CONTRIBUTIONS TO THE GEOLOGY AND PALEONTOLOGY OF SAN 

JUAN COUNTY, NEW MEXICO. 

1. STRATIGRAPHY OF A PART OF THE CHACO RIVER .VALLEY. 

By CLYDE MAX BAUER. 

INTRODUCTION. 

This preliminary paper is an attempt to set 

forth the principal features of the stratigraphy 

in a part of the San Juan Basin-to describe 

the succession of strata irrespective of possible 

correlations and thereby to establish a type 

section for the formations exposed and to 

bring out their relations to the strata immediately above and below. The paper presents 

only a part of the data collected by a field 

party of the United States Geological Survey 

in the season of 1915, in charge of the writer, 

and does not describe the economic resources 

of the area, such as coal, nor the general 

geologic problems. 

In mapping formation boundaries, streams, 

roads, and other surface features, the plane 

table and alidade were used. Where the 

slopes are steep and the strata nearly norizontal, sections were measured directly with a 

hand level. Elsewhere the alidade was employed for obtaining distances and differences 

in elevation, and the thickness of the intervening strata was calculated from these data. 

~ossils were collected at localities whose positions were accurately determined, both stratigraphically and geographically. 

The accompanying papers on the paleontology of the area, by C. W. Gilmore, T. W. 

Stanton3 and F. H. Knowlton/ discuss the 

fossil collections made by the field party. 

For these collections and a considerable part 

of t~e. other data, including mapping, much 

credit IS due to John B. Reeside, jr., who assisted the writer both in the field and in the 

office, and to H. R. Bennett, who assisted in 

1 U. S. Geol. Survey Prof. Paper 98, pp. 279-353, 1916 (Prof. P apers 

9&-Q, 98-R, 98-S). 

the field. Acknowledgments are also due to 

M. R. Campbell, who exercised general supervision over the work and made many helpful 

suggestions and criticisms. 

GEOGRAPHY. 

The area studied and mapped comprises 

about 1,500 square miles in northwestern New 

Mexico extending along Chaco River for about 

50 miles from the Great Hogback, on San Juan 

River, to Meyers Creek, 6 miles north of 

Pueblo Bonito. (See Pl. LXIV.) The area 

may be reached by the Denver & Rio Grande 

Railroad, a branch of which terminates at 

Farmington, on the northern edge, or by the 

Santa Fe Railway to Thoreau, which lies 

about 60 miles south of Meyers Creek. From 

Thoreau wagon roads lead northward and 

cross the Continental Divide at San Antonio 

and Sheep passes. The population of the 

area, which lies partly in the Navajo Indian 

Reservation, is composed largely of Navajo 

Indians, who raise sheep, goats, and ponies 

and are nomadic in their habits. Sagebrush, 

rubber weed, chico, and pear cactus are the 

most common plants of the desert plain. A 

few white traders have located stores (see Pl. 

LXVIII, B) in the area. 

The region is arid and stands from 5,200 to 

about 6,500 feet above sea level. The drainage goes mainly westward through arroyos 

cut sharply into the westward-sloping plain 

(see Pls. LXVI, 0, and LXXI, B) to Chaco 

River . . Between the arroyos are broad, gently 

rolling interstream plains, most of them surmounted by numerous long dunes of windblown sand and offering few exposures of the 

stratified rocks. The arroyos, on the other 

271 
272 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1916. 

hand, present excellent exposures of the 

strata, especially near their heads, where there 

are many areas of badlands (see Pls. LXVIII, 

A, and LXXI, B), in which vegetation and 

soil are lacking and the rocks can be studied 

in great detail. These badland areas are cut 

below the general level and most of them are 

therefore invisible from the upland, except 

uear their edges. 

San Juan River is the only permanent 

stream in the area. It is maintained to a 

large extent by the melting snows on the mountains at its source, and, although the water is 

muddy, it contains far less alkali than the 

water of the other streams Qf the region. 

Chaco River has a bed as wide as that of San 

Juan River, but, although it is over 150 miles 

long, water flows in the channel only at intervals and only for a few days at a time. Its 

bed during the remainder of the year is a 

barren sandy flat. The water supply for the 

area is therefore obtained almost entirely 

from wells and artificial lakes. The rain 

water, caught in artificial lakes or pools, is 

carefully conserved through the long, dry 

periods. The water from the wells is strongly 

alkaline and commonly salty, and in many 

places it is not fit for domestic use. However, 

through long experience, the Navajo Indians 

have sought out the best watering places and 

have sunk crude wells and constructed reservoirs for storing flood waters. 

STRATIGRAPHY. . 

GENERAL FEATURES. 

The name San Juan Basin has been used by 

several writers to refer to the area inclosed by 

the outcrop of the Cretaceous coal-bearing 

formations of northwestern New Mexico. This 

area is properly a structural basin, a.nd the 

writer would therefore limit the term to the 

region in which the strata dip toward a common center and exclude the Zuni Basin on the 

south, which is separated from the main 

basin by a structural divide. 1 The stratigra,phy of the west-central part of the San 

Juan Basin is described in this paper. The area 

1 Shaler, M. K., A reconnaissance survey of the western part of the 

Durango-Gallup coal field of Colorado and New Mexico: U. S. Geol. 

Survey Bul~ . 316, pp. 376-426, 1907. 

includes the outcrop of strata overlying the 

Mesaverde formation, which have in the pasx 

been referred to the Lewis, Laramie, Puerco, 

Torrejon, and Wasatch formations. 

The stratified rocks of this area consist of a 

succession of marine, brackish-water, and freshwater sediments, which now occur as sandstone, 

shale, coal, and conglomerate, in almost every 

gradation and combination possible. The dip 

of the strata throughout the greater part of the 

area is from 1° to 3° toward the center of the 

basin. In the Great Hogback, however, 

the beds lie in a sharp monocline dipping as 

much as 4 7° in an easterly direction. This 

steep dip persists only a short distance, however, and beyond it the beds flatten to dips 

of 3° or less. 

The sections given in Plate LXV show the 

thickness and character of the units measured along several arroyos, as shown on the 

map (Pl. LXIV). The area was entered from 

the north, and the first section was measured 

along San Juan River. (See A-A', Pl. LXIV.) 

A generalized profile of this section is also 

shown in figure 27 (p. 275). Here the exposures 

are good, permitting a division into mappable 

units on a basis of lithologic differences. The 

Mesaverde and Lewis formations and the Pictured Cliffs sandstone were accepted as described by previous workers in the San Juan 

Basin, 2 as the two former have been traced 

directly from their type localities and the San 

Juan River valley is the type locality for the 

Pictured Cliffs sandstone. 3 The beds above 

this sandstone were divided into mappable 

lithologic units. As the present work progressed southward the distinctness of these 

units became more and more evident, and the 

sections measured were easily correlated with 

that along the river. 

The following table gives the names and 

thicknesses of the several formations described 

in these pages, as well as the names previously 

used for them: 

2 Schrader, F. C., The Durango-Gallup coal field of Colorado and New 

Mexico: U. S. Geol. Survey Bull. 285, pp. 241-258, 1906. Shaler, M. K., 

A reconnaissance survey of the western part of the Durango-Gallup 

coal field of Colorado and New Mexico: u~ S. Geol. Survey Bull. 316, 

pp. 376-426, 1907. . 

a Holmes, W. H., Geology of the San Juan district: U.S. Geol. and 

Geog. Survey Terr. Ninth Ann. Rept., for 1875, p. 248, 1877. 
~~~~S~c~~~ffi~~ 10 

s LEGEND 

0 ~ ~ ~ ~ ~ K;.-t~ale Pl4:J J:r~~: ~ ~~ p;ctured Cl;ffs 

sandstone 

zoMiles 

Wasatch 

~ formation d Ojo Alamo containing f\.ercb. an sandstone Farm;ngton ss 

Tor"tl?n member MEX., FROM 

format•ons . N JUAN BASIN, N. Plate LXIX. 

AL PART OF THE S~ dicates the area shown on 

F 

WEST-CENTR The rectangle •n -

MAP 0 

B 

Mesaverde 

formation 

PROFESSIONAL PAPER 98 PLATE LXIV 

·.D 

Location o~ 

stratigraphic 

t·on shown sec 1 XX on Plates LXV' L 

MEYI::RS 

0 

Fossil 

location 
,, · 

" .. ·~ ' 

,, 

"' 

' ' ' ., 

,· 

' . 

•,. 

'\ .. 
STRATIGRAPHY OF A PART OF THE .CHACO RIVER VALLEY. 273 

Geologic formations in the west-central part of the San Juan Basin, N. Mex . 

This paper. 

Holmes, 1877 .a Shaler, 1907. b Gardner, 1909. c Sinclair and 

Granger, 1914.d Thickness Formation. (feet). 

Wasatch. Wasatch. Wasat ~h. Wasatch formation. 500+ 

(Undifferentiated Torrejon. Torrejon. 

[Absent in area de- Tertiary.) Torrejon and Puerco 

scribed.] formations. 390 

Puerco. Puerco . 

. . . . . . (?) ...•... Ojo Alamo. Oj o Alamo sandstone. 63-110 

........ (?) ••...... Kirtland shale, inLarami~. eluding Farming- 836-1,180 

ton sandstone mem- o-455 

Laramie. her. 

Laram~e. 

Fruitland formation. 194-292 

-. 

Pictured Cliffs. [Not described.] Pictured Cliffs sand- 49-275 stone. 

Sand shale group. I Lewis. Lewis. Lewis shale. 76-415 

Mesa Verde. Mesaverde. Mesaverde. Mesaverde formation. 1,980 

~ !,lolmes~:V· H., Geology ~f the San Juan district: U.S. Geol. and Geog. Survey Terr. Ninth Ann. Rept., for 1875, p. 244,1877. 

vey B~~~~ ~I6~;. ~i6,1tti.onnaissancc survey of the western part uf the Durango-Gallup coal field of Colorado and New Mexico: U. S. Geol. Sur1909~ Gardner, J. H ., The coal field between Gallina and Raton Spring, N.Mex., in the San Juan coal region: U.s. Geol. Survey Bull. 341, p. 338, 

d Sinclair, W.J., and Granger, Walter, Paleocene deposits of the San Juan Basin,N. Mex.:Am. Mus. Nat. Hist. Bull., vol. 33, pp. ~7-316,1914. 

MESAVERDE FORMATION. 

The Mesaverde, which is the lowest formation examined in this area, exhibits the same 

characteristics hare as in the type locality, the 

Mesa Verde National Park, except that it is 

somewhat thicker. Where the Great Hogback 

is cut by Chaco River the thickness of the 

Mesaverde is 1,980 feet. At this place it presents a striking monocline with an eastward 

dip of 35°-47°. The formation is composed 

here of a lower sandstone member, which contains coal in its upper part; a middle shaly 

member, which comprises thin-bedded sandstone, shale, and coal; and an upper massive 

sandstone member. This formation was not 

studied in detail and only its upper limit was 

mapped. 

LEWIS SHALE. 

The Lewis shale (see Pl. LXVI, B) is marine 

in origin and very similar to the shale at Fort 

Lewis, Colo., the type locality. 1 It is thinner 

t Cross, Whitman, U. S. Geol. Survey Geol. Atlas, La Plata folio 

(No. 60), 1899. 

here, however, than at Fort Lewis, being about 

475 feet thick on San Juan River, decreasing 

gradually southward as far as Coal Creek, 

where it is 76 feet thick, and increasing again 

to 103 feet on Meyers Creek. (See Pl. LXV.) 

The Lewis shale exhibits the same lithologic 

characteristics throughout the field. It is a 

greenish-gray sandy shale with local streaks 

of yellowish calcareous shale. On San Juan 

River it has also a prominent layer of buff 

lime concretions about 100 feet above its base. 

.Three collections of fossils were obtained from 

it and have been identified by T. W. Stanton. 

They are listed below. (See also Pl. LXV.) 

Collection 1 (9277): 

Anomia sp. 

Inoceramus? sp. 

Lucina sp. 

Lunatia sp. 

Baculites sp. 

Ma1.ine Montana fauna. 

Collection 10 (9273): 

Inoceramus barabini Morton. 

Placenticeras intercalare Meek and Hayden. 

Undetermined burrows. 
274 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1916. 

Collection 82 (9296): 

Ostrea inornata Meek and Hayden. 

Syncyclonema sp. 

Ledasp. 

Cardium speciosum Meek and Hayden. 

Liopistha undata Meek and Hayden. 

Lunatia sp. 

Placenticeras sp. 

Marine Montana fauna. 

PICTURED CLIFFS SANDSTONE. 

Overlying the Lewis shale conformably is the 

Pictured Cliffs sandstone (see Pl. LXVII, A) 

of near-shore marine origin. Its contact with 

the Lewis is gradational, but in the aggregate 

its lithology is distinct from that of the beds 

beneath. As the name indicates, it is a sandstone that forms cliffs, particularly on San Juan 

River immediately west of Fruitland, where 

there are prominent cliffs of copper-colored 

sandstone 20 to 40 feet high. Farther south 

it is a yellowish to light-gray or brown sandstone and not so massive. It diminishes in 

thickness from 245 feet on San Juan River to 

49 feet on Brimhall Wash, and from that place 

increases to 91 feet on Meyers Creek. (See 

Pl. LXV.) Halymenites major is abundant in 

this formation, and the following fossils, identified by T. W. Stanton, were also collected 

from it: 

Collection 2 (9278): 

Serpula sp. 

Inoceramus barabini Morton. 

Cardium speciosum Meek and Hayden. 

Tellina scitula Meek and Hayden?. 

Leptosolen? sp. 

Mactra gracilis Meek and Hayden?: 

Corbula sp. 

Turris? sp. 

Odontobasis? sp. 

Haminea sp. 

Actreon sp. 

Marine Montana fauna. 

FRUITLAND FORMATION. 

Conformably above the Pictured Cliffs sandstone lie the brackish and fresh water beds of 

the coal-bearing Fruitland formation, and the 

contact presents the usual characteristics of 

interfingering beds. The name Fruitland is 

derived from that of a settlement on San Juan 

River which lies on the outcrop of this formation. The formation consists of sandstone, 

shale, and coal. (See Pl. LXVII, B.) It is 

very irregularly bedded: and the several beds 

range from flandy shale and shaly or clayey 

sandstone in all conceivable proportions to 

I rocks that can be definitely called sandstone 

or shale. The variation in some places is so 

rapid both laterally and vertically that weathering of the unequally indurated rocks produces 

pillars, knobs, capped prisms, pyramids, and 

fantastic shapes of all sorts. This irregularity 

is most marked in the gray-white sandstone 

and gray sandy shale, but to some degree it 

affects also the coal beds. Nevertheless the 

coal beds, although they are lenticular, are 

more persistent than the sandstone and shale 

with which they are interbedded. Large concretions of iron carbonate which weather dark 

brown or black occur at several horizons. 

These concretions commonly contain barite, 

which has been introduced into them subsequent to the deposition of the strata, and many 

of them have in this manner been converted 

by veins of crystallized barite into large septaria. The Fruitland formation is more sandy 

than the overlying Ki:Ptland shale, into which 

it merges by a gradational zone containing in 

many places sandstone lenses that are apparently of fluviatile origin. The thickness of the 

Fruitland formation is fairly constant in this 

field, ranging from 194 to 292 feet. (See Pl. 

LXV.) The fossils of this and the succeeding 

formations up to the Puerco are listed and discussed in the papers by Messrs Gilmore, Stanton, and Knowlton already mentioned. 

KIRTLAND SHALE. 

The Kirtland shale lies conformably upon 

the Fruitland and is predominantly clayey. 

The name is taken from that of a post office on 

San Juan River. The strata are composed 

mostly of gray shale, with some brown, bluish, 

greenish, and yellowish shales, easily weathering gray-white sandstone, and the brown 

resistant sandstone of the Farmington member 

described below. Barite occurs in concretions and veins in these strata. The eroded 

surface of the Kirtland shale presents a billowy 

appearance, with well-rounded surfaces. It 

is readily affected by erosion, giving rise to 

extensive badlands. The shale, so far as 

known, is of fresh-water origin, although 

possibly it was formed in deltas and lagoons. 

It is divided, as shown in the San Juan River 

section (A-A', Pl. LXV), into three parts-a 

lower shale 271 feet thick, a sandy part, here 

named the Farmington sandstone member (see 

Pl. LXVIII, A), and an upper shale 110 feet. 

thick (see Pis. LXXI, A, and LXVI, 0). 
U. S" GEOLOGICAL SURVEY PROFESSIONAL PAPER 98 PLATE LXV 

Ft 

::·::::.:-

LEGEND 

§coal =Shale ~ . <:;:. >:::: ~Conglomeratic B ~orizon °~ ·0 Thickness of Sandy shale /'}''.:Sandstone tZ''-~ ca a to e 79 fossil locatiOn 51 "ormat·o · , .. .... .,.,, ·., . .-.o·.· ~ n -" n on Plates [)(IV, · " 1 n 

LXIX 

A'. 

o' 

E' 

c' 6s+lWJ~;ji::-::~ ___ _ 

---

. t.P(I 

farrf1J(l9 

------

•1'-'-.=:j 9 Miles r: ==J 10 Mt!es F.o-=: 

_,.. E 

--------- ___ ? ____________ _ -~"",_. 

D F' 

------

c 

B 

A 

STRATIGRAPHIC SECTIONS ALONG CHACO VALLEY, N. MEX., FROM SAN JUAN RIVER TO MEYERS CREEK. 

For locations see Plate LXIV. 

Scale 

aoo Feet 

600• 

400 

200 

0 

G 

Ojo Alamo 

F/uvie~tile 

f\irtland 

Fruitland 

P1ctured 

Cliffs 

Lewis 

Mesaverde 
l. 

; 
U. S. GEOLOGICAL SURVEY 

A. KIRTLAND SHALE OVERLAIN BY WASATCH 

FORMATION. ON SOUTH SIDE OF SAN JUAN 

RIVER OPPOSITE FARMINGTON, N. MEX. 

PROFESSIONAL PAPER 98 PLATE LXVI 

B. OUTCROP OF LEWIS SHALE ALONG 

CHACO RIVER, N. MEX., 1 MILE EAST OF 

POINT WHERE IT CUTS THROUGH THE 

GREAT HOGBACK. 

The Great Hogback is composed of rocks ofthe 

Mesaverde formation and appears in the distance. Exposure shows sandy beds in the 

Lewis shale. View looking northwestward. 

C. THE DESERT PLAIN VIEWED NORTHWESTWARD ACROSS THE VALLEY OF CHACO RIVER, 

N. MEX., SOUTH OF HUNTER WASH" 

Chaco River and other arroyos are intrenched from 75 to 200 feet in this plain, which slopes westward 25 feet 

to the mi I e. The Great Hogback is seen in the distance. Elevation above sea level at plane table, 5,680 feet. 

U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 98 PLATE LXVII 

.A. PICTURED CLIFFS SANDSTONE OVERLYING LEWIS SHALE ON NORTH SIDE OF 

COAL CREEK, N. MEX., 2 MILES FROM ITS MOUTH. 

View looking westward. 

B. OUTCROP OF LOWER PART OF FRUITLAND FORMATION 1 MILE SOUTHWEST 

OF HUNTER'S STORE, N. MEX. 

Coal bed is overlain by peculiarl y weathered gray-white sandstone. Flat in foreground underlain 

by shale. View looking southeastward. 
• U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 98 PLATE LXVIII 

A . FARMINGTON SANDSTONE MEMBER OF KIRTLAND SH...XLE NEAR THE HEAD OF 

COTTONWOOD ARROYO, N. MEX. 

Part of sandstone shown is 300 feet thick; upper part of Farmington sandstone, about 130 feet, is 

· eroded at this place. 

B. OJO ALAMO SANDSTONE AT OJO ALAMO STORE, N. MEX. 

Puerco formation overlying Ojo Alamo sandstone is shown in the distance. View looking northward. 
STRATIGRAPHY OF A PART OF THE CHACO RIVER VALLEY. 275 

The sandstone member forms a prominent 

bluff on San Juan River, where it is 455 feet 

thick, but toward the 

south it is gradually 

replaced by lenses of 

shale. On the head of 

Coal Creek the member disappears as a 

mappable unit, and 

farther south it is 

represented only by 

isola ted sandstone 

lenses in the Kirtland 

shale. A study of the 

sandstone lenses 

making up the Farmington shows that 

they are irregular 1n 

thickness, cross-bedded, and composed 

almost invariably of 

twoparts-atthe base 

an easily eroded yellowish sandstone carrying clay pellets of 

various sizes and in 

some lenses sandstone 

pebbles similar to the 

matrix, as large as 4 

inches 1n diameter, 

and at the top a markedly resistant brownish sandstone whose 

upper portion is commonlyof a dark chocolate-brown color on 

the exposed surface 

and dark gray on the 

fresh surface. All 

the lenses in the Farmington sands tone 

member lie on more or 

less irregular surfaces 

of interbedded shale 

and exhibit the characteristics of channel 

and flood-plain deposits. An individual 

lens will usually have 

a maximum thickness 

of 20 feet, a lateral 

extent of 15 or 20 

yards, and a length of several hundred yards. 

The upper part of the Kirtland shale (see Pis. 

LXVII, A, and LXXI, A) is remarkably uniform in thickness from San Juan River to the 

southern limit of the area, ranging from 40 to 

110 feet. It is composed of shale and lenses of 

easily weathered gray-white sandstone, and is 

thus very similar to the lower part. It is 

banded in many places with various colors, 

such as appear in the lower part of the Kirtland, 

but yellow, blue-gray, and purplish beds are 

more common. 

OJO ALAMO SANDSTONE. 

Overlying the Kirtland shale (see Pl. LXXI, 

A) with apparent conformity is a thin formation of conglomeratic sandstone and shale. 

These beds were first described by Barnum 

Brown/ of the American Museum of Natural 

History, New York, who named them Ojo 

Alamo, from the locality in which they were 

examined, but assigned no base and indicated 

no relation between them and the underlying 

beds. On Ojo Alamo Arroyo Brown found 

dinosaur-bearing shale below a conglomerate, 

which is overlain unconformably by the Puerco 

formation. The following statement is taken 

from his description: 

Less than a mile south of the store at Ojo Alamo the 

Puerco formation rests unconformably on a conglomerate 

that is composed of red, gray, yellow, and white pebbles. 

* * * Below the conglomerate there is a series of shales and 

sandstones, evenly stratified and usually horizontal. * * * 

The shales below the conglomerate that contain numerous dinosaur and turtle remains I shall designate as the Ojo 

Alamo beds. They were estimated to be about 200 feet 

thick, but owing to lack of time I was unable to determine 

their relation to the underlying formations. 

Later Sinclair and Granger/ of the same in--

stitution, while making a thorough investigation of the Puerco formation, examined the Ojo 

Alamo locality, and found that the dinosaurbearing shale on Ojo Alamo and Barrel Spring 

arroyos is split by a thin conglomerate, referred 

to by them as the "lower conglomerate." 

According to their interpretation 

The Puerco formation rests with marked erosional unconformity on a coarse cross-bedded conglomeratic yellowbrown sandstone * * * which varies in thickness 

1 Brown, Barnum, The Cretaceous Ojo Alamo beds of New Mexico, 

with description of the new dinosaur genus Kritosaurus: Am. Mus. Nat. 

Hist. Bull., vol. 28, pp. 267-274, 1910. 

2 Sinclair, W. J., and Granger, Walter, Paleocene deposits of the San 

Juan Basin, N.Mex.: Am. Mus. Nat. Hist. Bull., vol. 33, pp. 297-316, 

1914. 
276 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1916. 

from 28 to 66 feet. [This sandstone] rests disconformably on 

* * * rusty-yellow, bluish, greenish, and wine-red 

banded days with lenses of yellow channel sandstone. 

* * * A maximum thickness of some 5.8 feet was measured for this member. * * * [It contains] abundant 

but badly crushed dinosaur bones, ceratopsian, trachodont, and carnivorous, also turtles, crocodiles, and garpikes. [The sandstone lies on a "lower conglomerate,'' 

which] varies from a pebbly sandstone to a coarse conglomerate with waterworn, chatter-marked quartzite, jasper, 

andesite, and porphyrite pebbles. * * * Its source has 

not been traced. Its thickness varies from 6 to 8 feet. 

* * * This lower conglomerate lies in its turn disconformably on a series of bluish shales, or rather clay, for 

they are quite in~oherent. * * * · [This shale contains dinosaur bones.] A trip down Ojo Alamo Arroyo to a 

point some 8 miles below the store resulted in finding turtle 

and other reptile bones in shales apparently conformable 

with those just mentioned. 

The discrepancies in these descriptions and 

the failure of these investigators to assign a 

stratigraphic or paleontologic lower limit to 

the Ojo Alamo beds call for a more accurate 

definition of them. The present writer, therefore, made a careful study of these beds in the 

type locality. Sections (lettered H to W on 

Pl. LXX; locations of H, I, U, V, and W 

shown on Pl. LXIV, and of J to T on Pl. 

LXIX) were measured and compared. On Ojo 

Alamo and Barrel Spring arroyos (see Pl. LXXI, 

A, and sections 0 to S, Pl. LXX) the succession of shale and conglomerate as described 

by Sinclair' and Granger was noted. Sec.tion P, 

measured on Ojo Alamo Arroyo, shows 25 feet 

of the "upper conglomerate" (see Pl. LXVIII, 

B) lying on the 34 feet of wine-red and bluishgray banded shales interbedded with lenses of 

gray-white, easily eroded sandstone. This in 

turn lies on 9 feet of poorly consolidated conglomerate, which has an irregular base, the 

irregularities amounting to 2 or 3 feet in a 

horizontal distance of 50 feet. Below the 

lower conglomerate is a bluish-gray to greenishgray shale, banded here and there with purplish 

heds and gray-white sandstone lenses. This 

lower shale is lithologically similar to and conformable with the beds below. Both of the 

shales just mentioned contain dinosaur and 

turtle remains, as shown in section Q, measured 

on Barrel Spring Arroyo. However, the lower 

conglomerate has been traced laterally to points 

where the shale between it and the upper conglomerate is absent, and only a single litho-. 

logic unit is present. (See sections, Pl. LXX.) 

Moreover, the lower shale of Sinclair and 

Granger is lithologically like the shale below the 

lower conglomerate on Ojo Alamo Arroyo and 

is clearly a part of the Kirtland shah~. Furthermore, the shale that lies between the conglomerate beds on Ojo Alamo and Barrel Spring 

arrovos is cut in many places by irregular lenses 

of g~ay-white, easily eroded sandstone, which 

give it so irregular and indefinite an outline that 

it is not mappable. At localities H, I, J, L, M, 

T · U V and W this shale is not a definite unit. ' ' ' As Brown, Granger, and Sinolair do not agree 

on the upper limit of the formation, Brown 

placing it at the base of the "upper conglomerate" and Sinclair and Granger at the top, and 

as neither of them assigned a lower limit, it is 

necessary to redefine the lithologic Ojo Alamo 

as determined by the writer. As he found the 

formation to be essentially a sandstone including lenses of shale and conglomerate, it seems 

desirable to call it Ojo Alamo sandstone and 

to define it as consisting on Ojo Alamo Arroyo 

of two conglomera tic beds and the shale lenses 

which they include. Its thickness where it is 

overlain by the Puerco formation (see sections 

H N S and T) ranges from 63 to 110 feet. 

Ab~ut 70 per cent of the pebbles of the Ojo 

Alamo are of jasper,variously colored chert, or 

pink or white quartzite. Of the remainder, 

pebbles of sandstone, andesite, felsite, porphyrite, gneiss, and schist are fairly common, ~nd 

pebbles of granite and obsidian are also present. 

Practically all the pebbles are well rounded. 

They range in size from sand grains to a few 

that are 6 inches in diameter. The Ojo Alamo 

sandstone is highly cross-bedded, and the pebbles occur at different horizons or are scattered 

through it irregularly. In some places the 

lower 20 or 30 feet of it is almost lacking in 

pebbles. On Oj o Alamo Arroyo the lower bed 

of conglomerate is poorly consolidated, hut on 

the south side of Barrel Spring Arroyo it is 

quartzitic and very resistant, capping sev:e~al 

low buttes in the vicinity. Between locaht1es 

U and V also the lower bed is very resistant, 

forming the cap rock for many small buttes. 

PUERCO AND TORREJON FORMATIONS. 

The Puerco formation (see Pls. LXVIII, B, 

and LXXI B) overlies the Ojo Alamo sandstone with' an unconformity by erosion, the 

irregularity in the contact where seen amounting to 15 or 20 feet, but no discordance of dips 

between the two formations was noted. 
. : .. :; 

Kk • ....-J 

I 

r· .. /···--,_j 0 

·-./· /.·. · ·. ·'' 

/K kf) ., . ' . / 

l/;:::C>/ Kk 

Scale 

0 I 2 

W

~ asatch 

formation 

B 

Pu e rco a nd 

Torrejon 

formations 

__ / . ..;./ .·-----

,..,-

LEGEND 

EEJ . 

. 

Ojo Al a mo 

sandstone 

~ 

Kirtland 

~ shale 

containing 

Farmington ss 

member 

···--/··· 

Tpt 

c;] 

Location of 

section shown 

on Plate LXX 

MAP SHOWING DETAILS OF GEOLOGY IN VICINITY OF OJO ALAMO, N. MEX. 

J ... 

~-:· 

.. ~ ... ...........-'··· 

) 

/ 

0: 

Arfo'1r·:· 

,-1· .. ~·· · 

Tpt 

. . . . - .· · ... ·_ ..... ....... ·. 

·~-·- ...:.:.. 

1:1 

L::_j 

Fossil 

location 
U. S. GEOLOGICAL SURVEY 

H 

~~Shale 

J 

~~Sandy 'shale IWtW;}:{jsandstone 

K 

I 

·t::=::=. ~ .9. 6 Mtle!5 ---1: ,-:-:-:=---1 

s 

p Q 

_______ [~------

LEGEND 

II,Ji Cooglomocale I ..,p' I Si!;Oified log 

~~~(q~~~ 

M 

L 

\t );~;-9~ 

62 

T 

u 

~-

PROFESSIONAL PAPER 98 PLATE LXX 

a Erosional contactc:J7 fossil Hor~zon locat1on °~ on Plates LXIV, LXIX 

N 

Scale 

ISO Feet 

w 

100 

v 

50 

0 

SECTIONS OF OJO ALAMO SANDSTONE FROM PINA VETA CHINA TO THE HEAD OF MEYERS CREEK, N. MEX. 

For locations see Plates LXIV and LXIX. 
STRATIGRAPHY OF A PART OF THE CHACO RIVER VALLEY. 277 

Considerable interest has been attached to 

the Puerco formation because of the primitive 

mammalian fauna which it contains and because it is confined, so far as known, to the San 

Juan Basin in New Mexico, though Torrejon 

mammals have been collected from the Fort 

Union of Mon tana. 1 

The Puerco was first described by Cope 2 in 

1875. He believed it to overlie the "Laramie" 

conformably 3 on evidence presented to him by 

David Baldwin, a collector, who obtained most 

of the fossils from the Puerco for Cope. How-

~ver, Cope also states in his paper on the Eocene 

plateau that the Eocene Wasatch overlies the 

Puerco "with apparent conformability." 

Endlich 4 and Hohnes, 5 in their early reconnaissance work in Colorado and New Mexico, 

apparently mistook the Kirtland shale, or, as 

Gardner 6 suggests, the lower members of the 

Wasatch, for the Puerco, inasmuch as typical 

Puerco mammals have not been found outside 

of a small area near the center of the San Juan 

Basin in New Mexico and have not been found in 

the deposits described by Endlich and Holmes. 

The collecting by Baldwin under Cope's 

direction was actively carried on at intervals 

from 1880 to 1885, and numerous articles on 

the fauna were published. In 1892 J. L. 

Wortman took up the problems connected 

with the Puerco and headed an expedition to 

the San Juan Basin. His results were summarized in a paper by Osborn and Earle/ 

in whioh is quoted a statement from Wortman's notebook that "the Puerco beds so far 

as can be observed lie conformably upon the 

Laramie." Wortman again visited the region 

in 1896 and added much to the collections 

already obtained. W. D. Matthew 8 then began 

a systematic study of the Puerco fauna, and in 

1897 his paper on it was published. 

1 Douglass, Earl, The discovery of Torrejon mammals in Montana: 

Science, new ser., vol. 15, pp. 272-273, 1902. 

2 Cope, E. D., The Eocene plateau: Chief Eng. Ann. Rept. for 1875, 

pt. 2, Appendix G1, ch. 6, pp. 1008--1017. 

a Cope, E. D., The relations of the Puerco and Laramie deposits: Am. 

Naturalist, vol. 19, pp. 985-986, 1885. 

4 Endlich, F. M., The San Juan region: U . S. Geol. and Geog. Survey 

Terr. Ninth Ann. Rept., for 1375, pp. 189-190, 1877. 

o Holmes, W. H., La Plata Valley: Idem, pp. 245-267. 

6 Gardner, J. H., The Puerco and Torrejon formations of the Nacimiento group: Jour. Geology, vol. 18, No.8, pp. 702-741, 1910. 

1 Osborn, H. F., and Earle, Charles, Fossil mammals of the Puerco 

beds, collection of 1892: Am. Mus. Nat. Hist. Bull., vol. 7, pp. 1-2, 1895. 

s Matthew, W. D., A revision of the Puerco fauna: Am. Mus. Nat. 

Hist. Bull., vol. 9, pp. 259-323, 1897. 

In 1907 J. H. Gardner, 9 in connection with 

the mapping of the coal beds in this area, made 

some observations on the Puerco. His conelusions were published in 1910.10 His work 

was followed by the careful study of the Pueroo 

and Torrejon formations, including extended 

collecting, in 1912-13 by Walter Granger and 

W. J. Sinclair, whose stratigraphic results were 

published in 1914.U 

The Puerco formation was not studied in 

detail by the present writer, and only its general features will be set forth here. It is very 

lenticular and irregular in bedding and, like 

the underlying bedsJJ is of fluviatile origin. It 

consists of clay, sandy shale, easily weathered 

sandstone, and resistant sandstone. The 

striking feature of the Puerco formation, aside 

from its mammalian fauna, is its color, which 

is predominantly bluish gray and gray-white, 

but banded with lemon-yellow sand and winered clay. It contains also lenses and concretions of resistant sandstone cemented with 

manganese dioxide, which are ahnost black 

and present a bold contrast to the other strata 

of the region. Barite is common in isolated 

concretions, as well as in veins and in sheets. 

The Puerco is overlain by the Torrej on formation, which is very similar to it lithologically 

and was not separated from it by the writer 

in mapping. Owing to the close similarity in 

lithology such separation of the Puerco and 

Torrejon (see Pl. LXXI, B) as has been made in 

the past has depended entirely on fossil collections, 12 and although the fossils seem to indicate 

an unconformity between the two formations 

the writer has yet found no stratigraphic reason for such division. 

WASATCH FORMATION. 

The Wasatch formation, which probably 

exceeds 2,000 feet in thickness in the San Juan 

Basin, overlies the Torrejon unconformably 

and overlaps upon the Ojo Alamo and Kirt9 Gardner, J. H., The coal field between Gallina and Raton Spring, 

N.Mex., in the San Juan coal region: U.S. Geol. Survey Bull. 341, pp. 

335-351, 1909. 

10 Gardner, J. H., The Puerco and Torrejon formations of the Nacimiento group: Jour. Geology, vol. 18, No.8, pp. 702-741, 1910. 

n Sinclair, W. J., and Granger, Walter, Paleocene deposits of the San 

Juan Basin, N.Mex.: Am. Mus. Nat . Hist. Bull., vol. 33, pp. 297-316, 

1914. 

12 Matthew, W. D., A provisional classification of the fresh-water Ter. 

tiary of the West: Am. Mus. Nat. Hist. Bull., vol.12, pp. 19-77, 1899. 
278 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1916. 

land formations. It consists of an alternation Holmes, W. H., La Plata Valley: Idem, pp. 245-267. 

of conglomerate, conglomeratic sandstone, and Cope, E. D., The relations of the Puerco and Laramie 

shale. The basal member of the formation on deposits: Am. Naturalist, vol. 19, pp. 985-986, 1885. 

Cross, Whitman, Post-Laramie deposits of Colorado: 

San Juan River (see Pl. LXVI, A) has a thick- A J m. our. s c1., · 3d 1 44 19-42 1892 ser., vo . , pp. , . 

ness of 80 to 100 feet and consists of a well- Osborn, H. F., and Earle, Charles, Fossil mammals of 

indurated conglomeratic sandstone which con- the Puerco beds, collection of 1892: Am. Mus. Nat. Hist. 

tains pebbles of crystalline, volcanic, and sedi- Bull., vol. 7, PP· 1-2, 1895. 

mentary rocks. The pebbles range from sand Emmons, S. F., Cross, Whitman, and Eldridge, G. H., 

Geology of the Denver Basin in Colorado: U.S. Geol. Surgrains to pebbles 8 inches in diameter and, to- vey Mon. 27, p. 217, 1896. 

gether with the cross-bedding of the formation, Matthew, W. D., A provisional classification of the freshsuggest deposition by fairly rapid streams. water Tertiary of the West: Am. Mus. Nat. Hist. Bull., 

This lower member of the Wasatch is separated vol. 12, PP· 19-77, 1899. 

from a similar member above it by 50 to 75 feet· Cross, Whitman, U. S. Geol. Survey Geol. Atlas, La 

Plata folio (No. 60), 1899. 

of greenish-gray and yellowish sandy shale and Smith, J. H., The Eocene of North America west of 

a few thin beds of carbonaceous shale. This the 100th meridian: Jour. Geology, vol. 8, pp. 448-449, 

alternation of shale and conglomeratic sand-· 1900. 

stone is repeated many times in the section ex- Douglass, ~arl, The discovery of Torrejon mammals in 

posed along San Juan River. The formation Montana: Science, new ser., vol. 15, pp. 272-273, 1902. . . . . Schrader, F. C., The Durango-Gallup coal field of Colowas not studied m detail and only Its base was rado and New Mexico: u. s. Geol. Survey Bull. 285, 

mapped. One collection of fossil leaves from pp. 241-258, 1906. 

the Wasatch at locality 9 (see Pl. LXIV) is Taff, J. A., The Durango coal district, Colo.: U. S. 

discussed below by F. H. Knowlton: Geol. Survey Bull. 316, pp. 321-337, 1907. 

Shaler, M. K., A reconnaissance survey of the western 

This material is very fragmentary. It includes, apparently, two ferns, one Pteris-like and the other Anemia-like, 

but neither is sufficiently well preserved to be identified. 

There is also a monocotyledon that may be a palm ray or a 

large leaf of a sedge. The only dicotyledon present is a 

Sapindus' not unlike a large leaflet of S. angustijolia Lesquereux, a Green River species. 

This lot appears to be Tertiary, but it is too fragmentary 

to place positively. 

BIBLIOGRAPHY. 

part of the Durango-Gallup coal field of Colorado and New 

Mexico: U. S. Geol. Survey Bull. 316, pp. 376-426, 1907. 

Gardner, J. H., The coal field between Gallina and 

Raton Spring, N. Mex., in the San Juan coal region: 

U.S. Ge9l. Survey Bull. 341, pp. 335-351, 1909. 

Gardner, J. H., The Puerco and Torrejon formations 

of the Nacimiento group: Jour. Geology, vol. 18, No. 8. 

pp. 702-741, 1910. 

Brown, Barnum, The Cretaceous Ojo Alamo beds of 

New Mexico, with description of the new dinosaur genus 

Kritosaurus: Am. Mus. Nat. Hist. Bull., vol. 28, pp. 

The following are the principal publications 267-274, 1910. 

on the area considered in this paper: Lee, W. T., Stratigraphy of the coal fields of northerncentral New Mexico: Geol. Soc. America Bull., vol. 23, 

Cope, E. D., The Eocene pp. 571-685, 1912. plateau: Chief Eng. Ann. 

Rept. for 1875, pt. 2, Appendix G1, pp. 981-1017. 

Endlich, F. M., The San Juan region: U. S. Geol. and 

Geog. Survey Terr. Ninth Ann. Rept., for 1875, pp. 189-

190,1877. 

Holmes, W. H., Geology of the SanJuan district: Idem, 

pp. 241-244. . 

Sinclair, W. J., and Granger, Walter, Paleocene deposits 

of the San Juan Basin, N. Mex.: Am. Mus. Nat. Hist. 

Bull., vol. 33, pp. 297-316, 1914. 

Lee, W. T., Relation of the Cretaceous formations to 

the Rocky Mountains in Colorado and New Mexico: U.S. 

Geol. Survey Prof. Paper 95, pp. 27-58, 1915. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 98 PLATE LXXI 

A. VIEW EASTWARD FROM DIVIDE BETWEEN OJO ALAMO AND BARREL SPRING 

ARROYOS, N. MEX. 

Kirhand shale in foreground. Conical butte capped with lower part of Ojo Alamo sandstone. 

Butte at left consists of Kirtland shale at base, overlain by conglomeratic sandstone of Ojo 

Alamo, and that in turn by the middle or shale member of the same formation, with pebbles 

from the disintegrated upper conglomeratic member scattered over the top. 

B. EXPOSURE OF PUERCO AND TORREJON FORMATIONS MAKING BADLANDS 172 MILE.S 

ABOVE STORE ON OJO ALAMO ARROYO, N. MEX. 

Sky line in center of view shows evenness of interstream areas, which form a westward-sloping 

plain along Chaco Riyer, the same plain as that shown in figure 27. Altitude of plain, about 

6,400 feet.