-»

Stratigraphic Nomenclature of 

' Volcanic Rocks in the 

 Jemez Mountains, New Mexico

By R. A. BAILEY, R. L. SMITH, and C. S. ROSS

CONTRIBUTIONS TO STRATIGRAPHY

»

GEOLOGICAL SURVEY BULLETIN 1274-P

New Stratigraphic names and revisions 

in nomenclature of upper Tertiary and 

, Quaternary volcanic rocks in the 

Jemez Mountains
UNITED STATES DEPARTMENT OF THE INTERIOR 

WALTER J. HICKEL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

U.S. GOVERNMENT PRINTING OFFICE 

WASHINGTON : 1969

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

Washington, D.C. 20402 - Price 15 cents (paper cover)
CONTENTS

Page

Abstract.._..._________-...______.._-.._._____.. PI

Introduction. -_-________.._.____-_------___-_______------_-_---_-_ 1

General relations._____-___________--_--___-__--_-___-----___---__. 2

Keres Group..__________________--------_-___-_------------_------ 2

Canovas Canyon Rhyolite..__-__-_---_________---___-____-_--__ 5

Paliza Canyon Formation.___-_________-__-_-__-__-_-_______--- 6

Bearhead Rhyolite-___________________________________________ 8

Cochiti Formation.._______________________________________________ 8

Polvadera Group..______________-__-_------________--_-______---__ 10

Lobato Basalt______________________________________________ 10

Tschicoma Formation_______-__-_-____---_-__-______-______-- 11

El Rechuelos Rhyolite--_____---------_--------------_-_------- 11

Puye Formation_________________------___________-_--______-.__- 12

Tewa Group__._...._.______........___._.___.____......___...__ 12

Bandelier Tuff.______________.______________... 13

Tsankawi Pumice Bed._____________________________________ 14

Valles Rhyolite______.__-___---_____________.________..__ 15

Deer Canyon Member.______-_____-__.____--_--___-__-____ 15

Redondo Creek Member.__________________________________ 15

Valle Grande Member____-__-_--___-___--_-____-___-._-.__ 16

Battleship Rock Member...______________________________ 17

El Cajete Member____..._____________________ 17

Banco Bonito Member.___-_--_---_-_----_---_----._____--- 18

References . _ _________________-___---_----_-_-------_-__-------. 19

ILLUSTRATIONS

Page

FIGURE 1. Index map of the Jemez Mountains, New Mex., showing quadrangle boundaries and distribution of Keres, Polvadera, and 

Tewa Groups____________________________ P3 

2. Nomenclature of the Keres, Polvadera, and Tewa Groups.___ 4

in

STRATIGRAPHIC NOMENCLATURE OF VOLCANIC ROCKS 

IN THE JEMEZ MOUNTAINS, NEW MEXICO

By E. A. BAILEY, R. L. SMITH , and C. S. Boss

ABSTRACT

Upper Tertiary and Quaternary volcanic rocks of the Jemez Mountains are subdivided into three groups the Keres Group, in the south, the Polvadera Group, 

mainly in the north, and the Tewa Group, in the central and flanking parts 

of the mountains.

The Keres Group is divisible informally into two subgroups an older subgroup, consisting of the basalt of Chamisa Mesa and the Canovas Canyon Rhyolite, and a younger subgroup, consisting of the Paliza Canyon Formation and 

the Bearhead Rhyolite. The older subgroup is a basalt-rhyolite association; the 

younger subgroup is a more differentiated basalt-andesite-dadte-rhyolite 

association.

The Polvadera Group includes the Lobato Basalt; the andesites, dacites, and 

quartz latites of the Tschicoma Formation; and El Rechuelos Rhyolite. These 

formations constitute a still younger basalt-andesite-dacite-rhyolite association 

in the Jemez Mountains.

The Tewa Group includes the Bandelier Tuff, Cerro Rubio Quartz Latite, 

Cerro Toledo Rhyolite, and the Valles Rhyolite and represents the climax of 

rhyolitic volcanism in the Jemez Mountains.

Subdivision of the Bandelier Tuff is revised so that it consists of only two 

members the Otowi Member, which includes the Guaje Pumice Bed, and the 

Tshirege Member, which includes the Tsankawi Pumice Bed. The Valles Rhyolite 

is subdivided into six new members. Ages of many of the formations are refined 

by radiometric dating.

INTRODUCTION

The main purpose of this paper is to define and briefly describe 

new geologic formations recognized and mapped in the Jemez Mountains volcanic field in north-central New Mexico. The nomenclature 

of some previously described units is revised. The formations are 

shown on the geologic map of the Jemez Mountains (Smith and 

others, 1969).

Pi
P2 CONTRIBUTIONS TO STRATIGRAPHY 

GENERAL RELATIONS

The volcanic rocks of the Jemez Mountains (Ross and others, 

1961; Smith and others, 1961) are stratigraphically and petrologically 

divisible into three groups, herein named the Keres Group, the Polvadera Group, and the Tewa Group. The Keres Group occurs mainly 

in the southern Jemez Mountains and is overlapped and unconformably overlain by the Polvadera Group, which occurs mainly in the 

central and northern Jemez Mountains. The Tewa Group occurs in 

the central and flanking parts of the mountains and unconformably 

overlies both the Keres and Polvadera Groups (fig. 1).

In general, the rocks of the Keres and Polvadera Groups constitute 

two successive petrochemical cycles, ranging from basalt through intermediate rocks to rhyolite. The rocks of the Tewa Group constitute 

a climactic and terminal rhyolitic stage of volcanism.

Figure 2 shows the nomenclature of the Keres, Polvadera, and Tewa 

Groups listed in general stratigraphic succession.

The Keres and Polvadera Groups for the most part overlie buff 

arkosic sediments of late Tertiary age. These sediments constitute 

most of the alluvial fill of the Rio Grande graben and were initially 

called the "Santa Fe marl" (Hayden, 1869) and later the Santa Fe 

Formation (Bryan, 1938; Smith, 1938; Denny, 1940; Galusha, 1966). 

Spiegel and Baldwin (1963) proposed that the Santa Fe be raised 

to group status and separated it into the Tesuque and Ancha Formations in the vicinity of Santa Fe. Because of uncertainties in the correlation of the Tesuque and Ancha Formations with other Santa Fe 

beds in and adjacent to the Jemez Mountains, however, the term Santa 

Fe Formation, as used by Denny, Smith, and Galusha, is used in this 

paper. In the northern Jemez Mountains, the Santa Fe Formation includes the sediments above the Abiquiu Tuff of Smith (1938) and 

below the Lobato Basalt (new name, this paper). East of the Jemez 

Mountains, the Santa Fe Formation includes the sediments exposed 

below the Puye Formation and below the basalts of Cerros del Rio, 

although it is recognized that the uppermost of these beds east of 

the Kio Grande belongs to the Ancha Formation. Southwest of the 

Jemez Mountains, the Santa Fe Formation includes the sediments 

above the Zia Sand Formation of Galusha (1966) and below the basalt 

of Chamisa Mesa and the Cochiti Formation (new name, this paper).

KERES GROUP

The Keres (pronounced kear'-ees) Group is here proposed for a 

sequence of basaltic, andesitic, dacitic, and rhyolitic volcanic rocks 

forming the southern Jemez Mountains. The name is derived from an 

old name for the southern Jemez Mountains the Keresan Range
VOLCANIC ROCKS, JEMEZ MOUNTAINS, NEW MEXICO P3

106M5' 30' 106°15'

EXPLANATION

Tewa Group Polvadera Group Keres Group Basalts of Cerros

del Rio and Santa

Ana Mesa

FIQUBE 1. Index map of the Jemez Mountains, N. Mex., showing distribution 

of the Keres, Polvadera, and Tewa Groups and boundaries of the following 

quadrangles: (1) Youngsville, (2) Abiquiu, (3) San Juan Pueblo, (4) Jemez 

Springs, (5) Frijoles, (6) Espanola, (7) Jemez, (8) Santo Domingo Pueblo, 

(9) Agua Fria, (10) Bernalillo, (11) San Felipe Pueblo, and (12) Madrid.
P4 CONTRIBUTIONS TO STRATIGRAPHY

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VOLCANIC ROCKS, JEMEZ MOUNTAINS, NEW MEXICO P5

(Harrington, 1916, p. 409), which, was named for the Indians of the 

Keresan linguistic group who inhabited the surrounding area.

The Keres Group includes, from oldest to youngest, the basalt of 

Chamisa Mesa, the Canovas Canyon Khyolite, the Paliza Canyon 

Formation, and the Bearhead Rhyolite (new names, this paper).

The Keres Group may be divided informally into two subgroups 

an older subgroup, consisting of the basalt of Chamisa Mesa and the 

Canovas Canyon Khyolite, and a younger subgroup, consisting of 

the Paliza Canyon Formation and the Bearhead Rhyolite. The older 

subgroup is a predominantly basalt-rhyolite association; the younger 

subgroup is a more differentiated basalt-andesite-dacite-rhyolite 

association.

The Keres Group has an aggregate maximum thickness of more 

than 6,000 feet, but because of the lenticular nature of most of its 

component formations, the maximum thickness in any given place 

does not exceed 3,000 feet.

The Keres Group ranges in age from early through middle Pliocene. 

The group conformably overlies upper Miocene(?) and lower Pliocene arkosic sands of the Santa Fe Formation and interfingers with 

volcanic gravels of the Cochiti Formation. The Keres Group is unconformably overlain by middle and upper Pliocene and Pleistocene 

volcanic rocks of the Polvadera and Tewa Groups.

CANOVAS CANYON BHYOLITE

The name Canovas Canyon Rhyolite is proposed for a sequence of 

rhyolite flows, tuffs, domes, and associated shallow intrusions exposed 

in the eastern half of the Jemez quadrangle. The formation is named 

for exposures in Canovas Canyon, but the most typical exposures 

are to the east, in the Bear Springs area, particularly on Bear Springs 

Peak, which is one of several source vents for the formation.

The formation has a maximum thickness of 900 feet in the Bear 

Springs area, where it consists of alternating bedded tuffs, massive 

pumice breccias, and lava flows, which are locally intruded by small 

rhyolite bodies. The formation extends 7 to 8 miles south and southwest of Bear Springs and underlies most of Borrego Mesa, where it 

thins to less than 100 feet and consists mainly of bedded tuffs, although 

one isolated extrusive center occurs at Borrego Dome.

In the Bear Springs area the Canovas Canyon Rhyolite directly 

overlies arkosic sands of the Santa Fe Formation, which crop out only 

locally 0.7" mile southeast of Bear Springs Peak in a minor branch 

of Bear Springs Canyon and 0.6 mile northwest of Bear Springs Peak 

near the head of Canovas Canyon.

329-579 69 2
P6 CONTRIBUTIONS TO STRATIGRAPHY

On Borrego Mesa, tuffs of the Canovas Canyon Rhyolite conformably overlie the basalt of Chamisa Mesa, which in turn conformably 

overlies arkosic sands of the Santa Fe Formation. The basal contact 

of the formation is intermittently exposed along the western edge of 

the mesa as far south as Bodega Butte.

In the Borrego Mesa area, tuffs of the Canovas Canyon Rhyolite interfinger with gravels of the lower part of the Cochiti Formation and 

are conformably overlain by basalts of the Paliza Canyon Formation. 

In the Bear Springs area, where the relief near the rhyolite vents is 

great, the Canovas Canyon is overlapped, locally with steep contacts, 

by Paliza Canyon basalts and andesites.

The Canovas Canyon Rhyolite is probably early Pliocene in age. 

The formation postdates arkosic sands of the Santa Fe Formation thai 

Galusha (1966, p. 11) considers to be equivalent to the Valentine 

Formation of Nebraska (upper Miocene and lower Pliocene as indicated by Wood and others, 1941). The formation predates dacites of 

the Paliza Canyon Formation that have been radiometrically dated 

by G. B. Dalrymple (written commun., 1967) as 8.5 to 9.1 m.y. (million 

years) old.

PALIZA CANYON FORMATION

The name Paliza (pronounced pal-ee'-sah) Canyon Formation is 

proposed for a complex of basaltic, andesitic, and dacitic flows, tuffs, 

and breccias that crop out extensively in the Jemez Springs, Jemez, 

Frijoles, and Santo Domingo Pueblo quadrangles. The formation is 

named for exposures in Paliza Canyon, in the southeastern part of 

the Jemez Springs quadrangle, although the best exposures occur in 

upper Cochiti Canyon and on the east side of St. Peter's Dome in the 

Frijoles quadrangle, where the rocks have been carved into steep 

rugged slopes of nearly continuous outcrop.

The rocks represent the effusions of numerous coalesced composite 

volcanoes, and because such deposits are inherently lenticular, a type 

area, rather than a type section, is designated. In any given section, 

however, there is a general upward succession from basaltic through 

andesitic to dacitic rocks, although locally dacitic rocks may occur 

low in the succession.

The formation is thickest along a north-south axis extending from 

the north wall of the Valles caldera through Paliza and Peralta 

Canyons to Ruiz Peak, where exposures generally exceed 1,500 feet. 

The base of the formation is not exposed along this axis, but projection 

from the exposed base west of the axis indicates that the maximum 

thickness of the formation is about 3,000 feet.
VOLCANIC ROCKS, JEMEZ MOUNTAINS, NEW MEXICO P7

The Paliza Canyon Formation overlies rocks ranging in age from 

Permian to late Tertiary. On the western fringes of the Jemez Mountains on the east side of Bio Guadalupe, La Ventana quadrangle, and 

at the head of Canon de San Diego, Jemez Springs quadrangle, Paliza 

Canyon basalts and andesites unconformably overlie red beds of the 

Abo Formation (Permian). In lower Paliza Canyon, Jemez quadrangle, they unconformably overlie red shales of the Chinle Formation (Triassic). On the west wall of the Valles caldera and in upper 

San Juan Canyon, Jemez Springs quadrangle, Paliza Canyon basalts 

are in contact with light-grayish-buff sands and tuffaceous lake(?) 

sediments that are thought, on the basis of lithology, to be correlative 

with the Abiquiu Tuff of Miocene (?) age. At the east foot of St. Peter's 

Dome, Frijoles and Santo Domingo quadrangles, the formation rests 

conformably (?) on buff arkosic sands of the Santa Fe Formation of 

probable late Miocene (?) or early Pliocene age. In the Bear Springs 

area, Jemez quadrangle, Paliza Canyon basalts and andesites lap 

unconformably against the high-standing hills of Canovas Canyon 

Rhyolite, but on Borrego Mesa, to the southwest, similar basalts conformably overlie tuffs of the Canovas Canyon Rhyolite and sandy 

gravels of the Cochiti Formation.

The Paliza Canyon Formation is intruded and locally overlain by 

units of the Bearhead Rhyolite. The contact between the two formations is variable, being locally conformable and elsewhere disconformable or unconformable. The overall impression gained, however, 

is that the Bearhead Rhyolite erupted on an irregular erosional surface cut on the Paliza Canyon rocks.

In the north and northwest wall of the Valles caldera, Jemez Springs 

and Frijoles quadrangles, andesite flows of the Paliza Canyon Formation are overlain with apparent conformity by the thick dacite and 

quartz-latite flows of the Tschicoma Formation (Polvadera Group). 

However, the alteration of the andesitic rocks in comparison with the 

very fresh appearance of the dacitic rocks suggests a disconformity or 

unconformity between the formations. The Paliza Canyon Formation 

is also locally overlain unconformably by the Bandelier Tuff (Tewa 

Group).

The Paliza Canyon Formation is early to middle Pliocene in age. 

Three dacitic rocks from the formation have been dated by the potassium-argon method as being 8.5,8.8, and 9.1 m.y. old (G. B. Dalrymple, 

written commun., 1967). On Borrego Mesa, basalts in the lower part of 

the formation postdate late Miocene (?) and early Pliocene sediments 

of the Santa Fe Formation (Galusha, 1966) and are separated from 

them by about 200 feet of the Cochiti Formation, the Canovas Canyon 

Rhyolite, and the basalt of Chamisa Mesa. The formation predates
P8 CONTRIBUTIONS TO STRATIGRAPHY

basaltic and dacitic rocks of the Polvadera Group, which have radiometric ages of 7.4 m.y. and younger (G. B. Dalrymple, written 

commun., 1967).

BEABHEAD BHYOLITE

The name Bearhead Rhyolite is proposed for a thick accumulation 

of rhyolite tuffs, flows, domes, and associated shallow intrusions that 

are exposed in the northern parts of the Santo Domingo Pueblo and 

Jemez quadrangles and the southern parts of the Frijoles and Jemez 

Springs quadrangles. The formation is named for exposures on Bearhead Peak, one of the larger source vents of the formation.

Tuffaceous facies of the Bearhead Khyolite are here formally designated the Peralta Tuff Member, a name first used by Kirk Bryan 

and J. E. Upson (Stearns, 1953, pp. 499-500). The member is named 

for typical exposures in Peralta Canyon near its junction with Colle 

Canyon. The Peralta Tuff Member consists predominantly of bedded 

air-fall tuffs but includes probable hot-avalanche deposits, as well as 

reworked tuffs that are interbedded with and grade laterally into 

volcanic gravels of the Cochiti Formation.

The Bearhead Rhyolite rests for the most part on an irregular erosion surface cut mainly on andesitic and dacitic rocks of the Paliza 

Canyon Formation. Contact relations are well exposed in Sanchez, 

Cochiti, and Bland Canyons, in the Santo Domingo Pueblo quadrangle, and near Cerrito Yelo, in the Jemez quadrangle. At the mouth 

of Bland Canyon the Peralta Tuff Member rests conformably on tuff 

breccias of the Paliza Canyon Formation, and at Tent Rocks in Peralta Canyon the tuffs interfinger with the upper part of the Cochiti 

Formation.

The Bearhead Rhyolite is unconformably overlain southwest of 

Tent Rocks by pediment gravels that are probably correlative with 

those of the Ortiz pediment (Bryan, 1938, p. 215; Stearns, 1953).

The Bearhead Rhyolite is middle Pliocene in age. The formation 

postdates the Paliza Canyon Formation, which contains rocks that 

have been radiometrically dated as 8.5 to 9.1 m.y. old (G. B. Dalrymple, written commun., 1967), and it predates pediment gravels 

that appear to be correlative with those of the Ortiz pediment the 

Tuerto Gravel of Stearns (1953) and the Ancha Formation (Spiegel 

and Baldwin, 1963, p. 49 and fig. 20), which are considered to be of 

late Pliocene or early Pleistocene age.

COCHITI FORMATION

The Cochiti (pronounced co'-chi-tee) Formation is a thick sequence 

of volcanic gravel and sand, consisting of basalt, andesite, dacite, and
VOLCANIC ROCKS, JEMEZ MOUNTAINS, NEW MEXICO P9

rhyolite detritus derived from penecontemporaneous erosion of units 

of the Keres Group. The formation is named for exposures in the badlands west and southwest of Cochiti Pueblo, in the western half of the 

Santo Domingo Pueblo quadrangle, and the eastern half of the Jemez 

quadrangle. The formation is repeated by faulting, and its full 

thickness is nowhere exposed.

The formation is exposed from Borrego Mesa and Bodega Butte 

eastward to the Rio Grande and south of the Jemez Mountains to the 

southern end of Santa Ana Mesa.

The base of the formation is exposed only along its western edge 

and is placed at the top of the basalt of Chamisa Mesa, above which 

the enclosing arkosic sediments contain volcanic detritus from the 

Jemez Mountains. The lower part of the Cochiti, along the southern 

edge of Borrego Mesa and in the vicinity of Bodega Butte, is interbedded with tuffs of the Canovas Canyon Rhyolite, but to the north 

it overlies Canovas Canyon tuffs and is separated by them from the 

basalt of Chamisa Mesa.

In Canovas, Hondo, and Guacamalla Canyons, coarse gravels of the 

Cochiti Formation are interbedded with basalts and andesites of the 

Paliza Canyon Formation, and at Tent Rocks in Peralta Canyon, 

gravels of the upper part of the formation are interbedded with the 

Peralta Tuff Member of the Bearhead Rhyolite.

The formation becomes finer grained southward from the Jemez 

Mountains, and under Santa Ana Mesa it grades laterally into coarse 

sands which become redder by inclusion of more and more granitic 

debris at the expense of volcanic debris. These coarse sands were 

mapped by Spiegel (1961) as the "red member of the Santa Fe Group" 

and were believed by him to be older than the Cochiti Formation, 

which he called the "western facies of the Santa Fe Group"; intertonguing and the gradation between Jemez-derived volcanic debris 

and granitic debris, however, especially on the north and west side of 

Santa Ana Mesa, indicate that the two facies are, in large part, time 

equivalent.

The Cochiti Formation is unconformably overlain in the north by 

pediment gravels that are probably equivalent to those of the Ortiz 

pediment (Bryan, 1938; Stearns, 1953). It is overlain in the south by 

the basalts of Santa Ana Mesa.

The Cochiti Formation ranges in age from early through middle 

Pliocene. The formation interfingers with the Paliza Canyon Formation, which contains dacites that have radiometric ages of 8.5 to 9.1 

m.y. It postdates arkosic sands of the Santa Fe Formation (upper 

Miocene and lower Pliocene), and it predates pediment gravels considered equivalent to the Tuerto Gravel (upper Pliocene or lower 

Pleistocene) of Stearns (1953).
P10 CONTRIBUTIONS TO STRATIGRAPHY

The name Polvadera (pronounced pol-vah-dare'-ah) Group is here 

proposed for the sequence of basaltic, andesitic, dacitic, and ryholitic 

rocks that form part of the central and most of northern Jemez Mountains. The name is derived from Polvadera Peak, the second highest 

peak in the northern Jemez Mountains and one of the major volcanic 

centers of the group.

The Polvadera Group includes, from oldest to youngest, the Lobato 

Basalt (new name, this paper), the andesites, dacites, rhyodacites, and 

quartz latites of the Tschicoma Formation (Griggs, 1964, p. 42), and 

El Eechuelos Rhyolite (new name, this paper). The group is a basaltandesite-dacite-rhyolite association younger than that of the Keres 

Group, which it overlaps to the south.

The Polvadera Group has an aggregate thickness of about 5,000 

feet, but because most of the formations are lenticular and only in 

part coextensive, the maximum thickness in any one place does not 

exceed 3,500 feet.

The Polvadera Group unconformably overlies the Abiquiu Tuff of 

Smith (1938) and arkosic sands of the Santa Fe Formation in the 

north and unconformably overlies the Keres Group in the central 

Jemez Mountains. The group is unconformably overlain locally by 

rocks of the Tewa Group.

Rocks of the Polvadera Group range in age from middle Pliocene 

to early Pleistocene. A basalt from Polvadera Mesa (Lobato Basalt) 

has been dated radiometrically as 7.4 m.y., and one of the youngest 

domes of El Rechuelos Rhyolite has been dated as 2.0 m.y. (G. B. 

Dalrymple, written commun., 1967).

LOBATO BASALT

The name Lobato Basalt is proposed for the basaltic lavas that form 

the high-level mesas fringing the northern and northeastern sides of 

the Jemez Mountains. The formation includes the basalts of Clara 

Peak, Lobato Mesa, Polvadera Mesa, and Escoba Mesa in the Abiquiu 

quadrangle and of Cerro Pedernal and La Grulla Plateau in the 

Youngsville quadrangle. The formation is named for Lobato Mesa 

in the eastern half of the Abiquiu quadrangle, where the formation is K ,. 

thickest and most extensive. H. T. U. Smith (1938) briefly referred 

to the basalts on Lobato Mesa as the "Lobato basaltic lavas" but did not y 

describe them or formally name them. * ^

Lobato Mesa is designated the type area for the formation. Typical 

sections are well exposed on the eastern escarpment of the mesa. The 

formation has a maximum thickness of 600 feet on Lobato Mesa and 

consists of a succession of many flows ranging from 20 to 50 feet in
VOLCANIC ROCKS, JEMEZ MOUNTAINS, NEW MEXICO Pll

thickness. The flows are predominantly olivine-augite basalts, but hypersthene-, pigeonite-, and titaniferous augite-bearing varieties also 

occur.

The Lobato basalts rest on an erosional surface locally veneered by 

boulders and cobbles of Precambrian crystalline and metamorphic 

rocks and underlain by Abiquiu Tuff and arkosic sands of the Santa 

Fe Formation. The Lobato basalts are overlain for the most part by 

dacites and quartz latites of the Tschicoma Formation, but in Rio del 

Oso an early dacite flow of the Tschicoma Formation is interbedded 

with the basalts.

The Lobato Basalt is middle Pliocene in age. A radiometric age 

of 7.4 m.y. has been obtained on one flow from Polvadera Mesa 

(G. B. Dalrymple, written commun., 1967). The formation postdates 

the Abiquiu Tuff of Miocene(?) age and arkosic sediments of the 

Santa Fe Formation of probable late Miocene and early Pliocene 

age. The formation for the most part predates the Tschicoma Formation, which on the basis of radiometric dating is middle to late 

Pliocene in age.

TSCHICOMA FORMATION

The Tschicoma Formation has been defined and described by Griggs 

(1964, p. 42). Eecent radiometric dates of 6.7 to 3.7 m.y. (G. B. 

Dalrymple, written commun., 1967) on rocks from the formation 

indicate an age of middle to late Pliocene.

EL RECHUELOS RHYOLITE

The name El E-echuelos (pronounced el rech-way'-los) Rhyolite is 

proposed for the rhyolite that forms five small rhyolite domes and a 

small pumice cone in the northern Jemez Mountains. The formation 

is named for El Rechuelos, a small steep draw which drains the 

western side of Polvadera Peak in the Abiquiu quadrangle and which 

passes just south of the two largest domes of the formation.

The formation includes the small pumice cone of El Lagunito de 

Palo Quemador, 2.5 miles north of Polvadera Peak, two pumiceous 

rhyolite domes about 2 miles northwest of Polvadera Peak, a small 

obsidian dome 1.2 miles southwest of Polvadera Peak, and two lithic 

rhyolite masses at the head of Canoncito Seco, about 5 miles southwest 

of Polvadera Peak.

The several masses rest on dacitic rocks of the Tschicoma Formation, 

and a few are locally overlain by the Bandelier Tuff. A radiometric 

age of 2.0 m.y., which has been obtained on the largest of the domes, 

indicates an early Pleistocene age, but the two masses at the head 

of Canoncito Seco may be older, judging from their degree of 

denudation and alteration.
PI 2 CONTRIBUTIONS TO STRATIGRAPHY j.

PTJYE FORMATION

The Puye (pronounced poo'-yay) Gravel was named and first t. 

mapped in the Abiquiu quadrangle by H. T. U. Smith (1938), but 

no definition or description of the formation appeared in print until 

Griggs (1964) published the results of his mapping in the Los Alamos ^ 

area. Griggs separated the Puye into two members the Totavi Lentil, 

a basal river gravel, consisting mainly of Precambrian quartzites and 

crystalline rock types; and a f anglomerate member, consisting mainly *> 

of volcanic rocks derived from the Jemez Mountains. Griggs used 

the name Puye Conglomerate, rather than Puye Gravel, because the 

deposits are sufficiently consolidated to stand in vertical cliffs. The v 

name Puye Formation is proposed here, however, because most of the 

constituent materials of the formation are of ultimate pyroclastic 

origin, and many of the component beds, especially those close to the ^ 

source areas in the Jemez Mountains, are pumiceous tuffs and lithic 

lapilli tuffs that show only slight alluvial reworking. Mudflow (lahar) 

deposits also constitute a large part of the formation; their greater > 

coherence largely accounts for the clifflike outcrops. v

The Puye Formation is essentially a broad alluvial and pyroclastic 

fan flanking the east side of the northern Jemez Mountains. It bears ^ 

in a general way the same relation to the Polvadera Group rocks that 

the older Cochiti Formation bears to the Keres Group rocks in the 

southern Jemez Mountains. The formation is interbedded in Santa 

Clara Canyon with thick massive dacite and quartz latite flows of the ^ 

Tschicoma Formation, with which it is in large part penecontemporaneous. It is also interbedded with the basalts of Chino Mesa * 

(Cerros del Kio) (Griggs, 1964, p. 36).

The Puye Formation unconformably overlies arkosic sands of the 

Santa Fe Formation and is conformably overlain by the Otowi ) 

Member of the Bandelier Tuff. ^

The Puye Formation is middle to late Pliocene in age. Stratigraphic 

relations indicate that it is penecontemporaneous with the Tschicoma v 

Formation, several flows of which have been radiometrically dated K -, 

6.7 to 3.7 m.y. old (G. B. Dalrymple, written commun., 1967). The 

Puye predates the Otowi Member of the Bandelier Tuff, which has ^ 

been dated as 1.4 m.y. old. * ^

TEWA GROUP v

Nomenclature of the Tewa (pronounced Tay'-wah) Group was ,*-> 

mutually agreed upon by C. S. Koss, E. L. Smith, and R. L. Griggs in 

1952 and was published by Griggs (1964). The group includes the ** 

Bandelier Tuff, Cerro Toledo Rhyolite, Cerro Rubio Quartz Latite, v/ 

and the Valles Rhyolite, a voluminous sequence of rhyolitic tuffs and 

lavas that represent the climactic and terminal stage of volcanism in 

the Jemez Mountains. * ^
VOLCANIC ROCKS, JEMEZ MOUNTAINS, NEW MEXICO P13

No changes are proposed in the nomenclature of the group, but revision and further subdivision of some of its constituent formations are 

proposed below.

BANDELIER TUFF

The term "Bandelier Rhyolite Tuff" was first used by H. T. U. Smith 

(1938, fig. 4, p. 937). It was shortened to "Bandelier Tuff" by Griggs 

(1964, p. 46), and the unit was subdivided by him into three members. 

From bottom to top these were: (1) The Guaje Member, a bedded 

pumice-fall deposit, (2) the Otowi Member, a massive pumiceous tuff 

breccia of ash-flow origin, 'and (3) the Tshirege Member, a succession 

of cliff-forming welded ash flows. Although this 3-fold subdivision 

was suitable for mapping the Los Alamos area, subsequent recognition 

of the significance of a pumice-fall bed at the base of the Tshirege 

Member and additional knowledge of the overall character of the 

Bandelier, plus genetic considerations, have shown that the formation 

may be more naturally subdivided into two stratigraphic and genetically equivalent units, each consisting of a basal pumice fall overlain 

by a petrologically related succession of ash flows. In a previous paper 

(Smith and Bailey, 1966), these two subdivisions were referred to informally as the "upper" and "lower" members of the Bandelier. The 

Bandelier is here formally divided into two members. The lower 

member is designated the Otowi Member, which is extended to include 

(1) the basal pumice fall (Guaje Member of Griggs) and (2) the 

overlying ash-flow units (Otowi Member of Griggs). Griggs' Guaje 

Member is renamed the Guaje Pumice Bed. The upper member of the 

Bandelier is designated the Tshirege Member and includes (1) a basal 

pumice fall, here named the Tsankawi Pumice Bed, and (2) the overlying ash-flow units (Tshirege Member of Griggs). Formal names are 

not given to the ash-flow units of either the Otowi or Tshirege Members. The table below compares Griggs' subdivisions with those of this 

report and with the informal designations of Smith and Bailey (1966).

Griggs (1964)

Tshirege Member

Otowi Member

Guaje Member

Smith and Bailey 

(1966)

"upper 

member"

"lower 

member"

This report

Tshirege 

Member

Otowi ' 

Member

Ash-flow units

Tsankawi Pumice 

Bed

Ash-flow units

Guaje Pumice Bed
P14 CONTRIBUTIONS TO STRATIGRAPHY

The Tsankawi Pumice Bed, the only new name proposed, and the 

only unit of the Bandelier not yet described in the literature, is defined 

below.

TSANKAWI PUMICE BED

The Tsankawi (pronounced tsahn-kah'-wee) Pumice Bed is named 

for exposures in the general vicinity of Tsankawi Ruin on the Pajarito 

Plateau, Espanola quadrangle. Typical and readily accessible exposures may be seen at several places along the south side of Tsankawi 

Ruin mesa, in sees. 20 and 21, T. 19 N., R. 7 E.; in the middle of sec. 24, 

T. 19 N., R. 6 E., on the Los Alamos truck route in Sandia Canyon; 

and in readouts along New Mexico Route 4 where it crosses Potrillo 

and Ancho Canyons.

In the type area the Tsankawi ranges in thickness from 2 to 3% feet 

and typically consists of three distinct air-fall units that are recognizable over its entire extent. The lower, main unit, 16-36 inches thick, 

consists of coarse, crudely bedded ash and pumice lapilli reaching 

a maximum of 2 inches in diameter. Above this is a thin, 1- to 2-inchthick bed of crystal-rich ash. This in turn is overlain by 4-10 inches 

of medium coarse pumice and ash, similar to, but better sorted and 

more distinctly bedded than the lower, main unit.

Over most of the Pajarito Plateau, the Tsankawi Pumice Bed rests 

on nonwelded pumiceous tuff breccia (ash flows) of the Otowi Member 

of the Bandelier or on bedded tuffs and associated gravels of the Cerro 

Toledo Rhyolite.

At most exposures the Tsankawi Pumice Bed is directly overlain by 

nonsorted pumiceous tuff breccia of the Tshirege ash flows, but locally 

as much as 2 feet of reworked, crossbedded ash is between the pumice 

bed and the ash flows.

Initially, the Tsankawi Pumice Bed blanketed the entire Jemez 

Mountains area, for outcrops of it occur beneath the Tshirege ash flow 

units on all sides of the mountains. The bed is thickest to the west 

and northwest, on the Jemez Plateau and Mesa Pinabetosa, where it 

attains a maximum thickness of about 12 feet.

The typical pumice of the Tsankawi Bed is rhyolitic. It is light 

gray to white and has a fibrous structure and silky luster on fresh 

surfaces. It contains sparse phenocrysts of quartz and sanidine and 

rare black specks of oxides and ferromagnesian minerals. This typical 

pumice is not particularly useful in distinguishing the Tsankawi 

Pumice Bed from other pumice falls in the area, but the presence in 

the Tsankawi of 1-10 percent of relatively dense gray pumice containing abundant hornblende needles is diagnostic. This gray, hornblende-bearing pumice is unique to the Tshirege Member of the 

Bandelier, It occurs both in the basal pumice fall and the ash flow
VOLCANIC ROCKS, JEMEZ MOUNTAINS, NEW MEXICO PI5

units and is a useful criterion for identification of the Tsankawi Bed, 

as well as the Tshirege ash flows.

The Tsankawi Pumice Bed is Pleistocene in age and has been dated 

radiometrically as 1.1 m.y. old (Doell and others, 1968).

VALLES BHYOLITE

The name Valles (pronounced vah'-yes) Rhyolite was proposed 

(Griggs, 1964, p. 58) for the rhyelites within the Valles caldera. The 

formation includes all the rhyelites that erupted within the caldera 

after its collapse.

The formation is here subdivided into the following six members 

listed and described in order of decreasing age: Deer Canyon Member, 

Redondo Creek Member, Valle Grande Member, Battleship Rock 

Member, El Cajete Member, and Banco Bonito Member.

DEER CANYON MEMBER

The name Deer Canyon Member is given to petrographically distinctive rhyolites in the central part of the Valles caldera, mainly in 

the Jemez Springs quadrangle. The member is named for the domeflow and associated tuffs exposed in Deer Canyon on the southwest 

side of Redondo Border, but it includes two isolated outcrops of 

similar rhyolite exposed in upper Jaramillo and San Luis Creeks and 

a sequence of rhyolite tuffs and breccias exposed on the northeast extension of Redondo Peak. Deer Canyon is designated the type area. 

Here the rhyolite has a maximum thickness of about 100 feet, typically contains abundant large bipyramidal phenocrysts of quartz and 

blocky phenocrysts of sanidine, and lacks visible ferromagnesian 

minerals.

The Deer Canyon Member in most localities conformably overlies a 

thin veneer of red, sedimentary caldera fill, which in turn overlies the 

uppermost ash-flow units of the Tshirege Member of the Bandelier 

Tuff. In upper San Luis Creek, the Deer Canyon is overlain by a flow 

of the Redondo Creek Member of the Valles Rhyolite, and on the 

northeast extension of Redondo it is conformably overlain by coarse, 

sedimentary caldera fill.

The Deer Canyon Member postdates the Tshirege Member of the 

Bandelier Tuff and predates the Redondo Creek Member of the Valles 

Rhyolite.

REDONDO CREEK MEMBER

The name Redondo Creek Member is given to petrographically 

distinctive rhyolites in the central and western parts of the Valles 

caldera. The member is named for the rhyolite dome and associated 

dikes and flows exposed at the head of Redondo Creek, Jemez Springs 

quadrangle, but a thicker section occurs in the steep slopes on the
PI6 CONTRIBUTIONS TO STRATIGRAPHY

west side of Sulphur Creek between Sulphur Springs and La Cueva. 

Here the member has a maximum thickness of about 500 feet and 

consists mainly of perlitic flow breccias.

The Redondo Creek Member is distinguishable from other members 

of the Valles Rhyolite by its distinctive sanidine-rimmed plagioclase 

phenocrysts and by its complete lack of quartz phenocrysts. The rock 

typically contains conspicuous biotite phenocrysts.

The base of the Redondo Creek Member, where exposed, conformably overlies lake beds or sandy sediments of the Valles caldera fill. 

The member is unconformably overlain, mainly in the western part of 

the caldera, by units of the Valle Grande Member of the Valles 

Rhyolite.

VALLE GRANDE MEMBER

The name Valle Grande (pronounced vah'-yeh grahn'-deh) Member 

is given to the rhyolites that form the morphologically young domes, 

flows, and associated pyroclastic rocks in the moat of the Valles 

caldera. The member includes the rhyolite of the domical masses of 

Cerro del Medio, Cerros de los Posos, Cerros del Abrigo, Cerro Santa 

Rosa, Cerro San Luis, Cerro Seco, San Antonio Mountain, South 

Mountain, and Cerro La Jara. The member is named for Valle 

Grande, the large valley in the southeastern part of Valles caldera, 

from which many of the domes can be seen. A type section is not 

designated because of the isolated nature of the units forming the 

member and because of petrographic differences between them. The 

domes in the eastern part of the caldera (Cerro del Medio and Cerros 

de los Posos) are nearly free of phenocrysts, whereas those in the 

western and southern parts (San Antonio Mountain and South Mountain) contain conspicuous quartz, sanidine, plagioclase, biotite, hornblende, and pyroxene phenocrysts. Progressive mineralogical variation 

between these extremes and the annular distribution of the domes 

within the Valles caldera moat, however, indicate that they are petrologically related and are parts of a single geologic member.

Basal contacts of the Valle Grande Member are seldom exposed. 

Locally, basal pyroclastic units of the member conformably overlie 

or interfinger with young lake sediments in the caldera moat. In the 

western half of the caldera, the dome-flow of San Antonio Mountain 

overlies the Redondo Creek Member. The South Mountain dome-flow 

is the only unit of the Valle Grande Member that is directly overlain 

by younger members of the Valles Rhyolite. It is disconformably 

overlain in Jemez Creek by the Battleship Rock, El Cajete, and Banco 

Bonito Members.

Although tree covered, most of the domes of the Valle Grande 

Member are so young that they have not been modified appreciably by
VOLCANIC ROCKS, JEMEZ MOUNTAINS, NEW MEXICO P17

erosion, and some retain their original carapace of glassy pumiceous 

blocks. Twelve of the domes have been dated radiometrically and 

have ages ranging from about 0.4 to 1.0 m.y. (Doell and others, 1968).

BATTLESHIP ROCK MEMBER

The name Battleship Eock Member is given to a sequence of local 

rhyolitic ash-flow deposits cropping out at the head of Canon de 

San Diego, in the Jemez Springs quadrangle. The member is named for 

Battleship Eock, which is also designated the type section, in sec. 5, 

T. 18 N., E. 3 E.

Near Battleship Eock the member is 400 feet thick and consists of 

a succession of ash flows that are in part welded. Location of the 

eruptive vent for the Battleship Eock Member is not known with certainty, but the distribution and petrographic similarity of the Battleship Eock Member with the El Cajete Member and the Banco 

Bonito Member suggest that the vent was in the vicinity of El Cajete.

Over most of the extent of the member, the base is not exposed, but 

at Battleship Eock the unit rests unconformably on red beds of the 

Abo Formation (Permian) and on fossiliferous limestones of the Magdalena Group (Pennsylvanian) and seems to have once filled a narrow 

gorge cut in these formations. The upper surface of the Battleship Eock Member locally has been deeply incised by streams and is in 

most places disconformably overlain by the porphyritic obsidian flow 

of the Banco Bonito Member of the Valles Ehyolite.

Contact relations about 1 mile northeast of Battleship Eock indicate that the member postdates the South Mountain dome-flow of 

the Valle Grande Member, which has been dated radiometrically as 

0.49 m.y. old (Doell and others, 1968). The Battleship Eock Member 

predates both the El Cajete Member, which contains fragments of 

Battleship Eock welded tuff, and the Banco Bonito Member, which 

overlies the El Cajete.

EL CAJETE MEMBER

The El Cajete (pronounced el kah-heh'-teh) Member of the Valles 

Ehyolite is a mantle-bedded air-fall deposit of rhyolite pumice lapilli 

and blocks. It is named for its source vent, El Cajete crater, which 

is about 2 miles south of Eedondo, in the Jemez Springs quadrangle. 

Because of its incoherence and the vegetational cover, natural outcrops 

of the member are rare. Excellent exposures are provided, however, by 

many roadcuts along New Mexico State Eoute 4 between Triple H 

Eanch and the crossing of the East Fork of Jemez Creek.

The El Cajete pumice forms a nearly continuous blanket over the 

countryside for 5 miles south of El Cajete crater, and isolated patches 

of it occur throughout the southern Jemez Mountains. Thin remnant
PI8 CONTRIBUTIONS TO STRATIGRAPHY

patches also are known to be nearly 30 miles from El Cajete, for example, in the canyon of the Santa Fe River, near La Bajada, in the 

Aqua Fria quadrangle. In the rim of El Cajete crater and in El Cajete 

Canyon, the member has a maximum thickness of about 250 feet.

The youngest rock directly overlain by the El Cajete Member is 

the South Mountain dome-flow of the Valle Grande Member of 

the Valles Rhyolite. Inclusions of Battleship Rock welded tuff in the 

El Cajete Member, however, indicate that the El Cajete postdates the 

Battleship Rock Member also. The El Cajete Member is overlain only 

by the Banco Bonito Member. A charcoal sample (U.S.G.S. No. W1553), collected from a thin ash-flow unit overlying El Cajete pumice 

in a roadcut at the crossing of Route 4 with the East Fork of Jemez 

Creek, was dated as greater than 42,000 years B.P. (before present) 

(Meyer Rubin, written commun., 1965).

BANCO BONITO MEMBER

The name Banco Bonito (pronounced bahn'-ko bon-ee'-toe) Member of the Valles Rhyolite is proposed for the porphyritic obsidian 

flow that fills the southwestern moat of the Valles caldera. It is named 

for Banco Bonito, the steep slope forming the south margin of the 

flow in the central part of the Jemez Spring quadrangle.

The Banco Bonito obsidian flow issued from a vent immediately 

west of El Cajete crater, flowed west 3 miles, and then bifurcated into 

two tongues, one of which flowed north and the other south, each an 

additional 2 miles. Although sparsely forested with ponderosa pine, 

the flow is virtually unmodified by erosion, and concentric pressure 

ridges on the flow surface are well preserved.

The basal contact of the Banco Bonito flow is well exposed only 

along its western margin, in the vertical cliff forming the east wall 

of upper San Diego Canyon. Here the flow fills steep narrow valleys 

cut into underlying welded ash flows of the Battleship Rock Member. 

On its southern margin, the flow unconformably overlies red beds of 

the Abo Formation and disconformably overlies the South Mountain 

flow of the Valle Grande Member and the El Cajete Member of the 

Valles Rhyolite.

The Banco Bonito obsidian flow is the youngest eruptive unit in 

the Jemez Mountains and is probably not more than 100,000 years old. 

The flow postdates the youngest unit of the Valle Grande Member 

which has been dated as 0.43 m.y. old (Doell and others, 1968). It also 

postdates a thin ash-flow unit that has been dated as greater than 

42,000 years B.P. by carbon-14. Conformity of the basal contact of the 

obsidian flow with the thin ash-flow unit and the well-preserved surface features on the obsidian flow suggest that its age is nearer 42,000 

years than 0.43 m.y.
VOLCANIC ROCKS, JEMEZ MOUNTAINS, NEW MEXICO P19 

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o