally 

the rock is strongly sheared.

The small wedge of conglomerate south of locality 

D (fig. 28) is a unit of pebble conglomerate and sedimentary breccia set in a red mudstone matrix. The 

clasts are granite gneiss that resembles the Precambrian granite gneiss that lies immediately west of the 

conglomerate; the clasts differ from those in the several thin conglomerate beds a few hundred feet stratigraphically above, which contain pebbles and cobbles of 

quartzose sandstone. Barring the added complication 

of undiscovered additional local faults, this wedge of 

gneiss conglomerate may lie some distance above the 

bottom of the Biebee of this area as a tongue intercalated into the Willow Canyon, which is believed to 

form a thrust plate upon the Precambrian rocks 

(Drewes, 1970,197lb).

In the Box Canyon area (loc. B, fig. 28), two types 

of Glance occur in separate thrust plates. The rocks 

of the two plates may have been telescoped for an 

unknown distance, and the Glance of the upper, or 

eastern, plate may actually have overridden that of the 

western plate, inasmuch as regional evidence suggests 

that the relative movement of the upper plate during 

the Piman phase of the Laramide orogeny (Drewes, 

1969; unpub. data) was northeastward. The Glance 

of the lower plate of the three western outcrop areas 

at locality B is a sedimentary breccia and arkosic conglomerate almost wholly made up of detritus derived 

from the underlying Continental Granodorite. Bedding 

is virtually absent from the lower half of the formation where it is exposed along the Box Canyon road 

(Drewes and Finnell, 1968, p. 319, 321); bedding is 

faintly developed, as intercalated sandy lentils and red 

mudstone stringers, in the upper half. Where the 

Glance laps across the upended Bolsa Quartzite and 

Abrigo Limestone, the dominantly arkosic detritus also 

includes some angular clasts of quartzite. This part of 

the Glance seems to be a fanglomerate that was deposited in the immediate vicinity of its source rocks.

The Glance of the upper plate in the Box Canyon 

area is typically a red limestone cobble-and-pebble conglomerate, moderately strongly foliated parallel to the 

bedding. This f acies of Glance contains abundant limestone clasts, about 2-12 inches across, set in a matrix 

of well-indurated red limy sandstone that makes the 

rock strongly resistant to weathering. The conglomerate of the southern third of this sheet also contains a 

subordinate number of clasts of dolomite, quartzite, and 

granodiorite. The abundance of quartzite and granodiorite clasts increases upsection, apparently reflecting 

the progressive stripping of the younger carbonate 

source rocks. A slightly different interpretation of the 

significance of the upward change in clast types was 

suggested by Heatwole (1966), who recognized the 

essentials of this lithologic change but emphasized the
SANTA RITA MOUNTAINS C47

possibility of a significantly different age for the limestone-clast lower beds and the polymictic upper beds.

The Glance in the Syramore Canyon area, (loc. #, 

fig. 28) is also a limestone pebble conglomerate, unlike 

the scattered conglomerate beds in the overlying formations of the Bisbee. The rocks in the Bisfoee are 

mildly metamorphosed. They form fairly resistant 

outcrops that extend from the canyon bottom just above 

the ranch to a spur on the north wall of the canyon, and 

they also form a low discontinuous ledge farther northeast of the ranch.

ENVIRONMENT OF DEPOSITION

The Glance by definition is a coarse clastic rock and 

thus must have been derived from a source area of 

considerable relief. The variation in clast type from 

one lens to another of the conglomerate, and locally 

even within a single conglomerate body, shows that 

the source terranes were eroded to different stratigraphic levels over short distances. Although this condition could be provided solely by a rugged relief in 

the source area, it would be facilitated by differential 

vertd'cal movement, perhaps even by faulting, of structural blocks to juxtapose some Triassic volcanic, Paleozoic limestone, and Precambrian granodiorite terranes.

The size of the detritus deposited at the foot of a 

mountainous area does not only depend on the relief of 

the mountains or on the distance between the site of 

deposition and the mountains, but it also depends on 

the lithology of the rock in the mountains, as is 

illustrated by the recent deposits along the western 

flank of the northern Santa Rita Mountains. Little 

coarse detritus is being shed from the hills that are 

underlain by the Continental Granodiorite, a rock 

which disaggregates readily upon weathering; however, coarse gravels are being deposited at the foot of 

volcanic and limestone hills north and south of the 

granodiorke hills. Thus, after lithification, these 

gravels will have a basal conglomerate facies developed 

to the south and north of the granodiorite hills that 

will be separated by an arkose facies adjacent to the 

granodiorite hills. This arkose facies will be indistinguishable from the arkoses that will be deposited upon 

the basal conglomerate as the present cycle of erosion 

and deposition progresses and the volcanics and limestone are stripped off the underlying granodiorite. With 

this situation in mind, it seems plausible that some of 

the arkose identified as Willow Canyon is a lateral, or 

facies, equivalent of the typical Glance. Thus, the 

lenticularity of the Glance could be the result of provenance variations, as well as of topographic conditions.

WILLOW CANYON FORMATION

The Glance Conglomerate of the Box Canyon area 

(loc. B, fig. 28) grades upward over an interval of a 

few hundred feet into finer grained and progressively 

better bedded and sorted rocks. Above the horizon at 

which thick conglomerate beds cease, the rock is assigned to the Willow Canyon Formation. Along most 

of this contact, however, the position of the Willow 

Canyon cannot be located wy ith precision because outcrops are sparse. The Willow Canyon Formation consists dominaiitly of arkose about 2,200 feet thick; it 

contains a considerable number of thin conglomerate 

beds and toward its top some siltstone beds and a few 

limestone lentils. Locally, the formation shows rapid 

lateral changes in facies: it may even grade laterally into 

the Glance lithology.

DISTRIBUTION

Willow Canyon rocks have been identified only 

north of the Sawmill Canyon fault zone. The largest 

belt that is underlain by the formation abuts the fault 

zone (loc. 7>, fig. 28). The rocks of this outcrop belt, 

which are considerably altered, are faulted along most 

of three sides and are overlain to the east by the Apache 

Canyon Formation; locally they appear to lie conformably on a small wedge of Glance. The Willow Canyon 

crops out in a klippe north of locality D and also is 

present in grabens between localities D and B. Willow 

Canyon rocks reappear in a belt that extends from about 

2 miles south of Box Canyon, locality B, to 1 mile north 

of the canyon. This belt of rocks is also typically bounded 

by faults; but at and north of Box Canyon, it resits 

conformably upon the Glance. Both mildly metamorphosed and severely altered rocks of the Willow Cainyon are exposed in six large structural blocks, largely 

along the east, flank of the range, in and north of the 

Rosemont district. The identification of the rocks in 

one of the northern blocks is in doubt, and to a lesser 

degree this uncertainty extends to rocks of the adjacent 

blocks. Along the western margin of these blocks, the 

Willow Canyon and Willow Canyon(?) of this area 

are faulted against Paleozoic rocks or locally against 

the Glance; to the east, beyond the edge of the area 

shown in figure 28, they are unconfonnably overlain by 

younger Cretaceous or Tertiary rocks. In the Helvetia 

district, on the west flank of the range, a small area 

within the Helvetia klippe is also underlain by altered 

rocks assigned to the Willow Canyon.

Willow Canyon rocks are extensively exposed in the 

basin of Sycamore Canyon (loc. <7, fig. 28), where they 

are locally conformable above Glance and extensively 

conformable beneath the Apache Canyon Formation. 

The rocks of the main mass of the Willow Canyon are
C48 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

folded into a syiicline and a slightly overturned anticline; they are slightly metamorphosed to the north 

and are faulted and intruded along the western margin of the mass. The formation is also exposed in small 

fault slices along the tear and thrust fault system 

which bounds the main mass of Willow Canyon; in 

some of the slices, the rocks are more intensely metamorphosed, and in all of them the rocks are considerably 

sheared. Near the ranch and southwest of locality #, 

the Willow Canyon of the lowest thrust plate overlies 

the Glance with apparent conformity. Northwest of 

locality C, numerous inclusions of metasedimentary 

rocks presumed to be Willow Canyon, only a few of 

which are shown schematically in figure 28, are included in a graiiodiorite and quartz monzonite intrusive 

complex of the lowest thrust plate. Near the ranch, 

there are also several small masses of poorly exposed 

arkosic rock assigned to the Willow Canyon and of 

intensely metamorphosed arkosic (?) rock of Willow 

Canyon (?) designation.

LITHOLOGY

Most observations on the stratigraphy of the Willow Canyon Formation were obtained from the three 

largest outcrop areas, at localities Z>, B, and C (fig. 

28). In the southernmost of these areas, the rocks vary 

laterally from a sandstone-rich facies near locality D 

to a siltstone facies toward both the northeast and 

the southeast. The transitions between these facies are 

much better exposed to the northeast (than to the southeast. To the southeast, the rocks of the lower part of 

the formation consist of abundant brown sandstone 

beds and sparse gray siltstone and shale. The bedding 

of many of the sandstones is subtly graded; more 

rarely, channel-scour markings and crossbedding are 

also present. The abundance of the shale and siltstone 

beds increases gradually upsection, and a few beds are 

limy. Scraps of molluscan fossils appear in a few beds.

Near locality D (fig. 28) the Willow Canyon rocks 

are largely grayish-red to yellowish-brown coarsegrained arkose with scattered thin beds of conglomerate, conglomeratic sandstone, and greenish-gray siltstone. Beds in the arkose are commonly %-A feet thick, 

and some include a few finer laminations. The conglomeratic beds are made up chiefly of grit and of 

pebbles less than 2 inches across; but they also contain 

some scattered cobbles which consist mainly of sandstone, less comonly of silicic volcanic rock, and least 

commonly of fine-grained siliceous rock, possibly chert. 

One mile northeast of locality Z>, the conglomerate 

and grayish-red to yellowish-brown sandstone beds are 

fewer and finer grained, and the intercalated greenishgray siltstone beds are more abundant and thicker. 

The coarser beds interfinger with the finer ones, and

the coarser beds that are high in the formation transgress northeastward beyond the limit of those low in 

the formation.

The lowest few hundred feet of the formation in the 

klippe north of locality D and also those at least a mile 

northeast of locality D contain some scattered beds, 

each a few feet thick, of chip-bearing red mudstone. 

The chips in these beds are unsorted, and some are 

fragments of orthoclase. These beds closely resemble 

the consolidated equivalents of the weakly developed 

soils formed on the low terrace deposits of streams 

that drain areas underlain by the Continental Graiiodiorite. By analogy, they are believed to be regolith beds, 

which have either formed in place or been brought in 

from nearby areas by sheet wash or colluvial action 

rather than by streams.

The Willow Canyon Formation of the Box Canyon 

area, locality B (fig. 28), is sufficiently different from 

that near locality Z), to the south, that detailed correlation of units within the formation has not been 

possible. A short distance south of Box Canyon, the 

formation consists of alternating beds of grayish-orange-pink conglomeratic arkose and arkosic grit and 

beds of pale-reddish-brown arkosic sandstone, in units 

tens of feet to a few hundred feet thick. The lightcolored coarse-grained beds form low ribs of outcrops 

and are usually thinner than the other units; northward toward Box Canyon they are gradually thinner, 

and some of the upper beds wedge out. The pebbles 

in the southern part of these beds are quartzite and 

make up scarcely 1 percent of the units; most pebbles 

are no larger than an inch across, although a few are 

3 inches across. In contrast to the lighter colored gritty 

beds, the red beds are better sorted and bedded and in 

many places are crossbedded. Toward the north, their 

grain size also decreases, so that near Box Canyon 

many of these units are siltstone. On the south flank 

of Box Canyon, one of the red-bed units contains limy 

nodules 1-2 inches across; nodules such as these appear sporadically in many of the red-bed formations. 

In thin section (fig. 29) one such red-bed unit is seen 

to consist of 30 percent quartz grains, a slightly larger 

percentage of feldspars that include chiefly albitized 

plagioclase but also some microcline and orthoclase, 

and a few percent of volcanic rock fragments, all in 

an abundant fine-grained matrix.

The largest graben block north of Box Canyon and 

northwest of locality B (fig. 28) also consists of alternating light-colored grit beds and red sandstone and 

siltstone of this facies of the Willow Canyon Formation. The rocks of the other graben blocks are arkose 

or arkosic conglomerate mixed in places with red beds; 

they thus resemble most closely the rocks of the Willow Canyon in locality />.
SANTA RITA MOUNTAINS C49

FIGURE 29. Photomicrograph of an arkose from the red beds 

of the Willow Canyon Formation in the Box Canyon area. 

Crossed nicols. Grains: perthitic orthoclase (O), microcline 

(M), quartz (Q), and plagioclase (P).

The identification of the red sedimentary rocks of 

the structural blocks in and north of Kosemont is a 

problem because of their poor exposure and their intense iron-oxide alteration. The southernmost structural block contains two short lenses of thin platy 

limestone, like those most commonly associated with 

the Apache Canyon Formation but which also appear 

in the Willow Canyon and Shellenberger Canyon. In 

the second structural block, at locality E, a thick massive unit of coarse volcanic conglomerate is overlain by 

a thick unit of arkose and arkosic conglomerate. Inasmuch as the upper unit resembles the Willow Canyon 

and the lower unit differs markedly from .nearby exposures of the Glance, both are mapped as Willow 

Canyon. Volcanic conglomerate also appears in the 

Willow Canyon farther north; therefore, that rock 

type is not unique in the formation. In the next block 

to the north, the drab-colored sandstone and thin beds 

of conglomerate, in places also intensely flooded with 

iron oxide, probably are Willow Canyon, and possibly 

the rocks in the next block to the north are too. However, along the east edge of the area of figure 28, a 

rhyolitic tuff appears to be interbedded in the red 

clastic rocks of this block; thus, conceivably this sequence, as well as that in some of the adjacent blocks, 

is a pre-Bisbee Mesozoic unit. Finally, the poorly exposed beds in the northernmost structural block are 

also a red-bed sequence of sandstone, siltstone, and 

conglomerate. The base of the block contains some 

lentils of limestone conglomerate, which are suggestive 

of the Glance, and the upper third of the block contains red mudstone and some tuffaceous(?) sandstone. 

A Willow Canyon correlation is favored for this sequence, although again the alternate possibility of a 

correlation with older rocks remains.

In the Sycamore Canyon area, locality C (fig. 28), 

the Willow Canyon Formation consists of arkose and 

arkosic conglomerate that typically crop out in only 

small areas and weather pale brownish gray. Low in 

the formation, a thick volcanic conglomerate unit is 

interbedded with the arkose, and in the upper third 

some units are gray siltstone. The volcanic conglomerate lies on the ridge north of Sycamore Canyon, 

where it appears as a poorly exposed massively bedded 

drab-colored rock containing abundant subangular 

clasts of rhyolitic and dacitic composition of unknown, 

but presumed local, provenance. The dominant rock 

of the formation in this area is a yellowish-brown 

arkose, which is usually coarse grained; in places, a 

grit or conglomeratic arkose occurs whose pebbles are 

subrounded sandstone or quartzite. A little calc-silicate 

hornf els in the middle of the formation indicates that 

some calcareous siltstone is also present.

In thin section, a sample of arkose from north of 

Sycamore Canyon is seen to contain about equal 

amounts of quartz and feldspar grains and finegrained interstitial material, which includes cementing 

and alteration products. In contrast to the reddishbrown arkose of the Box Canyon area, however, the 

feldspars consist largely of microline grains. Fragments of perthitic orthoclase, resembling only the large 

crystals in the Continental Granodiorite, are also present. This arkose apparently was derived from an area 

that was underlain entirely by Precambrian rocks.

FAUNA AND AGE

Limy black shale beds from southeast of locality D 

(fig. 28) contain some fragments of molluscan fossils. 

One such bed, a third of a mile east of the Snyder mine 

(Drewes, 1971a), contains the following fauna, identified by E. G. Kauffman of the U.S. Geological Survey 

(USGS Mesozoic locality 28T15) :

Mactra sp. indet. 

Ostrea sp. immature 

Corbiculal sp.
C50 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

Thracia sp. cf. T. gracilis Meek and Hayden 

Nuculava sp. cf. N. sp. B. of Stephenson 

Tellina sp.

Kauffman indicates that this is a marine fauna, except for the Corbiculal sp., which is a brackish- to 

fresh-water element. The fossils are not sufficiently well 

preserved or diagnostic to allowT a placement more precise than Cretaceous.

ENVIRONMENT OF DEPOSITION

Like the Glance Conglomerate beneath it, the WilIOWT Canyon Formation showT s by its lateral variations 

and its abundant content of coarse clasts that it wT as 

deposited mainly in a piedmont environment by 

streams. During Willow Canyon time, the mountains 

wTere more subdued or were farther from the site of 

deposition than they wT ere during Glance time, but 

they still contained locally a variety of rock types that 

provided dominantly granitic, but some volcanic, detritus. Even during Willow Canyon time, the progressive 

subduing of the source areas is marked by the gradual 

upwT ard decrease in grain size of the sediments. The lenticularity and the poor sorting of the deposits are 

compatible with deposition by running water, conceivably in a semiarid environment like the present 

environment in southwestern Arizona.

The abundance of detritus in the northern Santa 

Rita Mountains that has been derived from a Precambrian granitic source suggests that the source area lay 

to the wT est, because in other directions the available 

nearby exposures indicate the Paleozoic cover to be 

extensive and also because the available Precambrian 

contains relatively little granitic rock.

APACHE CANYON FORMATION

The Apache Canyon Formation, a sequence of siltstone and arkose 1,500-2,000 feet thick, conformably 

overlies the Willow Canyon Formation. This formation showT s less lateral variation in lithology than do 

the underlying ones, but it also becomes increasingly 

finer grained upsection. Its basal contact is broadly 

gradational, generally being placed at the approximate 

position at wThich siltstone is dominant over arkose. 

Locally, more specific positions wTere selected for this 

contact based on convenient marker beds, and so it is 

unlikely that it is a fully synchronous horizon as 

mapped.

DISTRIBUTION

The Apache Canyon Formation is recognized on 

the west flank of the central part of the mountains and 

in two places on the east flank of the northern end. 

On the west flank at locality F (fig. 28), the Apache 

Canyon underlies a northwest-trending belt of low hills 

between Montosa Canyon to the south and the lower

reaches of Agua Caliente Canyon to the north. To the 

southwest, these rocks are separated by faults from 

either Permian limestone wThich underlies rugged hills 

or Triassic volcanics wThich underlie a pediment. They 

are separated by a fault or by an intrusive contact 

from younger granitic rock to the northeast. The ends 

of the belt of Apache Canyon rocks are also faulted. 

The rocks within the belt dip steeply southwestward 

and are moderately to strongly hornfelsed and epidotized.

East of locality D (fig. 28), Apache Canyon rocks 

appear in the trough of the Boston Gulch syncline 

(Drewes, 1970). The rocks of the southern part of this 

area generally dip steeply northeastward but locally 

are folded so that dips vary; in the northern part of 

the area, they dip more gently southeastward. The 

rocks lie conformably upon the WillowT Canyon to the 

west and are unconformably overlain by gravel to the 

east. Near locality D, epidotized and slightly hornfelsed rocks form an elliptical contact aureole 1 mile 

by 2 miles in extent centered around a swarm of quartz 

latite porphyry intrusives.

A sinuous belt of Apache Canyon Formation also 

lies east of locality C (fig. 28) on the east side of the 

basin of Sycamore Canyon. The rocks there lie conformably between the overlying and underlying formations of the Bisbee Group and dip moderately steeply 

southeastward to northeastward, depending on their 

location along the several folds that produce the sinuosity of this outcrop belt. To the south, the Apache 

Canyon is faulted out, and to the north it is intruded 

or covered by gravel.

LITHOLOGY

In each area, the Apache Canyon Formation consists 

dominantly of siltstone and mudstone but includes 

considerable fine-grained sandstone and arkose, a small 

amount of pebble-and-chip conglomerate, and a few 

thin beds of limestone. East of locality D (fig. 28), for 

example, siltstone and shale make up about 70 percent 

of the rock and sandstone 25 percent, wT ith the sandstone in beds 1-3 feet thick. Usually the siltstone beds 

are medium dark gray to greenish gray and weather 

to a brownish gray, but at locality F some of them are 

pale red to grayish red. Locally, graded bedding, channel-scour features, and crossbedding are present, and 

some of the red mudstone along the upper part of Agua 

Caliente Canyon at locality F is limy. Strongly crossbedded arkose is shown in figure 30, and slightly hornfelsed siltstone with limy nodules in the bed behind the 

pick is showT n in figure 31. In thin section, the arkose 

is also seen to contain several percent fragments of 

volcanics. The dominant feldspar among the clasts is 

orthoclase, and the plagioclase grains are of albite.
SANTA RITA MOUNTAINS C51

}'

FIGURE 30. Outcrop of crossbedded arkose of the Apache 

Canyon Formation along Agua Caliente Canyon.

The pebbles in the intercalated conglomerate beds 

are usually less than 1 inch across. At locality F (fig. 

28), they are porphyritic to vitrophyric volcanics of 

rhyolitic to dacitic composition, which are possibly derived from the Mount Wrightson Formation. Elsewhere, such as at locality D, they are of fine-grained 

siliceous material, possibly chert, and in places they 

are also of sandstone.

Intercalated limestone beds are either thin platy to 

laminated rocks or are blocky-fracturing calcarenite. 

They range in thickness from a few inches to a few 

feet and in color from light gray to grayish browTn. 

Most of them are unfossiliferous; however, sparse unidentifiable fragments of clams and gastropods have 

been collected from three limestone lenses, which are 

half a mile south-southwest of Greaterville, north of 

the lower reaches of Fish Canyon, and high on the 

spur a quarter mile north of Montosa Canyon. These 

beds resemble some of the fossiliferous beds of the 

adjacent formations, whose faunas thrived in a brackish-water or saline environment.

FAUNA

A small molluscan fauna was collected from some 

thin limestone beds assigned to the Apache Canyon 

Formation, located about half a mile southwest of 

Greaterville and about 1,000 feet east of the Greaterville-Fish Canyon road. N. F. Sohl (written commun., 

1970) identified the gastropods Neridoimis and Nerita 

in this assemblage, and Erie Kauffman (written commun., 1970) lists many bivalves of a single species, cf. 

Meretrix or Transenella sp. indet., which is new for the 

Cretaceous of the interior States. Both groups of fossils are common in an estuarine environment and suggest a brackish-water situation.

FIGURE 31. Outcrop of slightly hornfelsed mudstone and siltstone of the Apache Canyon Formation along Agua Caliente 

Canyon.

ENVIRONMENT OF DEPOSITION

The Apache Canyon sediments wrere deposited in a 

lowland, chiefly by streams, and partly in local shortlived ponds or lagoons, whose waters were probably 

brackish or saline. The source rocks were still dominantly granitic but in part volcanic. The preponderance of gray and green shale and siltstone over red 

beds, even away from contact aureoles, suggests that 

reducing conditions existed at the deposition sites. 

Limy deposits accumulated in shallow bodies of water; 

a fewT of these seem to have supported a fauna of clams 

and gastropods. The association of the bodies of water 

with reducing environments in nearby mudflats suggests that a high water table at least helped to inhibit 

oxidation.

SHELLENBERGER CANYON FORMATION

A sequence of black shale and siltstone that contains 

intercalated sandstone and limestone beds conformably 

overlies the Apache Canyon Formation of the Sycamore Canyon area, east of locality C (fig. 28). This 

sequence is assigned to the Shellenberger Canyon Formation of the Bisbee Group, a formation that is normally about 1,500 feet thick. Scarcely half of the formation is present within the Sahuarita quadrangle 

(Drewes, 1971b) ; an unmetamorphosed part of it is 

present on the southern limb of a large anticline and a 

moderately metamorphosed part on the northern limb 

of that fold. The lower contact is broadly gradational, 

and so for convenience it is placed above a fairly extensive limestone marker bed.

To the south, the dominant rocks are dark-gray fissile shale, laminated shale, some black shale with siliceous nodules, and siltstone with well-developed cross-
C52 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

bedding, graded bedding, and ripple marks. Relatively 

thin beds of limestone and olive-brown sandstone, like 

those in the underlying formation, are also present, as 

are lentils of iiitraformatioiial conglomerate and chip 

conglomerate whose fragments are of siliceous material. Beds of limestone are rarely as much as 3 feet 

thick and are similar to those in the Apache Canyon 

Formation in most respects. Limestone with paper-thin 

laminae, in places finely creiiulated, and fossil hash 

beds are more common in this formation than in the 

underlying rocks, however. Locally, two marker beds 

about 30 feet apart contain a hash of molluscan shells; 

these beds are similar to beds recognized by T. L. Finiiell (oral commun., 1968) in the Empire Mountains. 

The rocks of the Shelleiiberger Canyon Formation 

are believed to have been deposited largely in a lagoonal 

or estuariiie environment. The relative abundance of 

limestone beds in this formation and in the top of the 

Apache Canyon Formation and the occurrence of marine fossils in the Empire Mountains (T. L. Fimnell, 

oral commun., 1968) suggest that these rocks may be 

generally correlative with the Mural Limestone of the 

Bisbee Group in its type area. The marine incursion represented by the Mural is inferred to have advanced 

northwestward from the region of north-central Mexico 

to Bisbee and on to the vicinity of the northern part of 

the Santa Rita Mountains. This incursion roughly coincided with the maximum degradation of the uplands 

that supplied the abundant coarse detritus during most 

of early Bisbee time.

TURNEY RANCH FORMATION

In the northern part of the Santa Rita Mountains, 

just beyond the edge of the Sahuarita quadrangle and 

locality C (fig. 28), the shales of the Shellenberger 

Canyon are conformably overlain by a sequence of 

alternating siltstones and fairly quartzose sandstones 

that are assigned to the Turney Ranch Formation, the 

highest unit of the Bisbee Group. This sequence reappears in several places farther south in the Santa 

Rita Mountains, where it is at least 1,500 feet thick. 

From outcrop area to outcrop area, the 'lithology of 

the formation is seen to vary slightly along strike in 

such a way that locally it resembles the lithology of 

other Cretaceous rocks. In these southern areas, however, the base of the formation is unexposed, and inasmuch as the top is an unconformity, different stratigraphic intervals may be represented in the several

areas.

DISTRIBUTION

Rocks of the Turney Ranch Formation appear in the 

core of a tightly folded anticline in the Adobe Canyon 

area 1 mile northeast of locality A (fig. 28). The Turney Ranch Formation is unconformably overlain by 

the Fort Critteiiden Formation, and to the southeast 

both formations are covered by gravel deposits. Part 

of the southwestern contact is faulted. The Turney 

Ranch is exceptionally well exposed along the many 

deeply incised small canyons and is accessible by a 

small road up Adobe Canyon.

Rocks of this formation also crop out in a narrow 

northwest-trending zone that extends along the flanks 

of the two canyons named Saw^mill Canyon, wy hose 

common divide lies approximately along the boundary 

between the Sahuarita and Mount Wrightson quadrangles. In this zone, the rocks are either faulted 

against or are unconformably (?) overlain by the Fort 

Critteiideii Formation 011 the southwest, and they are 

faulted against Triassic or older rocks of the Sawmill 

Canyon fault zone on the northeast. The rocks in this 

outcrop zone are broken by faults in two places. The 

rocks of the southeastern segment of the zone, locality 

H (fig. 28), are in a fault block along the edge of the 

Saw7mill Canyon zone and dip moderately steeply 

northeastward. Those in the other two segments commonly dip moderately steeply to steeply southwestward 

but locally are warped into tight folds subparallel to 

the Sawmill Canyon fault zone, so that dip directions 

change abruptly. Axial-plane faults break the stratigraphic continuity around some of these folds.

LITHOLOGY

In both of these areas, red mudstone or siltstone is 

three to four times as abundant as the intercalated 

beds of sandstone. The outcrop expression of the formation changes markedly in response to the variation 

in thickness and induration of the sandstone beds.

In the Adobe Canyon area, northeast of locality A 

(fig. 28), the sandstone beds are thickest, and many 

are quartzitic. Inasmuch as they are upended 011 the 

east flank of the anticline there, the quartzite beds 

weather out to form prominent ribs of rock and walls 

which jut out into the canyon. Bath Tub Tank is a 

natural pool, augmented by a small concrete dam, 

which is formed in a group of quartzite beds. A stratigraphic section of almost 1,500 feet of the Turney 

Ranch is measured in Adobe Canyon (fig. 32). Its base 

lies about 1,000 feet southwest of Bath Tub Tank 

near a large alligator juniper along the western fork 

of a gully tributary to Adobe Canyon from the west 

(SWViSWVi sec. 24, T. 20 S., R. 15 E., uiisurveyed). 

The rocks are almost completely exposed along the 

tributary gully and along a part of Adobe Canyon. 

The top of the section is at the base of an olive-gray 

conglomerate, just west of the roadhead.
SANTA RITA MOUNTAINS C53

A typical sandstone or quartzite unit is a very 

light gray medium-coarse-grained thick-bedded rock 

about 40 feet thick. Pebbles are scattered in the lowest 

beds, and finer sand is common in the upper ones. 

Large sweeping crossbedding is present in many beds. 

The sandstone units low in the formation are more 

arkosic and less well indurated than those high in the 

formation, and they tend to grade into the adjacent 

siltstone units. Some of the beds are reddish brown and 

are separated from neighboring gray sandstone beds by 

thin siltstone units (fig. 33).

Two thin sections of a typical quartzite, unit 19 of 

the measured section, collected from 1 mile northwest 

of the section and from a third of a mile south of it, 

show the rock to be an impure quartzite with wellsorted grains 0.2-0.3 mm in size. The grains are either 

subrounded or have been partly resorbed to form an 

interlocking mosaic in which some of them have silica 

overgrowths. Quartz grains make up 80-90 percent of 

the rock, granular argillaceous material (perhaps 

altered feldspar or reworked clay chips) and intergranular argillaceous material make up 5 10 percent, 

and schorlitic tourmaline, zircon, magnetite, and pyrite 

appear in trace amounts. A few flakes of sericite lie 

between quartz grains, and apatite is included within 

the quartz grains.

A typical siltstone unit is about 150 feet thick and 

contains 10-30 percent each of intercalated thin sandstone beds and of shale. It is grayish red and massive 

or thick bedded where not sandy. It may contain zones 

2-10 feet thick of irregularly shaped limestone nodules 

and pods, most of which are less than 1 inch across but 

some of which are as much as 6 inches across; the pods 

make up as much as 30 percent of a zone. Small chips 

of organic debris appear in some of the upper siltstone 

units, one of which, unit 18 of the measured section, 

contains small fragments of clams, gastropods, and 

silicified wood. One fine-grained sandstone block from 

a siltstone unit contains an intricately chambered feature that may have been algae or seaweed.

The Turney Ranch Formation at locality H (fig. 28) 

differs from that along Adobe Canyon in that the sandstone units are commonly only 5-20 feet thick, are more 

arkosic, and are so weakly indurated as to make only 

low rows of outcrops or rubble-covered ribs. Like their 

counterparts in Adobe Canyon, however, they are sufficiently extensive to be mapped separately (Drewes, 

unpub. data). Most of the 16 or more groups of sandstone beds are fine grained to medium coarse grained 

and pale brownish gray; the basal parts of a few of 

them are gritty or conglomeratic sandstone. The typical siltstone unit is 30-100 feet thick, is pale red, and is

poorly exposed. Some of the lower units contain small 

limestone nodules.

About a third of the way from localities H to G 

(fig. 28), in the SWi/4 sec. 35, T. 19 S., R. 15 E., only 

one sandstone bed, on the hill west of the cattle tank 

(Drewes, 1971a), is sufficiently well indurated to make 

a persistent outcropping ledge. However, other lightcolored sandstone beds are exposed along some of the 

more deeply incised gullies that trend across the strike 

of the beds; on the slopes, these beds typically are 

hidden by the colluvium which is derived from the 

more abundant redder rocks. Similar lithologies are 

exposed along the northwestern Sawmill Canyon, 

about two-thirds of the way from localities H to G. In 

that area, a quartzite bed forms a rugged rib of rock 

for about 1 mile but gradually blends into the adjacent 

rock types over a distance of another mile in both 

directions as the unit becomes thinner and less quartzitic. Farther to the northwest, the rocks are slightly 

metamorphosed, in part at least dynamically, and the 

red mudstone and siltstones are harder. Some of these 

beds contain zones in which small cavities are prevalent, each roughly 1 inch long and alined parallel to 

the bedding. These appear to have been formed by the 

solution of the limy nodules like those that are present 

in some of the red beds to the south.

Near locality G (fig. 28), there are as many as four 

massive units of quartzite beds, some of which are 

truncated by the overlying unconformity. A sample of 

one of these beds, seen under the microscope, shows a 

typical mosaic texture of metaquartzite. Clay minerals 

and quartz cement of the matrix make up only 15 percent of the rock, quartz grains make up more than 80 

percent, and traces of clastic zircon, tourmaline, iron 

oxide, leucoxene, albite, orthoclase, and apatite make 

up the remainder.

ENVIRONMENT OF DEPOSITION

The Turney Ranch rocks are believed to have been 

deposited in a near-shore environment. The quartzitic 

sandstone beds of the Adobe Canyon area resemble 

beach deposits in their degree of sorting and their 

crossbedding. The fragments of molluscan fossils also 

suggest an aqueous environment, if not actually a 

marine situation. However, the abundant fragments of 

fossil wood in one of the siltstone units in the Adobe 

Canyon area indicate a site of deposition on or near the 

shore. Likewise, I believe the limestone nodules in red 

siltstone and mudstone were probably formed, as 

caliche nodules, in a subaerial environment. This time 

of lagoonal or estuarine deposition came to a close with 

the first uplift and deformation that culminated in the 

Laramide orogeny.
C54 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

1400

1300

1200-

1100

1000 - -

900-

800

FEET

700

22

 r 20

600

500

400-

19

300-

18

200-

17

16

14

100

12

 © 

11 Base of formation 

faulted out

FIGUBE 32. Measured stratigraphic section of the Turney 

Ranch Formation, Adobe Canyon, Santa Rita Mountains.

Description of units shown in figure 32

Conglomerate of the Fort Crittenden Formation. 

Turney Ranch Formation:

22. Siltstone (90 percent) and sandstone (10 percent). Siltstone, reddish-gray and massive. Sandstone, lightgreenish-gray to yellowish-gray; base of beds gritty 

to coarse grained, remainder medium coarse grained. 

21. Sandstone. Light greenish gray; mainly medium coarse 

grained except bottom 4 ft, which is coarse grained 

and contains basal grit conglomerate. This unit 

thickens to north.

20. Sandstone (50 percent) and siltstone (50 percent). 

Sandstone, yellowish-gray to grayish-red, mediumfine-grained ; in subunits as much as 6 ft thick. 

Siltstone, reddish-gray, massive. Lower part of unit 

includes:

a. Limy sandstone,

b. Conglomeratic sandstone containing chips, and 

c. Siltstone, containing 5 percent very fine grained 

sandstone and 1 percent limestone nodules, 

mainly %-2 in. in diameter.

19. Quartzite. Very light gray, well sorted, fine grained 

to medium coarse grained; sweeping crossbedding; 

upper part of unit grades into sandstone. Site of 

Bath Tub Tank.

18. Siltstone. Reddish gray, massive; scattered limestone 

nodules as much as *4 in. in diameter, mainly near 

top of unit; some fine-grained reddish-gray sandstone 

near top and bottom of unit.

17. Quartzitic sandstone. Light gray to pinkish gray, mostly medium coarse grained; contains coarse sandstone 

and chip conglomerate near base of unit. 

16. Siltstone. Reddish gray, massive; contains 5 percent 

reddish-gray fine-grained sandstone at base of unit. 

15. Sandstone and quartzitic sandstone. Light gray, mostly 

medium coarse grained, very well sorted, slightly 

arkosic; base of unit is a very coarse grained slightly 

limy sandstone with sweeping crossbedding and scattered chips.

14. Siltstone. Reddish gray, massive; contains 3 percent 

limestone nodules especially concentrated in upper 1 ft.

13. Quartzitic sandstone. As in unit 17. Basal chip conglomerate and sandstone has limestone chips as much 

as y2 in. across.

12. Siltstone (80 percent) and sandstone (20 percent). 

Siltstone, reddish-gray, massive; includes 2 ft of clay 

shale containing markings of possible organic origin 

beneath sandstone subunit. Sandstone, as in unit 17. 

Forms lens high in unit that thins rapidly to south. 

11. Quartzitic sandstone. Light gray, medium coarse 

grained; in 4- to 72-in.-thick beds; contains some 

sweeping crossbeds; thins rapidly to north. 

10. Siltstone (75 percent) and sandstone (25 percent). 

Siltstone, grayish-red, massive; includes a little 

light-greenish-gray shale; contains two zones near 

top of unit* which include 5 percent limy nodules as 

much as 1 in. in diameter. Sandstone, light-brownishgray to pinkish-gray, fine-grained, slightly limy; includes a small amount of chip conglomerate. 

9. Sandstone. Very fine grained to silty sandstone (40 

percent), and medium-coarse-grained slightly limy 

sandstone (60 percent) ; in beds 1-9 ft thick that are 

faintly color laminated and crossbedded.
SANTA RITA MOUNTAINS C55

Turney Ranch Formation Continued

8. Sandstone (50 percent) and siltstone (50 percent). 

Sandstone, light-gray to pinkish-gray and less commonly pale-greenish-gray to pale-red; in beds 2-18 in. 

thick; faintly laminated and crossbedded; some beds 

contain mud flakes. Siltstone, grayish-red, massive.

7. Mudstone (90 percent) and sandstone (10 percent). 

Mudstone, grayish-red, massive. Sandstone, grayishred; consists of three intercalated beds, each 6-18 

in. thick.

6. Siltstone (60 percent) and sandstone (40 percent). 

Siltstone, grayish-red, massive. Sandstone, light-gray 

to pinkish-gray, fine- to medium-fine-grained; faintly 

laminated by dark minerals; contains a subunit of 

chip conglomerate 8 ft thick near base of unit, whose 

chips include limestone and volcanics and are commonly % in. and rarely as much as 2 in. in diameter.

5. Sandstone (80 percent) and siltstone (20 percent). 

Sandstone, light- to pinkish-gray, medium-coarsegrained ; in beds 3-36 in. thick; faintly laminated by 

dark minerals and crossbedded. The bases of some 

sandstone beds contain a small amount of chip conglomerate. Siltstone, grayish-red; in beds 1-3 ft 

thick.

4. Sandstone (70 percent) and mudstone (30 percent). 

Sandstone, grayish-pink to pale-red, fine- to mediumcoarse-grained; in beds 6-36 in. thick. Mudstone, 

grayish-red, silty; especially abundant near top and 

bottom of unit.

3. Mudstone. Grayish red, mostly massive; contains a 

1-ft-thick sandstone bed near top of unit; also contains a limestone module zone near middle of unit, 

in which nodules constitute as much as 20 percent.

2. Sandstone. Grayish red, coarse grained, with parting 

of fine-grained sandstone; contains 1 percent limestone chips.

1. Mudstone. Grayish red, massive; contains nodules of 

light-gray aphanitic limestone 1-6 in. across that 

make up as much as 20 percent of some beds. 

Base of formation faulted out.

FIGURE 33. Typical sandstone beds of the lower part of the 

Turney Ranch Formation cropping out along Adobe Canyon 

about half a mile northwest of Bath Tub Tank.

POST-BISBEE ROCKS

FORT CRITTENDEN FORMATION

Along the east flank of the Santa Eita Mountains, 

the Fort Crittenden Formation, a sequence of red and 

brown conglomerate and sandstone and of fossiliferous 

black shale, as much as 5,500 feet thick, unconformably 

overlies the Turney Ranch Formation of the Bisbee 

Group. A small body of these rocks is also present on 

the west flank of the range, where it is overlain with 

apparent conformity by volcanics of the Salero Formation, some of which have been dated as uppermost Cretaceous by geologic and isotopic methods.

The rocks of the Fort Crittenden were included by 

Schrader (1915, p. 51-54, pi. 2) in an unnamed unit 

of sedimentary rocks chiefly of Cretaceous age. They 

were later included by Stoyanow (1949, p. 59-60) in 

his Fort Crittenden Formation, and this formation 

along with the underlying Fort Buchanan Formation 

made up his Sonoita Group. As a result of the present 

study in the area, the Fort Crittenden Formation of 

Stoyanow has been modified (Drewes, 1968, p. ClO) to 

include at least 4,000 feet more of conglomerate, sandstone, and fanglomerate above the original top of the 

formation. Furthermore, the Sonoita Group is formally 

abandoned as a stratigraphic unit, because it included 

such diverse formations as the Turney Ranch, a part 

of the already established Bisbee Group of Early Cretaceous age, the Gardner Canyon of Triassic age, and 

the modified Fort Crittenden of Late Cretaceous age.

The Fort Crittenden Formation consists of five informal members; four are sedimentary rocks, and one 

is lenticular volcanic rock. The sedimentary members 

are, in rising succession, the shale member, the lower 

red conglomerate member, the brown conglomerate 

member, and the upper red conglomerate member. The 

four sedimentary members show at least a small 

amount of interfingering with adjacent members, in 

addition to their dominant sequential order. This interfingering is most pronounced between the lower red 

conglomerate and the brown conglomerate, as shown 

in figure 34. Some of the brown clastic rocks are scattered within the red conglomerates, and a few tongues 

of red rocks also appear within the dominantly brown 

beds. The fifth member, a rhyolitic tuff, is intercalated 

chiefly in the upper red conglomerate but also in the 

adjacent part of the brown conglomerate. To emphasize its geologic significance, I consider it a separate 

member because it is the first record of volcanism 

associated with the magmatic activity of the Laramide 

orogeny, and it occurs over a distance of at least 10 

miles and may occur as far distant as northern Sonora.
OCn

p 

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Fort Crittenden Formation

A.
SANTA RITA MOUNTAINS C57

DISTRIBUTION

The Fort Crittenden Formation crops out in at least 

three areas in the Santa Rita Mountains, only two of 

which are in the Mount Wrightson (Drewes, 197la) 

and Sahuarita (Drewes, 19Tlb) quadrangles. The other 

areas occur in the extreme northeastern tip of the 

mountains; they will be described separately by T. L. 

Finnell (impub. data) in his report on the Empire 

Mountains.

The main body of the formation underlies a belt that 

extends from the lower reaches of Big Casa Blanca 

Canyon northward to the Sawmill Canyon fault zone 

(fig. 28) and then diagonally across the range to the 

spur between the mouths of Florida and northwestern 

Sawmill Canyon. In general, these rocks form a graben 

bounded by faults on the northeast and the southwest. 

To the northwest and southeast, they are overlain by 

piedmont gravel. In the core of the tight anticline in 

Adobe Canyon, however, the Turney Ranch Formation 

lies unconformably beneath the Fort Crittenden, as 

shown by the truncation of one of the marker beds (a 

in figure 34). The rocks within the graben block are 

folded subparallel to the bounding faults; dips are 

very steep in Adobe Canyon and near Florida Canyon 

but are moderate to gentle elsewhere.

The formation also underlies a small zone between 

Montosa and Agua Caliente Canyons on the west flank 

of the mountains. This zone lies parallel to, and about 

1 mile west of, the belt of Apache Canyon Formation 

at locality F in figure 28, and the rocks of the zone dip 

moderately westward. Although the rocks of this zone 

are much faulted, those along the southwestern edge 

probably have depositional contacts. The contact relations are best illustrated on the north wall of Montosa 

Canyon (Drewes, impub. data).

LITHOLOGY

SHALE MEMBER

The shale member underlies the flanks of the tightly 

folded Bath Tub Tank anticline in Adobe Canyon, 

where it is more than 550 feet thick on the east flank 

of the fold but thins rapidly around the crest and is 

only 4-10 feet thick on the west flank. A composite 

stratigraphic section of this member was measured 

along the thick sequence on the east side of the fold 

(fig. 35). The lowest rocks were measured along Adobe 

Canyon, as a continuation of the section of the Turney 

Ranch Formation (fig. 32). The remainder of the rocks 

were measured east of El Pilar Tank, a quarter of a 

mile to the north, where the shale member is completely 

exposed.

The most characteristic rock of the shale member is a 

dark-gray shale and mudstone, but the member also

contains siltstone, limy sandstone, conglomeratic sandstone, and conglomerate. These rocks may be grouped 

into four units; in rising sequence, they include a lenticular basal conglomerate, a shale and siltstone unit, 

a clam-siltstone, and a shale unit. The base of the shale 

member is everywhere covered, but along the flanks of 

the fold, the beds adjacent to the contact are parallel. 

Only the appearance of a lenticular basal conglomerate 

and the truncation of the uppermost several hundred 

feet of the conglomerate around the crest of the fold 

suggest that a slight angular unconformity underlies 

the shale member.

The basal conglomerate and conglomeratic sandstone 

form a tongue that is 100 feet thick near the roadhead 

in Adobe Canyon but pinches out north of El Pilar 

Tank (fig. 34). The rock is massive to faintly bedded 

and is so friable that good exposures are sparse. Most 

of the rock is drab colored, but locally, as along Adobe 

Canyon, the lower half of the conglomerate unit weathers to reddish gray. The clasts are mostly of pebble 

and cobble size, but a few are boulders. They consist 

of (1) volcanics, some of which were derived from the 

Mount Wrightson Formation, (2) sandstone, some of 

which may be Turney Ranch, and, more rarely, (3) 

Paleozoic limestone. The clasts lie in beds or are scattered in a friable fairly well bedded sandstone and 

silty sandstone.

The shale and siltstone unit of the shale member of 

the Fort Crittenden Formation is slightly more than 

125 feet thick. Conglomeratic siltstone at its base marks 

a lithologic transition from the underlying conglomerate unit. The beds above the transition zone consist 

of about 75 percent reddish-gray to medium-dark-gray 

thin-bedded silty shale, 5 percent grayish-orange finegrained sandstone in beds 2-5 feet thick, and 20 percent siltstone intercalated in the shale and most abundant near the sandstone beds. Small nodules of limestone and chips of clams appear in the upper half qf 

the unit.

The clam-siltstone, 125 feet thick, has the most heterogeneous lithology of the four units (fig. 36). It is probably unit 3 of Stoyanow (1949, p. 60) in which the 

conglomerate content has been overemphasized owing 

to the extreme brevity of his description. In the measured section (fig. 35), there are a few feet of pebble 

conglomerate in the center of the unit and a little conglomeratic sandstone at its base, which together make 

up less than 5 percent of the unit. Although the abundance of conglomerate does vary along strike of the 

beds, it is nowhere significantly more abundant than 

in the measured section. However, inasmuch as the pebbles are relatively resistant rock, they are concentrated 

on weathered surfaces and give the impression of great
C58 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

FEE

600

500

Turney Ranch 

Formation

FIGURE 35. Measured stratigraphic 

section of part of the Fort Crittenden Formation.

Description of units shown in figure 35

Basal part of lower red conglomerate member of Fort Crittenden Formation:

6. Conglomerate. Brown; pebbles and cobbles in a sandy 

matrix; includes 10 percent yellowish-gray to palegrayish-orange siltstone in beds 2-18 in. thick; some 

sandstone is very coarse grained (units 6 and 5 are

brown units in the predominantly red lower red conglomerate member).

5. Sandstone (50 percent) and siltstone (50 percent). Siltstone, yellowish-gray to pale-grayish-orange. Sandstone, brown, medium coarse to very coarse grained; 

in beds 2-18 in. thick. 

Shale member of Fort Crittenden Formation:

4. Shale. Dark-gray fissile shale and some massive mudstone ; contains molluscan fragments; also contains 

2 percent of sandstone in beds 6-18 in. thick.

3. Clam-siltstone. Pale-reddish-purple siltstone; contains 

clam detritus (80 percent) ; includes fossiliferous 

black shale and mudstone intercalated with siltstone 

(10 percent) ; also includes brownish-gray sandstone 

in beds 1-3 ft thick (8 percent), and conglomerate 

(2 percent). 

Shale member of Fort Crittenden Formation Continued

2. Shale (60 percent) and siltstone (40 percent). Shale, 

reddish-gray to grayish-orange, very thin bedded. 

Siltstone, reddish-gray to medium-gray ; includes about 

5 percent sandstone and a trace of conglomerate and 

of limestone; also contains some molluscan chips and 

limy nodules. 

Break in continuity of section.

1. Conglomerate. Pebbles, cobbles, and boulders in a sandy 

matrix; clasts of volcanics and sandstone; chiefly 

reddish gray, but top is greenish gray. 

Turney Ranch Formation:

Siltstone and sandstone.

abundance. Pale-reddish-purple to brownish-gray siltstone and sandstone make up about 85 percent of the 

unit, black shale and mudstone make up about 10 percent, and thin lenses of limestone and limy sandstone, 

along with the conglomerate, make up the remainder. 

Black calcite shells of clams and gastropods are very 

abundant in some siltstone beds and in the intercalated 

mudstone; many whole valves and even paired mudstone-filled valves weather out. Some shells are slightly 

compressed, probably as a result of folding of the rock; 

but most shells are undef ormed, and their internal morphology is well preserved.

The shale unit is about 120 feet thick and consists 

almost entirely of dark-gray mudstone, shale, and silty 

shale, in equal amounts; it also contains about 2 percent sandstone. The mudstone is poorly bedded or is 

imbedded, and it also contains abundant clams and gastropods. The shale is flaky to highly fissile and commonly is silty but in places is a clay shale; most is 

dark gray, but it grades into olive gray, especially to 

the north, where the silt content increases. The intercalated sandstone beds are 6-18 inches thick, medium 

coarse grained, well sorted and locally crossbedded, 

feldspathic and quartzose, and light brownish gray. 

E. B. Leopold checked several specimens of this unit 

for pollen without success.
C59

FIGURE 36. Typical outcrop of the clam-siltstone unit of the shale member of the Fort Crittenden Formation, located just east 

of the head of the road in Adobe Canyon. The clam-siltstone unit underlies the steeper slope with the ledgy oiitcrop, center; the 

shale and siltstone unit underlies the gentler slope, lower right corner; and the shale unit underlies the gentler slope, upper 

left corner.

LOWER RED CONGLOMERATE MEMBER

The lower red conglomerate member lies conformably above the shale member. It is about 1,000 feet 

thick along the line of the structure section shown in 

figure 38 but probably varies considerably in thickness 

owing to the rapid interfingering with brown conglomerate at the top and possibly also owing to attenuation on the flanks of the folds. Although red color 

and conglomerate lithology are most characteristic of 

the unit, it contains brown beds and intercalated sandstone and siltstone beds resembling those of the next 

overlying member. A lenticular yellowish-gray to grayish-orange sandstone and conglomerate at the bottom 

are units 5 and 6 in the measured section (fig. 35).

The lower red conglomerate member crops out on 

the northeast and northwest flanks of the basin along 

Adobe Canyon, and it underlies the basin that centers 

on an unnamed syncline to the west of the Bath Tub 

Tank anticline. The red conglomerate extends southward to Big Casa Blanca Canyon, where it is faulted 

on the west and overlapped by gravel on the east.

A typical sequence of beds in this member consists 

of 35 percent pebble-and-cobble conglomerate, 50 percent sandstone, and 15 percent siltstone and mudstone, 

an assortment shown in figure 37. The beds are commonly 2-10 feet thick, but some are finer laminations, 

and a very few are crossbeds; scour marks appear on 

bedding surfaces. Fresh and weathered surfaces alike 

are grayish red. The conglomerate is polymictic; the 

clasts consist dominantly of laminated and nonlaminated intensely indurated rhyolitic volcanics (probably 

derived from the Mount Wrightson Formation) and 

subordinately of granitic rock (largely of Jurassic 

origin) and of sandstone, quartzite, and siltstone (of 

Paleozoic or Mesozoic origin). Some red conglomerate 

west of Adobe Canyon is a monomyctic volcanic pebble 

conglomerate whose clasts are subrounded or subangular and are set in a sandy and argillaceous matrix.
C60 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

FIGURE 37. Typical beds of the lower red conglomerate member of the Fort Grittenden Formation along Adobe Canyon about half 

a mile northwest of El Pilar Tank. The hammer lies on a thick bed of conglomerate; to the left of this bed, red siltstone is 

dominant over sandstone beds to form several small ribs.

Sandstones, and presumably the finer grained clastic 

rocks, are subarkose to subgraywacke. Northward, as 

well as stratigraphically upward, the lower red conglomerate intertongues into the brown conglomerate 

member.

BROWN CONGLOMERATE MEMBER

About 2,030 feet of dominantly brown conglomerate 

overlies the lower red conglomerate member in the 

northeastern part of Adobe Canyon and adjacent canyons. The base of the brown conglomerate member is 

placed beneath an 80-foot-thick brown unit at about the 

5,200-foot contour on the northeast flank of the Adobe 

Canyon basin (Drewes, 197la; unpub. data). This contact continues around two minor folds on the ridge 

between Adobe and Hog Canyons, from which an incompletely exposed stratigraphic section extends 

roughly along the line of the structure section shown 

in figure 38. Around the northern end of the Adobe 

Canyon basin, however, more abundant brown beds 

appear lower in the section, and the mapped base of 

the member drops in stratigraphic level (Drewes,

unpub. data). So defined, the brown conglomerate 

member underlies an extensive area from Hog Canyon 

and the upper reaches of Adobe Canyon northwestward to the west side of the Santa Rita Mountains.

This member also consists of heterogeneous rock 

types, although brown conglomerate is its most typical 

rock. Unweathered rocks are light greenish gray, but 

the weathered ones are pale yellowish brown. Between 

Adobe Canyon and Cave Creek, the member contains 

intercalated red beds large enough to be mapped at a 

scale of 1:12,000. Most of the beds of the member are 

a few feet thick, but they range in thickness from 1 to 

50 feet. The rocks consist of pebble-and-cobble conglomerate (10-40 percent), sandstone and arkose (20- 

50 percent), and siltstone and mudstone (20-30 percent). A few grain-size and color changes are systematic. The red beds intercalated in the brown conglomerate member, for example, decrease in thickness and 

in grain size northward, which suggests that their 

provenance lay in the southern quadrants. Clasts in the 

brown conglomerate are dominantly granitic and prob-
Formation Crittenden Fort 

'. 'o

TERTIARY CRETACEOUS

AND 

QUATERNARY

Formation Crittenden Fort 

sCRETACEOUS

i a. 

SYNCLINE TANK PILAR 

ANTICLINE TANK PILAR 

TANK BATH_T_UB 

\ ANTICLINEM / 

190

ViLNVS VJ-IH 
C62 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

ably were derived from a Precambrian source to the 

north. The finer grained brown beds are arkose, also 

believed to have come from the north. Some arkose 

beds exposed a few hundred feet west of the jeep road 

in Hog Canyon and others in probably the same general horizon that crop out between Cave Creek and 

Aliso Spring contain fragments of silicified wood, and 

in one place along Cave Creek scraps of dinosaur(?) 

bone were found.

One mile north of Cave Creek, the brown conglomerate member is sheared along crests of tight chevron 

folds, and stratigraphic control within the member is 

lost. The Fort Crittenden rocks of the Florida and 

Sawmill Canyons area are like those of the brown 

conglomerate member, but it is unclear whether these 

rocks occupy the stratigraphic position of the brown 

conglomerate in Hog Canyon or whether they are a 

northern facies of one of the red conglomerate members. Under these conditions, separation of the Fort 

Crittenden from the similar-appearing Bisbee Group 

is difficult.

UPPER RED CONGLOMERATE MEMBER

111 Hog Canyon, at least 1,400 feet of red conglomerate conformably overlies the brown conglomerate 

member. The base of this red unit is relatively sharp. 

Interfingering with the underlying brown beds is 

minor; very few beds, and only those beds of brown 

conglomerate and sandstone which are thin, are intercalated in the upper red conglomerate. The rocks of 

the Fort Crittenden Formation on the west flank of 

the mountains at Montosa Canyon probably also belong 

to this member.

The rocks of the upper red conglomerate member are 

like those of the lower red conglomerate member in 

most respects. However, the rocks of the upper member 

in Hog Canyon include abundant coarse nearly monomyctic reddish-brown sedimentary breccia. Fragments 

in the breccia beds range in size from 2 to 24 inches 

and are almost wholly of a quartzitic sandstone that 

resembles most closely the sandstone beds in the fault 

block of the Turney Eanch Formation juxtaposed on 

the northeast. A few clasts of Paleozoic carbonate 

rocks are also in the sedimentary breccia beds. The 

rounding and sorting of these beds seems to increase 

stratigraphically upward and possibly also northward. 

In addition, the upper red conglomerate member, unlike the lower one, contains tuff beds, which are mapped 

as the rhyolitic tuff member.

RHYOLITIC TUFF MEMBER

On the west flank of the Santa Kita Mountains, 

about 65 feet of rhyolitic tuff is intercalated near the 

top of the Fort Crittenden Formation. On the east 

flank, however, the tuff makes several beds too thin to

be mapped at a scale of 1:48,000, but they are shown 

schematically in figures 34 and 38. The thicker tuff bed 

and most of the thinner ones are in the upper red conglomerate member, but a few thin ones appear at the 

top of the brown conglomerate member in the Hog 

Canyon area. In the Montosa Canyon area, the thick 

tuff bed is poorly exposed in five separate fault blocks; 

the largest and best exposed outcrops lie about 1,000 

feet west of the place where the Montosa Canyon road 

descends into that canyon from the north side (SW1/^ 

sec. 19, T. 20 S., K. 13 E.). The rock here is a much 

fractured and moderately intensely altered tuff and 

underlies gentle knolls and shoulders that rise above 

the adjacent conglomerate terrane.

The tuff is a pale-greenish-gray to light-brownishgray finely crystalline rock. Phenocrysts of quartz, 

plagioclase, and altered biotite are visible in specimens 

of the thicker body, but only sparse quartz and feldspar crystals appear in the thin beds. Shard textures 

and finely f ragmental textures are barely recognizable 

in hand specimen.

In thin section, the thick tuff unit is seen to be a 

recrystallized crystal-lithic tuff. Crystals make up 

about a third of the rock and consist largely of potassium feldspar, albite, partly resorbed quartz, and a 

biotite that is completely altered to hydromica and disseminated grains of iron oxide; a little titaniferous 

magnetite, apatite, zircon, and amphibole (?) are also 

present. The abundance and size of zircon crystals are 

adequate for isotopic dating. The phenocrysts are commonly 0.5 mm in diameter, but a few are as much as 

3 mm across. Lithic fragments in one specimen are of 

an intensely oxidized volcanic rock which has alined 

crystal laths. A small amount of devitrified volcanic 

glass is preserved in cavities in quartz and, before 

alteration, was probably abundant throughout the now 

thoroughly altered groundmass. Clay minerals, sericite, 

hydromica, iron oxide, and epidote are moderately 

abundant.

The tuff differs from the next overlying volcanics in 

its rhyolitic rather than andesitic composition, a compositional difference indicated by a lighter color, by 

relatively abundant quartz crystals, and by the sparsity 

of ferromagnesian minerals of the tuff. Furthermore, 

the rhyolitic rock is probably an airfall tuff, whereas 

the andesitic rock is a flow breccia.

The tuff of the thin beds of the Hog Canyon area 

is finer grained than that to the west; phenocrysts are 

commonly 0.3 mm in diameter and rarely as much as 1 

mm across. The phenocrysts are the same kind as those 

to the west, thus permitting a correlation of the beds 

across the mountains. This correlation is reinforced by 

the correlation of the associated red conglomerate. If
SANTA RITA MOUNTAINS C63

this correlation is valid, the source of the tuff probably 

was to the west, the direction in which both the beds 

are thicker and the crystal fragments are coarser.

FAUNA AND AGE

The Fort Crittenden Formation has yielded a fairly 

abundant fauna that provides a reliable Late Cretaceous age and indicates a probable late Late Cretaceous 

age (Santonian, Campanian, and Maestrichtian Stages) 

of Europe. Most fossils have been collected in the 

Adobe Canyon area but were reported without adequate description of locality or of the stratigraphy of 

the collection site. In some reviews of the faunas collected in this formation, a spuriously precise age is 

introduced as a result of oversimplifying or ignoring 

the uncertainties of the original fossil determinations. 

For example, a close comparison in the size of fossil 

teeth with those of a dinosaur, X, has been reported 

to mean that the author making this comparison 

claimed the teeth were actually those of dinosaur X.

Schrader (1915, p. 55) reported the occurrence of 

the following fossils, identified by T. W. Stanton, from 

an unspecified locality in Adobe Canyon. The bracketed comments are mine.

Unio sp., related to U. rectoidcs White [clams] 

Viviparus sp. [gastropod]

Viviparus sp., related to 8. ivyomingensis Meek [gastropod] 

Physa sp. [gastropod]

Most likely these were collected from the shale member 

near the roadhead in Adobe Canyon.

Stoyanow (1949, p. 59, 60) reported, in addition to 

these genera, Sphaerium sp. and the remains of fish 

and turtle and dinosaur teeth, the size of which Barnum Brown compared to the size of the teeth of Gorgosaums libratus.

Miller (1964, p. 378-383) described in considerable 

detail additional fossils from Adobe Canyon.

Hadrosaurian, gen. indet. [dinosaur jaw]

Plastomenus sp. [turtle scute]

Asperidetes sp. [turtle scute]

Elopid, gen. indet. [fish jaw]

Lepidosteus sp. [fish scale]

Amioid, gen. indet. [fish vertebra]

Protelliptiol sp. [elongate clam]

Unio sp. [round clam]

Viviparusl sp. [conically spired gastropod]

Physa, cf. P. reesidei [elliptoidal-shaped gastropod]

The hadrosaurian remains apparently were collected 

from either the base of the shale member or high in the 

underlying Bisbee Group at the east end of El Pilar 

Tank. Miller (1964) stated that the tarponlike elopid 

fish remains were considered by J. T. Gregory to be 

closely related to Pachyrhizodus. Most likely they were 

collected from the shale member. The fish vertebra 

and most of the fish scales were probably also obtained

from the shale member, but some scales may have come 

from the underlying rocks. The clams and gastropods 

likewise were presumably collected from the shale 

member, where they are most abundant.

D. W. Taylor (written commun., 1963) has identified the following fossils, collected in the present study, 

from the clain-siltstone unit of the shale member at a 

site 1,250 feet east of El Pilar Tank (SW^NE^ sec. 

24, T. 20 S., K. 15 E., unsurveyed).

U.S. Geological Survey Mesozoic locality No. 28710 (field 

No. 62D26f) :

Plesielliptio sp. [elongate clam]

Bellamya sp. [gastropod]

Small high-spired gastropod, indet.

Another collection of fossils from the same horizon in 

the draw about 600 feet east-northeast of the roadhead 

in Adobe Canyon (NW^SE^ sec. 24, T. 20 S., K. 15 

E., unsurveyed) were also identified by him.

U.S. Geological Survey Mesozoic locality No. 28711 (field No. 

62D66f) :

PlcsieUiptio sp. [elongate clam] 

Bellamya sp. [gastropod] 

Eupcra sp. [round(?) clam]

Plesielliptio sp., and Bettatnya sp. were also collected 

from the shale member on the west flank of the El 

Pilar Tank anticline where the shale crosses the 5,200- 

foot contour line (SEi/4SEi/4 sec. 14, T. 20 S., K. 15 

E., unsurveyed).

The Protellioptio and Unio fauna of Miller is very 

likely the same as the Plesielliptio and Eupera fauna 

of Taylor, according to W. A. Cobban (oral commun., 

1968).

H. W. Miller and K. W. Schwab (written commun., 

1966) further identified and described a large variety 

of microfossils, including fish teeth, an ostracode Cypridopsis, a mosquito, hystrichomorphs, chitmozoans, 

charophytes, and fungus remains. They indicate that 

these fossils are of mixed origin, including reworked 

Paleozoic and earlier Mesozoic forms as well as Late 

Cretaceous ones. Of these, the Late Cretaceous fossils 

also indicate a fresh-water, quiet-water, and muddy 

bottom environment.

Unidentified silicified wood and scraps of dinosaur 

bones collected from several localities in the brown conglomerate member provide no further data useful in 

dating or in ecological interpretation.

The age of the combined fauna listed above is late 

Late Cretaceous Santonian to Maestrichtian and 

more likely late than early in this interval. However, 

no single collection seems sufficiently adequate for an 

unequivocal age determination. Additional support to 

this age is available from an isotopic determination, 

assuming that the correlation of the upper red conglomerate of the Fort Crittenden Formation across the
C64 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

mountains is correct. A rhyodacite welded tuff from 

the sequence of rocks overlying the red conglomerate 

on the west side of the mountains contains biotite that 

gives a potassium-argon age of 72 m.y., as described in 

the following section. The Fort Crittenden Formation 

also overlies the uppermost rocks of the Bisbee Group, 

whose middle units contain fossils of late Early Cretaceous age. In summary, the Fort Crittenden Formation is probably of Late Cretaceous but not latest Cretaceous age.

CORRELATION

Sedimentary rocks of unquestioned Late Cretaceous 

age are scarce in the region around the Santa Kita 

Mountains, but undoubtedly more will be recognized when areas thus far only mapped in reconnaissance are studied in detail and when other redbed sequences are dated. The deposits which have a 

lithology and age most similar to the lithology and age 

of the Fort Crittenden Formation are the Cabullona 

Group in Sonora, Mexico, TO miles southeast of Adobe 

Canyon and 18 miles east-southeast of Bisbee. These 

rocks, according to Taliaferro (1933), unconformably 

overlie the Lower Cretaceous Bisbee Group and make 

a sequence about 8,000 feet thick which contains, in rising succession, (1) the Snake Kidge Formation, of red 

conglomerate and sandstone, 2,000 feet thick; (2) the 

Camas Sandstone, of crossbedded sandstone and red 

and green shale, 1,200 feet thick; (3) the Packard 

Shale, a dark gray shale containing thin beds of bentonite and capped by white sandstone, 1,800-2,500 feet 

thick; (4) the upper red beds, of sandstone and shale, 

2,000 feet thick; and (5) the light-gray rhyolite tuff, 

800 feet thick. Both marine and nonmarine fossils are 

present, and adrosauriaii remains from the upper part 

of the Snake Eidge Formation are probably of Santonian age, an age apparently preferred for the entire 

Cabullona Group.

The Fort Crittenden Formation has also been recognized by Hayes in the northwestern corner of the 

Huachuca Mountains (Hayes and Kaup, 1968), about 

a quarter of the distance from the Santa Eita Mountains to the Cabullona area. The rocks of this area consist of at least 1,500 feet of interbedded shale, sandstone, and conglomerate, which are also dominantly 

reddish brown but include some greenish-gray to darkgray beds. They rest unconformably upon folded and 

faulted rocks high in the Bisbee Group and are themselves folded; thus, the structural relations also resemble those in Adobe Canyon.

East and northeast of Adobe Canyon, there are also 

some rocks which I believe may be correlated with the 

Fort Crittenden Formation. In the Winchester Mountains, 10 miles northeast of the Little Dragoon Mountains, Cooper and Silver (1964, p. 76-77) described red 

and green conglomerate, sandstone, and shale about 

4,000 feet thick, which contains intercalated rhyolitic 

tuff and which is overlain by andesitic sedimentary and 

volcanic rocks. Likewise, in the Chiricahua Mountains, 

about 30 miles northeast of Bisbee, the Javelina formation of Epis (1956) consists of conglomerate and sandstone, apparently lying unconformably between the 

Bisbee and andesitic volcanics, a stratigraphic position 

suggestive of the Fort Crittenden.

To the north and west, similar rocks are reported, 

although they are assigned various stratigraphic positions. Fort Crittenden rocks were recognized by T. L. 

Finnell (oral commun., 1968) in the northeast corner 

of the Santa Eita Mountains, where they also contain 

some rhyolitic tuff lenses. J. E. Cooper (oral commun., 

1968) described rocks in Demetrie Wash in the Sierrita Mountains as consisting of a lower tongue of conglomerate, siltstone, and sandstone overlain by rhyolite 

tuff and andesite breccia. At least the lower tongue in 

Demetrie Wash may be correlated with the Fort Crittenden Formation, and the breccia may be correlated 

with the lowest two members of the Salero Formation.

Each of these areas of southeastern Arizona has a 

similar succession of Cretaceaus rocks. From older to 

younger, they are: (1) Bisbee; (2) unconformably overlying conglomerate, sandstone, and shale, which are 

dominantly red and commonly contain lenses of rhyolite tuff at or near their tops; (3) andesitic volcanic 

breccia, locally including andesitic sandstone; and (4) 

rhyodacitic tuff, commonly welded. This regional similarity strongly suggests that the units are generally 

correlative, and although specific units such as the rhyolitic tuff may not be completely synchronous, the volcanic rocks may be of roughly the same age, having 

come from several vent areas during the waxing phase 

of magmatism that culminated early during Laramide 

orogeny.

ENVIRONMENT OF DEPOSITION

The Fort Crittenden Formation was deposited subaerially in a tectonic environment. The abundance of 

coarse locally derived clastic rocks and of rocks of arkose and subgraywacke lithologies in the formation indicates that the detritus of which they were formed 

came from areas of considerable relief, was transported 

only a short distance, and was rapidly deposited. The 

presence of fossil land plants and animals also indicates 

a subaerial environment one which was characterized 

by a mingling of local lacustrine and more widespread 

fluvial and piedmont conditions.

Eeviewed in more detail, the local record indicates 

that following a little uplift and erosion during post-
SANTA RITA MOUNTAINS C65

Bisbee-pre-Fort Crittenden time, gravels were deposited at the base of uplifted areas. A lake or freshwater lagoon covered a small area near the site of the 

present Adobe Canyon and briefly lapped over the 

gentle rise on its southwestern shore. Organic-rich mud 

and silt was deposited in the lake, which supported an 

abundant molluscan fauna and an assortment of fish, 

turtle, and dinosaur life. Gradually the lake, or at least 

the part of it that is represented by the present Adobe 

Canyon area, was filled by gravels brought in by 

streams. These gravels were contributed by at least two 

drainage systems, whose domination in the area fluctuated; one system brought in arkosic detritus from 

the northeast, and the other contributed volcanic detritus from the southwest and perhaps also from the 

southeast. The increased abundance of fanglomerate 

that was deposited toward the end of this time resulted 

from a gradual increase in local relief that is believed 

to have been associated with an early phase of the 

Laramide orogeny. Rhyolitic tuff that was deposited 

in the gravels late during Fort Crittenden time was 

probably a preliminary sign of the major volcanic episode that followed, and its deposition brought to a close 

the time of deposition of abundant clastic rocks in the 

Late Cretaceous.

SALERO FORMATION

Dacitic volcanic rocks, about 5,000 feet thick, that 

grade upward and laterally into arkosic sedimentary 

rocks overlie the red beds of the Fort Crittenden Formation with apparent conformity and are intruded by 

latest Cretaceous plutons. In past studies, parts of this 

sequence have been variously identified because they 

underlie structurally separate areas, consist of diverse 

rock types, and are subtly crosscut and little altered by 

the plutons. Schrader (1915, pi. 2), for instance, considered most of these rocks to be Tertiary andesite and 

rhyolite that postdate the major plutonic bodies; this 

is a reasonable first approximation that seems supported by the equally gentle attitudes of some volcanics of this sequence and of some overlying glassy 

volcanics of undoubted Tertiary age. Even in the current study, the geologic relation between the nonglassy 

older volcanics, which have been separated from the 

glassy Oligocene volcanics, and the latest Cretaceous 

plutons is not everywhere unequivocal; however, in 

places the plutons demonstrably intrude the dacitic 

volcanics. This field relation is supported by the isotopic ages of about 72 m.y. for the volcanics and 62-68 

m.y. for the plutons. The sequence of older volcanics 

is assigned to the Salero Formation (Drewes, 1968, p. 

Cll) of Late Cretaceous age.

DISTRIBUTION

The Salero Formation is exposed over more than 15 

square miles, chiefly in areas that extend from the 

drainage divide south of Aqua Caliente Canyon to the 

south edge of the Mount Wrightson quadrangle. The 

main outcrop area lies between Montosa Canyon and 

Mata Site Spring, 2^ miles south of the Salero mine 

(Drewes, 197la); an outlier of the formation caps the 

quartz monzonite on the ridge north of Montosa Canyon, and some of these volcanics overlie red beds in 

the pediment north of that canyon. Small bodies of the 

Salero Formation form the wallrocks and numerous 

roof pendants and inclusions within the Josephine 

Canyon Diorite between Hangmans Canyon and 

Squaw Gulch. The formation also is the host rock to a 

second cupola of similar intrusive rock in the San 

Cayetano Mountains, a small range in the southwest 

corner of the Mount Wrightson quadrangle. The Grosvenor Hills Volcanics between the two cupolas of Josephine Canyon Diorite are probably underlain by a 

sheet of the Salero Formation, which is exposed in two 

inliers in the northern part of the volcanics. A small 

body of Salero also crops out along a thrust fault half 

a mile north of the Johnson ranch house in Sycamore 

Canyon (fig. 28; Drewes, 197lb). Much more of this 

rock lies east of this outcrop, just outside the area of 

the Sahuarita quadrangle.

BASAL UNCONFORMITY

In most places, the Salero Formation lies unconformably on the Jurassic Squaw Gulch Granite, but 

in the pediment north of Montosa Canyon it overlies 

the Upper Cretaceous Fort Crittenden Formation with 

probable conformity. The basal contact is poorly exposed in the pediment north of Montosa Canyon, on 

whose north bank, roughly a quarter of a mile west of 

the place where the Montosa Canyon road leaves the 

terrace along the canyon, the underlying red beds, the 

contact, and the overlying volcanics all dip about 45° 

westward. A little rhyolitic tuff is interbedded in the 

top of the Fort Crittenden Formation, and a few small 

bodies of red beds appear to be intercalated in the basal 

part of the Salero Formation; such an interstratification suggests a slight overlapping of depositional environments that is particularly compatible with a conformable contact.

Over large areas, the Salero Formation overlies the 

pale-orange-gray coarse-grained Squaw Gulch Granite 

with a highly irregular angular unconformity. Typically, the granite forms a paleotopography of hills and 

canyons, which are now partly exhumed from beneath 

the Salero. In the area of low rolling hills west of the 

Salero Ranch, the partly exhumed old granite knolls
C66 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

are low; likewise, small residual patches of the Salero 

Formation occupy old topographic depressions that 

were cut on the large body of granite in sec. 32, just 

south of Cottonwood Canyon. The height of the old 

granite knobs which underlie the formation increases 

in the hills near the Bull Spring mine, where some 

granite crops out only in present canyon bottoms, some 

underlies only flanks of present hills, and some caps 

present hills. Along Josephine Canyon half a mile 

southwest of Bull Spring mine, the pre-Salero surface 

forms a canyon as deep as, or slightly deeper than, the 

present canyon, which has been superposed on the 

ancient canyon for a short distance; the present canyon 

is floored by the Salero Formation, most of the present 

canyon walls are granite, and the gentle hills away 

from the present canyon are capped by the Salero 

Formation.

The old erosion surface forms a steep canyon flanked 

by some very prominent knobs between Salero Mountain and the San Ramon mine, largely in sees. 12 and 

13, T. 21 S., R, 14 E. The ancient knobs of granite in 

that area have been exhumed to form knobs on the 

present land surface. Tuffaceous and arkosic sediments, 

including fanglomerate and some sedimentary breccia, 

filled the ancient canyon and now form unfaulted 

nearly flat-lying beds that surround the knobs. 

Younger diorite and a fine-grained quartz monzonite 

border phase of the diorite locally cut the arkose and 

granite. The absence of especially coarse sedimentary 

breccia deposits from the arkose member of the Salero 

Formation at the foot of the ancient knobs suggests 

that the knobs were eroded primarily by disaggregation of grains, as is common around many granite 

knobs today. The local relief on the ancient canyon 

was more than 800 feet, similar to the present local 

relief of the area.

LITHOLOGY AND PETROGRAPHY

The Salero Formation is divisible into five members, 

of which four make a stratigraphic sequence and one 

is a lateral fades, largely of one of the sequential members. From older to younger, the sequential members 

are a lower member, of dacitic flows and tuff breccia; 

an exotic-block member, which has a dacitic volcanic 

matrix; a welded-tuff member, of rhyodacite; and an 

upper member of volcanic and sedimentary rocks composed of conglomerate, agglomerate, tuff, quartzite, and 

red beds. The fifth member is the arkose member, a 

fanglomerate deposit that is largely a lateral facies of 

the welded-tuff member but locally underlies it and 

elsewhere intertongues with the upper member. The 

sequential members are distributed in the main outcrop area from north to south; the arkose member

occurs mostly along the eastern edge of the main outcrop area of the Salero Formation, between Josephine 

Canyon and the Salero mine.

LOWER MEMBER

Dacitic to andesitic lava flows and tuff breccia at 

least 400 feet thick form the lower member of the 

Salero Formation. These rocks are best exposed along 

the upper part of Cottonwood Canyon, along the road 

1 mile northeast of the Montosa mine in the NW1/^ sec. 

21, T. 20 S., R. 14 E., and south of Agua Caliente 

Spring in and around sec, 24, T. 20 S., R. 13 E. 

(Drewes, 197la). The composition of the lower member volcanics is like that of the volcanics of the overlying more widespread exotic-block member, but it 

differs from them in that it does not include the exotic 

blocks. It may thus only be a locally developed facies in 

the lower part of the Salero Formation. Lower-member 

rocks underlie the northern part of the outcrop area of 

the Salero and dip gently southward.

The rocks of the lower member consist of a mixture 

of volcanic types, and very locally they include a few 

sedimentary beds. Northwest of the Montosa mine, the 

rocks are unlayered, intensely fractured, and altered 

and are either lava flows or sills. Likewise, in the upper 

part of Cottonwood Canyon, unlaminatd and unbrecciated rocks may be flows or small intrusives. A mile 

northeast of the Montosa mine, the rock is largely a 

tuff (?) breccia, which locally may be welded. A thin 

lens of tuffaceous sandstone and gritty arkosic conglomerate appears 1 mile east of the Montosa mine, 

and two small patches of red beds appear to be intercalated in the dacite sheets northwest of the mine.

In hand specimen, the dacitic rock appears as a 

greenish-gray to medium-gray finely porphyritic rock 

whose phenocrysts of feldspar are dominant over 

amphibole laths. The dacitic rocks are commonly moderately intensely argillized and epidotized, but locally, 

especially east of the Montosa mine, they are pyritized 

and more intensely argillized. Most likely, this intense 

alteration is related to the proximity of the contact 

with the uppermost Cretaceous quartz monzonite, but 

the geologic relations along this contact are somewhat 

unclear.

In thin section, the combined phenocrysts are seen to 

make up about half the rock. They are rarely more 

than 2.5 mm long,' and they are set in a granular 

groundmass whose crystals are 0.05-0.1 mm across (fig. 

39). Feldspar phenocrysts (20-30 percent of the rock) 

are largely albitized plagioclase, and several specimens 

also contain potassium (?) feldspar. Amphibole (10-15 

percent of the rock) commonly appears as pseudomorphs of chlorite and iron oxides. Some rocks also
SANTA RITA MOUNTAINS C67

IKi4 "?- v»' j :v^g;.'5R;A»\H- :

FIGURE 39. Photomicrograph of a fairly unaltered specimen 

(field No. G5D680) of a dacite flow of the lower member of 

the Salero Formation. Phenocrysts : hornblende (H), biotite 

(B), magnetite (M), plagioclase (P), and quartz (Q). Groundinass is largely quartz (white) and feldspathic minerals 

(gray).

contain a few percent biotite, now completely altered 

to sericite, epidote, clay minerals, leucoxene, iron oxide, 

and a few percent pyroxene. Ilmenitic magnetite and 

apatite are common accessory minerals, and sphene 

may also be present. Abundant alteration minerals, as 

mentioned above, obscure the composition of the 

groundmass.

Chemical and spectrographic analyses are given in 

table 7 (specimen 1) of a relatively unaltered dacitic 

porphyry of the lower member collected from a flow (?) 

in the SE. cor. NEi/4NEy4 sec, 24, T. 20 S., K. 13 E.

EXOTIC-BLOCK MEMBER

Conformably overlying the lower member is about 

1,000 feet of dacite breccia, which contains many allochthonous blocks derived from pre-Salero formations. 

These allochthonous blocks, here called exotic blocks, 

come from formations that are exposed in place somewhere in the Santa Kit a Mountains but not all at a 

single locality.

The exotic-block member has a broadly gradational 

basal contact with the lower member and laps beyond 

the southern edge of that member onto the Squaw 

Gulch Granite. Its gentle southwest dip across similarly sloping terrane gives it a broad outcrop area that 

extends from Montosa Canyon to Josephine Canyon. 

In many places, the exotic-block member can be distinguished, even at a distance, from the underlying 

dacitic rocks by its randomly scattered bold outcrops 

of relatively vivid and variegated reddish-gray, grayish-orange-pink, very light gray rock on otherwise 

somber-toned slopes, although elsewhere it blends in 

with the adjacent members. The jeep road constructed 

between Cottonwood Canyon and the Bull Spring mine 

in 1965 (since the publication of the topographic map) 

passes through much of this terrane, and exposures 

along this road show some varieties of exotic blocks, 

as well as their matrix.

In the field, the exotic-block member appears as a 

nearly massive sheet that consists of three components: 

exotic blocks, coarse volcanic fragments, and friable 

pulverized material. The coarse volcanic fragments 

and the friable pulverized material comprise the matrix of the exotic blocks. This matrix is a poorly exposed 

bluish-gray to greenish-gray dacitic porphyry that is 

strongly argillized and considerably epidotized and 

chloritized. The coarse fragments are typically 3-6 

inches across, and the pulverized material is unsorted 

and mostly silt-sized to grit-sized debris. In one part 

of the member about i/^-l mile north of Bull Spring 

mine, however, few fragments are more than 1 inch 

across, and the fine debris possibly contains an admixture of tuff. This finer grained tuffaceous( ?) variety of 

the exotic-block member lies at the top of the member; 

it is 400 feet thick to the north but wedges out southward near Josephine Canyon.

In thin section, the fragments of the matrix are seen 

to be subtly brecciated (fig. 40) in such a manner that 

the chips are distinctly outlined in some places but 

blend in with the groundmass in others. These chips 

are a fraction of a millimeter to at least several millimeters across and consist of small phenocrysts set in 

hyalopilitic to hyaloophitic material. Phenocrysts of 

albitized plagioclase, biotite, and amphibole are commonly 0.2-2 mm long and, together with traces of 

quartz, titaniferous magnetite, apatite, and leucoxene 

pseudomorphs after sphene, in various combinations, 

make up 40-60 percent of the rock. Microlite laths are 

0.01-0.03 mm long and make up 10-55 percent of the 

rock, and glass or altered glass makes up 5-30 percent 

of the rock. The material between the chips is cataclastic and consists of abundant debris of the phenocryst assortment present in the chips, set in a granular
C68 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

^ ^fe^l^^i" -' I____1 rr"TI____I ^ftjfl

FIGURE 40. Photomicrographs of a dacitic fragment in the matrix to the exotic blocks, exotic-block member of the Salero Formation. Left, chip-breccia texture; B, outline of area of photomicrograph on right, plane-polarized light. Right, groundmass of 

the chips, crossed nicols. In both photomicrographs, the crystals are plagioclase (P), relict biotite (B), magnetite (M), 

quartz (Q), apatite (ap), feldspar (F), and sericite (S).

to cryptocrystalline base that may be recrystallized 

(fig. 40). Both chips and interstitial material are pervasively sericitized; the feldspars are thoroughly 

altered to clay minerals; and the ferromagnesian minerals are almost completely altered to epidote, chlorite, 

and iron oxides.

Chemical and spectrographic analyses of a sample of 

matrix of the exotic blocks, collected from a blasted 

cut on the new unmapped jeep trail in the NW. cor. 

SE^SWi^ sec. 33, T. 20 S., K. 14 E., are given in table 

7 as specimen 2. This specimen and that of the lower 

member, specimen 1, are most like those of Nockolds' 

(1954) average dacite and trachytes (p. 1015, 1016), 

but neither of the analyses fits Nockolds' analysis 

closely. This difference may be due to chemical changes 

resulting from a genesis and alteration more complex 

than that of the samples considered by Nockolds.

The pulverized matrix of the coarse dacite fragments closely resembles the groundmass of the finer 

chips of which the dacite fragments are made, and it

seems likely that both this matrix and the groundmass 

constitute the same component of the volcanic rock 

complex. The pulverized matrix also contains abundant 

phenocryst debris (50-80 percent of the component) in 

a finely granular to cryptocrystalline base (fig. 41). 

X-ray powder patterns indicate that at least this component of the rock contains a small amount of potassium feldspar. Sericite, kaolinite, nontronite(?), calcite, epidote, iron oxide, and secondary quartz are 

abundant alteration products.

Exotic blocks, seemingly scattered at random 

throughout the member, have been briefly described by 

me (in Simons and others, 1966, p. D9-D21, fig. 5). 

They are rocks of Cretaceous or older age, all older 

than the Salero Formation, and they range in length 

from less than 1 inch to as much as 1,000 feet. The 

composition and distribution of nearly 200 of the 

larger more common types of blocks and of somewhat 

smaller blocks of the less abundant types of blocks 

are also indicated on the geologic map of the Mount
SANTA RITA MOUNTAINS C69

FIGURE 41. Photomicrographs of the pulverized component to the exotic blocks, exotic-block member of the Salero Formation.

Left, plane-polarized light. Right, crossed nicols.

Wrightson quadrangle (Drewes, 197la). The blocks 

are slightly less plentiful along the northeastern edge 

of the outcrop area of the member than they are elsewhere but otherwise seem to be uniformly distributed 

and without apparent stratigraphic order with respect 

to each other. The most abundant and generally the 

largest exotic blocks are assorted flow-layered latite, 

rhyodacite, and andesite volcanics that were derived 

from the Triassic Mount Wrightson Formation. Blocks 

of Jurassic Squaw Gulch Granite are next in size and 

abundance, and where the exotic-block member rests 

directly upon that granite, much granite grus has been 

incorporated into the pulverized part of the dacite matrix. Blocks of Triassic Piper Gulch Monzonite and 

brown quartzitic sandstone, of the Mount Wrightson 

Formation, are also present, as are a few small blocks 

of granite and gneiss of Precambrian origin. Blocks of 

Paleozoic rocks add much to the color variations of 

the slopes that are underlain by the exotic-block member; most of these blocks were derived from the Permian limestones, of which fossiliferous Concha Limestone is the most commonly identifiable, but some 

blocks were derived from Cambrian Bolsa Quartzite 

and from brown dolomite of the Devonian Martin 

Limestone. Blocks or pods of friable red siltstone and 

sandstone, such as those that appear along the unmapped jeep trail in the SW^SW^ sec. 33, T. 20 S., 

R. 14 E., and also in the gully east of the road below 

the unnamed small mine shown in the SEi^NW1^ sec. 

29, T. 20 S., R. 14 E., resemble the red beds of the 

Bisbee Group or Fort Crittenden Formation. The 

exotic blocks generally form discrete unshattered subequant unoriented angular bodies, but the red siltstone 

seems plastically deformed. Some limestone blocks are 

embayed by fine-grained pulverized dacite, in which 

are included chips of granite and other rocks (Simons 

and others, 1966, fig. 6).

Potential source areas for all the exotic blocks that 

are included in the member are within several miles of 

their present location. The Mount Wrightson Formation, for instance crops out extensively along the crest 

of the range 3 miles to the northeast and in small areas
C70 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

in the pediment 2 miles to the northwest. Squaw Gulch 

Granite is widespread, in part directly beneath the 

exotic-block member, and a little Precambrian gneissic 

granite appears both northeast and west of the main 

mass of the exotic-block member. Piper Gulch Monzonite xenoliths are found in Cretaceous plutons to the 

northeast, and hence this formation may have been more 

widespread before those plutons were emplaced. Cretaceous and Paleozoic rocks appear immediately to the 

north of the member. However, at present, no area as 

large as even a few square miles contains the entire 

assortment of source rocks found among the exotic 

blocks.

WELDED-TUFF MEMBER

The welded-tuff member consists of rhyodacite 

welded tuff and small amounts of unwelded tuff breccia, 

at least 1,200 feet thick, which overlie the exotic-block 

member. The welded-tuff member forms an almost unbroken sheet of more than 6 square miles that reaches 

from Cottonwood Canyon southeastward to near the 

Salero mine and southward to the San Cayetano Mountains and that appears in several inliers and upfaulted 

blocks between the San Cayetano Mountains and 

Salero. This tuff is also present in and east of Sycamore 

Canyon at the northern end of the Santa Rita Mountains. The widespread distribution of inliers and outliers of this welded tuff indicate that the tuff initially 

extended well over 30 square miles in the southern part 

of the mountains alone. Throughout this area, its average thickness probably was about 500-600 feet, thus 

indicating that at least 3 cubic miles of material accumulated to form this unit. The abundance of detritus 

of this welded tuff in post-Salero rocks indicates that 

the initial volume deposited may have been several 

cubic miles larger.

The welded tuff rests with probable disconformity 

and possible local conformity upon the exotic-block member. North of Cottonwood Canyon and just east of the 

Glove Mine (Drewes, unpub. data), the field relations in 

a structurally complex area indirectly indicate that the 

base of the welded tuff is a disconformity. A tear fault 

in that area separates the lower exotic-block member 

of the Salero Formation from Paleozoic rocks, but the 

faulting does not extend upward into the welded-tuff 

member; in this member, the layering is warped upward and subparallel to the position of the tear fault. 

The rocks are believed to have been faulted during the 

exotic-block-member and welded-tuff-member interval 

or simultaneously with the emplacement of, but before 

the final welding of, the tuff. Locally, northeast of Bull 

Spring mine, the upward gradation in the exotic-block 

member from a coarse volcanic breccia to a finer one 

that has a tuffaceous(?) matrix suggests an upward

gradation and conformable relations between the members. Thus, if the contact beneath the welded-tuff member near the Glove mine is disconformable, that disconformity is a minor one. The minor irregularities along 

the contact between the exotic-block member and the 

welded-tuff member are believed to reflect initial variations in the position of the top of the exotic-block member, rather than erosion of that top, because there are 

no epiclastic lenses associated with the contact irregularities.

To the south, the welded tuff laps across the edge of 

the exotic block member and onto the Squaw Gulch 

Granite, where it buries an ancient hill-and-canyon 

topography already described. The basal contact of the 

welded-tuff member in this area commonly dips gently 

southwestward parallel to its sheeting.

The welded-tuff member is a nearly homogeneous unit 

in which sheeting and fracturing are usually well 

developed. Toward the southeast, there is a gradual 

transition from welded tuff to an unwelded tuff which 

contains arkosic admixtures near the underlying 

granite. However, where the arkosic tuff forms bodies 

sufficiently large to be mapped, it is grouped with the 

arkose member rather than with the welded-tuff member. Like the underlying members, the welded tuff has 

a uniform somber-colored brownish-gray or greenishgray appearance on the weathered surface and is medium gray where unweathered. Outcrops are small on 

hills but extensive along the shallow canyons northwest 

of the Salero Ranch. The rock is subtly layered and is 

cut by several sets of joints which are inclined at about 

right angles to the layering. Small dark-greenish-gray 

pods of altered flattened pumiceous material lie parallel 

to the sheeting and are the most conspicuous on weathered joint surfaces. Inasmuch as these are absent or are 

very inconspicuous to the southeast, that part of the 

tuff is believed to be unwelded. A few percent of lithic 

fragments, commonly %-2 inches across but as much 

as 6 inches across, are scattered in the welded tuff; the 

fragments consist largely of material like the tuff itself but include a few pieces of strongly laminate flows 

of the Mount Wrightson Formation and of Squaw 

Gulch Granite. Only a few chips of Piper Gulch 

Monzonite, quartzite, and Precambrian gneiss and chlorite schist are present.

Phenocrysts make up about half (40-60 percent) of 

the rock and are of uniform size (2^t mm long) and 

of uniform relative proportion throughout the area; 

this characteristic is one of the most distinctive features 

of this member (fig. 42). In hand specimen, feldspars 

which have dull cleavage surfaces and which contain 

bronze to greenish-gray altered biotite are always seen 

to be abundant; and quartz, although seen to be some-
SANTA RITA MOUNTAINS C71

uiidlHEE.* J-'ftc:

W^i&^^

FIGURE 42. Hand specimen of fairly unaltered rhyodacite of 

the welded-tuff member of the Salero Formation. The size 

and abundance of phenocrysts, especially of the biotite, are 

distinctive features of this rock. Biotite, B; plagioclase, P.

what less abundant than the other phenocrysts, is much 

more abundant than in the lowTer members.

In thin section, the laminar texture of alined crystals, 

crystal fragments, and devitrified pods is even more 

conspicuous than in the hand specimen. (Figure 42 wT as 

taken normal to the sheeting to showT biotite books 

rather than the sheeting.) Although pumiceous fragments are flattened, the intensity of the compaction is 

only moderate. Thus, the shards, wThich are sparse and 

are best seen under magnification greater than that 

used in figure 42, are generally only slightly deformed. 

Plagioclase in two-thirds of the specimens is a sodic 

andesine (An = 82-40), and in the remainder it is 

albitized. Biotite forms small euhedral crystals and 

deformed flakes, most of wThose cores are altered to 

nontronite (?), penninite, or other chlorite, and wThose 

rims are iron oxide. However, in a few specimens, the 

cores of biotite are unaltered and show a pleochroism 

in yellowish brown to dark browT n, and in one specimen 

the biotite is sufficiently unaltered to be dated isotopically. Traces of magnetite and apatite are ubiquitous, 

traces of zircon common, and traces of sphene and a 

potassium feldspar sparse. One specimen contains a 

xenocryst of schorlitic tourmaline. Epidote, chlorite, 

sericite, clay minerals, iron oxide, leucoxene, and calcite 

are typical alteration minerals. The specimen showyn in 

figure 43 is typical of rhyodacite of this unit, except that it contains xenocrysts of orthoclase of Jurassic granite. Other parts of the thin section of figure 

43 also contain granite xenoliths. Modal analyses of 

typical specimens of wTelded tuff are presented in table

FIGURE 43. Photomicrograph of rhyodacite from the weldedtuff member of the Salero Formation, showing compacted 

pumice (?) pods, a broken xenocryst of perthitic orthoclase 

(O) derived from the Squaw Gulch Granite, argillized 

plagioclase (P), quartz (Q), chloritized biotite (B), hornblende (H), magnetite (M), and epidote (E), all in a vitric 

groundmass. Plane-polarized light.

8. Chemical and spectrographic analyses of a specimen 

collected from the SEi/4SEV4 sec. 17, T. 21 S., E. 14 E., 

and also isotopically dated are presented in table 7 

(specimen 3). The chemical analysis resembles fairly 

closely that of Nockolds' (1954, p. 1014) average rhyodacite.

ARKOSE MEMBER

The arkose member consists of gently westward 

dipping arkosic rocks at least 500 feet thick that lie 

between the welded-tuff member and the granite 

terrane east of the tuff and that extend from Josephine 

Canyon southward to the Salero mine. A thin sheet of 

similar arkose commonly underlies adjacent parts of 

the welded tuff and is also intercalated in the basal part 

of the upper member, so that the stratigraphic interval 

occupied by the arkose is slightly greater than that 

occupied by the welded-tuff member. The arkose member unconformably overlies or laps against the Jurassic
C72 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

TABLE 7. Chemical and spectrographic analyses and norms of 

members of the Salero Formation

Specimen No_ 

FieldNo_.___ 

Member_____.

1

65D680 

Lower

12

66D1095 

Exotic block

3

64D499 

Welded tuff

Chemical analyses (percent) 2

Si02 ___

A12 03 __

Fe2 O3 _

FeO

MgO__

CaO__

Na2O

K20___

H2O-.

H2 0+.

Ti02 __

P2 05 __

MnO__

CO2 __.

59. 1

16.7

3. 6

2.9

2. 8

3.9

3. 8

3. 5

. 28

1. 8

. 85

. 30

. 25

.09

58.7

18. 6

6. 1

.28

2.4

3. 2

5. 0

2.7

. 22

1. 1

. 80

. 35

. 09

. 30

59. 1

17.7

5.9

. 22

2. 6

2. 8

5. 6

2.8

. 15

1. 3

. 75

. 36

. 07

. 11

Total_____ 100 100 99

Setniquantitative spectrographic analyses 3

63. 2

16. 8

2.7

1. 2

. 80

3.9

3.7

3. 4

.80

1. 5

.47

. 17

. 09

1. 2

100

B_______________ 0 0.005 0.01 0

Ba___________ .1 .1 .2 .15

Be_____ __ ___ 0 .0001 .00015 .0003

Ce__________ 0 .01 .01 0

Co______________ .002 .0015 .002 .001

Cr______________ .001 .0005 .0005 .0015

Cu________ .001 .0002 .0007 .0015

Ga____________ .001 .001 .002 .002

La__________ .003 .005 .007 .005

Mo_____________ .0003 00 0

Nb _________ 0 .002 .0003 0

Ni____________._ <. 003 <. 003 .0003 . OQl

Pb____________ .005 .0001 .003 .0015

Sc__________ .001 .001 .0015 .001

Sr______________ .1 .07 .15 .1

¥_____________ .015 .003 .01 .01

Y___________ .0015 .0015 .0015 .002

Yb _______ .00015 .0001 .00015 .0002

Zr______________ .007 .015 .02 .01

Norms (percent)

Q __---_ _ 11.537 10.674 7.291 22.894

C_______________ .497 3.172 1.490 3.133

or_____________ 20.709 15.980 16.636 20.087

ab_____ _ ____ 32.196 42.376 47.643 31.292

an______________ 16.841 11.712 10.903 10.649

w/en_______ 6.982 5.987 6.510 1.992

mt______________ 

y \fs________ 

5.226 

1.414 

0 

000

0 2.799

hm _______ 0 6.110 5.932 .770

a__ ___________ 1.616 .785 .617 .893

ru____________ 0 .388 .429 0

ap______________ .711 .830 .857 .403

cc ________ . 205 .683 .251 2.729

Total

(rounded) _ 97.94 98.70 98.56 97.64

1 Two columns of data represent analyses of two portions of the same specimen.

2 Rapid rock analyses determined by methods described by Ward, Lakin, Canney, 

and others (1963) supplemented by atomic absorption methods. Analysts: Lowell 

Artis, Samuel Botts, P. L. D. Elmore, Gillison Chloe, H. Smith, and John Glenn.

3 Results are reported in percent to the nearest number in the series 1, 0.7, 0.5, 0.3, 

0.2, 0.15, 0.1, and so forth, which represent approximate midpoints of group data on a 

geometric scale. The assigned group for semiquantitative results will include the 

quantitative value about 30 percent of the time. Elements looked for but not found: 

Ag, As, Au, Bi, Cd, Ge, Hf, Hg, In, Li, Nd, Pd, Pr, Pt, Re, Sb, Sm, Sn, Ta, Te, 

Th, Tl, U, W, and Zn. Analysts: W. B. Crandell, J. L. Harris, and A. L. Sutton.

TABLE 8. Modal analyses (in percent) of rhyodacite from the 

welded-tuff member of the Salero Formation

Specimen No_---------------------- 3

FieldNo- - - -- - 63D499

4 

64D608

5 I 5a 

64D641 64D641

(inclusions)

Quartz_ _________________

Plagioclase_ ______________

Orthoclase and perthite__ 

Biotite_ _________---_-_-_

Amphibole_ ______________

Magnetite, ______________

Apatite__ _ _______________

Zircon_ _________________

Sphene_ _________________

Xenoliths and xenocrysts__ 

Groundmass_ ____________

1. 5 

31.5

0

6. 1

4.3

1. 6 

. 1 

. 1

0

2 . 6

1. 1

42. 0

0

6.4

3. 0

1.7

. 1

. 1

0

0

2. 3 

29. 8 

0

4.7

6.9

. 8

Trace

Trace

. 1

1 15. 6

5. 0 

33.0 

5. 0 

3. 0 

8. 0 

1. 0 

0 

0 

Trace

54. 2 45. 6 45.0

Total___________ 100.0 100.0 100.0 100. 0

1 The xenoliths and xenocrysts of specimen 5 are tabulated in column 5a. The specimen probably contains more xenocrystic plagioclase than was recognized. The chief 

contaminant'in the specimen is Jurassic granite, but volcanic contaminants are also 

present.

2 Orthoclase.

Squaw Gulch Granite on a rugged surface that has 

been described above.

The basal part of the member and that part lapping 

against the granite consist of an arkosic sedimentary 

breccia whose fragments are wholly or predominantly 

made up of the granite. In the upper reaches of the 

two forks of Alto Canyon, the arkose also contains a 

few fragments of Piper Gulch Monzonite, and farther 

north in Bond Canyon it also contains a few clasts of 

volcanics and quartzite of the Mount Wrightson Formation. The fragments in the arkose are unsorted to 

poorly sorted, are angular, and commonly are 2-10 

inches in diameter, but near Alto Canyon some sheets 

of sedimentary breccia contain blocks as much as 5 

feet across.

In many places, the basal rocks are unsorted and 

seem to be a granite grus with little or no admixed 

tuff. A short disance above the basal rocks, beds of 

coarse gritty arkose alternate with conglomerate or 

fanglomerate. The arkose beds are relatively thin and 

few near the granite to the east, but within 1 mile west 

of the granite they thicken and are numerous. The 

conglomerate beds, in a complementary manner, thin 

equally rapidly westward, and their fragment size 

decreases. The westernmost tongues of conglomerate 

form the more conspicuous low cliffs along the front 

of the mountains just east of the Alto townsite; the 

intervening beds there are more friable units of arkosic 

sandstone.

Several groups of siltstone beds, each as much as 10 

feet thick, are intercalated in the arkosic rocks north 

of the crest of the ridge at the Alto mines. These beds 

are distinctly anomalous to the general distribution 

pattern of coarser rocks to the east and finer ones to 

the west, and they appear to represent deposits of a
SANTA RITA MOUNTAINS C73

very local environment. They are important, however, 

because in the NE^SE^iSE^ sec, 12, T. 21 S., R. 14 

E., they contain fragments of plant fossils, which consist of grasslike or sedgelike material and of a narrow 

leaf. R. A. Scott (1966, written commim.,) reported the 

presence also of poorly preserved pollen of pine from 

a sample of this siltstone.

The matrix of most of the arkose contains greenishgray tuff, and the proportion of tuff to granite detritus 

increases westward. Near the underlying granite to the 

east, some sedimentary breccia can be distinguished 

from the granite only where tuff separates the clasts. 

Farther west, near the Salero Ranch-Josephine Canyon 

road, tuff beds are intercalated with the sandstone. 

The mapped contact between the dominaiitly arkosic 

beds and the dominantly tuffaceous ones is broadly 

gradational, with some tuff beds appearing 1,000 feet 

farther east and a few tuffaceous sandstone and conglomerate beds appearing in the tuff 1,500 feet to the 

west.

Thin sections of the arkose member substantiate 

most of the megascopic features already described. The 

groundmass material is too strongly argillized to indicate the original composition of the volcanic components. However, the crystal fragments in the matrix 

are albitized plagioclase, potassium feldspar, chloritized biotite, magnetite, apatite, zircon, and leucoxene; and lithic fragments are at least as abundant as 

the crystal fragments. Secondary minerals include the 

usual sericite, chlorite, epidote, calcite, and a little 

quartz. Most likely the volcanic components were derived from the rhyodacite tuff.

UPPER MEMBER

Mixed sedimentary rocks and dacitic to rhyolitic 

volcanic rocks conformably overlying the welded-tuff 

member of the Salero Formation make up the upper 

member. These rocks crop out in three elongate areas: 

in the San Cayetaiio Mountains, southwest of the 

Salero mine, and on the ridge east of the Weatherhead 

Ranch (Drewes, 19Tla). In each of these places, the 

rocks are too poorly exposed or their component units 

are too lenticular to establish a useful sequence or to 

provide a basis for calculation of their thickness. However, if the sequences are assumed to be virtually unfaulted, they are each estimated to be about 2,000-2,500 

feet thick and possibly are even thicker. The rocks of 

the three areas are sufficiently similar that they may 

represent the same stratigraphic sequence, interrupted 

over short distances by a cover of younger volcaiiics 

or by a younger pluton. Additional small masses of 

wallrock, roof pendants, and inclusions in and around 

the pluton of Josephine Canyon Diorite between the

Salero mine and Soiioita Creek are also correlated with 

the upper member.

The basal contact of the upper member appears to 

be conformable with the underlying welded-tuff member, but relations are nowhere fully clear. At the north 

end of the San Cayetaiio Mountains, this contact is 

a faulted bedding plane that lies at the base of a cliffmaking sandstone and conglomerate unit, The movement on the fault is believed to be minor and the thickness of beds sheared out along the fault negligible, 

because the fault is probably a local structural feature 

that is associated either with the emplacement of a 

nearby small pluton or with stress adjustments that 

occurred during the gentle tilting of the San Cayetano 

fault block. One mile west of the Salero mine, poorly 

exposed flat-lying welded and unwelded tuff grades 

upward into tuffaceous conglomerate and sandstone 

that contain some intercalated tuff beds; the contact 

in that area is placed beneath the lowest fairly thick 

epiclastic beds. Northeast of the Weatherhead Ranch, 

the basal contact of the upper member is inferred 

to lap onto, or is faulted against, the Squaw Gulch 

Granite.

In the San Cayetano Mountains, the rocks of the 

upper member consists of interbedded tuff breccia, 

welded(?) tuff, volcanic breccia, sandstone, conglomerate, and sedimentary breccia, which make a southward-rising sequence that is interrupted and mildly 

hornfelsed by a thick sill of porphyritic latite and by 

a stock or cupola of Josephine Canyon Diorite. The individual volcanic units range in thickness from about 

30 to 150 feet and together form less than 25 percent of 

the rock. They are most abundant near the middle of 

the sequence, Tuffs low in the sequence are dacitic; 

those higher in the sequence are rhyolitic. Fragments 

from a dacitic volcanic breccia low in the sequence contain amphibole, biotite, and accessory minerals much 

like those in the volcaiiics of the lower members of the 

Salero Formation. A pale-greenish-gray rhyolitic tuff 

breccia from near the middle of the sequence contains 

volcanic xenoliths and relict shards, as well as abundant 

pheiiocrysts of quartz, albite, and potassium feldspar, 

a few pheiiocrysts of chloritized biotite, and traces of 

magnetite, apatite, and zircon. This tuff resembles some 

of the tuff breccia high in the welded-tuff member, 

except that it contains more quartz.

Sedimentary rocks of the San Cayetano sequence 

are largely yellowish-brown sandstone and grit 

conglomerate; however, some beds are reddish gray, 

and the rocks range in coarseness from siltstone 

to cobble-bearing pebble conglomerate. Most of these 

beds contain tuffaceous material; some of them are 

subgraywacke and others are arkose. The clastic frag-
C74 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

ments are largely of local volcanic origin, but they also 

include much detritus derived from the Squaw Gulch 

Granite and a little derived from the volcanics of the 

Mount Wrightson Formation. A silty shale unit 10 feet 

thick on the southwest spur of Mount Shibell (NW1^- 

NE14 sec. 24, T. 22 S., E. 13 E., unsurveyed) contains 

scraps of plant fossils that resemble pine needles. The 

rocks of this sequence are mildly metamorphosed; 

epidotization and chloritization increase southward, 

and hornfelsing is strongest in beds low along the east 

flank of the range and near Mount Shibell. The 

hornfelsed beds contain patches of red rocks, which 

suggests that they were originally a red-bed sequence 

whose red color was largely lost through the metamorphism.

The upper member southwest of the Salero mine also 

is composed of tuffaceous and arkosic sandstone, volcanic conglomerate and breccia, and tuff breccia. Coarse 

volcanic breccia is more abundant in that area than in 

the San Cayetano sequence, and red siltstone is absent. 

Drab-colored tuffaceous sandstone, as much as 700 feet 

thick, forms the lowest unit of this sequence. It appears 

to grade upward and laterally from the arkose member 

through a gradually diminishing admixture of granite 

detritus. These beds thin to the west, where they overlie 

the flat-lying tuff that caps the welded-tuff member.

A sheet of dacite tuff breccia and agglomerate as 

much as 1,400 feet thick overlies the tuffaceous sandstone with minor, and perhaps only a local, unconformity. North-northeast of Cinigita Tank (S^ sec. 25, T. 

21 S., E. 14 E.), the breccia sheet is slightly discordant 

over the sandstone, but to the northeast it appears to 

be conformable. To the northwest, this contact is so 

poorly exposed that its position can be only estimated. 

Tuff breccia intertongues with the agglomerate, and 

the contacts between some of the larger tongues provide useful local marker horizons. One tuff breccia unit 

may be welded. Epiclastic beds likewise are intercalated 

in the upper part of the pyroclastic beds and seem to 

be more abundant to the east than to the west.

Petrographically, the volcanic sequence of the upper 

member near the Salero mine resembles that of the 

lower member, much as do the dacitic volcanics low in 

the San Cayetano sequence. They are commonly an 

altered plumose-patterned vitrophyre in which the 

phenocryst content is 30-40 percent. Most phenocrysts 

are no more than 3 mm long, but some are twice that 

length. The phenocryst content comprises abundant 

albitized plagioclase; several percent each of quartz, 

amphibole, and biotite; and traces of magnetite, apatite 

sphene, zircon, and, rarely, clinopyroxene. All the rocks 

are strongly argillized and contain sericite, epidote, 

chlorite, leucoxene, iron oxide, calcite, and possibly

secondary quartz. The alteration is not noticeably more 

intense adjacent to the Josephine Canyon Diorite, 

which truncates and intrudes the eastern edge of this 

sequence, than it is away from that intrusive.

The sequence of the upper member exposed northeast 

of the Weatherhead Eanch consists largely of rhyodacite volcanics and intercalated feldspathic quartzite, 

which is faulted to the south and is altered by the 

Josephine Canyon Diorite to the north. In much of the 

area, beds dip gently south to west, but in the faulted 

part they commonly dip more than 45° to the south and 

locally are upended. To the north, the lowest unit of the 

sequence is a subtly layered rholitic flow, which is overlain by 30 feet of white metaquartzite and then 30-50 

feet of brownish-gray quartzite. Under the microscope, 

the white quartzite is seen to consist of partly interlocking quartz grains, iron oxide, zircon and an argillic 

material that makes up about 30 percent of the rock. 

Zones of sheared and recrystallized quartz also indicate 

that the quartzite is considerably deformed. Strongly 

altered volcanics, probably a tuff breccia, overlie the 

quartzite, and these are overlain by hornfelsed arkosic 

sandstone and a little conglomerate which contains 

pebbles of Squaw Gulch Granite. More strongly altered 

volcanics, which wedge out southeastward, and another 

lens of quartzite overlies the conglomerate. The middle 

of the sequence northeast of Weatherhead Eanch is 

largely light-brownish-gray to pale-purplish-gray 

rhyolitic to dacitic lava that contains several small 

lenses of quartzite, sandstone, and conglomerate. Under 

the microscope, the lava is seen to consist of strongly 

altered feldspar remnants, zircon, sericite, schorlitic 

tourmaline, chlorite, iron oxide, and abundant clay 

minerals. The upper part of the Weatherhead Eanch 

sequence is epiclastic, consisting of tuffaceous sandstone 

overlain by conglomerate. The clasts from low in the 

conglomerate are largely of volcanics of the Salero 

Formation, granite debris increases toward the top, and 

scattered clasts resemble the strongly laminated volcanics of the Mount Wrightson Formation.

Most of the wallrock remnants, roof pendants, and 

inclusions in the Josephine Canyon Diorite south and 

west of the Weatherliead Eanch are arkosic sandstone, 

conglomerate, and quartzite that bear a close resemblance to the rocks of the Weatherhead Eanch sequence 

of the upper member.

AGE AND CORRELATION

The Salero Formation is isotopically dated as late 

Late Cretaceous, an age which fits the geologic relations and isotopic ages of other rocks. Biotite that is 

sufficiently unaltered so that it is datable was concentrated from the analyzed specimen from the welded-
SANTA RITA MOUNTAINS C75

tuff member (table 7, specimen 3). According to H. H. 

Mehnert, R. F. Marvin, and Wayne Mont joy (Drewes, 

1968, p. C12), this biotite has a potassium-argon age 

of 72.5 ± 2.2 m.y. The Salero Formation is geologically 

dated as post-Fort Crittenden Formation and preJosephine Canyon Diorite. Inasmuch as the Fort Crittenden is dated by fossils as late (?) Late Cretaceous 

and the Josephine Canyon Diorite is isotopically dated 

as latest Late Cretaceous (Drewes, 1968, p. C12), the 

age of the Salero is substantiated as late Late Cretaceous.

Rocks that have a composition and age generally 

similar to those of the Salero Formation are relatively 

widespread in southeastern Arizona. The key units are 

an underlying dacitic to andesitic breccia and an overlying rhyodacitic to rhyolitic tuff; they may include 

unwelded rocks and possibly even hypabyssally intruded tuff. The Salero-like rocks near the Santa Rita 

Mountains may be closely correlative volcanics, some 

of which may even have been extruded from the same 

vent or vents as the type Salero rocks; those in more 

distant mountains almost certainly were extruded from 

separate vents and merely reflect a comparable stage of 

development of the widespread magmatic phase of 

the Laramide orogeny.

Fairly close to the Santa Rita Mountains and to the 

southeast in the Flux Canyon area of the Patagonia 

Mountains and about 1 mile south of the southeast 

corner of the Mount Wrightson quadrangle, dacitic 

breccias contain exotic blocks. The largest of these 

blocks is the body of Paleozoic limestone at the Flux 

mine, but many of the small blocks resemble the volcanics of the Mount Wrightson Formation. These 

dacitic breccias are probably correlative with the exoticblock member of the Salero Formation, and although 

they undoubtedly were extruded from separate vents, 

the vents probably were on the same major structural 

feature (Drewes, unpub. data).

The rocks on the first hills east of Sonoita Creek and 

roughly 4 5 miles northeast of Patagonia resemble the 

welded-tuff member of the Salero Formation. Similar 

rocks, which overlie andesitic volcanics, were also 

mapped along the southwest flank of the Canelo Hills 

by R. B. Raup (oral commun., 1967). Likewise, the 

biotite-rich tuff of the volcanic and sedimentary rocks 

of Jones Mesa, which is isotopically dated 72 m.y. (R. 

B. Raup, unpub. data), and their underlying andesitic 

volcanics are thought to be correlative with the weldedtuff and exotic-block members, respectively.

At the northeast end of the Santa Rita Mountains, 

there are also some rhyodacite welded tuffs of late Late 

Cretaceous age that are indistinguishable from the 

welded-tuff member. Some of the andesitic rocks in the

lowlands between this end of the mountains and the 

Empire Mountains may be correlative with the lower 

members of the Salero.

In the Sierrita Mountains, 15 miles to the west, J. R. 

Cooper (oral commun., 1967) mapped andesitic volcanics along Demetrie Wash and an overlying rhyolite 

tuff at Red Boy Peak. These rocks are believed to be 

correlative with the lower three members of the Salero.

In the Tucson Mountains, about 40 miles to the northwest, Brown (1939) and Kinnison (1958) mapped a 

thick sequence of rocks of late Late Cretaceous age: the 

Silver Bell Formation (Wood, 1959), which is an 

andesitic breccia that contains exotic blocks, and the 

overlying Cat Mountain Rhyolite (Brown, 1939), 

which is a welded tuff whose plagioclase was isotopically dated as about 65-70 m.y. by Bikerman and Damon 

(1966, p. 1232). In the Roskruge Range, 15 miles west 

of the Tucson Mountains, Bikerman (1967, p. 1032) 

dated the upper part, of his Roskruge Volcanics, which 

resemble the Cat Mountain Rhyolite, as 66-72 m.y. by 

several isotopic methods that made use of several 

minerals. Of these, the potassium-argon age on biotite 

gives the oldest age and plagioclase the youngest age, 

an age that is virtually the same as that of the plagioclase of the Cat Mountain Rhyolite.

In the vicinity of Tombstone, about 30 miles east of 

the Santa Rita Mountains, at least some of the Uncle 

Sam Porphyry (Gilluly, 1956, p. 94-101) appears to 

be a welded tuff whose phenocryst type and abundance 

and whose widespread chloritization resemble those 

characteristics of the welded-tuff member of the Salero. 

A specimen of the Uncle Sam Porphyry collected from 

the west edge of the outcrop area, about 2 miles south 

of Arizona Highway 82 and 3 miles west of the San 

Pedro River, however, contains fresh biotite which was 

dated by the potassium-argon method as 71.9 ±2.4 m.y. 

by R. F. Marvin, H. H. Mehnert, and V. M. Merritt 

(written commun., 1968).

The Sugarloaf Quartz Latite (Gilluly, 1956, p. 90- 

92) also resembles the welded-tuff member of the 

Salero. Biotite obtained from the north spur of the 

type area at Sugarloaf Hill near Gleeson (fig. 1) was 

given an isotopic potassium-argon age of 72.8 ±2.5 m.y. 

by R. F. Marvin, H. H. Mehnert, and V. M. Merritt 

(written commun., 1969).

ENVIRONMENT OF DEPOSITION AND ORIGIN

Several aspects of the rocks of the Salero Formation 

indicate that they are erogenic deposits. The relief on 

the basal unconformity, the size of the clasts in the 

arkose member, and possibly also the presence of exotic 

blocks indicate deposition by high-energy agents. Even 

more indicative is the close temporal association of the
C76 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

deposition of the Salero with both the development of 

large structural features and the emplacement of plutons. Although the structural and plutonic topics are 

scheduled for discussion in collateral articles, a few of 

the conclusions bearing on the origin and emplacement 

of the Salero Formation are introduced here to indicate 

the extent of support that is available for the interpretation that the Salero is an erogenic deposit.

During early Salero time, the report area was locally 

rugged. The coarseness of the clasts in the sedimentary 

breccia of the arkose member that lies upon the granitic 

terrane indicates that deposition occurred at the foot 

of a high area. The coarsest arkose does not form only 

a widespread basal sheet but commonly intertongues 

with finer deposits throughout a thick stratigraphic 

sequence, which further suggests that the relief was at 

least maintained throughout the time of deposition of 

the arkose member. Similarly, the unconformity beneath the arkose member is an irregular surface interpreted as a paleotopography of deep canyons and 

rugged knobs or spurs. In the Cottonwood-Montosa 

Canyons area, where volcanics form the lowest member of the Salero and where there is no direct indication of the amount of the local relief, some rocks may 

have accumulated in a local basin and may include 

some rocks that were not deposited subaerially. Around 

Josephine Canyon, where the exotic-block member 

forms the basal deposits of the Salero, the surface 

underlying the member is believed to have sloped southwestward, because the most probable source of the 

exotic blocks lies to the northeast and the mode of 

transport probably was gravity controlled.

At the first stage of development of the volcanic complex of the Salero, the magma present near or at the 

surface had about the composition of dacite. A little 

of this magma may have breached the surface to form 

normal lava flows, such as those along the lower reaches 

of Montosa Canyon. Most of the magma, however, is 

suspected to have had a different history, one that was 

more violent but apparently not unique to the Santa 

Rita Mountains, as judged from the occurrence of exotic 

block deposits of the Salero type in the rocks of the 

Tucson and Patagonia Mountains and perhaps also 

farther to the east.

Three features of the dacitic rock itself are especially 

pertinent to the mode of origin of the rock. First, fragmentation and pulverization of the matrix to the exotic 

blocks is pervasive. Clearly the mode of origin involved 

the release of a vast amount of energy. Together with 

the absence of any signs of sorting or layering, aside 

from the local capping wedge of tuffaceous(?) exoticbearing rock, the pulverization further indicates a 

highly turbulent movement. Second, the type of intricate penetration of the pulverized but fluid mass of 

rock (or semisolid magma?) into the dacitic fragments 

of the matrix, as well as into some of the exotic blocks, 

suggests that the mass was either corrosive or was 

under considerable pressure, or both. A permissive 

penetration of shattered fragments would produce a 

much sharper and more reticulate pattern of penetration than has been seen. Apparently then, the dacite 

complex was not deposited in a normal surface environment as a volcanic breccia flowT . Third, the groundmass 

of the pulverized matrix and of the matrix of the chips 

within the dacitic fragments is finely crystallized, and 

the rock is pervasively epidotized and sericitized. Apparently, after extrusion, the pulverized dacitic rock 

was still sufficiently hot and contained sufficient fluids 

to result in this fine crystallization and intensive 

alteration.

Four features of the rocks and structural features 

which are adjacent to the dacitic complex are also pertinent to the mode of origin of the dacite:

1. The lack of sorting of the exotic blocks with respect 

to each other suggests turbulent transport. The 

lithologic diversity of the blocks makes it difficult 

to picture them as having been plucked from the 

wall of a conduit, although some blocks may have 

been derived in this manner, because stratigraphic 

sections sufficiently complete to provide this diversity are not found. The indication of a fairly 

high pressure environment also makes it difficult 

to believe that the blocks were plucked from the 

base of a postulated surface flow or resulted from 

an infalling of landslide debris into such a flow. 

But the wide assortment of exotic blocks coupled 

with the suggestion of high pressure is fairly 

compatible with a postulated origin of foundering of the roof of a shallow intrusive body.

2. Another local field relation of the dacitic complex, 

however, does suggest that a surface environment 

caused a little contamination. In the area where 

the exotic-block member lies unconformably upon 

the Squaw Gulch Granite, granite grus has been 

incorporated into the base of the dacite breccia. 

Furthermore, the breccia rests upon the old surface itself, so that in places it appears to have 

been an extrusive mass.

3. The differences in the structural relations of the 

dacitic complex and of the overlying rhyodacite 

welded tuff to the rocks lying to the northwest 

are also instructive but are only summarized here. 

The dacitic rock is separated from adjacent 

Mesozoic and Paleozoic sedimentary rocks by a 

tear fault, whereas the welded tuff flowed against 

these rocks. The Paleozoic rocks moved over the
SANTA RITA MOUNTAINS C77

lower Mesozoic rocks on a thrust fault that abuts 

into, and does not appear beyond, the tear fault. 

At least some of the movement on the thrust is 

thus coeval with movement on the tear fault. 

These observations indicate that the faulting 

must be older than, or of the same age as, the cooling of the welded tuff. The thrust plate contains 

the entire suite of Paleozoic formations. A few 

miles northwest of the tear fault, the plate also 

contains volcanics of the Mount Wrightson Formation and red beds, probably both of Triassic 

age, and volcanics of the Fort Crittenden Formation ; this is an assortment of formations such as 

those that occur as exotic blocks in the dacitic 

complex. The important point, though, is that 

some thrust faulting is virtually contemporaneous 

with the formation of the dacitic complex.

4. The geologic relations of the volcanic complex to 

the adjacent plutonic rocks must be considered. 

Immediately northeast of the Salero Formation 

lie several large plutons of Triassic, Jurassic, and 

Late Cretaceous ages, the youngest of which intrudes the Salero Formation. These plutons were 

emplaced along a major structural zone that 

trends northwestward across the mountains and 

had been active at least since Triassic time. Of 

the several Late Cretaceous plutons, the slightly 

older Josephine Canyon Diorite and Madera 

Canyon Granodiorite and the slightly younger 

quartz monzonite of Quantrell and Elephant 

Head stocks, all dated as about 68 m.y. old, are 

of special interest here. The change from a magma 

that first produced dioritic rock to a magma that 

produced quartz monzonitic rock parallels the 

change from a magma that first produced dacitic 

volcanics to one that produced the rhyodacitic 

volcanics, a change that occurred about 72 m.y. 

ago. Apparently then, at the present level of exposure, two magmas were active during an interval of time lasting at least 4 m.y. The earliest 

magma to penetrate the rocks reached the surface 

and became part of the wallrocks and roof rocks 

for the magma masses that moved upward 

slightly later. The details of the plutonic development and the ramifications of the situation outlined here are to be the objective of a planned 

companion paper to this series of reports; but of 

importance to explaining the origin of the dacitic 

complex are the indications that two magmas apparently were available near the surface for a 

considerable time. 

The separate pieces of the volcano-tectonic picture

described above may now be assembled to show how I

believe the exotic-block member may have been formed. 

During pre-Salero time, the region was uplifted and 

deeply eroded so that much of the southern part of 

the area was largely stripped to the level of the large 

Jurassic granite pluton. The remaining cover of bedded 

rocks of Mesozoic and Paleozoic age to the north was 

thrust faulted (perhaps as a surface thrust), and the 

upper plate was broken into two segments by a northeast-trending tear fault. Dacitic-dioritic magma was 

injected as a sill beneath the southern segment of the 

upper plate, and locally the magma reached the surface. 

The roof of the sill, however, became unstable, perhaps 

as a result of a continued rising of the area that shortly 

thereafter became the site of intrusion of the Late 

Cretaceous plutons, and the roof shifted downslope 

toward the southwest. The sudden release of pressure 

on the magma in the sill produced a flash degassing; as 

a result, the semisolid body was fluidized and was thus 

enabled to flow southwestward with great rapidity and 

turbulence. Movement of the northern segment of the 

thrust plate continued up to this time to produce the 

tear fault between the rapidly cooling dacitic complex 

and the plate of Paleozoic rocks. The distal end of the 

dacitic sill became a surface flow, and some granite 

grus was incorporated in it as it moved over the ancient 

hilly topography.

The sudden relaxation of pressure in the upper part 

of the dacitic-dioritic magma conduit system may have 

triggered the rapid upward movement of the rhyodacite-quartz monzonite magma to bring about the 

outpouring of rhyodacite tuff. The wide distribution of 

the rhyodacite tuff in a mountainous terrain suggests 

that the tuff was ejected with considerable explosive 

force; the large volume of the tuff and the absence of 

intercalated bedded units suggest that it probably was 

a composite air-fall tuff which formed a single cooling 

unit. The southern part of the air-fall tuff may have 

been deposited farthest from the vent or may have been 

thinnest, because it remained unwelded and graded 

laterally into epiclastic deposits. After this rapid and 

violent volcanism, abundant epiclastic material and 

some additional pyroclastics were deposited at least in 

the southern part of the area.

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Geol. Soc. America Bull., v. 62, no. 11, p. 1331-1346.

Bikerman, Michael, 1967, Isotopic studies in the Roskruge Mountains, Pima County, Arizona: Geol. Soc. America Bull., 

v. 78, no. 8, p. 1029-1036.

Bikerman, Michael, and Damon, P. E., 1966, K/Ar chronology 

of the Tucson Mountains, Pima County, Arizona: Geol. Soc. 

America Bull., v. 77, no. 11, p. 1225-1234.
C78 MESOZOIC STRATIGRAPHY IN SOUTHEASTERN ARIZONA

Brown, W. H., 1939, Tucson Mountains, an Arizona basin range 

type: Geol. Soc. America Bull., v. 50, no. 5, p. 697-760.

Bryant, D. L., 1968, Diagnostic characteristics of the Paleozoic 

formations of southeastern Arizona, in Titley, S. R., ed., 

Arizona Geol. Soc. Guidebook 3, Southern Arizona, 1968: 

p. 33-47.

Bryant, D. L., and McClymonds, N .B., 1961, Permian Concha 

Limestone and Rainvalley Formation, southeastern Arizona: Am. Assoc. Petroleum Geologists Bull., v. 45, no. 8, 

p. 1324-1333.

Cooper, J. R., 1970, Preliminary geologic map of the Twin 

Buttes quadrangle, Pima County, Arizona: U.S. Geol. 

Survey open-file report.

Cooper, J. R., and Silver, L. T., 1964, Geology and ore deposits 

of the Dragoon quadrangle, Cochise County, Arizona: U.S. 

Geol. Survey Prof. Paper 416, 196 p.

Creasey, S .C., 1967, Geologic map of the Benson quadrangle, 

Cochise and Pima Counties, Arizona: U.S. Geol. Survey 

Misc. Geol. Inv. Map 1-470.

Drewes, Harald, 1966, Road log for southern Santa Rita Mountains, Santa Cruz and Pima Counties, Arizona: U.S. Geol. 

Survey open-file report, 6 p.

 1967, A geochemical anomaly of base metals and silver 

in the southern Santa Rita Mountains, Santa Cruz County, 

Arizona, in Geological Survey research 1967: U.S. Geol. 

Survey Prof. Paper 575-D, p. D176-D182.

 1968, New and revised stratigraphic names in the Santa 

Rita Mountains of southeastern Arizona: U.S. Geol. Survey 

Bull. 1274-C, 15 p.

 1969, The Laramide orogeny of Arizona southeast of 

Tucson, in Abstracts for 1968: Geol. Soc. America Spec. 

Paper 121, p. 501.

 1970, Structural control of geochemical anomalies at 

Greaterville, southeast of Tucson, Arizona: U.S. Geol. 

Survey Bull. 1312-A, 49 p.

 1971a, Geologic map of the Mount Wrightson quadrangle, southeast of Tucson, Santa Cruz and Pima Counties, Arizona: U.S. Geol. Survey Misc. Geol. Inv. Map 

1-614 (in press).

 1971b, Geologic map of the Sahuarita quadrangle, southeast of Tucson, Pima County, Arizona: U.S. Geol. Survey 

Misc. Geol. Inv. Map 1-613 (in press).

Drewes, Harald, and Finnell, T. L. (leaders), 1968, Mesozoic 

stratigraphy and Laramide tectonics of part of the Santa 

Rita and Empire Mountains southeast of Tucson, Arizona, 

Field Trip 2, in Titley, S. R., ed., Arizona Geol. Soc. Guidebook 3, Southern Arizona, 1968: p. 315-324.

Dumble, B. T., 1902, Notes on the geology of southeastern Arizona : Am. Inst. Mining and Metall. Engineers Trans., v. 31, 

p. 696-715.

Bpis, R. C., 1956, Geology of the Pedregosa Mountains, Cochise 

County, Arizona: California Unv. unpub. Ph. D. thesis.

Feth, J. H., 1948, Permian stratigraphy and structure, northern Canelo Hills, Arizona: Am. Assoc. Petroleum Geologists 

Bull., v. 32, no. 1, p. 82-108.

Finnell, T. L., 1970, Preliminary geologic map of the Empire 

Mountains quadrangle, Pima County, Arizona: U.S. Geol. 

Survey open-file report.

Gilluly, James, 1956, General goelogy of central Cochise County, 

Arizona, with sections on age and correlation by A. R. 

Palmer, J. S. Williams, and J. B. Reeside, Jr.: U.S. Geol. 

Survey Prof. Paper 281, 169 p.

Hayes, P. T., and Drewes, Harald, 1968, Mesozoic sedimentary 

and volcanic rocks of southeastern Arizona, in Titley, S. R.,

ed., Arizona Geol. Soc. Guidebook 3, Southern Arizona, 

1968: p. 49-58.

Hayes, P. T., and Landis, E. R., 1961, Lower member of Mural 

limestone of Early Cretaceous age, Bisbee quadrangle, 

Arizona, in Short papers in the geologic and hydrologic 

sciences: U.S. Geol. Survey Prof. Paper 424-B, p. B125- 

B127.

 1964, Geologic map of the southern part of the Mule 

Mountains, Cochise County, Arizona: U.S. Geol. Survey 

Misc. Geol. Inv. Map 1-418.

Hayes, P. T., and Raup, R. B., 1968, Geologic map of the 

Huachuca and Mustang Mountains, southeastern Arizona: 

U.S. Geol. Survey Misc. Geol. Inv. Map 1-509.

Hayes, P. T., Simons, F. S., and Raup, R. B., 1965, Lower 

Mesozoic extrusive rocks in southeastern Arizona The 

Canelo Hills Volcanics: U.S. Geol. Survey Bull. 1194-M, 9 p.

Heatwole, D. A., 1966, Geology of the Box Canyon area, Santa 

Rita Mountains, Pima County, Arizona: Arizona Univ. 

unpub. M. S. thesis, 70 p.

Kinnison, J. B., 1958, Geology and ore deposits of the southern 

section of the Amole Mining district, Tucson Mountains, 

Pima County, Arizona: Arizona Univ. unpub. M.S. thesis.

Lootens, D. J., 1965, Structure and petrography of the east side 

of the Sierrita Mountains, Pima County, Arizona: Dissert, 

Abs., v. 26, no. 4, p. 2135.

Miller, H. W., Jr., 1964, Cretaceous dinosaurian remains from 

southern Arizona: Jour. Paleontology, v. 38, no. 2, p. 

378-384.

Nockolds, S. R., 1954, Average chemical compositions of some 

igneous rocks: Geol. Soc. America Bull., v. 65, no. 10, p. 

1007-1032.

Ransome, F. L., 1904, The geology and ore deposits of the Bisbee 

quadrangle, Arizona: U.S. Geol. Survey Prof. Paper 21, 

168 p.

Schafroth, D. W., 1965, Structure and stratigraphy of the Cretaceous rocks south of the Empire Mountains, Pima and 

Santa Cruz Counties, Arizona: Arizona Univ. unpub. 

Ph. D. thesis.

Schrader, F. C., 1915, Mineral deposits of the Santa Rita and 

Patagonia Mountains, Arizona, with contributions by 

J. M. Hill: U.S. Geol. Survey Bull. 582, 373 p.

Silver, L. T., 1969, Precambrian batholiths of Arizona, in Abstracts for 1968: Geol. Soc. America Spec. Paper 121, 

p. 558-559.

Simons, F. S., Raup, R. B., Hayes, P. T., and Drewes, Harald, 

1966, Exotic blocks and coarse breccias in Mesozoic volcanic 

rocks of southeastern Arizona, in Geological Survey research 1966: U.S. Geol. Survey Prof. Paper 550-D, p. D12- 

D22.

Stoyanow, Alexander, 1949, Lower Cretaceous stratigraphy in 

southeastern Arizona: Geol. Soc. American Mem. 38, 169 p.

Taliaferro, N. L., 1933, An occurrence of Upper Cretaceous sediments in northern Sonora, Mexico: Jour. Geology, v. 41, 

no. 1, p. 12-37.

Tyrrel, W. W., Jr., 1957, Geology of the Whetstone Mountain 

area, Cochise and JPima Counties, Arizona: Yale Univ. 

unpub. Ph. D. thesis.

Ward, F. N., Lakin, H. W., Canney, F. C., and others, 1963, 

Analytical methods used in geochemical exploration by the 

U.S. Geological Survey: U.S. Survey Bull. 1152, 100 p.

Wilson, E. D., Moore, R. T., and O'Haire, R. T., 1960, Geologic 

map of Pima and Santa Cruz Counties, Arizona: Arizona 

Bur. Mines.

Wood, P. A., 1959, Tertiary deposits in southern Arizona: 

Arizona Geol. Soc. Guidebook, p. 58-59.
INDEX

A Page 

Abrigo Limestone -- ----_ ___ __ 44

Adobe Canyon..____________________ 36,57,59,60,63

Age, Bathtub Formation. ----_-_-___.___ 43

Canelo Hills Volcanics_-_-_-------_--_-.__ 25

Fort Crittenden Formation.____________ 63

Gardner Canyon Formation..-. --________ 24

Mount Wrightson Formation.--_- _____ 14

Salero Formation...______________________ 74

Temporal Formation- --_---------_-_.____ 33

Agua Calieiite Canyon. __ ..____ 50

Analyses, Bathtub Formation, middle member. ___________________________ 38,39,40

Bathtub Formation, upper member- _____ 42, 43

chemical. ._ __.________.__ 13,32,40,43,67, 68, 71

Gardner Canyon Formation, siltstone

member. _________________________ 20

modal ___________ 13,20,31,33,38,39,40,42,43,71

Mount Wrightson Formation-...-________ 13

Salero Formation, exotic-block member. _. 68 

lower member..-_____________________ 67

welded-tuff member. _________________ 71

spectrographic. __._-__.____ 13,32,40, 43, 67,68, 71

Temporal Formation, lower and middle

members undivided._____________ 32

middle member. ___ .___- ______ 31

upper member.-----_--.------________ 33

See also Norms. 

Apache Canyon Formation. __________________ 50

Apache Group...._-_.___-___.______ -__.____ 5

Artis, Lowell, analyst-....___.____-_.__ 16,32,41,72

B 

Bathtub Formation.------------..__.--______ 35

age. ------------.-._--.---_-_._.-._..-____ 43

analyses-----------_------_-_-_-- 38,39,40,42,43

contact relations._. --_----------__.-_ 34, 35,44

correlation...-____________________________ 43

distribution._____________________________ 36

environment of deposition ________________ 43

facies changes--_________________________ 36

lower member, lithology.- ________________ 36

source-_______________________________ 36

middle member, lithology- -.------____ 37,38,40

petrography. ______________________ 38, 39,40

type area.________________________________ 36

upper member, lithology----------------- 42

petrography.- ________________________ 42

Bath Tub Tank anticline-------------------- 59

Big Casa Blanca Canyon. ._.__-___ _ 33, 36, 38, 57, 59 

Bisbee Group..___________________________ 43,64,69

Bog Spring-.-.-----_-_-___-___.______--______ 7

Bolsa Quartzite- - ___________________________ 5,44, 69

Boston Gulch syncline----------------------- 50

Botts, Samuel, analyst _________________ 16,32,41, 72

Box Canyon ..--......__________.____.__ 44,46,48

Cabullona Group_---__-_-.__________________ 64

Caliche paleozones- - -_____________--_-.______ 20, 53

Camas Sandstone____________________________ 64

Canelo Hills.-------__-________-_____--___. 22, 24, 75

Canelo Hills Volcanics.-- - ___________________ 24, K

Cat Mountain Rhyolite --_---_-----_--_____-_ 75

Cave Creek .-_____.__._ _______________. 17, 60, 62

Chinle Formation.-.---.-_-_,_-____.__.______ 17

Chiricahua Mountains__-____________________ 64

Chloe, Gillison, analyst________________ 16,32,4'1, 72

[Italic page numbers indicate major references]

Page 

Colina Limestone. --__-_-_____-_-_---__._____ 5,46

Colorado Plateau-----_____-_-_-_-_--_________ 17

Concha Limestone- ----------------------- 5,14,69

Contact metamorphism, Bisbee Group. ______ 44

Mount Wrightson Formation, lower member ___.__.__________._..--_------ 7

Final Schist--_______-___-_-_____-_______- 5

Salero Formation___-------------------___ 66

upper member.-------___----------__ 73

Contact relations, Abrigo Limestone --.-- ___ 44 

Apache Canyon Formation..---.--...... 50

Bathtub Formation.__________________ 34, 35,44

Bisbee Group_--_-__.__________--__-._.__ 43,64

Bolsa Quartzite-------------------------- 44

Canelo Hills Volcanics ------------------- 25

Concha Limestone_..--------_------___-- 14

Continental Granodiorite.---------_----. 44

Epitaph Dolomite------------------------ 17,18

Epitaph Formation..-------------------- 6

.Fort Crittendeii Formation.. _ _._. 55, 57, 64, 65 

Gardner Canyon Formation _.._.---_____ 6,17

Glance Conglomerate.------------------- 35,44

Mount Wrightson Formation ____----___ 6,14,27

Rainvalley Formation ___-.._--------.- 6,14,17

Shellenberger Canyon Formation _-__-_.- 51 

Squaw Gulch Granite. - - - - 26, 33, 65,67, 70, 72, 73

Temporal Formation. ____.-_-------.----. 26, 35

Turney Ranch Formation. -_-----_--_____ 52, 57

Willow Canyon Formation_______________ 47

See also Unconformities. 

Continental Granodiorite ----------------- 12, 44,46

Correlation, Bathtub Formation ------------- 43

Bisbee Group...------------------------- 43

Canelo Hills Volcanics------------------- 25

Fort Crittendeii Formation.....___-_____ 64

Gardner Canyon Formation -.__--__-_-_- 24 

Glance Conglomerate -------------------- 34,43

Mount Wrightson Formation __-.--_-_-_- 15 

Salero Formation.------------------------ 64,75

Shellenberger Canyon Formation ______ 52

Temporal Formation. -------------------- 34

Cottonwood Canyon. _________--__----------- 66

Crandell.W.B..analyst...------------- 16,32,72

Cretaceous stratigraphy, --------------------- %6

D

Demetrie Wash -_- - - - - 75

Distribution, Apache Canyon Formation.---- 50

Bathtub Formation.-.-.. ------------- 36

Canelo Hills Volcanics ---------------- 25

Fort Crittenden Formation. ------------- 57

Gardner Canyon Formation-------------- 17

Glance Conglomerate.----- --------- 44

Mount Wrightson Formation.-. _ - 7

Salero Formation--------.-------------.-- 65

Sh ellenb erg er C any on Formation- -_-_-_ 51

Temporal Formation--------------------- 26

Turney Ranch Formation- ._._._._______. 52

Willow Canyon Formation. __ --_-______ 47

Dragoon Mountains.------------------------- 43

E 

Earp Formation. - ____________ __--_ _-.-_-_- 5,46

ElPilar Tank anticline --------------- 63

Elephant Head stock_-_-_____.--------------- 77

Elmore, P. L. D., analyst------.---- 16,32,41,72

Empire Mountains. _-_____--__-__------__- 25, 44, 52

Environment of deposition, Apache Canyon

Formation.-.. ------------------- 51

Bathtub Formation-..------------------- 43

Cretaceous rocks. ------------------------ 26

Fort Crittenden Formation. ------------- 63,64

Gardner Canyon Formation-...- ._- 25 

Glance Conglomerate-------------------- 47

Mount Wrightson Formation.. -- --- 14,17 

Salero Formation-------------- --------- 75

Shellenberger Canyon Formation__-____._ 52

Temporal Formation. --------------- - 35

Triassic and Early Jurassic rocks. -------- 6

Turney Ranch Formation,_- ---_-. - 53

Willow Canyon Formation..._-_-_-___ 50

Epitaph Dolomite-..------------------- 5,17,18,20

Epitaph Formation...---------------------- 6

F

Facies changes, Bathtub Formation, lower 

member ____._- ---------------

Bisbee Group ..__. -- - --

Glance Conglomerate. . -----------------

Mesozoic volcanics ---------------------

Mount Wrightson 'Formation, middle

member. .. .- -- -. -

Salero Formation _ . ---- ------

Temporal Formation. __- ---. ------

topographic control ---------------------

Willow Canyon Formation. ___-___-___-__ 

Faulting, Gardner Canyon Formation-,..----

Glance Conglomerate. _ ------------------

Salero Formation.-.------------------- 70,

Willow Canyon Formation. ___-----__--_-

Florida Canyon. -_-_-. - - ----- -------

Flux Canyon..---- ----------------------

Fort Buclianan Formation. ------------------

Fort Crittedeii Formation..----.- ---------- -

age.

brown conglomerate member, lithology- - - 

source -------------------------------

contact relations-..----------------- 55. 57,

correlation. _ ._-..-_-- ---------- ---------

distribution. ----------------------------

environment of deposition. __..-_---_--- 

fossils --------------------------- 57 , 58,

geologic events- --------------------------

lower red conglomerate member, lithology. 

source. -------------------------------

rhyolitic tuff member, lithology . ....- 

petrography-..--. --------------------

source --------------------------------

shale member, lithology- -----------------

upper red conglomerate member, lithology- ----------------------------

Fossils , amioid _.__.__ -----_-----------

Apache Canyon Formation.- ---.------

Asperidetes sp. --------------------------

Bellamy a sp __ -_-- -------- ---------

bone fragments- _ ------------------------

charophytes- -----------------------------

chitmozoans. -----------------------------

clams - ------------------------ 51, 53, 57.

coal..--. -------------------------------

Corbicula sp, -----------------------------

Cypridopsis, ------------------------------

dinosaur fragments -----------------------

79

36

44

44,47

16

10

66

28,35

47

47,48

17

44,46

73,77

47,48

7

16,75

55

55,69

63

60

60

64,65

64

57

63,64

62,63

64

59

59

62

62

63

57

62

63

51

63

63

62,63

63

63

58,63

20

49

63

62,63
80 INDEX

Fossils Continued

elopid. ----- --------- ---_ _-_-_ _____._

Eupera sp. ------------------ -_-___ _ _ _ _ _

flsh fragments. ------ - - -- ---_ _._

Fort Crittenden Formation _ _ ._._ 

brown conglomerate member- ........

shale member. .......................

fungi.. _------..-.----..-._.._._....-.--..

gastropods.. .--.-------..------_- 46,51,53,

Glance Conglomerate clasts --------------

hadrosaurian- -__-_-_--__-._..____._._.___

hystrichomorphs -__--_-____--___-__.__-__

leaf-- ---.-.. -.--...-... _--.-.-_.._ 

Lepidosteus sp ----------------------------

Mactra sp.. .--_--_----__----_-_.----._._--

marine .--.-..--------.-....-.........-...

Meretrix -- - -- - 

microf ossils. --_.------_-._-_.__-____-_-___

molluscs _ .---_--_-._---..._-_-___-_._ 48, 

mosquito __-_-__--____-_____-_____-_-_____

Neridomus. .-..-------.-.-.---.---.-.-.-..

Nuculava spostracode. 

Physa sp ---------------------------------

pineneedles. - _ -_-_-- _- 

plant fragments ---_-__-___-__._.-____- 20,

Plastomenus sp. _ - -

Plesielliptio sp ----------------------------

pollen. -- _ _ -_- _ _ 

Protelliptio sp----- -. ---------------

reeds. ------------------------------------

Salero Formation, arkose member. .......

upper member __-_.___ ____-___-___.__

Shellenberger Canyon Formation _----_._

Sphaerium sp. ----------------------------

teeth. -._--__._-------._.-_..__---.-_--_-_

Tellina sp _._-_--.--.-._.-_.-.---_-_--._-- 

Thracia sp. -------------------------------

Transenella.. ......---.....-...-..-.-.....

Turney Ranch Formation.. _ .............

turtle fragments --.---------_-----_---_-_-

Unio sp ----------------------------------

Viviparus sp ------------------------------

Willow Canyon Formation ............ 48,

wood -_-__-_--_.._-_--__-_-.-.-.----.-. 53,

Page 

63 

63 

63 

63

62

57,58

63

58,63

46

63

63

73

63

49

50

51

63

49,52

63

51

51

50

63

49

63

74

73,74

63

63

73

63

20

73

74

52

63

63

50

50

51

53

63

63

63

49,50

62,63

G

contact relations. -.--..-.-.-.-----------.-

correlation _____--_-_-__-__--___---__-...-

distribution..............................

environment of deposition_-_-_._.________

exotic blocks_--------_-----------.---.---

mudstone member, lithology _-_.----__-_-

petrography__________________________

siltstone member, lithology.--------------

petrography. .........................

source.._-_.-_---_-__-----_-..--....--

type area. -_ __ __ __ -__ -. 

Geosynclinal deposits, Precambrian __________

Glance Conglomerate _-_._.-__-___--_........

contact relations ------------------------

correlation_ .-_----------..._.-________._

distribution .. _ _ -.. ...-_ 

environment of deposition, _..-.__________

exotic blocks---.----------.__.-._________

facies changes.-.--__ _- -_ _____ __

fossils. ---- - 

lithology. -----.---___..-------------_..__

source.-------..----.....-..--------.-....

Glenn, John, analyst...----._____._____ 16,32,

Gringo Gulch................................

Grosvenor Hills Volcanics -. --_ ______

H Page 

Hamilton, J. C., analyst.---.-.----------.-.- 41

Harris, J. L., analyst.---.--.---.------ 16,32,41,72

Helvetia klippe. _.- -- -----_-.-- -__ 47

Hog Canyon..__-_---------_---.-------.-_-_- 60,62

Huachuca Mountains_ -__--__ ___-_______ 34,43

Isotopic dates, Canelo Hills Volcanics..___-._ 25 

Cat Mountain Rhyolite. ----------------- 75

Elephant Headstock. --.-----...-.-.-.. 77

Gardner Canyon Formation_---------- 14

mudstone member.__________________ 24

Josephine Canyon Diorite. --------------- 75, 77

Madera Canyon Granodiorite------------ 77

Mount Wrightson Formation, middle

member..--.--_-__._-.--._.-._._- 6,14 

Final Schist..---------------------------- 5

plutonic rocks in Bathtub Formation_.. 35,43 

plutonic rocks in Mount Wrightson Formation.-..--.------------------.--- 14

plutonic rocks in Salero Formation._.. ___ 65 

Precambrian granitic bodies -------------- 5

Quantrell stock------------- -- ----.- 77

Roskruge Volcanics---------- - ---------- 75

Salero Formation..._ -. - 65

welded-tuff member. _ _-____ _- 74

Sugarloaf Quartz Latite. __-__ _- _- 75 

Temporal Formation, lower member. _ -. _ 34 

tuff of Jones Mesa. _--- - 75

Uncle Sam Porphyry ---- -. 75

J, K 

Javelina formation. 64

Jones Mesa.____..__-------------------------- 75

Josephine Canyon. _- - 26

Josephine Canyon Diorite _ - 65,73,74,77

Jurassic geologic events. - _ __ 25

Jurassic stratigraphy.------------------------ 6

Kauffman, E. G., fossil identifications------- 49

Laramide orogeny.--------- --. - 2, 5,46,55,64, 75

Lithology, Apache Canyon Formation....... 50

Bathtub Formation, lower member.._.. 36 

middle member......------------ 37,38,40

upper member -------------------- 42

Canelo Hills Volcanics-.................. 25

Fort Crittenden Formation, brown conglomerate member. .------------ 60

lower red conglomerate member..... _ 59

rhyolitic tuff member -------------- 62

shale member 57

upper red conglomerate member...... 62

Gardner Canyon Formation, mudstone

member. _ _ _ 20

siltstone member..................... 19

Glance Conglomerate__---------------- 46

Mount Wrightson Formation, lower member.....--------.-..---------- 7

middle member.-.--- --.----------_ 9

upper member_._- _____ _._.____ 13

Salero Formation, arkose member........ 71

exotic-block member_--------------- 67

lower member - - - -_ - 66

upper member_.-------------------- 73

welded-tuff member--..__ _- 70

Shellenberger Canyon Formation.------ 51

Temporal Formation, lower member. _ _ _ _ 29

lower and middle members undivided ------------------------ 31

middle member. _____________________ 30

upper member --. -.-_-.-___._ _ 32 

Turney Ranch Formation..-------------- 52

Willow Canyon Formation.__ _ __-____ 48

Little Casa Blanca Canyon. - - -_ 38 

Little DragoonMountains ------------------ 5

M Page

Madera Canyon Granodiorite__ - _._ 77 

Mansfield Canyon.-..---. ......... 7,12,26,28,36

Martin Limestone.- - -. .. _ _. 69

Metamorphism, Apache Canyon Formation.. 50

Bisbee Group._---- - -_ _-_ 47

Canelo Hills Volcanics ..-..-_______.___. 25

contact. See Contact metamorphism.

Gardner Canyon Formation_._________ 17,23

Salero Formation, upper member...-.._._ 74 

Turney Ranch Formation._______________ 52, 53

Willow Canyon Formation......_....___. 48

Metasomatism, Mount Wrightson Formation__--.- _ -__ _ _.-__ . 13 

Modes. See Analyses, modal. 

Montosa Canyon....---- - _ . _ __ 62,65, 76

Mount Wrightson...--... -_-...-.---....-- 7

Mount Wrightson Formation. ________ 6, 33, 46, 51, 69

age----...-------- ---- .-. _ 14

analyses------------------------_-_--_---. 13

contact relations----- ------.. ----- 6,14,27

correlation.- ____ ___._ 15

distribution --- .- . 7

environment of deposition._______________ 14,17

facies changes-------------------------- 10

lower member, lithology--- _ __ 7

petrography.--_----__________________ 7

middle member, lithology.__ - 9

petrography..__._____._______._____._ 10

source.....------------------------ - 12

upper member, lithology. ___---__-_-----_ 13

petrography.-_---------------_-----_-_--.13

Mount Wrightson quadrangle--------- 7,11,16,20, 57

Mule Mountains-- -------------------------- 43

Mural Limestone---------------------------- 44,52

Mustang Mountains-------------------------- 25

N, O

Norms, Bathtub Formation, middle member. 40 

Mount Wrightson Formation___ __ 13 

Temporal Formation, lower and middle

members undivided--. _ _ -._ 32

Oxframe Formation. 16

Packard Shale----.------- --- ----------- 64

Paleotopography, beneath Salero Formation.. 65 

beneath Temporal Formation__- _ 27 

in Salero Formation. _ - - 76

Paleozoic geologic events-.- ---------------- 4,5

Paleozoic rock units-- - --- - 5

Patagonia Mountains-.-- - ---------- - --- 14,16,75

Petrography, Bathtub Formation, middle

member--------------------- 38,39,40

Bathtub Formation, upper member ----- 42

Fort Crittenden Formation, rhyolitic

tuff member------------------- 62

Gardner Canyon Formation, mudstone

member.-----------.--.---------- 23

siltstone member. -------------------- 20

Mount Wrightson Formation, lower member.---------------------------- 7

middle member.------------------- 10

upper member-.--------- ---------- 13

Salero Formation, arkose member-.._-_- 73 

exotic-block member.-.----- ------- 67

lower member._______- ------------- 66

upper member___-_- _ 74

welded-tuff member------------------ 71

Temporal Formation, lower member _... - 29 

lower and middle members undivided. 32 

middle member __ - - 31

upper member____ - 33

Turney Ranch Formation. --------------- 53

Pillow lava, Mount Wrightson Formation _ _ _ _ 13

PinalSchist.--.---------------------- ----- 5

Piper Gulch Monzonite ------------------- 46,69
INDEX 81

Page

Plutonic rocks, beneath Temporal Formation. 27 

Cretaceous -----_______--_-___--_-________ 77

Mount Wrightson Formation..-.-______-_ 7

Precambrian...____-_-----_._-_-__....... 5,33

Salero Formation_ ____-__.

structural control_........

Willow Canyon Formation - 

Post-Bisbee rocks.-----___._-..

Pre-Bisbee rocks....._________.

Precambrian geologic events_. 

Precambrian rock units. --..--. 

Purpose of report...............

Quantrell stock. 77

Rainvalley Formation.................... 5, 6,14,17

Recreation Redbeds________________________ 25

Red Boy Peak............................... 75

Related studies_-..._-___________________... 2,4

RodolfoWash._______ _ ____________________ 25

Roskruge Range._-_--_ _ _ _ 75

Roskruge Volcanics. -------------..---------. 75

Sahuarita quadrangle_ __ -_ 7,11,51,57 

Salero Formation.._________________________ 65

age.-------------.------------------------ 74

analyses--_----.___-_-__-__-__-_--_____ 67, 68,71

arkose member, lithology.........________ 71

petrography. ____._.....-.----_-....__ 73

contact relations_----------------------- 65

correlation _____________.--_..---______ 64,75

distribution.-___ __ _ _ _ _ 65 

environment of deposition ________________ 75

exotic-block member, alteration.......... 76

lithology..___...__...______-.._.__.__ 67

origin.......__-......-__-.-_--.....__ 76,77

petrography. __ ______.___..._.________ 67

source- 69

facies changes. -----___---------_-_-_-_-_- 66

fossils..-_- -__--- __ .......... 73,74

Salero Formation Continued Page 

geologic events.--.._--_--_-_._-_-___-_-._ 76 

lower member, lithology..________________ 66

petrography. -_-_-_-___-___-____._-. 66

upper member, basal contact.....________ 73

lithology... ________.______-__-_-_.. 73

petrography --_.-__._-_____._._._-_.._ 74

source-----_-__-__._-__-_--_______-__- 74

welded-tuff member, lithology ___ _ 70 

petrography ___________.-._._-._.___._ 71

sheeting.-._.____._____.-._.__ ______ 70

San Cayetano Mountains._ __-___________--_-_ 65,73

Sawmill Canyon___.____________________ 7,17,19,20

Sawmill Canyon fault zone_ _ 7,17,25,35,46,47,52,57 

Scherrer Formation ___________________________ 5,20

Sedimentary structures, channel-scour marks. 48,50 

crossbedding..______ 11,13,17,48,50, 51, 53,58, 59

graded bedding______________.______... 48,50,52

ripple marks -__ _ _ -_ 52

Shellenberger -Canyon Formation ____________ 51

Sierrita Mountains.-_._____-_..__-___- 16,25,64,75

Silver Bell Formation- ____-_ _ - 75

Smith Gulch ---_______---____-_---- 32

Smith, H., analyst.___.._________. _-_ 16,32,41,72

Snake Ridge Formation...______.._-_____---- 64

Sonoita Group________________-_.--.-_---_--- 55

Squaw Gulch Granite. _ - 26,33,46,65,67,69,70,72,73 

Sugarloaf HiU.....___._____-_____--_.--.-- 75

Sugarloaf Quartz Latite. ___ -- 75

Sutton, A. L., analyst __ - - 72

Sycamore Canyon.--.-- 18,25,44,47,49,51,65,70

Taylor, D., analyst__.____._______------_--_ 41

Taylor, D. W., fossil identifications----------- 63

Temporal Formation. __________--_---_.--_-__ 26

age____-_-.__-___________________._-._.___ 33

analyses------------------------------ 31,32,33

contact relations --------------------- 26,27,35

correlation.______________________________ 34

distribution. _ _----._____....-._-_---- 26

Temporal Formation Continued Page 

environment of deposition. . _-_. ______ 35

facies changes.-. -_-- ----- -- ____ 28,35

lower and middle members undivided,

lithology ______._._.___.-._--___._ 31

petrography. __-__-_--_-.__-_-.-._._-_ 32

lower member, lithology- ___-- __ _- 29

petrography.- _-----_-_-_---------_- 29

source ---.._-_._--__-__-_-_--___-_._-_ 30 

middle member, lithology ---------------- 30

petrography _-___-_- _-- - -- 31 

source, _.-_--__________---_-_-_--_-__--__- 35

upper member, lithology _____ __ _- 32

petrography.-.-. __-_---_--------_---- 33

Temporal Gulch. .-.______.-___ 7,25,26,31,33,36,38

Triassic geologic events. _-_- --_---_--- 25 

Triassic stratigraphy _ ___-_-___ - _-__ 6 

Tucson Mountains.-------------------------- 25,75

Turney Ranch Formation ------------------ 52, 57

U 

Uncle Sam Porphyry ___.___..___ -____-_-_- 75

Unconformities, beneath Salero Formation. _ _ 65 

beneath Temporal Formation ____________ 27

in Bathtub Formation -__ _ - 42

in Gardner Canyon Formation. ___-_---_. 19

in Salero Formation ------------ 70,71,76

sub-Cretaceous..------------------------- #5

sub-Triassic. -_-_-------_----------------- 6

W

19

47

47

47

50

Wasp Canyon.. -____-_._----__-_-_-_-_----

Willow Canyon Formation.. ___ _-- 

contact relations.. --- --« --

distribution. -_______..-.____-_-_-_-_--

environment of deposition 

facies changes- _.____... __ 47,48

fossils-. -.-- _ _-- -_- -- 48,49,50 

lithology.. .-__-_ .-- ------- 48

source. ._ _-_- _--_ -- 50

Winchester Mountains.-.--------------------- 64

D. S. GOVERNMENT PRINTING OFFICE : 1971 O - 404-482