Stratigraphic Terminology 

of the Dakota Sandstone 

and Mancos Shale, 

West-Central New Mexico

GEOLOGICAL SURVEY BULLETIN 1372-J
1 *

t I

t I

I I
Stratigraphic Terminology 

of the Dakota Sandstone 

and Mancos Shale, 

West-Central New Mexico

By E. R. LANDIS, C. H. DANE, and W. A. COBBAN

CONTRIBUTIONS TO STRATIGRAPHY

GEOLOGICAL SURVEY BULLETIN 1372-J

A study of the generally transgressive rock 

sequence at the base of the Cretaceous 

System four new rock units are described

UNITED STATES GOVERNMENT PRINTING OFFICE. WASHING ION : 1973
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress catalog-card No. 73-600171

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

Washington, D. C. 20402 - Price 45 cents domestic postpaid or 3<* cents GPO Bookstore 

Stock Number 2401-00364
CONTENTS

Page

Abstract.................................................................................................................. Jl

Introduction and acknowledgments........................................ ......................... 1

Stratigraphy.......................................................................................................... 2

Twowells Sandstone Tongue of the Dakota Sandstone and the

Whitewater Arroyo Shale Tongue of the Mancos Shale............... 8

Paguate Sandstone Tongue of the Dakota Sandstone............................ 11

Clay Mesa Shale Tongue of the Mancos Shale........................................ 16

Cubero Sandstone Tongue of the Dakota Sandstone.............................. 17

Oak Canyon Member of the Dakota Sandstone....................................... 18

Upper part.................................................................................. ........ 18

Lower part .......................................................................................... 20

Lower part of Mancos Shale....................................................................... 21

Dakota Sandstone.......................................................................................... 22

Local sequences.............................................................................................. 23

Laguna area........................................................................................... 24

Grants and Mount Powell areas. ................................................. 25

Gallup area ..... ............................................................................. 31

Acoma area.............. ......................................................................... 33

The Narrows area................................................................................. 35

Alamo Day School area........................................................................ 37

La Ventana area.. .. ..................................................................... 39

Selected bibliography............................................................................................ 42

ILLUSTRATIONS

Page

FIGURE 1. Index map of west-central New Mexico and adjacent area...... J3

2. Diagram showing stratigraphic terminology of the Dakota

Sandstone and Mancos Shale. . . . . 10

3. East-west graphic columnar representation of measured sections..... ........................................................................ .. . . 12

4. North-south graphic columnar representation of measured

sections................... . ........................................... ......... 14

in

CONTRIBUTIONS TO STRATIGRAPHY

STRATIGRAPHIC TERMINOLOGY OF THE

DAKOTA SANDSTONE AND MANGOS SHALE,

WEST-CENTRAL NEW MEXICO

By E. R. LANDIS, C. H. DANE, and W. A. COBBAN

ABSTRACT

The generally transgressive rock sequence that constitutes the lower part 

of the Cretaceous System in west-central New Mexico the intertongued 

Dakota Sandstone and Mancos Shale is here divided into named formal and 

informal rock units of regional significance. The formally named rock units, 

four of which are named in this report, are developed in fullest degree in the 

Laguna area. They are, in descending order, the Twowells Sandstone Tongue 

of the Dakota Sandstone, the Whitewater Arroyo Shale Tongue of the Mancos 

Shale, the Paguate Sandstone Tongue (new) of the Dakota Sandstone, the 

Clay Mesa Shale Tongue (new) of the Mancos Shale, the Cubero Sandstone 

Tongue (new) of the Dakota Sandstone, and the Oak Canyon Member (new) 

of the Dakota Sandstone, which can be informally divided into distinctive 

upper and lower parts. Eastward and southward from Laguna most of the 

sequence is mapped as the marine Mancos Shale. Westward and northwestward from Laguna most of the sequence is mapped in the fluviatile and 

paralic Dakota Sandstone.

INTRODUCTION AND ACKNOWLEDGMENTS

The intertonguing generally regressive rock sequences in the 

middle and upper parts of the Cretaceous System in northwestern 

New Mexico and adjacent areas have long been divided into named, 

regionally correlated rock units. This report presents part of the 

results of regional investigation of the intertonguing generally 

transgressive sequence in the lowermost part of the Cretaceous 

System in west-central New Mexico and adjacent areas.

As an outgrowth of earlier studies in the southern San Juan 

Basin, we have been studying, since July 1966, the Dakota Sandstone and lower part of the Mancos Shale in west-central New 

Mexico and nearby areas. Many stratigraphic sections were measured, and molluscan faunas were collected. Rock units were traced 

laterally in some areas of complex structural and stratigraphic 

geology. The present work was guided by, and still incorporates

Jl
J2 CONTRIBUTIONS TO STRATIGRAPHY

some, data of earlier studies dating back to 1954, some of the results of which have previously been reported (Dane and Bachman, 

1957; Dane, 1959, 1960a, 1960b; Dane and others, 1971). Many 

earlier workers, such as Gilbert (1875), Ho well (1875), Holmes 

(1877) perhaps the earliest worker to apply the name "Dakota" 

to rocks in northwestern New Mexico and Dutton (1885), recognized the great lateral continuity of the Cretaceous rock units 

but left many problems to be solved by later and more detailed 

investigations. Among the many regional studies and syntheses 

listed in the "Selected Bibliography," the contributions of Sears, 

Hunt, and Hendricks (1941), Pike (1947), Young (1960), and 

Owen (1963, 1966) were of particular value in the study of the 

sedimentary rocks deposited in west-central New Mexico during 

the first great transgression of the epeiric Cretaceous sea.

We have benefited from discussions, in the office and in the field, 

with many colleagues interested in the Cretaceous stratigraphy 

of the Western United States. We particularly thank C. H. Maxwell and D. G. Wyant for much aid and encouragement, and E. G. 

Kauffman, who provided inspiration and help in the beginning 

stages of the present study.

STRATIGRAPHY

The Dakota-Mancos rock sequence in west-central New Mexico 

is developed to its fullest degree and is well exposed in the area 

near the pueblo of Laguna (fig. 1). This area has been well studied 

in the past, and the rock units have been described and mapped by 

Hunt (1936), Moench (1963a, b), Moench and Puffett (1963a, b), 

Schlee and Moench (1963a, b), Moench (1964a, b), Moench, 

Schlee, and Bryan (1965), and Moench and Schlee (1967). The 

areas studied by these workers are of considerable extent, but 

broad regional relationships could only be suspected by them. In 

addition, the state of knowledge about the fauna in the rock sequence allowed only suggestions about gross lateral rock-unit relations.

We studied the Dakota-Mancos rock sequence in the area near 

Laguna, then extended the study over a much larger area (fig. 1) 

in order to establish broad regional relationships. The intertonguing generally transgressive sequence at the base of the Cretaceous System in west-central New Mexico can be divided into 

regionally correctable rock units. Four of these units are here 

formally named as members and tongues of either the Dakota 

Sandstone or the Mancos Shale.

In descending order, the sequence in the Laguna area comprises 

the Two wells Sandstone Tongue of the Dakota Sandstone (Dane
DAKOTA SANDSTONE AND MANGOS SHALE, NEW MEXICO J3 

109e 108° 107'

MC K I N L E Y 

xMount Powell

uerque 

Laguna\ :.BERN/ALILLO

The Narrows 

VALENCIA

20 40 KILOMETERS

FIGURE 1. Index map of west-central New Mexico and adjacent area.

and others, 1971), the Whitewater Arroyo Shale Tongue of the 

Mancos Shale (Dane and others, 1971), the Paguate Sandstone 

Tongue of the Dakota Sandstone, the Clay Mesa Shale Tongue of 

the Mancos Shale, the Cubero Sandstone Tongue of the Dakota
J4 CONTRIBUTIONS TO STRATIGRAPHY

Sandstone, and the Oak Canyon Member of the Dakota Sandstone. 

The rock units are here discussed and described in descending 

order because (1) the upper two units are established, previously 

named rock units, in contrast to the lower units, which are newly 

named in this report; (2) the upper four units are conceptually 

simple and easily described and understood, in contrast to the 

lower two units, which require more detailed description and discussion because of lithologic diversity and complex lateral relations; and (3) the report does not attempt to present a detailed 

geologic history of the rock units.

The type sections for the newly named rock units the Paguate, Clay Mesa, Cubero, and Oak Canyon are presented in 

the Laguna measured section which follows. Other measured sections are discussed under "Description of Local Sequences."

Laguna measured section

[NE*4SEi4 sec. 20 and SW^NW^ sec. 21, T. 10 N., R. 5 W., Laguna 7y2 -minute quadrangle, 

Valencia County, N. Mex. Measured by E. R. Landis, W. A. Cobban, and C. H. Maxwell, 

Oct. 4, 1969, and by E. R. Landis and W. A. Cobban, Oct. 17, 1970]

Top of measured section.

Ft in

Mancos Shale, main body (incomplete) :

1. Limestone, slightly clayey, light-gray; weathers yellowish gray with very soft pale greenish cast; fossiliferous; contains "Gryphaea" sp. and Inoceramus sp.; 

angular chips and pieces...............-.... ............................... 6

2. Shale, medium-gray; weathers grayish yellow; flaky;

forms soft slope...................................................................... 4 0

3. Limestone, slightly clayey, gray, lenticular; weathers 

white; nodular; contains "Gryphaea" newberryi and 

Sciponoceras gracile. USGS Mesozoic loc. D7088.......... 5

4. Shale; same as unit 2.............................................................. 7 6

5. Shale, silty, medium-gray, flaky; grades abruptly downward to soft grayish-orange-weathered slope-forming 

silty sandstone. Entire unit has abundant "Gryphaea" 

newberryi (broad form). USGS Mesozoic loc. D7087.... 14 0

Total Mancos Shale, main body (incomplete)............ 26 5

Twowells Sandstone Tongue of the Dakota Sandstone:

6. Sandstone, silty, light-gray; weathers grayish orange; 

mostly in very irregular horizontal beds 2 in. to 4 ft 

thick; fine to mostly very fine grained; forms rough 

jagged bold cliffs............................... . ...... . - 51 0

7. Sandstone; weathers yellowish gray; laminated to shaly, 

very fine grained; soft groove former; sharp upper 

and lower contacts. USGS Mesozoic loc. D7086 (Exogyra levis and others) is float probably from overlying 

sandstone (unit 6)........................................ .......... .. 8

8. Sandstone, silty to very silty, yellowish-gray, very fine 

to fine-grained; some dark-colored rounded fine grains;
DAKOTA SANDSTONE AND MANGOS SHALE, NEW MEXICO J5

Ft in

Twowells Sandstone Tongue of the Dakota Sandstone Con.

parallel crossbeds 3-6 in. thick within horizontal beds

15 in. to 3 ft thick; forms massive cliff......................-. . 22 0

Total Twowells Sandstone Tongue of the Dakota

Sandstone........................................................................ 73 8

Whitewater Arroyo Shale Tongue of the Mancos Shale:

9. Covered....................................................................................... 32 6

10. Siltstone, clayey to sandy, medium-dark-gray, chunky...... 4 0

11. Covered....................................................................................... 6 0

12. Partly covered; seems to be all medium-gray shale.. - . 12 0

13. Bentonite.................................................................................... 2

14. Shale, medium-gray, flaky; 4 ft above base is 2-ft-thick 

and 5-ft-long cone-in-cone limestone concretion that 

weathers to grayish-yellow angular pieces...................... 16 4

15. Bentonite .............................................................................. 2

16. Siltstone; clayey at top to sandy at base; weathers dark

yellowish brown; shaly to chunky; forms soft slope...... 15 0

17. Covered........................................................................................ 4 0

Total Whitewater Arroyo Shale Tongue of the Mancos Shale ................................................................... 90 2

Paguate Sandstone Tongue of the Dakota Sandstone:

18. Sandstone, light-gray; weathers grayish orange; fine 

grained; mostly subrounded; not as well cemented as 

underlying unit and weathers back from edge of cliff 

formed by underlying unit........................................... .... 2 0

19. Sandstone, light-gray; weathers grayish yellow to grayish orange; fine grained; massive in lower 5 ft but 

bedded crudely in upper 8 ft. Upper part of unit is 

coarser grained than lower and has abundant borings 

and trails................................................................................ 13 0

20. Sandstone, silty; weathers grayish orange; forms massive crumbly soft ledge........................................................ 2 3

21. Sandstone, light-gray; weathers grayish yellow to grayish orange; fine to medium grained; mostly subrounded; horizontal beds 4 in. to 1 ft thick; abundant 

tracks, trails, borings, and Ophiomorpha; softer than 

underlying unit.......................................................... ......... 3 6

22. Sandstone, light-gray; weathers grayish yellow to grayish orange; fine grained; mostly subangular; forms 

massive cliff with dark-brown-weathered limy ledge at 

top........ , .. . ..................... 12 6

23. Siltstone, medium-gray to dark-yellowish-brown; carbonaceous in lower part, less carbonaceous and more 

sandy in upper part; forms soft slope. USGS Mesozoic 

loc. D7085 (Exogyra sp.) from 1 ft below top......... 16 8

24. Sandstone, light-gray; weathers yellowish gray; very 

fine grained; laminated; limy; has a few smeary carbonaceous spots; lower part is interbedded with siltstone same as underlying unit; upper 3 ft is very limy, 

weathered dark brown, very fossiliferous. Forms soft
J6 CONTRIBUTIONS TO STRATIGRAPHY

Ft in

Paguate Sandstone Tongue of the Dakota Sandstone Con.

irregular ledge. USGS Mesozoic loc. D7084 (Acanthoceras amphibolum and others) from 3 ft below top...... 12 0

Total Paguate Sandstone Tongue of the Dakota 

Sandstone........................................................................ 61 11

Clay Mesa Shale Tongue of the Mancos Shale:

25. Siltstone, sandy, clayey, carbonaceous; weathers grayish 

yellow; forms weak ledge; grades upward to overlying 

unit........................................................................................... 8 2

26. Shale, very silty, medium-dark-gray to brownish-gray, 

chunky; grades upward into overlying unit; sparse 

gray limestone concretions 1 ft in diameter near 

middle...................................................................................... 17 0

27. Partly covered; seems to be all same as underlying unit 15 0

28. Shale, medium-dark-gray to brownish-gray, flaky;

slightly silty near middle.................................................... 10 0

29. Covered; probably shale as above and below...................... 3 0

30. Shale, medium-dark-gray to brownish-gray, flaky; medium-gray smooth limestone concretions as much as 

10 in. thick and 4 ft long near middle of unit................ 10 0

31. Covered........................................................................................ 6 6

Total Clay Mesa Shale Tongue of the Mancos Shale 69 8

Cubero Sandstone Tongue of the Dakota Sandstone:

32. Sandstone, clayey and silty, carbonaceous, medium-darkgray; finer grained upward as unit grades to silty 

shale at top............................................................................ 2 5

33. Sandstone, light-gray; weathers grayish orange; fine 

grained; disturbed beds 3 in. to 1 ft thick, with abundant borings, trails, and Ophiomorpha; weathers to 

rough, holey, iron-stained ledge.......................................... 7 0

34. Sandstone, silty, light-gray; weathers grayish orange; 

very fine grained; plant fragments in lower part, less 

silty upward with less plant debris; massive; forms 

faceted ledge. USGS Mesozoic loc. D7083 (Exogyra 

sp.) from 7 ft above base; USGS Mesozoic loc. D7082 

(Exogyra sp.) from 2 ft above base................................ 24 0

35. Sandstone, silty, medium-gray; partly weathered to 

grayish yellow; very fine to fine grained; has carbonaceous plant debris and dark spots and streaks; 

forms soft slope; grades into overlying unit.................. 15 0

36. Sandstone, silty, light-gray; weathers yellowish gray; 

very fine grained; laminated and interlaminated with 

carbonaceous siltstone same as underlying unit; forms 

soft slope.............................................................................. 2 __1

Total Cubero Sandstone Tongue of the Dakota Sandstone .............................................................................. 50 6

Oak Canyon Member of the Dakota Sandstone: 

Upper part:

37. Siltstone, very sandy; weathers yellowish gray; carbonaceous; forms soft slope.................................................... 10
DAKOTA SANDSTONE AND MANGOS SHALE, NEW MEXICO J7

Ft in

Oak Canyon Member of the Dakota Sandstone Con. 

Upper part Con.

38. Shale, medium-dark-gray, flaky.............................................. 2

39. Limestone, silty; medium gray at base to light gray at 

top; forms massive hard ledge. USGS Mesozoic loc. 

D7081 (Plicatula arenaria and others) from upper 

part......................................................................................... 8

40. Partly covered; seems to be all dark-gray very silty

shale and siltstone; forms soft slope................................ 13 10

41. Siltstone, limy; weathers grayish yellow; massive;

weathers to soft rounded pieces........................................ 4

42. Limestone, silty, medium-light-gray; weathers pale 

brown to dark yellowish brown; forms massive hard 

fossiliferous ledge in places; laterally changes to platy 

limy siltstone. USGS Mesozoic loc. D7080 (Exogyra 

sp. and many others).-.................................................-.-.... 1 4

43. Siltstone, very clayey, and silty shale; sandy (very fine 

grained) in part; dark gray; shaly to chunky; forms 

soft slope............................................................................... 3 3

44. Bentonite..................................................................................... 4

45. Partly covered; upper few feet is dark-gray chunky silty 

shale similar to unit 43; lower part is similar to underlying unit. Some carbonaceous material in lower 

1 ft............................................................................................ 10 0

46. Shale, dark-gray, flaky to chunky; uppermost 7 in. is

silty.......................................................................................... 8 3

47a. Partly covered; mostly shale as in unit 46; bentonite

streak near top.................................................................. . 1 2

Total upper part.............................................................. 40 2

Lower part:

47b. Partly covered; mostly carbonaceous silty sandstone that

is gypsiferous in lower 1 ft................................................ 3 6

48. Sandstone, silty, carbonaceous, light- to medium-gray;

weathers grayish yellow; forms massive soft slope...... 3 2

49. Sandstone, silty; carbonaceous, but less so than overlying and underlying units; grains mostly subangular 

and very fine; irregular beds 2-6 in. thick; trails, borings, and other markings; forms rounded ledge............ 3 0

50. Sandstone, silty, carbonaceous, light- to medium-gray;

weathers grayish yellow; forms massive soft slope...... 4 0

51. Covered........................-- ..................................................... 4 0

52. Partly covered; seems to be all flaky slightly carbonaceous dark-gray shale................................................... .... 7 0

53. Sandstone; weathers grayish orange to dark yellowish 

orange; very fine grained; carbonaceous material 

(plant debris) abundant near base, less abundant upward; forms massive ledge which has rough irregular 

purplish-streaked top....... .................................................. 1 6

54. Sandstone, silty, carbonaceous (plant debris and streaks 

and patches) ; weathers light gray; very fine grained; 

forms soft slope; grades into overlying unit.................. 2 2
J8 CONTRIBUTIONS TO STRATIGRAPHY

Ft

Oak Canyon Member of the Dakota Sandstone Con. 

Lower part Con.

55. Sandstone; weathers grayish orange; mostly fine grained 

and rounded; bottom 3 in. contains lensing patches of 

coarse grains and granules; lower 3 ft is mostly massive; upper part of unit consists of irregular beds 

1-15 in. thick which contain borings and markings and 

which are siltier and softer than lower part. Forms 

ledge with underlying unit........................................ . 5

56. Sandstone; weathers pale yellowish brown; clayey in 

part; fine to coarse grained and granular. Coarser 

material is subangular quartz and subangular to subrounded rock fragments that are mostly white to palered quartzite. Lower contact is regular, but along 

length of outcrop it seems to be a very smooth channeling or truncating contact..............................................

Total lower part...................................................... 33 10

Total Oak Canyon Member of the Dakota Sandstone 74

Jackpile sandstone (informal term of economic usage) of Morrison Formation.................................................................................. Unmeasured

TWOWELLS SANDSTONE TONGUE OF THE DAKOTA SANDSTONE AND THE 

WHITEWATER ARROYO SHALE TONGUE OF THE MANGOS SHALE

The Twowells Sandstone and Whitewater Arroyo Shale Tongues, 

originally named by Owen (1966; see also Owen, 1963), are recognized as described by Dane, Landis, and Cobban (1971).

In the Laguna area the Twowells is mostly silty, fine to very 

fine grained sandstone that forms bold jagged cliffs. However, in 

some places, as between Laguna and Seboyeta (fig. 1), the upper 

part of the unit is softer and siltier and makes a subdued outcrop. 

The Twowells is persistent throughout most of west-central New 

Mexico. It extends as far north as Window Rock, Ariz., and La 

Ventana, N. Mex. (fig. 1) (Dane and others, 1971). As shown in 

figure 3, the Twowells thins west of Laguna because beds that 

form part of the Twowells at Laguna are included with the upper 

part of the Whitewater Arroyo Shale Tongue of the Mancos Shale 

in the Grants and Mount Powell areas. The Twowells persists 

southward from the Laguna area at least as far as the Alamo 

Day School measured section (figs. 2 and 4) near the Rio Salado 

(fig. 1) and was recognized by Landis, Cobban, and C. H. Maxwell 

at D Cross Mountain (fig. 1).

The Whitewater Arroyo is composed of soft, slope-forming shale 

and siltstone containing bentonite layers and yellow-weathering 

cone-in-cone limestone concretions.
DAKOTA SANDSTONE AND MANGOS SHALE, NEW MEXICO J9

The Whitewater Arroyo Shale Tongue of the Mancos Shale is 

present over much of west-central New Mexico wherever the 

overlying Twowells Sandstone Tongue and either the underlying 

Paguate Sandstone Tongue of the Dakota Sandstone or the underlying main body of the Dakota are present. As shown in figures 

1, 2, and 4, the Paguate Sandstone Tongue pinches out south of 

Laguna, and in the measured sections at Acoma and at Alamo Day 

School, the equivalents of the Whitewater Arroyo are included in 

the lower part of the Mancos Shale. North of La Ventana area 

(fig. 1), the Twowells becomes too thin to recognize (Dane and 

others, 1971), and the equivalents of the Whitewater Arroyo compose the lower part of the Mancos Shale.

The Twowells Sandstone Tongue of the Dakota Sandstone is 

fossiliferous at many places where it has been examined. The 

upper part of the Twowells and (or) the immediately overlying 

sediments commonly contain large numbers of a distinctive broad 

form of "Gryphaea" newberryi Stanton (Dane and others, 1971). 

In addition, Exogyra levis Stephenson and some distinctive but 

as-yet-undescribed Exogyra, Plicatula goldenana Stephenson, 

Acanthocardia iritis (White), Pinna sp., and the ammonites 

Metoicoceras sp. and Calycoceras sp. were collected from the Twowells in the measured sections shown in figures 3 and 4. The 

Whitewater Arroyo Shale Tongue of the Mancos Shale, which is 

not as fossiliferous as the Twowells, is commonly characterized 

by much the same fauna but in addition contains other distinctive 

Exogyra that are as yet undescribed. In many areas a large ammonite described by Haas (1949) as Mantelliceras canitaurinum 

was collected from the Whitewater Arroyo, but the same or similar ammonites may be present in the Twowells Sandstone Tongue. 

The fauna of the Twowells is of the age of the higher part of the 

Hartland Shale Member, the middle member of the Greenhorn 

Limestone of southwestern Kansas and southeastern Colorado 

(Dane and others, 1971), and the fauna of the Whitewater Arroyo 

is slightly older but still of the age of the Hartland.

As pointed out previously (Dane and others, 1971), the fauna, 

physical character, and regional stratigraphic relations indicate 

that the Twowells Sandstone Tongue is an extensive offshore 

shallow-water marine shelf sandstone derived from a source area 

to the southwest. A source to the southwest for the Twowells was 

suggested (Dane and others, 1971) because the upper part of the 

Twowells seems to be slightly younger toward the southwest, the 

unit is thicker in that direction, and the metamorphic-type heavy 

minerals found in it suggest a southerly source (Owen, 1963, 

p. 221).
J10 CONTRIBUTIONS TO STRATIGRAPHY

FIGURE 2. Stratigraphic terminology of the Dakota

The fauna of the Whitewater Arroyo Shale Tongue indicates a 

shallow-water marine shelf environment similar to the depositional environment of the Twowells. However, part of the Whitewater Arroyo is composed of clay shale that contains bentonites 

and limy concretions but does not contain megafossils. These parts 

probably represent deposition in quieter and, perhaps, deeper 

water.

Older stratigraphic terminology for the Twowells and Whitewater Arroyo sequence is shown in figure 2. The Twowells has 

been confused in the past with a younger sandstone of Carlile age
DAKOTA SANDSTONE AND MANCOS SHALE, NEW MEXICO Jll

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that was named the Tres Hermanos Sandstone by Herrick (1900). 

(See Dane and others, 1971.) The Whitewater Arroyo, which was 

named as a shale member of the Dakota Sandstone by Owen 

(1966), had previously been considered to be a shale unit of the 

Mancos Shale (fig. 2), and this previous usage is here retained.

PAGUATE SANDSTONE TONGUE OF THE DAKOTA SANDSTONE

The Paguate Sandstone Tongue of the Dakota Sandstone, whose 

type section is units 18-24 of the Laguna measured section, is 

named for the town of Paguate, 7 miles north of Laguna (fig. 1).
J12 CONTRIBUTIONS TO STRATIGRAPHY

WEST

GALLUP AREA

(Cliff Dwellers

Canyon section)

MOUNT POWELL 

AREA

GRANTS 

AREA

EAST

LACUNA 

AREA

Morrison 

Formation

FIGURE 3. East-west graphic columnar representation of measured sections.

Much of the town is built upon an outcrop of this sandstone. In 

the Laguna area the Paguate is composed mostly of very fine and 

fine-grained sandstone, silty in part, but has some interbedded 

siltstone and a very minor amount of medium-grained sandstone. 

Some of the sandstone beds are very limy and weather to darkbrown rounded concretionary masses. Some of the limy parts are 

extremely f ossilif erous, as in the top part of unit 24 of the Laguna 

measured section.
DAKOTA SANDSTONE AND MANGOS SHALE, NEW MEXICO J13 

EXPLANATION

Clayey

Formational 

contact

Intraformational 

contact

The Paguate is recognizable northeastward from the Laguna 

area to about 6 miles south of La Ventana, where its identity becomes obscure (fig. 1). For most of this distance the Paguate is a 

bold cliff-forming sandstone unit, but it thins rapidly near its 

distal end, and although thin sandstone and siltstone beds are 

present at the appropriate stratigraphic position near La Ventana 

and northward, the unit is probably not traceable beyond La Ventana area. Westward from the Laguna area the Paguate is well 

developed to a point about a dozen or so miles west of Grants, 

where it merges with the main body of the Dakota Sandstone 

(fig. 3). The Paguate of the Laguna and Grants area is, therefore, 

the lateral equivalent of beds in the uppermost part of the main 

body of the Dakota at Mount Powell and Gallup (fig. 3). A subsurface study of the Dakota in the San Juan Basin by Tyrrell 

(1959) indicated that the Paguate merges with the main body of 

the Dakota Sandstone along a line trending from the Mount Powell area east of Gallup northeastward to a point near the center 

of the San Juan Basin.

Southward from the Grants area the Paguate forms a bold outcrop to a point near The Narrows measured section (fig. 4), and 

from there it thins rapidly to extinction in a southward direction. 

The Paguate can be observed to pinch out about 15 miles westsouthwest of Laguna; it is not present in the Acoma measured 

section (fig. 4) or in the Alamo Day School measured section 

(fig. 4) and therefore seems not to have been deposited in the area 

south and southeast of Laguna.
J14 CONTRIBUTIONS TO STRATIGRAPHY

SOUTH

ALAMO DAY THE NARROWS 

SCHOOL AREA AREA

aguate Sandstone 

Tongue of Dakota 

Sandstone Bfc=

Morrison 

Formation

FIGURE 4. North-south graphic columnar representation of measured

sections.

The Paguate Sandstone Tongue of the Dakota Sandstone is 

sparsely fossiliferous in many localities, and in the Laguna area 

the limy sandstone in the lower part is abundantly fossiliferous, 

both in total numbers of individuals and in numbers of species. 

The fauna includes Exogyra cf. E. oxyntas (Coquand), Exogyra 

levis Stephenson, an as-yet-undescribed Exogyra, Idonearca depressa Meek, Phelopteria gastrodes Meek, "Gryphaea" cf. "G." 

kellumi (Jones), Acanthocardia iritis (White), Turrilites acutus
DAKOTA SANDSTONE AND MANGOS SHALE, NEW MEXICO J15

NORTH

LA VENTANA AREA 

(Tafoya Dam section)

B

Main 

body

ill

O TJ £

ti*

O 0

Jl

EXPLANATION

Lower 

part

LA VENTANA AREA

(Sen Miguel Canyon

section) Calcareous

Formational 

contact

Intreformetionel 

contact

Partly covered

Passy, Acanthoceras amphibolum Morrow, Paracompsoceras landisi Cobban, Eutrephocerast sp., and many others. The fauna is 

near the age of the Lincoln Limestone Member of the Greenhorn 

Limestone of southeastern Colorado.

The Paguate Sandstone Tongue in the Laguna area is a complex rock sequence composed of a mixture of open-marine shelf 

sandstones and nearshore marine siltstones and sandstones which 

in total make up a generally regressional marine sequence that 

also records some shoreline fluctuation. The lower contact is conformable and gradational into the Clay Mesa Shale Tongue of the 

Mancos Shale. The upper contact in many places is poorly exposed because the lower part of the Whitewater Arroyo weathers 

back from the ledge-forming upper part of the Paguate, and in 

these places the contact of the two units seems to be very sharp, 

perhaps disconformable. In the few exposures where the lower
J16 CONTRIBUTIONS TO STRATIGRAPHY

part of the Whitewater Arroyo is exposed, as in the Laguna measured section, the Paguate seems to grade rapidly upward into 

silty beds in the lower part of the Whitewater Arroyo.

The fauna of the Paguate is similar to that of the Twowells in 

that it represents an open-marine shelf environment. The distribution of the Paguate indicates a northwesterly or westerly source 

for the clastic material that makes up the unit.

Figure 2 shows some of the older terminology that has been 

applied to the Paguate Sandstone Tongue of the Dakota Sandstone 

in the west-central New Mexico area. Other appellations have been 

informally applied but have not gained wide usage; for example, 

the Paguate in most places falls into the "middle Dakota" of 

Tyrrell (1959).

CLAY MESA SHALE TONGUE OF THE MANCOS SHALE

The Clay Mesa Shale Tongue of the Mancos Shale, whose type 

section is units 25-31 of the Laguna measured section, is named 

for exposures on the east and south side of Clay Mesa, about 

3 miles northwest of Laguna. The Clay Mesa Shale Tongue is 

composed mostly of medium- to dark-gray clay shale, silty in part, 

but has bentonites, limy concretions, and thin limestone beds. The 

tipper part of the Clay Mesa commonly includes a few sandy beds 

and is siltier than the rest of the unit. The bentonites, thin limestone beds, and limy concretions are more common in the lower 

half of the rock unit. The Clay Mesa forms soft slopes between 

the resistant ledge- and cliff-forming sandstones above and below 

it, which define the top and bottom of the Clay Mesa Tongue.

The Clay Mesa wedges out in the main body of the Dakota Sandstone between the Grants and Mount Powell areas (figs. 1, 2, and 

3), is equivalent to beds in the lower half of the lower part of the 

Mancos Shale in the Acoma and Alamo Day School areas, and is 

equivalent to beds in at least the upper part of the lower part of 

the Mancos Shale in The Narrows area.

The Clay Mesa and equivalent beds are in general more fossiliferous than the Whitewater Arroyo Shale Tongue of the Mancos Shale. The upper part of the Clay Mesa and its equivalents 

contain Acanthoceras amphibolum Morrow, "Gryphaea" cf. "G." 

kellumi (Jones), and Inoceramus rutherfordi Warren; the middle 

and lower parts contain Acanthoceras alvaradoense Moreman and 

Plicatula sp.; and several levels throughout the tongue contain 

Ostrea beloiti Logan, Tarrantoceras sp., and Pecten sp.

The Clay Mesa Shale Tongue of the Mancos Shale and equivalent beds in the lower part of the Mancos Shale are composed 

mostly of fine-grained elastics deposited in quiet marine waters. 

The underlying coarser grained sediments grade very rapidly up-
DAKOTA SANDSTONE AND MANGOS SHALE, NEW MEXICO J17

ward into the clay shales and laterally extensive bentonites and 

limy beds of the Clay Mesa Tongue. The upper part of the Clay 

Mesa is commonly silty and (or) sandy, and the Clay Mesa grades 

slowly upward to the coarser elastics of the Paguate Sandstone

Tongue. The Clay Mesa thus records a 

water deposition relatively nearer 

from shore followed by progressiv 

tion. The fauna of the Clay Mesa fol

is, the fauna of the finer grained pirts of the Clay Mesa and

equivalents is commonly of open-mari 

as ammonites, whereas the fauna of 

Mesa at top and base is commonly of

as oysters and clams.

As shown in figure 2, the Clay Mes i has generally been considered to be a unit of the Mancos Shale 

Tyrrell (1959), have included the Ch 

subdivisions of the Dakota Sandstone.

CUBERO SANDSTONE TONGUE OF THE DAKOTA SANDSTONE

The Cubero Sandstone Tongue of t le Dakota Sandstone, whose 

type section is units 32-36 of the laguna measured section, is

named for exposures on the east side

8 miles west of Laguna. The Cubero 

fine to fine-grained sandstone that i

part. In some areas almost 25 percent of the Cubero is composed

of siltstone and clay shale that com

material, mostly in the form of coriminuted plant debris. The

Cubero, particularly the upper part, 

unit similar to the Paguate and Two\

The Cubero Sandstone Tongue merges with the main body of

the Dakota Sandstone along a line

from a point a few miles west of Grs.nts (fig. 1), becomes unrecognizable or merges with the main body of the Dakota Sandstone 

about 14 miles south of La Ventana (ig. 1), and is not recognized 

at The Narrows or at Alamo Day Sciool, though equivalent beds 

are present.

The Cubero is not as f ossilif erous a; 

of the Dakota. The most important o 

Exogyra columbella Meek and Exogy

period of shallow to deeper 

shore to relatively farther 

sly shallower water deposiows the same pattern; that

ne, deeper water type, such 

;he siltier parts of the Clay 

shallower water type, such

Some authors, for example 

y Mesa as part of informal

of Cubero Mountain, about 

is mostly composed of very 

3 silty and carbonaceous in

ain abundant carbonaceous

is a resistant ledge-forming 

/ells.

trending roughly northeast

the other sandstone tongues

the very limited fauna are

 a acroumbonata Kauffman,

which are found in the lower part of 1 he Cubero at some localities, 

and Exogyra aff. E. columbella Meek and a larger, as-yet-undescribed Exogyra, which are found in the middle and upper parts 

of the Cubero. Very few ammonites have been found in the Cubero, 

compared with overlying rock units, but Calycoceras sp. has been 

collected.
J18 CONTRIBUTIONS TO STRATIGRAPHY

In most of its area of occurrence, the lower, generally finer 

grained part of the Cubero contains marine fossils. This lower 

part of the Cubero is similar to the lower parts of the Paguate and 

Twowells Sandstone Tongues and reflects a similar depositional 

environment. The upper part of the Cubero resembles the upper 

parts of the Paguate and Twowells in being generally unfossiliferous except for large quantities of "trace fossils" and in being 

coarser grained than the lower part. The Cubero apparently reflects deposition of increasingly coarser sediments in a shallowing 

sea; this was followed by an abrupt transition to deposition in 

deeper waters, in which the lower part of the Clay Mesa Shale 

Tongue of the Mancos Shale, was deposited.

Figure 2 shows some of the older informal terminology that has 

been applied to the Cubero in west-central New Mexico. The 

Cubero has been included by some workers in other informal units, 

such as the "middle Dakota" (Tyrrell, 1959).

OAK CANYON MEMBER OF THE DAKOTA SANDSTONE

The Oak Canyon Member of the Dakota Sandstone, whose type 

section is units 37-56 of the Laguna measured section, is named 

for exposures on the sides of the small mesas west of Oak Canyon, 

about 4-5 miles northeast of Laguna. The Oak Canyon in the 

Laguna-Acoma-Grants area is a complex assemblage of fluviatile, 

lagoonal, estuarine, and open-marine rocks composed of shales, 

silty sandstones, and sandstones, all of which are commonly carbonaceous, and clay shale, bentonite, limy siltstone, and limestone. 

In most of its area of occurrence the Oak Canyon can be subdivided roughly into two parts: an upper part that consists mostly 

of fine-grained open-marine sediments, and a lower part that contains some relatively coarser grained paralic sediments.

UPPER PART

The upper part of the Oak Canyon Member, units 37-46 and 

the upper part of unit 47 of the Laguna measured section, is composed mostly of clay shale and silty clay shale, though it also 

contains substantial quantities of clayey siltstone and siltstone. 

Thin bentonites that seem to be widespread over much of the 

Laguna-Acoma area are found in the lower part of this sequence, 

and dark-brown-weathering limestone and silty limestone units 

(units 39 and 42 of the Laguna measured section) that are very 

fossiliferous at most localities are found in the upper part. The 

limestones, which in places pass laterally into limy siltstone beds 

or discrete rounded limestone concretions, and the bentonites are 

by far the most persistent and recognizable units in the upper 

part of the Oak Canyon Member.
DAKOTA SANDSTONE AND MANGOS SHALE, NEW MEXICO J19

The upper part of the Oak Canyon Member grades upward into 

the Cubero Sandstone Tongue of the Dakota Sandstone and downward into the lower part of the Oak Canyon Member. The upper 

and lower parts can be distinguished in most areas by placing the 

contact at the top of the highest sandstone bed beneath the marine 

fossil-bearing shale and bentonite sequence that constitutes the 

bulk of the upper part of the Oak Canyon. When so placed, the 

contact is at the position chosen by Moench and Schlee (1967, 

p. 22 and 24) as the contact between the Dakota Sandstone and 

the lowest shale unit of the Mancos Shale in the Laguna area 

(fig. 2). However, Moench and Schlee (1967, p. 22 and 24) pointed 

out that the sandstone bed at the top of the Dakota as it was 

mapped by them is absent in some places; furthermore, according 

to C. H. Maxwell (written commun., 1970, 1971), the sandstone 

beds in the lower part of the Oak Canyon Member of this report 

are lenticular, and other criteria for distinguishing the upper and 

lower parts must be used. In the area southwest of Laguna, Maxwell preferred to place the contact between the upper and lower 

parts of the Oak Canyon at the top of strata that contain comparatively large pieces of plant debris (megascopic) in contrast to 

overlying strata that contain lesser quantities of comminuted carbonaceous material (microscopic), or none. Maxwell also stated 

that the contact is also marked by "limestone and (or) siderite 

(weathered to goethite) oolites, or ironstone crusts or nodules." 

In practice, in the area southwest of Laguna, this means that the 

contact between the upper and lower parts of the Oak Canyon 

Member is placed immediately below or within a few feet below 

the upper of the bentonites shown in the Laguna section in figure 3 

and a few feet below the lowest limestone beds or concretions 

that is, some place in unit 45 of the Laguna measured section.

If recognition of the upper part of the Oak Canyon is based 

upon the presence of fine-grained open-marine sediments, the rock 

unit is barely recognizable as far west as Grants but is present 

at Acoma, and lateral equivalents are present as far northeast as 

about 14 miles south of La Ventana (fig. 1). Beds equivalent to 

the upper part of the Oak Canyon either were not deposited or 

are composed of sandstone at The Narrows and at Alamo Day 

School.

The fossiliferous silty limestone units in the upper part of the 

Oak Canyon Member are in general the most consistently fossiliferous units in the entire intertonguing Dakota-Mancos sequence. 

These beds are lithologically similar to and faunally identical with 

the Thatcher Limestone Member of the Graneros Shale of southeastern Colorado. The Thatcher contains the oldest marine mega-
J20 CONTRIBUTIONS TO STRATIGRAPHY

fossil assemblage found in the Upper Cretaceous rocks of the 

Western Interior. The faunal assemblage found in the upper part 

of the Oak Canyon Member is mostly oysters, clams, and gastropods, though ammonites have been collected at several localities. 

Common species are Exogyra columbella Meek, Pinna petrina 

White, Camptonectes cf. C. cavanus (Stephenson), Psilomya aff. 

P. concentrica (Stanton), Arrhoges modesta (Cragin) ?, and Plicatula arenaria Meek; less common species are Inoceramus eulessanus Stephenson, Turrilites acutus Passy, Calycoceras sp., and 

Borissiakoceras sp. These animals are largely shallow-water openmarine forms.

The largely open-marine sediments of the upper part of the 

Oak Canyon Member were deposited during transgression of the 

Cretaceous sea into the Laguna-Acoma area from the east and 

northeast. The gradation upward of the Oak Canyon Member to 

the Cubero Sandstone Tongue records deposition during a seaward 

retreat of the shoreline.

The upper part of the Oak Canyon Member was treated as part 

of the Mancos Shale by some previous authors (fig. 2), either as a 

separate shale unit, as part of a shale and sandstone unit, or as 

part of a unit that included the Cubero Sandstone Tongue. After 

considering alternatives from a regional viewpoint, we decided to 

treat the sediments here described as the upper part of the Oak 

Canyon Member of the Dakota .Sandstone as an informal subdivision of a member because of the difficulty of selecting a contact 

of more than local significance between the unit discussed here and 

the underlying sediments. This definition does not preclude mapping this informal unit wherever possible and desirable.

LOWER PART

The lower part of the Oak Canyon Member of the Dakota Sandstone, the lower part of unit 47 and units 48-56 of the Laguna 

measured section, is composed of coarse to very fine grained sandstone that is in places conglomeratic, containing granule- and 

pebble-size clasts, and in places silty. Carbonaceous, almost coaly, 

shales and medium- to dark-gray shale containing small amounts 

of comminuted plant debris are common and in some localities are 

a major constituent of the unit. Bentonite beds are found in 

the unit but are not common. No megafossils have been found in 

the unit, but many of the sandy beds (such as units 49 and 55 

in the Laguna measured section) have abundant borings, marks, 

tracks, and trails. The lowest bed of the unit is generally a sandstone that may be conglomeratic (as unit 56 of the Laguna measured section), but the sandstone is not everywhere present, and
DAKOTA SANDSTONE AND MANGOS SHALE, NEW MEXICO J21

in many areas the basal beds of the lower part of the Oak Canyon 

Member are shale.

Inherent in the definition of the lower part of the Oak Canyon 

Member is the requirement that the upper part of the Oak Canyon 

constitute a recognizable unit. Wherever this requirement is not 

met, the equivalent rocks either constitute part of an undivided 

Oak Canyon Member or constitute part or all of a unit designated 

either as Dakota Sandstone or as the main body of the Dakota 

Sandstone. In some areas it is possible that beds equivalent in time 

to all or part of the Oak Canyon (particularly the lower part) 

were never deposited.

No megafossils have been collected from the lower part of the 

Oak Canyon Member, but plant microfossils from shales in the unit 

have been identified by R. H. Tschudy (written commun., 1967) as 

palynomorphs of Early Cretaceous age. The flora, which is similar 

to that of the Thermopolis Shale of Montana and Wyoming, is mostly 

of Albian age, though one sample yielded palynomorphs of possible 

Aptian age. The samples from two of five localities, both south of 

La Ventana, appeared to contain winnowed assemblages, thus 

introducing an element of doubt about the age of deposition of the 

sampled rocks. Two of the five samples, including one from the 

Laguna area, contained hystrichospheres and dinoflagellates, indicating marine deposition, of the enclosing rocks.

The lower part of the Oak Canyon Member unconformably 

overlies nonmarine rock units assigned a Jurassic age in most of 

west-central New Mexico and successively truncates older Jurassic 

formations and some Triassic units southward from the Laguna 

area to the Alamo Day School area. The rocks composing the lower 

part of the Oak Canyon were deposited marginal to the shoreline 

as the Cretaceous sea advanced westward through west-central 

New Mexico. Some of the rocks, particularly local basal conglomeratic sandstone beds, may be fluviatile deposits shoreward of the 

strandline, but the bulk of the rocks are lagoonal, littoral, or 

shallow marine deposits marginal to the shoreline.

In most areas the beds of the lower part of the Oak Canyon 

Member have been assigned as part or all of the Dakota Sandstone 

by previous authors. They have been included in informal units, 

such as the "lower Dakota" (Tyrrell, 1959), by some authors.

LOWER PART OF MANCOS SHALE

The lower part of the Mancos Shale in west-central New Mexico 

comprises marine rocks in the sequence that have not been, or 

cannot be, assigned to one or more of the previously discussed and 

named rock units of member rank that are part of either the
J22 CONTRIBUTIONS TO STRATIGRAPHY

Dakota Sandstone or the Mancos Shale. As thus defined, the lower 

part of the Mancos Shale shown in figures 2 and 4 is made up of 

rocks of different time equivalency in different parts of the area. 

For example, the lower part of the Mancos Shale at The Narrows 

includes rocks laterally and temporally equivalent to the Clay Mesa 

Shale Tongue of the Mancos Shale, and it includes lateral equivalents of some parts of the Paguate and Cubero Sandstone Tongues 

and, perhaps, Oak Canyon Member of the Dakota Sandstone. 

In the Acoma area the lower part of the Mancos Shale includes 

rocks lithogenetically equivalent to the Whitewater Arroyo and 

Clay Mesa Shale Tongues of the Mancos Shale, but it cannot be 

subdivided because of the absence of the Paguate Sandstone 

Tongue of the Dakota Sandstone. Similarly, the lower part of the 

Mancos Shale in the Alamo Day School area cannot be subdivided 

because neither the Paguate nor the Cubero Sandstone Tongue is 

recognized in the area.

As defined, the lower part of the Mancos is composed mostly of 

marine rocks, and the dominant lithology is clay shale. The shale 

is silty in places and contains subordinate quantities of siltstone, 

sandstone, limy beds or concretions, and bentonites.

The lower part of the Mancos Shale contains a fauna similar to 

that of the rock units that are its temporal and lithological equivalents. The most common fossils are open-water marine animals, 

which are found in the limy or concretionary parts of the unit.

The very fine grained sediments, extensive bentonites (fig. 4), 

limy beds and concretions, and offshore fauna of the lower part 

of the Mancos Shale all indicate deposition in quiet open-marine 

offshore waters.

DAKOTA SANDSTONE

The rocks called the main body of the Dakota Sandstone in some 

areas and simply the Dakota Sandstone in other areas are marginal marine and nonmarine rocks which make up the lowest part 

of the sequence in west-central New Mexico and which cannot be 

included, or have not yet been included, in one of the other named 

rock units in the sequence.

The foregoing definition thus includes (1) the rocks beneath the 

lowest recognized tongue of the Mancos Shale in areas such as 

Mount Powell and Gallup (figs. 2 and 3), and (2) the basal sandstone beds of the sequence in areas such as Alamo Day School and 

The Narrows (fig. 4), where correlation of these basal beds with 

any other named part of the Dakota is undesirable or impossible 

at this time.

The main body of the Dakota in the Mount Powell area is about 

175 feet thick, but the unit thins westward it is only about 115
DAKOTA SANDSTONE AND MANGOS SHALE, NEW MEXICO J23

feet thick in the Gallup measured section and is as little as 68 feet 

thick at other places in the Gallup area. Some of this westward 

thinning may be internal, but most of the difference in thickness 

is caused by the onlapping relationship of the Dakota to the underlying rocks. The rocks assigned to the Dakota Sandstone in areas 

such as The Narrows are probably the lateral equivalents of some 

part of the Oak Canyon Member in the Laguna-Acoma area, but 

they do not have the distinctive lithologic features of the Oak 

Canyon; therefore, the rocks at the base of the sequence at The 

Narrows, for example, are grouped, at this time, as Dakota Sandstone. For similar reasons the basal sandstone beds of the sequence 

at Alamo Day School are simply called the Dakota Sandstone, and 

no attempt is made at lateral correlation of the unit.

The parts of the sequence in west-central New Mexico that are 

here assigned to the Dakota Sandstone of Early and Late Cretaceous age have been so considered by most previous authors.

In general, the rocks assigned to both the Dakota Sandstone and 

the main body of the Dakota Sandstone do not contain megaf ossils. 

However, in some places marine megaf ossils are present in the 

upper part of the main body of the Dakota, as at Mount Powell 

and at Gallup. The fauna includes Inoceramus rutherfordi Warren, Ostrea beloiti Logan, Idonearca sp., Tellina sp., dymbophora 

aff. C. securis Stephenson, Exogyra levis Stephenson, and an 

as-yet-undescribed Exogyra. These fossils are of Late Cretaceous 

age. The lower part of the Oak Canyon Member is of Early Cretaceous age, as shown by the plant microf ossils, and the lower part of 

the main body of the Dakota in the Mount Powell and Gallup areas 

may also be of Early Cretaceous age. In the absence of information to the contrary, the main body of the Dakota and those rocks 

assigned in figures 2, 3, and 4 as Dakota Sandstone must be considered to be of Early and Late Cretaceous age.

Most of the main body of the Dakota is composed of fluviatile 

sandstone and siltstone and of lagoonal and littoral carbonaceous 

siltstone, sandstone, and clay shale. A few parts are composed of 

sandstone and clay-shale beds that may have been deposited in 

estuarine or bay environments open to marine waters.

LOCAL SEQUENCES

Figure 2 shows stratigraphic terminology of the Dakota Sandstone and Mancos Shale according to various authors in different 

parts of west-central New Mexico and also presents the terminology proposed in this report. The vertical spacing of units within 

each of the columns of figure 2 is believed to accurately represent 

lateral correlation relationships but carries no implication of relative thickness relations.
J24 CONTRIBUTIONS TO STRATIGRAPHY

Figures 3 and 4 are graphic representations of sections measured in west-central New Mexico, showing generalized lithology, 

lateral correlation, and relative thickness relations of the rock 

units of the Dakota and Mancos in the areas listed in figure 2. An 

additional measured section at Mount Powell, near midway between the Gallup and Grants areas is shown in figure 3 to aid 

in visualizing lateral changes in thickness of some parts of the 

rock sequence.

LACUNA AREA

The intertongued Dakota-Mancos rock sequence, as described in 

the Laguna measured section and as shown in figures 2, 3, and 4, 

is persistent over a considerable area north of the pueblo of Laguna and east of the Mount Taylor volcanic pile (fig. 1). Hunt 

(1936) mapped the Dakota-Mancos sequence during a study of 

fuel resources in the southern part of the San Juan Basin. In the 

Laguna area, as shown in figure 2, Hunt (1936, text) applied the 

name Dakota (?) to a basal unit composed dominantly of sandstone and recognized a "lower part of the Mancos shale" made up 

of three units composed mostly of shale and three units composed 

mostly of sandstone. He suggested (p. 40) that "it seems probable 

that the Dakota (?) sandstone west of Mount Taylor is at the horizon of one of these sandstones, and therefore that the Dakota (?) 

sandstone west of Mount Taylor is younger than the sandstone 

called by the same name east of the mountain." This relationship 

was perhaps also implied by Hunt's selection (1936, geol. map) of 

Kdi and Kd2 as the map designations for units composed of sandstone and shale in the lower part of the Mancos Shale.

Nine ly^-minute quadrangles were mapped as a part of a study 

of the uranium resources of the Laguna district. (See citations 

p. J2.) In the Laguna quadrangle, Moench (1963a) recognized 

and mapped subdivisions of the Dakota and Mancos similar to 

the subdivisions described by Hunt (1936, text), and the same 

scheme was used throughout the mapped area and in text discussion (Moench and Schlee, 1967). (See fig. 2.)

Both Hunt (1936) and Moench and Schlee (1967) recognized 

that the upper part of the Oak Canyon Member of the Dakota 

contained marine shale, siltstone, and limy beds, in contrast to 

the lower part of the Oak Canyon, which is composed mainly of 

sandstone and siltstone that is generally carbonaceous and is probably of paralic origin. Presumably for this reason, Moench and 

Schlee mapped the upper part of the Oak Canyon as a shale unit 

in the lower part of the Mancos Shale and mapped the lower part 

of the Oak Canyon Member as the Dakota Sandstone. Hunt (1936,
DAKOTA SANDSTONE AND MANGOS SHALE, NEW MEXICO J25

p. 39) pointed out that the restricted Dakota, as later mapped by 

Moench and Schlee and as designated the lower part of the Oak 

Canyon Member in the present report, is absent in places; perhaps 

for this reason, he mapped a unit, identified as Dakota (?) Sandstone on his map, that is essentially the Oak Canyon Member of 

the present report.

GRANTS AND MOUNT POWELL AREAS

The Dakota and Mancos in the Grants area are similar to the 

sequence at Laguna, though they are somewhat different in thickness and lithology. All the named rock units of the Laguna area 

are recognized at Grants, but some units, particularly the Clay 

Mesa Shale Tongue of the Mancos and the upper part of the Oak 

Canyon Member of the Dakota, are coarser grained and less fossiliferous than they are at Laguna. This lithologic difference is 

expectable because both of the cited units lose their lithologic 

identity farther west, between Grants and Mount Powell (figs. 1 

and 3). During geologic mapping in the Grants area, Thaden, 

Merrin, and Raup (1967) recognized five informally designated 

mappable units in the Dakota-Mancos sequence (fig. 2). Earlier, 

Thaden, Santos, and Ostling (1966) had found that northwest of 

Grants the Dakota-Mancos sequence consisted of only four mappable units (fig. 2), and in the Mount Powell area and westward, 

we, together with J. F. Robertson and M. W. Green, found that 

only three mappable parts of the sequence are present (fig. 3).

Grants measured section

[SE14 sec. 4 and NE^NE^ sec. 9, T. 10 N., R. 9 W., Grants SE 7%-minute quadrangle, Valencia County, N. Mex. Measured by C. H. Dane and E. R. Landis, Oct. 2, 1967]

Top of measured section.

Mancos Shale, main body (incomplete) : pt ,-w

1. Shale, very dark gray; contains "Gryphaea" newberryi 

(broad form) and Exogyra levis. USGS Mesozoic loc. 

D6216....................................................................................... 5+ 0

2. Bentonite..................................................................................... _____8

Total Mancos Shale, main body (incomplete)............ 5 8+

Twowells Sandstone Tongue of the Dakota Sandstone:

3. Sandstone, yellowish-gray, soft; weathers back from 

underlying unit; contains Exogyra sp. USGS Mesozoic loc. D6215...................................................................... 5 0

4. Sandstone, yellowish-gray; forms resistant ledge.............. 3 0

5. Sandstone, pale-yellowish-gray; softer than adjacent

beds........................................................................................... 7 6

6. Sandstone, pale-yellowish-gray to gray, mostly fine 

grained; forms massive ledge; gradational to underlying unit. Brown-weathered limy concretionary parts 

as much as 5 ft thick and 8 ft long in upper part.
J26 CONTRIBUTIONS TO STRATIGRAPHY

Ft

Twowells Sandstone Tongue of the Dakota Sandstone Con.

Pinna sp. and Inoceramus sp. in lower part. USGS 

Mesozoic loc. D6214.............................................................. 29

Total Twowells Sandstone Tongue of the Dakota 

Sandstone.............................................................. ....... 45

Whitewater Arroyo Shale Tongue of the Mancos Shale:

7. Siltstone, pale-yellowish-gray, and about 25 percent very 

fine grained 1- to 12-inch-thick sandstone beds; forms 

soft slope................................................................................ 28 0

8. Covered; soft slope.................................................................... 50 0

Total Whitewater Arroyo Shale Tongue of the Mancos Shale.......................................................................... 78 0

Paguate Sandstone Tongue of the Dakota Sandstone:

9. Sandstone, yellowish-gray; massive to beds as much as 

2 ft thick; forms ledge; has brown-weathered limy 

concretions as much as 4 ft thick and 5 ft long that 

contain Exogyra sp., Idonearca sp., and gastropods. 

USGS Mesozoic loc. D6213.................................................. 36 0

10. Sandstone, silty, yellowish-gray; forms massive soft

slope......................................................................................... 11 0

11. Sandstone, pale-yellowish-gray; forms massive soft slope; 

has reddish-brown-weathering limy beds a few inches 

to 1 ft thick in upper part.................................................. 10 0

Total Paguate Sandstone Tongue of the Dakota

Sandstone............................... ........................................ 57 0

Clay Mesa Shale Tongue of the Mancos Shale:

12. Shale, silty, medium-gray; forms soft slope........................ 19 0

13. Covered; forms soft slope........................................................ 30 0

Total Clay Mesa Shale Tongue of the Mancos Shale ~~490

Cubero Sandstone Tongue of the Dakota Sandstone:

14. Sandstone, pale-reddish-gray, fine to very fine grained;

massive to beds as much as 2 ft thick; forms ledge...... 29 0

15. Sandstone, pale-reddish-gray, fine to very fine grained,

massive; softer than overlying unit.................................. 8 0

16. Sandstone, pale-yellowish-gray, very fine to fine-grained,

massive, soft.......................................................................... 3 0

17. Sandstone, silty, pale-olive-gray, very fine grained; 

poorly bedded in beds a few inches thick; forms soft 

slope......................................................... ... ..... . ........... 13 0

18. Sandstone, pale-yellowish-gray, fine to very fine grained; 

forms massive weak ledge; silty in lower 3 ft as it 

grades into underlying unit................................................ 8 0

Total Cubero Sandstone Tongue of the Dakota

Sandstone....................................-..........-................. 61 0

Oak Canyon Member of the Dakota Sandstone: 

Upper part:

19. Shale, silty, medium-gray............................... .. ..... ........ 12 0

20. Sandstone, silty, yellowish-gray; interbedded with me-
DAKOTA SANDSTONE AND MANGOS SHALE, NEW MEXICO J27

Ft in

Oak Canyon Member of the Dakota Sandstone Con. 

Upper part Con.

dium- to light-gray silty shale in beds %-2 in. thick.... 10 0

21. Shale, silty, olive-gray.............................................................. 12 0

Total upper part...................................... ....................... 34 0

Lower part:

22. Sandstone, grayish-orange, medium-grained; crossbedded 

at angles up to 45° in subparallel wedges as much as 

several feet thick; forms ledge.......................................... 25 0

23. Shale, carbonaceous, medium-brown; interbedded with 

white very fine grained silty sandstone in beds 2-6 in. 

thick.......................................................................................... 2 0

24. Sandstone, pale-brownish-gray, fine to very fine grained; 

laminated to bedded (2- to 3-in.-thick beds) in upper 

part; has Vz- to l-in.-thick partings of silty shale and 

siltstone; forms ledge................. ............................ ..... 7 0

25. Shale, pale-brown; silty and carbonaceous in upper part; 

8-in.-thick lenticular very fine grained white sandstone 

near top.................................................................................. 3 0

26. Sandstone, grayish-orange to grayish-red; mostly fine 

grained but some coarse grains in uppermost 1 ft; 

even bedded in beds a few inches to 2 ft thick in lower 

part; crossbedded in upper part; carbonaceous in lower 

6-12 in.; forms ledge............................................................ 21 0

27. Shale, carbonaceous, silty, dark-gray.................................... 7

Total lower part................................................ 58 7

Total Oak Canyon Member of the Dakota Sandstone 92 7

Morrison Formation:

28. Claystone, green. ... . . .. Unmeasured

Mount Powell measured section

sec. 8, T. 14 N., R. 13 W., Thoreau 7y2 -minute quadrangle. McKinley County, 

N. Mex. Measured by E. R. Landis and W. A. Cobban, with J. F. Robertson and M. W. 

Green, Oct. 7, 1969, and by E. R. Landis and W. A. Cobban, May 25, 1970]

Top of measured section.

Mancos Shale, main body (incomplete) : Ft in

1. Shale, limy, medium-gray; interbedded with platy laminated light-gray limestone that weathers grayish yellow and contains Inoceramus labiatus.. ............................ 8+ 0

2. Shale, limy, medium-gray................................... ..................... 7 6

3. Limestone, light-gray; weathers to hard chips and flakes 6

4. Shale, limy, medium gray; contains "Gryphaea" newberryi in lower half.................... .. 8 6

5. Bentonite....... .............................................................................. 4

6. Shale, limy, medium-gray............................................. ........... 5 0

7. Limestone, light-gray ; weathers white, soft, and rounded ; 

contains Sciponoceras gracile, "Gryphaea" newberryi, 

Exogyra levis, Psilomya sp., Allocrioceras annulatum, 

Kanabiceras septemseriatum, and Metoicoceras whitei.
J28 CONTRIBUTIONS TO STRATIGRAPHY

Ft

Mancos Shale, main body (incomplete) Con.

USGS megafossil loc. D7342 from this unit and the 

underlying unit......................................................................

8. Shale, limy, medium-dark-gray; contains "Gryphaea"

newberryi.... ............................................................................. 9

9. Shale, limy, medium-dark-gray; about 1 ft above base 

is a 2-in.-thick lenticular bed of flaky and chippy lightgray limestone........................................................................ 14

Total Mancos Shale, main body (incomplete)............ 53 7+

Twowells Sandstone Tongue of the Dakota Sandstone:

10. Sandstone; weathers grayish yellow; fine to medium 

grained, mostly subrounded grains; silty at base, 

coarser upward; massive at base, poorly laminated at 

top; forms massive ledge. "Gryphaea" newberryi 

(broad form) throughout but abundant at top; none 

of the broad form observed above this unit. USGS 

megafossil loc. D7341............................................................ 5

11. Sandstone, silty, carbonaceous; weathers very light 

gray; very fine to fine grained, subangular to subrounded; forms soft slope. May have "Gryphaea" 

newberryi (broad form) in uppermost part.................... 3

12. Sandstone, silty, slightly carbonaceous; weathers grayish

yellow; very fine grained; forms soft ledge.................... 3

13. Sandstone, light-gray, fine-grained, massive; harder than 

adjacent units; forms ledge................................................

14. Sandstone, silty, slightly carbonaceous; weathers grayish yellow; very fine grained; forms soft ledge............ 2

Total Twowells Sandstone Tongue of the Dakota 

Sandstone........................................................................ 14

Whitewater Arroyo Shale Tongue of the Mancos Shale:

15. Siltstone, sandy; grades rapidly downward to silty shale, 

which forms bulk of unit; medium-dark-gray shale at 

base; a 2-in-.-thick bentonite about 22 ft above base; 

forms soft slope. Basal 10 ft contains Exogyra sp. 

USGS megafossil loc. D7340.............................................. 37 0

16. Sandstone, silty; weathers yellowish gray; very fine 

grained, subangular to subrounded; poorly laminated 

to chunky; forms soft ledge. USGS megafossil loc. 

D7339: Acanthocardia iritis, "Mantelliceras" cf. "M" 

canitaurinum, Gryphaea sp., Pinna sp., Inoceramus 

sp., Exogyra sp., and Camptonetes sp................................ 2 0

17. Shale, silty, medium-gray........................................................ 10 0

18. Partly covered; mostly medium-gray shale, partly silty 

throughout but becoming siltier and sandier downward. Contains yellow-orange-weathered limestone concretions as much as 4 ft long and 2 ft thick with 

poorly developed cone-in-cone structure. Concretions 

are developed along bentonite beds, one of which is 

several inches thick and is 3 ft below top of unit.
DAKOTA SANDSTONE AND MANCOS SHALE, NEW MEXICO J29

Ft in

Whitewater Arroyo Shale Tongue of the Mancos Shale Con. 

USGS megafossil loc. D7338 is from float about 10 ft 

above base of unit: Exogyra sp., Turritella sp., and 

Acantkocardia sp.................................................................. 45 0

Total Whitewater Arroyo Shale Tongue of the Mancos Shale.................................................................... 94 0

Dakota Sandstone, main body:

19. Sandstone, very silty; weathers yellowish gray; slightly 

carbonaceous; fine grained, subrounded to subangular; 

forms soft slope.................................................................... 5 0

Section offset northward.

20. Partly covered; seems to be all sandstone similar to the 

underlying sandstone unit; has brown-weathered hard 

rounded concretionary limy parts several feet thick 

and as much as 10 ft in diameter that weather to very 

angular plates. Thickness approximate............................ 4 0

21. Sandstone, grayish-olive to dusky-brown, calcareous; 

mostly fine grained to very fine grained; upper part 

has angular to subangular hard rock fragments of 

sand to pebble size along with fossils, which are mostly 

Ostrea beloiti but also Inoceramus rutherfordi, Tellina 

sp., and Cymbophora aff. C. securis. USGS Mesozoic 

Iocs. D7336 and D7337..... .............................................. 1 3

22. Limestone, light-gray; weathers brown; hard; has wavy

contact with underlying unit.............................................. 3

23. Sandstone; weathers grayish yellow; calcareous; very 

fine grained, subrounded to subangular, subspherical; 

some carbonaceous streaks; in beds 2 to 3 in. thick; 

weathers to soft rounded edge; plates and cobbles.... . 1 4

24. Covered; soft slope; very silty and sandy.......................... 4 6

25 Sandstone; similar to unit 28 below; a 2- to 6-in.-thick 

yellow-weathered laminated silty recess former near 

middle causes unit to weather to two ledges; some 

low-angle (few degrees or less) cross-lamination.......... 1 11

26. Partly covered; soft slope; nearby exposures show unit 

to be interbedded grayish-orange to yellowish-gray 

very fine grained silty sandstone in beds as much as 

3 in. thick and yellow to white laminated and crosslaminated carbonaceous-streaked sandy siltstone. ... 6 0

27. Partly covered; seems to be similar to underlying unit.... 2 6

28. Sandstone, silty; weathers grayish yellow to grayish 

orange; very fine grained, subangular to subrounded, 

subspherical; horizontal beds %-2 ft thick, some lowangle cross-lamination within beds; forms smoothfaceted angular ledge.... ................................................. 3 9

29. Partly covered; soft slope; may be mostly yellow-weathered siltstone and sandstone........................................... .. 8 6

30. Sandstone; weathers light yellowish gray to grayish 

orange; fine grained, subangular to subrounded quartz, 

subspherical; mostly massive but has some weak horizontal beds %-3 ft thick; breaks into slabs 3 ft wide
J30 CONTRIBUTIONS TO STRATIGRAPHY

Ft in

Dakota Sandstone, main body Con.

by 6-10 ft long. This forms the uppermost strong resistant ledge in the Dakota.................................................. 8 0

31. Sandstone; weathers yellowish brown wiih red iron 

streaks; fine grained, subrounded, subspherical; horizontal beds 2-3 in. thick, some current ripples ^ in. 

deep, 3 in. long; unit grades upward but is softer 

than overlying unit, so it commonly forms a recess...... 1 2

32. Partly covered; seems to be all carbonaceous siltstone 

and shale in upper part; coaly in upper 1 ft and white 

clayey siltstone in uppermost 2 in.................................... 4 6

33. Sandstone; weathers yellowish gray to grayish orange; 

fine grained, subrounded quartz; poor horizontal bedding; forms massive bold ledge the "Dakota main 

ledge"....................................................................................... 38 0

34. Sandstone; weathers moderate reddish orange; fine 

grained, subrounded; massive; faint traces of bedding 

near top result in break between this unit and the 

overlying unit; forms bold cliff.......................................... 14 6

35. Siltstone, light-gray, laminated, soft.................................... 1

36. Sandstone, pebbly; weathers moderate reddish orange 

to moderate reddish brown; mostly very fine and fine 

grained but poorly sorted, so grains as large as medium and coarse are abundant; most grains are subrounded; unit includes as much as 25 percent rounded 

granules and pebbles of quartz and as much as 30 

percent dark igneous (?) rocks in lenticular bodies 

within the otherwise massive, faintly crossbedded, resistant ledge former.............................................................. 2 1

37. Sandstone; silty, as in underlying unit; interbedded with 

laminated clayey carbonaceous siltstone and carbonaceous silty shale; soft; forms recess; top contact even 

but sharp................................................................................ 3 8

38. Sandstone, silty; weathers grayish orange; fine to very 

fine grained, subangular to subrounded; crosslaminated; forms massive soft ledge........................................ 1 4

39. Siltstone, sandy; weathers light gray; laminated and

crosslaminated; platy; forms soft slope.......................... 4 0

40. Sandstone; weathers grayish yellow; fine grained, subangular to subrounded; in horizontal beds %-3 ft 

thick that are crosslaminated and crossbedded; forms 

ledge.......................................................................................... 10 0

41. Sandstone, silty, carbonaceous, fine grained to very fine 

grained, subangular to subrounded, massive, soft; 

grades in upper part to carbonaceous sandy siltstone; 

sharp wavy contact with overlying unit; forms soft 

recess........................................................................................ 4 9

42. Sandstone; weathers light gray to orange; very fine to 

fine grained, subangular to subrounded; sparse plant 

debris throughout; silty in lower 2 in. and upper 4 in.; 

soft............................................................................................ 1 0
DAKOTA SANDSTONE AND MANGOS SHALE, NEW MEXICO J31

Ft in

Dakota Sandstone, main body Con.

43. Siltstone, sandy; increasingly carbonaceous upward;

forms soft recess....-....................................... ..................... 11

44. Sandstone; weathers grayish yellow to grayish orange; 

mostly very fine to fine grained, subangular and subrounded; mostly poor horizontal beds 2 in. to 2 ft 

thick; massive to blocky; forms ledge.............................. 5 9

45. Sandstone, very silty; carbonaceous streaks; weathers 

yellowish gray to white; very fine grained, subangular; massive; soft; sharp irregular basal contact but 

gradational to overlying unit.............................................. 1 10

46. Sandstone; weathers grayish orange to yellowish gray; 

fine to very fine grained, subangular; lower 3 ft is 

massive single ledge, upper 2% ft is poorly bedded 

horizontally and has some cross-lamination and bedding; forms ledge.................................................................. 5 6

47. Sandstone, very silty; carbonaceous streaks; weathers 

yellowish gray to white, with iron streaks; mostly 

very fine grained, subangular; gradational upward 

and downward; soft unit at base of overlying ledge.... 1 6

48. Shale; increasingly carbonaceous upward; silty in upper

6 in.......................................................................................... 4 0

49. Partly covered; seems to be all carbonaceous shale.......... 2 0

50. Partly covered; seems to be sandstone similar to underlying unit................................................................................ 6 0

51. Sandstone; weathers grayish yellow to grayish orange; 

mostly fine grained, subangular to subrounded; poor 

horizontal beds 2 in. to 10 ft thick, with low-angle internal crossbedding; breaks to blocky large boulders; 

forms rough ledge.....-...................... ................................. 17 0

Total Dakota Sandstone, main body.............................. 176 7

52. Covered; soft interval............................................................ 12 0

Morrison Formation:

53. Claystone, green and purple............................................. .. Unmeasured

GALLUP AREA

The section measured in Cliff Dwellers Canyon is generally 

representative of the Dakota-Mancos sequence throughout the 

Gallup area. In parts of the Gallup area and to the north and west 

of Gallup, the uppermost sandy part of the Twowells that characteristically contains abundant specimens of "Gryphaea" newberryi 

Stanton (broad form) unit 1 of the Cliff Dwellers Canyon measured section is separated from the main, underlying mass of 

the Twowells by shale and silty shale, and it seems to constitute 

a separate recognizable rock unit (Dane and others, 1971). Not 

enough is known about the distribution and character of this unit 

to justify a formal stratigraphic designation at this time.
J32 CONTRIBUTIONS TO STRATIGRAPHY

Cliff Dwellers Canyon (Gallup) measured section

[NEi4 sec. 30, T. 16 N., R. 17 W., Gallup E T^-minute quadrangle, McKinley County. N. Mex. 

Measured by C. H. Dane and G. O Bachman, May 25, 1957, and supplemented by C. H. 

Dane, E. R. Landis, and W. A. Cobban, Apr. 27, 1967]

Top of measured section. Top of exposure. Ft in 

Twowells Sandstone Tongue of the Dakota Sandstone:

1. Coquina of "Gryphaea" newberryi (broad form); has

sandy calcareous matrix...................................................... 4 8

2. Sandstone, medium- to fine-grained; silty in upper part; 

makes persistent ledge; contains some brown calcareous concretionary masses.................................................. 44 0

Total Twowells Sandstone Tongue of the Dakota

Sandstone........................................................................ 48 8

Whitewater Arroyo Shale Tongue of the Mancos Shale:

3. Covered........................................................................................ 5 6

4. Sandstone, hard, persistent; weathers orange and white.. 9

5. Shale, gray; sandy in upper half.......................................... 8 0

6. Sandstone, thin-bedded, gray.................................................. 1 6

7. Shale, gray.................................................................................. 6 0

8. Bentonite..................................................................................... 6

9. Shale, gray; contains Exogyra sp. to within 3 ft of top.. 18 0

10. Bentonite, thin; not measurable............................................ ....

11. Shale, gray; contains Exogyra sp. in upper 2 ft. USGS

Mesozoic loc. D5765.............................................................. 14 0

Total Whitewater Arroyo Shale Tongue of the Mancos Shale........................................................................ 54 3

Dakota Sandstone, main body:

12. Sandstone, yellowish-gray, fine-grained, calcareous; contains Exogyra levis in abundance. USGS Mesozoic 

loc. D5764-.- ..............-.___.......___............... 2 0

13. Shale, sandy, yellowish-gray; contains many thin beds 

of yellowish-gray fine-grained sandstone and a soft 

thin-bedded ripple-marked sandstone %-3 ft thick 

whose base is 11% ft above the base of the unit. This 

sandstone is overlain by some carbonaceous shale. A 

slope-forming unit.. ........................................................... 19 0

14. Sandstone, yellowish-gray, medium- to coarse-grained; 

forms prominent ledge; evenly bedded in basal 4 ft, 

strongly crossbedded above, especially in middle part. 

Top 10 ft is even bedded. About 20 ft above the base 

is a bed 2-3 ft thick of granule-sized conglomerate...... 52 0

15. Shale, dark-gray, carbonaceous to coaly.............................. 3 6

16. Sandstone, coarse-grained; contains lenses up to granulesized grains; irregularly thin bedded; weathers brown 

on top...................................................................................... 7 0

17. Shale, dark-gray; carbonaceous for the most part; poorly

exposed in a slope.................................................................. 21 0

18. Sandstone; persistent dark-gray ledge capping very 

light gray to white medium-grained sandstone cliffs 

of Jurassic age. At the base is yellowish-red-weathering grit or coarse sandstone 6 in. thick that contains
DAKOTA SANDSTONE AND MANGOS SHALE, NEW MEXICO J33

Ft in

Dakota Sandstone, main body Con.

a few pebbles, to % in. in dimension, of chert, quartz, 

and quartzite. Basal contact irregular, with relief of 

6 in. within 2-3 ft horizontally; contact is sharp, but 

probably not everywhere at same level. There is probably some reworking of the underlying sandstone into 

the basal Dakota in places, and locally the basal bed 

of the Dakota is gray shale. Bedding of the unit as a 

whole is irregularly and weakly parallel, but in part 

it is crossbedded.................................................................... 10 0

Total Dakota Sandstone, main body.............................. 114 6

Sandstone of Jurassic age.................................................................... Unmeasured

ACOMA AREA

The lower part of the Dakota-Mancos sequence caps mesas over 

a considerable part of the distance between Laguna and Acoma, 

but the upper part has been largely removed by erosion. The complete sequence crops out south of Acoma and is present at the 

surface over large areas between Acoma and the Rio Salado 

(fig. 1). As mentioned previously, the Paguate Sandstone Tongue, 

which is a prominent element of the sequence in the Laguna area, 

pinches out southwest of Laguna and is not present in the Acoma 

area and southward. The Cubero Sandstone Tongue of the Dakota 

Sandstone, units 13-17 of the Acoma measured section, has a 

softer, finer grained middle part (units 14-16). The Cubero becomes thinner south of the Acoma area and is not recognizable 

in the D Cross Mountain area (fig. 1). The Oak Canyon Member 

in the Acoma area is similar to the equivalent rocks in the Laguna 

area.

Acoma measured section

[SE%SE% sec. 36, T. 8 N., R. 8 W., Blue Mesa and East Mesa 7%-minute quadrangles, Valencia County, N. Mex. Measured by C. H. Dane, E. R. Landis, and W. A. Cobban, Aug. 2 

and 8, 1966]

Top of measured section. Top of exposure. Ft in 

Twowells Sandstone Tongue of the Dakota Sandstone:

1. Sandstone; weathers grayish orange; fine grained; 

crossbedded within horizontal beds as much as 4 ft 

thick; forms massive bold ledge........................................ 45+ 0

Total Twowells Sandstone Tongue of the Dakota

Sandstone................. .................................................... 45+ 0

Mancos Shale, lower part:

2. Covered; uppermost part is silty shale and siltstone 

transitional to overlying unit, and lower part includes 

medium-gray shale................................................................ 188

3. Bentonitic clay, light-gray to greenish-gray; locally contains cone-in-cone limestone concretions..........................

4. Shale, medium- to dark-gray; "Gryphaea" cf. "G." kel-
J34 CONTRIBUTIONS TO STRATIGRAPHY

Ft in

Mancos Shale, lower part Con.

lumi as float in upper part of unit. USGS Mesozoic

loc. D5393................................................................................ 14 0

5. Shale, medium- to dark-gray; has rounded brecciated 

and healed limestone concretions as much as 2 ft in 

diameter that contain Acanthoceras alvaradoense. 

USGS Mesozoic loc. D5332.................................................. 4 0

6. Shale, medium- to dark-gray.................................................. 17 0

7. Bentonite streak........................................................................ ....

8. Shale, medium- to dark-gray.................................. ............. 6

9. Bentonite streak........................................................................ ....

10. Shale, medium- to dark-gray.................................................. 3 0

11. Shale, dark-gray; contains limestone concretions, very 

dark gray, discoidal, and as much as 3 ft in diameter. 

Ostrea beloiti, Acanthoceras sp., Plicatula sp., Veniella 

sp., and Tarrantoceras sp. USGS Mesozoic loc. D5331 6

12. Shale, dark-gray........................................................................ 4 0

Total Mancos Shale, lower part.................................... 231 8

Cubero Sandstone Tongue of the Dakota Sandstone:

13. Sandstone, clayey and partly silty, yellowish-gray, very 

fine grained; carbonaceous (plant) fragments; tracks, 

trails, and borings; in beds l%-4 ft thick, thinnest in 

upper part; Exogyra sp. USGS Mesozoic loc. D5330.... 22 9

14. Siltstone, clayey, dark-gray, carbonaceous, lenticular...... 1 3

15. Sandstone, clayey, medium-gray, very fine grained, carbonaceous............................................. ................................... 1 0

16. Shale, very silty, carbonaceous, medium-gray................... 7 6

17. Sandstone, clayey, yellowish-gray, very fine grained; 

thin silty shale interbeds; in beds 1-4 ft thick, thickest 

beds toward top; forms weak ledge.................................. 11 0

Total Cubero Sandstone Tongue of the Dakota

Sandstone........................................................................ 43 6

Oak Canyon Member of the Dakota Sandstone: 

Upper part:

18. Shale, very silty, dark-gray.................................................... 5 0

19. Siltstone, calcareous, gray to brown, lenticular, fossiliferous; contains Exogyra columbella, Plicatula arenaria, Psilomya levis, Turritella sp., Psilomya aff. P. 

concentrica, Pinna sp., and "Gryphaea" sp. USGS 

Mesozoic loc. D5329............................................................ 8

20. Shale, silty, dark-gray........................................................ 8 0

21. Bentonite.. ............................................................................... 1

22. Shale, dark-gray........................................................ 5 0

23. Bentonite; some soft white limy concretions. ................ 4

24. Shale, silty, dark-gray; carbonaceous (plant) fragments 20 0

25. Bentonite..................................................................................... 1

26. Shale, medium-gray; has a white lenticular sandstone

as much as 4 in. thick in upper part................................ 2 5
DAKOTA SANDSTONE AND MANGOS SHALE, NEW MEXICO J35

Ft in

Oak Canyon Member of the Dakota Sandstone Con. 

Upper part Con.

Total upper part................................................................ 41 7

Lower part:

27. Sandstone, yellowish-gray, very fine grained, soft and

poorly bedded.......................................................................... 1 2

28. Sandstone, clayey, carbonaceous, very dark gray.............. 2 4

29. Sandstone, medium-gray, very fine grained; abundant

carbonaceous fragments; forms persistent ledge.......... 2 5

30. Shale, dark-gray........................................................................ 1

31. Sandstone, white, very fine grained....--......-......... ............ 1

32. Shale, silty, carbonaceous, medium- to dark-gray; interbedded with siltstone and sandstone in beds <1 in. 

thick......................................................................................... 15 3

33. Sandstone, white, very fine grained, hard............................ 3

34. Shale, silty, dark-gray; siltstone beds <1 in. thick interbedded in upper part......................... ................................ 6 5

35. Sandstone, light- to moderate-brown, coarse to very 

coarse grained; contains granules and small pebbles of quartz and both light- and dark-colored quartzite; in lenticular beds, internally crossbedded, <l-6 in. 

thick; hard ledge contrasting sharply with underlying 

soft white sandstone of Jurassic age; unit wedges out 

within 50 ft along outcrop and is intermittent in occurrence over an area of several square miles.............. 2 10

Total lower part................................................................ 30 10

Total Oak Canyon Member of the Dakota Sandstone 72

Sandstone of Jurassic age.................................................................... Unmeasured

THE NARROWS AREA

Southward from the Grants area the upper part of the DakotaMancos sequence the Twowells Sandstone Tongue, the Whitewater Arroyo Shale Tongue, and the Paguate Sandstone Tongue 

 are recognizable as far as The Narrows area (fig. 1). The rocks 

equivalent to the Clay Mesa Shale Tongue of the Laguna area are 

closely similar to equivalent rocks in the Acoma area, but the 

Cubero Sandstone Tongue was not observed south of a point about 

12 miles south of the Grants area. Therefore, the lower part of 

the sequence is divided into a unit designated the lower part of 

the Mancos Shale, which is equivalent to rocks included in other 

areas in the Clay Mesa Shale Tongue and the Cubero Sandstone 

Tongue, and into a unit designated the Dakota Sandstone, which 

is equivalent to rocks included in other areas in the lower part of 

the Oak Canyon Member of the Dakota Sandstone.

Lithogenetic equivalents of the upper part of the Oak Canyon 

Member were not recognized in The Narrows area, and the time
J36 CONTRIBUTIONS TO STRATIGRAPHY

relationship of the rocks in the lower part of the measured section 

are unknown. The thick sandstone units (units 30 and 31, The 

Narrows measured section) are probably equivalents of the lenticular sandstone that is the basal unit of the Acoma measured 

section.

The Narrows measured section

[NE% sec. 4 and NW*,4 sec. 3, T. 7 N., R. 10 W., North Pasture 7%-minute quadrangle, 

Valencia County, N. Mex. Measured by C. H. Dane and E. R. Landis, Sept. 13, 1967, and by 

E. R. Landis and W. A. Cobban, Oct. 16, 1970]

Top of measured section. Top of exposure. Ft in 

Twowells Sandstone Tongue of the Dakota Sandstone:

1. Sandstone, yellowish-gray, soft............................... ............ 5+ 0

2. Sandstone, yellowish-gray, calcareous, slabby-bedded........ 1 6

3. Sandstone, grayish-yellow, soft; contains "Gryphaea" 

newberryi (broad form), Exogyra levis, Exogyra sp., 

Pinna sp., Acanthocardia iritis, and Pecten (Camptonectes) sp. USGS Mesozoic loc. D6133.......................... 1 0

4. Sandstone, grayish-orange to pale-brown, fine-grained; 

forms massive cliff; upper part contains Calycoceras 

obrieni, Acanthocardia iritis, and Exogyra levis. 

USGS Mesozoic loc. D6132............................................... 25 0

5. Sandstone, silty, yellowish-gray, lumpy-bedded . ........... 2 6

6. Sandstone, silty, grayish-orange, slightly calcareous, 

very fine grained; in beds 4-8 in. thick; very fossiliferous, with Exogyra levis, Exogyra sp., Acanthocardia 

iritis, Pinna sp., and many others. USGS Mesozoic 

loc. D6131.............................................................................. 6 0

Total Twowells Sandstone Tongue of the Dakota

Sandstone........................................................................ 41+ 0

Whitewater Arroyo Shale Tongue of the Mancos Shale:

7. Shale, silty, dark-gray.............................................................. 5 0

8. Siltstone, yellowish-gray; forms weak ledge........................ 9

9. Siltstone, yellowish-gray, clayey; interbedded gray silty

shale......................................................................................... 44 0

10. Shale, medium-gray.................................................................. 13 0

11. Bentonite...................................................................................... 1

12. Shale, medium-gray, flaky...................................................... 6 0

13. Bentonite..................................................................................... 1

14. Shale, medium-gray.................................................................. 11 0

15. Limestone concretions, medium-gray, fractured; in medium-gray shale.................................................................... 1 0

16. Shale, medium-gray.................................................................. 9

17. Siltstone, clayey, light-gray.................................................... 15 0

18. Covered; soft slope.................................................................... 45 0

Total Whitewater Arroyo Shale Tongue of the

Mancos Shale.................................................................. 141 8

Paguate Sandstone Tongue of the Dakota Sandstone:

19. Sandstone, yellowish-gray to pale-brown, fine-grained; 

massive to beds 2 ft thick in lower part, thinner bedded 

in upper part, with ripple marks; "trace fossils";
DAKOTA SANDSTONE AND MANGOS SHALE, NEW MEXICO J37

Ft in

Paguate Sandstone Tongue of the Dakota Sandstone Con.

forms ledge........................................................................... 15 0

Total Paguate Sandstone Tongue of the Dakota

Sandstone...............................................-.--.... .............. 15 0

Mancos Shale, lower part:

20. Siltstone, clayey, light-olive-gray; sparse limy concretions.......................................................................................... 8 6

21. Shale, slightly silty, light-olive-gray.................................. 20 0

22. Shale, dark-gray...................................................................... 15 0

23. Bentonite..................................................................................... 1 4

24. Shale, dark-gray...................................................................... 13 6

25. Shale, medium- to dark-gray.. . . .. 30 0

26. Shale, medium- to dark-gray; fractured gray limy concretions; has "Gryphaea" cf. "G." kellumi...................... 10 0

27. Covered; soft slope-. . ......................... 28 0

Total Mancos Shale, lower part............ ................... 126 4

Dakota Sandstone:

28. Sandstone, pale-brown, fine-grained; in beds <l-3 in.

thick, thicker beds in upper part.............. ....................... 11 0

29. Partly covered; lower part is mostly dark-gray shale, 

upper part is light-gray shale and shaly siltstone; 

forms slope.............................................................................. 18 0

30. Sandstone, white to brown; crossbedded. ledges 2-4 ft

thick; softer in lower part; forms weak ledge................ 29 0

31. Sandstone, pale-brown, massive; rests with smoothly irregular contact on white "bleached" zone at top of 

underlying cliff-forming sandstone of Jurassic age...... 35 0

Total Dakota Sandstone ........................................... 93 0

Sandstone of Jurassic age.................................................................... Unmeasured

ALAMO DAY SCHOOL AREA

The Dakota-Mancos sequence is poorly exposed southward from 

the Acoma area. Except for exposures in the Paradise Canyon 

area (fig. 1), only fragmental exposures were observed between 

Acoma and the Rio Salado. In the area of the Alamo Day School 

on the Alamo Navajo Reservation, the lower part of the DakotaMancos sequence is well exposed, but the upper part is commonly 

concealed. In the D Cross Mountain area, west of the Alamo Day 

School area, the rocks underlying the Twowells Sandstone Tongue 

of the Dakota Sandstone are soft dark shale and siltstone, and 

the unexposed parts of the Alamo Day School measured section 

are inferred to be similar rocks.

The Twowells Sandstone Tongue of the Alamo Day School area 

is silty, soft, and massive, and it crops out as a weak rounded 

nonobvious ledge. The Paguate Sandstone Tongue of the Dakota 

Sandstone in the Laguna area is not present in the Alamo Day
J38 CONTRIBUTIONS TO STRATIGRAPHY

School area, and the unit designated the lower part of the Mancos 

Shale in figures 2 and 4 thus may include lithogenetic equivalents 

of the Whitewater Arroyo and Clay Mesa Shale Tongues of the 

Mancos and time equivalents of the Paguate Sandstone Tongue 

and, perhaps, the Cubero Sandstone Tongue of the Dakota Sandstone. The Dakota Sandstone at the base of the sequence includes 

lithogenetic equivalents of the lower part of the Oak Canyon Member of the Dakota Sandstone of the Laguna area, but it may be 

younger and not time equivalent.

Alamo Day School measured section upper part

[SE^SWi/i sec. 13, T. 3 N.. R. 7 W., Table Mountain 7%-minute quadrangle, Socorro County, 

N. Mex. Measured by C. H. Dane, E. R. Landis, and W. A. Cobban, Apr. 29, 1967, and by 

E. R. Landis, June 13, 1968]

Top of measured section.

Mancos Shale, main body (incomplete) : Ft in

1. Shale, dark-gray; much selenite............................................ 5+ 0

2. Bentonite; thickness approximate.......................... ............. 4

3. Shale; weathers light gray and flaky.................................... 22 0

4. Bentonite; thickness approximate................. ...................... 2

5. Shale; weathers light gray and flaky.. ............................... 2 0

6. Interval unmeasured; thickness estimated ....................... 20 0

7. Bentonite..................................................................................... 2

8. Shale; weathers light gray and flaky; has light-gray 

limestone nodules about 3 ft above base; "Gryphaea" 

newberryi in float................................ ............................... 6 0

Total Mancos Shale, main body (incomplete)............ 55 8+

Twowells Sandstone Tongue of the Dakota Sandstone:

9. Sandstone, silty, calcareous; weathers pale yellowish 

gray; very fine grained; mostly massive; soft. USGS 

Mesozoic loc. D5772 has Plicatula sp. and Metoicoceras sp.................................................................................... 12 0

10. Concretions, limestone, silty to sandy; weathers pale

yellowish gray........................................................................ 1 0

11. Sandstone, calcareous; weathers pale yellowish gray;

very fine grained.................................................................. 10+ 0

Total Twowells Sandstone Tongue of the Dakota

Sandstone........................................................................ 23+ 0

Mancos Shale, lower part (incomplete) :

12. Interval unmeasured; thickness estimated.......................... 115 0

Total Mancos Shale, lower part (incomplete)............ 115 0

Alamo Day School measured section lower part

[SE^NE1^ sec. 12, T. 3 N., R. 7 W., Pueblo Viejo Mesa 7y2 -minute quadrangle, Socorro

County, N. Mex.]

Top of measured section.

Mancos Shale, lower part (incomplete) : Ft in

13. Shale, may not be in place; incomplete section.................. 30± 0
DAKOTA SANDSTONE AND MANGOS SHALE, NEW MEXICO J39

Ft in

Mancos Shale, lower part (incomplete) Con.

14. Shale, gray; grades up into gray shaly siltstone or mudstone......................................................................................... 55 0

15. Limestone, brownish-gray, very silty to sandy; weathers

to brown angular fragments............-......... .................... 11

16. Bentonite..................................................................................... 1

17. Shale, dark-gray; 2Vz ft below top are rounded mediumgray calcareous concretions that weather gray. USGS 

Mesozoic loc. D5771, from concretions, contains Inoceramus rutherfordi, Ostrea beloiti, Acanthoceras 

amphibolum, and Tarrantoceras sp.................................... 24 6

18. Shale, gray; upper 6 in. contains gray limy sandstone 

concretions that have tendency toward cone-in-cone 

structure................................................................................. 17 3

19. Bentonite..................................................................................... 1

20. Shale, gray................................................................................ 1 8

21. Bentonite..................................................................................... 2

22. Shale, silty, gray; lower part is soft, clayey, silty sandstone....................................................... ................................. 7 6

23. Sandstone, silty, soft; carbonaceous in lower part; upper 1-3 in. is hard quartzitic ledge former with "trace 

fossils"..................................................................................... 3 0

24. Partly covered; mostly gray shale........................................ 27 5

25. Bentonite..................................................................................... 1

Total Mancos Shale, lower part (incomplete)............ 167 8

Dakota Sandstone:

26. Partly covered; mostly sandstone that is silty, carbonaceous, and very fine grained; poor subparallel bedding; soft; weathers grayish orange................................ 5 0

27. Partly covered; mostly sandstone that is silty, clayey,

very carbonaceous, very fine grained, and soft................ 3 0

28. Sandstone, yellowish-gray, fine-grained; coarser upward; 

crossbedded in tabular sets a few inches to 1 ft thick; 

in some places upper few beds are coarse grained with 

granules and pebbles. Top few inches is a brown ironstained cap.............................................................................. 8 0

29. Sandstone, carbonaceous, fine-grained, soft; grades upward to overlying unit.......................................... ............. 1 0

Total Dakota Sandstone........-...-.-.-........-...----- 17 0

Triassic rocks (incomplete) :

30. Claystone, pale-yellowish-green; a few inches of ironstained clay at top......... ......................................... 10+ 0

Total Triassic rocks (incomplete).................................. 10+ 0

LA VENTANA AREA

The Dakota-Mancos sequence crops out in hogbacks along the 

west flank of the Sierra Nacimiento on the east side of the San 

Juan Basin near La Ventana. The exposures are incomplete and
J40 CONTRIBUTIONS TO STRATIGRAPHY

partly covered, but lateral tracing between nearby partial sections 

allows reasonable certainty about the sequence of rock units. The 

upper part of the Dakota-Mancos sequence is fairly well exposed 

in the Tafoya Dam section, and the lower part was examined 

where San Miguel Canyon cuts through the Dakota hogback northeast of La Ventana.

A sequence of soft limy sandstone about 12^ feet thick (units 

19 and 20, Tafoya Dam section) probably represents the Twowells Sandstone Tongue of the Dakota Sandstone. Some sandy 

shale and sandstone (units 25 and 26, Tafoya Dam section) may 

possibly be an extremely attenuated representative of the Paguate 

Sandstone Tongue of the Dakota Sandstone, but they are not so 

designated in the La Ventana area because rocks in the same 

stratigraphic position at other nearby places are all shale. The 

resistant ledge-forming sandstone part of the Dakota-Mancos sequence in the area (units 1 and 2, San Miguel Canyon section) 

may be the lateral equivalent of the Cubero Sandstone Tongue of 

the Dakota Sandstone, and the shale and sandstone sequence that 

underlies the ledge-forming sandstone may be equivalent to the 

Oak Canyon Member of the Dakota. However, the rocks in La 

Ventana area are not here so divided because the rocks in much 

of the outcrop area between La Ventana and the Rio Puerco are 

partly or wholly concealed or have not been examined in detail 

and because no fossils have been found that would aid in correlation.

Tafoya Dam measured section

[SW14SE14 sec. 14, T. 19 N.. R. 1 W., La Ventana 15-minute quadrangle, Sandoval County, 

N. Mex. Measured by C. H. Dane, Oct. 1959, and by C. H. Dane, E. R. Landis, W. A. Cobban, E. G. Kauffman, and G. R. Paulson in 1963-65]

Top of measured section.

Mancos Shale, main body (incomplete) : Ft ln

1. Limestone; weathers very light gray................. ................ 1 0

2. Shale, calcareous, medium-gray.............................................. 9 0

3. Bentonite..................................................................................... 2

4. Shale, calcareous, medium-gray.............................................. 3 6

5. Bentonite..................................................................................... 2

6. Shale, calcareous, medium-gray................. .......................... 6 0

7. Bentonite, iron-stained, gypsiferous...................................... 11

8. Shale, calcareous, medium-gray.............................................. 7 10

9. Bentonite, gypsiferous.............................................................. 4

10. Shale, calcareous, medium-gray..... ...................................... 10 0

11. Limestone, gray, concretionary; contains Sciponoceras

gracile...................................................................................... 6

12. Shale, calcareous, medium-gray............................................. 32 0

13. Bentonite..................................................................................... 6

14. Shale, medium-dark-gray; calcareous in part...................... 17 0

15. Bentonite..................................................................................... 2
DAKOTA SANDSTONE AND MANGOS SHALE, NEW MEXICO J41

Ft in

Mancos Shale, main body (incomplete) Con.

16. Shale, medium-dark-gray.................... ... .. ...................... 1 6

17. Bentonite..................................................................................... 2

18. Shale, medium-dark-gray...... ........ .................................... 10 6

Total Mancos Shale, main body (incomplete)............ 101 3

Twowells Sandstone Tongue of the Dakota Sandstone:

19. Sandstone, light-yellowish-gray; clayey in part; has 

rounded limy concretionary masses as much as 8 in. 

thick and 1 ft long in the upper part................................ 10 6

20. Concretions, limy, sandy; as much as 4 ft long; contains

"Mantelliceras" canitaurinum............................................ 2 0

Total Twowells Sandstone Tongue of the Dakota

Sandstone......................................................................... 12 6

Mancos Shale, lower part:

21. Mostly covered; principally shale................ ....................... 3 6

22. Bentonite..................................................................................... 1

23. Mostly covered; principally shale.......................................... 40 0

24. Bentonite..................................................................................... 1

25. Shale, silty, medium-gray; sandy in middle................ . . 1 10

26. Sandstone, glauconitic; mostly medium grained but has 

some coarse grains and some black and red siliceous 

granules; has Inoceramus cf /. nahwisi and Metoicoceras praecox.......................................................................... 3

27. Shale, silty and sandy.............................................................. 1 2

28. Mostly covered; has thin (1-in.?) bentonite bed 2 ft

above base.............................................................................. 5 3

29. Sandstone, very limy, very light yellowish gray; interbedded with platy light-gray sandy limestone................ 1 5

30. Bentonite..................................................................................... 2

31. Shale, dark-gray........................................................................ 4 8

32. Bentonite..................................................................................... 1

33. Shale, very dark gray.............................................................. 9

34. Bentonite..................................................................................... 11

35. Shale, very dark gray.............................................................. 2 4

36. Bentonite.... ......-...-...........................-....-.....-.-............. 1

37. Shale, dark-gray; has l-in.-thick light-gray-weathering

siltstone near middle.. ....................................................... 35 1

38. Limestone, black; weathers very light gray; lenticular.... 3

39. Shale, dark-gray......... ........................................................ 17 0

40. Sandstone, gray; abundant trails and borings; contains

"Gryphaea" sp...................................................................... 4

41. Shale, dark-gray........................................................................ 17 10

Total Mancos Shale, lower part...................................... 133 1

Top of ledge-forming Dakota Sandstone.

San Miffuel Canyon measured section

. 1 an 

Hex.

Top of measured section.

[Near line between sees. 1 and 2, T. 19 N., R. 1 W., La Ventana 15-minute quadrangle, Sandoval County, N. Mex. Measured by C. H. Dane and E. R. Landis, July 12, 1966]
J42 CONTRIBUTIONS TO STRATIGRAPHY

Dakota Sandstone, main body: Ft in

1. Sandstone, silty, light-yellowish-gray; in beds as much 

as 2 ft thick alternating with 6-in.-thick beds of gray 

siltstone.................................................................................... 11 0

2. Sandstone, light-gray; weathers pale red in upper part; 

in beds 8-20 in. thick; abundant borings and trails 

in upper part; upper 31 ft forms resistant ledge, lower 

part is softer, massive, light gray to white................ . 66 0

3. Partly covered; seems to be all flaky light-brown-weathered shale................................................................................ 54 0

4. Sandstone, very light gray; weathers grayish orange to 

moderate brown; very fine grained; brown to black 

plant fragments and carbonaceous streaks and spots.... 2 8

5. Partly covered; seems to be all dark-gray shale................ 4 2

6. Bentonite..................................................................................... 1 10

7. Shale, carbonaceous, silty, very dark gray to light-brown 7 5

8. Sandstone, very light gray, .very fine grained; interbedded light-gray to white siltstone.................................. 2 5

9. Sandstone; weathers grayish yellow to pale brown; fine 

grained; some plant fragments in upper part; resistant beds as much as 2Vz ft thick...................................... 6 0

Total Dakota Sandstone, main body............................ 155 6

Morrison(?) Formation:

10. Sandstone, white, mostly fine grained, crossbedded; some

pebbly coarse-grained laminae............................................ Unmeasured

SELECTED BIBLIOGRAPHY

Bartram, J. G., 1937, Upper Cretaceous of Rocky Mountain area: Am. Assoc.

Petroleum Geologists Bull., v. 21, no. 7, p. 899-913. 

Cobban, W. A., and Reeside, J. B., Jr., 1952, Correlation of the Cretaceous

formations of the Western Interior of the United States: Geol. Soc.

America Bull., v. 63, no. 10, p. 1011-1044. 

Dane, C. H., 1959, Historical background of the type locality of the Tres

Hermanos sandstone member of the Mancos shale, in New Mexico Geol.

Soc. Guidebook, 10th Field Conf., west-central New Mexico, 1959:

p. 85-91. 

 1960a, The boundary between rocks of Carlile and Niobrara age in

San Juan Basin, New Mexico and Colorado: Am. Jour. Sci., no. 258A,

p. 46-56 (Bradley Vol.).

-1960b, The Dakota sandstone and Mancos shale of the eastern side

of San Juan Basin, New Mexico, in New Mexico Geol. Soc. Guidebook, 

llth Field Conf., Rio Chama Country, 1960: p. 63-74.

Dane, C. H., and Bachman, G. 0., 1957, The Dakota sandstone and Mancos 

shale in the Gallup area [N. Mex.], in Four Corners Geol. Soc. Guidebook, 2d Field Conf., southwestern San Juan Basin, 1957: p. 95-98.

Dane, C. H., Landis, E. R., and Cobban, W. A., 1971, The Twowells Sandstone Tongue of the Dakota Sandstone and the Tres Hermanos Sandstone 

as used by Herrick (1900), western New Mexico, in Geological Survey 

research 1971: U.S. Geol. Survey Prof. Paper 750-B, p. B17-B22.

Dutton, C. E., 1885, Mount Taylor and the Zuni Plateau [N. Mex.], in U.S. 

Geol. Survey 6th Ann. Rept: p. 105-198.
DAKOTA SANDSTONE AND MANGOS SHALE, NEW MEXICO J43

Gilbert, G. K., 1875, Geology of portions of New Mexico and Arizona, explored and surveyed in 1873, in U.S. Geog. and Geol. Explor. and Surveys

West of 100th Meridian, v. 3: p. 503-567. 

Haas, Otto, 1949, Acanthoceratid Ammonoidea from near Greybull, Wyoming:

Am. Mus. Nat. History Bull., v. 93, art. 1, p. 1-39, pis. 1-15. 

Herrick, C. L., 1900, Report of a geological reconnaissance in western Socorro

and Valencia Counties, New Mexico: Am. Geologist, v. 25, no. 6,

p. 331-346. 

Holmes, W. H., 1877, Geological report on the San Juan district [Colo.], in

U.S. Geol. and Geog. Survey Terr. Ann. Rept., 9th, for year 1875:

p. 237-276. 

Howell, E. E., 1875, Plateau system of portions of eastern Utah, northern

Arizona, and western central New Mexico, in U.S. Geog. and Geol. Explor.

and Surveys West of 100th Meridian, v. 3: p. 265-301. 

Hunt, C. B., 1936, The Mount Taylor coal field: U.S. Geol. Survey Bull. 860-B,

p. 31-80. 

Kauffman, E. G., 1967, Coloradoan macroinvertebrate assemblages, central

western interior, United States, in A symposium on paleoenvironments

of the Cretaceous seaway in the western interior: Colorado School Mines,

p. 67-143.

 1969, Cretaceous marine cycles of the western interior: Mtn. Geologist, v. 6, no. 4, p. 227-245.

Krumbein, W. C., and Nagel, F. G., 1953, Regional stratigraphic analysis of 

"Upper Cretaceous" rocks of Rocky Mountain region: Am. Assoc. Petroleum Geologists Bull., v. 37, no. 5, p. 940-960.

Lamb, G. M., 1968, Stratigraphy of the lower Mancos Shale in the San Juan 

Basin: Geol. Soc. America Bull., v. 79, no. 7, p. 827-854.

Lee, W. T., 1916, Relation of the Cretaceous formations to the Rocky Mountains in Colorado and New Mexico: U.S. Geol. Survey Prof. Paper 95-C, 

p. 27-58.

Lee, W. T., and Knowlton, F. H., 1917, Geology and paleontology of the 

Raton Mesa and other regions in Colorado and New Mexico: U.S. Geol. 

Survey Prof. Paper 101, 450 p. [1918].

Moench, R. H., 1963a, Geologic map of the Laguna quadrangle, New Mexico: 

U.S. Geol. Survey Geol. Quad. Map GQ-208.

 1963b, Geologic map of the Seboyeta quadrangle, New Mexico: U.S. 

Geol. Survey Geol. Quad. Map GQ-207.

 1964a, Geology of the Dough Mountain quadrangle, New Mexico: 

U.S. Geol. Survey Geol. Quad. Map GQ-354.

_1964b, Geology of the South Butte quadrangle, Valencia County,

New Mexico: U.S. Geol. Survey Geol. Quad. Map GQ-355. 

Moench, R. H., and Puffett, W. P., 1963a, Geologic map of the Arch Mesa

quadrangle, New Mexico: U.S. Geol. Survey Geol. Quad. Map GQ-211. 

 1963b, Geologic map of the Mesa Gigante quadrangle, New Mexico:

U.S. Geol. Survey Geol. Quad. Map GQ-212. 

Moench, R. H., and Schlee, J. S., 1967, Geology and uranium deposits of the

Laguna district, New Mexico: U.S. Geol. Survey Prof. Paper 519, 117 p. 

Moench, R. H., Schlee, J. S., and Bryan, W. B., 1965, Geologic map of the

La Gotera quadrangle, Sandoval and Valencia Counties, New Mexico:

U.S. Geol. Survey Geol. Quad. Map GQ-371. 

Owen, D. E., 1963, The Dakota Formation of the San Juan Basin, New

Mexico and Colorado: Kansas Univ. Ph. D. dissert., Ann Arbor, Mich.,

Microfilms, Inc., 352 p.
J44 CONTRIBUTIONS TO STRATIGRAPHY

 1966, Nomenclature of Dakota Sandstone (Cretaceous) in San Juan 

basin, New Mexico and Colorado: Am. Assoc. Petroleum Geologists Bull., 

v. 50, no. 5, p. 1023-1028.

Pike, W. S., Jr., 1947, Intertonguing marine and nonmarine Upper Cretaceous 

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America Mem. 24, 103 p.

Reeside, J. B., Jr., 1944, Maps showing thickness and general character of 

the Cretaceous deposits in the western interior of the United States: 

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the United States, chap. 18 in Treatise on marine ecology and paleoecology: Geol. Soc. America Mem. 67, v. 2, p. 505-542. 

Santos, E. S., 1966a, Geologic map of the San Mateo quadrangle, McKinley

and Valencia Counties, New Mexico: U.S. Geol. Survey Geol. Quad.

Map GQ-517.

 1966b, Geologic map of the San Lucas Dam quadrangle, McKinley 

County, New Mexico: U.S. Geol. Survey Geol. Quad. Map GQ-516.

Santos, E. S., and Thaden, R. E., 1966, Geologic map of the Ambrosia Lake 

quadrangle, McKinley County, New Mexico: U.S. Geol. Survey Geol. 

Quad. Map GQ-515.

Schlee, J. S., and Moench, R. H., 1963a, Geologic map of the Moquino quadrangle, New Mexico: U.S. Geol. Survey Geol. Quad. Map GQ-209.

 1963b, Geologic map of the Mesita quadrangle, New Mexico: U.S.

Geol. Survey Geol. Quad. Map GQ-210. 

Sears, J. D., 1934, The coal field from Gallup eastward toward Mount Taylor,

pt. 1 of Geology and fuel resources of the southern part of the San Juan

Basin, New Mexico: U.S. Geol. Survey Bull. 860-A, p. 1-29 [1935]. 

Sears, J. D., Hunt, C. B., and Hendricks, T. A., 1941, Transgressive and

regressive Cretaceous deposits in southern San Juan basin, New Mexico:

U.S. Geol. Survey Prof. Paper 193-F, p. 101-121. 

Thaden, R. E., Merrin, Seymour, and Raup, 0. B., 1967, Geologic map of the

Grants SE quadrangle, Valencia County, New Mexico: U.S. Geol. Survey

Geol. Quad. Map GQ-682.

Thaden, R. E., and Ostling, E. J., 1967, Geologic map of the Bluewater quadrangle, Valencia and McKinley Counties, New Mexico: U.S. Geol. Survey

Geol. Quad Map GQ-679. 

Thaden, R. E., Santos, E. S., and Ostling, E. J., 1966, Geologic map of the

Goat Mountain quadrangle, McKinley County, New Mexico: U.S. Geol.

Survey Geol. Quad. Map GQ-518.

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McKinley Counties, New Mexico: U.S. Geol. Survey Geol. Quad. Map

GQ-680. 

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Grants quadrangle, Valencia County, New Mexico: U.S. Geol. Survey

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[Colo.-N. Mex.]: Am. Assoc. Petroleum Geologists, Rocky Mtn. Sec.,

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Contributions to

Stratigraphy,

1972________

GEOLOGICAL SURVEY BULLETIN 1372

This volume was published 

as separate chapters A -/
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director
CONTENTS

[Letters designate the separately published chapters]

(A) Changes in stratigraphic nomenclature by the U.S. Geological Survey, 

1971, by George V. Cohee and Wilna B. Wright.

(B) Stratigraphic nomenclature of Cambrian and Lower Ordovician rocks 

of easternmost southern Arizona and adjacent westernmost New 

Mexico, by Philip T. Hayes.

(C) Strodes Creek Member (Late Ordovician) a new map unit in the 

Lexington Limestone of north-central Kentucky, by Douglas F. D. 

Black and Norman P. Cuppels.

(D) McHugh complex of south-central Alaska, by Sandra H. B. Clark. 

(E) Stratigraphic divisions and geologic history of the Laney Member of

the Green River Formation in the Washakie Basin in southwestern

Wyoming, by Henry W. Roehler. 

(F) The upper Paleozoic Madera Group in the Manzano Mountains, New

Mexico, by Donald A. Myers. 

(G) The Lower Cretaceous Figuera Lava and Fajardo Formation in the

stratigraphy of northeastern Puerto Rico, by Reginold P. Briggs. 

(H) Lower and middle Tertiary stratigraphic units of the San Emigdio and

western Tehachapi Mountains, California, by T. H. Nilsen, T. W.

Dibblee, Jr., and W. 0. Addicott. 

(I) New Cretaceous formations in the western Wyoming thrust belt, by

William W. Rubey. 

(J) Stratigraphic terminology of the Dakota Sandstone and Mancos Shale,

west-central New Mexico, by E. R. Landis, C. H. Dane, and W. A.

Cobban.