A Summary of 1ertiary Volcanic 

Stratigraphy of the Southwestern 

High Plateaus and Acljacent 

Great Basin, Utah 

GEOLOGICAL SURVEY BULLETIN 1405-B 
A Summary of lertiary Volcanic 

Stratigraphy of the Southwestern 

High Plateaus and Aqjacent 

Great Basin, Utah 

By PETER D. ROWLEY, JOHN J. ANDERSON, 

and PAULL. WILLIAMS ' 

CONTRIBUTIONS TO STRATIGRAPHY 

GEOLOGICAL SURVEY BULLETIN 1405-B 

Stratigraphic setting of rocks of the 

south flank of the Marysvale volcanic pile 

and intertonguing regional ash-flow tuffs. 

of Great Basin sources, southwestern Utah 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1975 
UNITED STATES DEPARTMENT OF THE INTERIOR 

THOMAS S. KLEPPE, Secretary 

GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

Library of Congress Cataloging in Publication Data 

Rowley, Peter D. 

A summary of Tertiary volcanic stratigraphy of the southwestern high plateaus and adjacent 

Great Basin, Utah. 

(Contributions to stratigraphy) (Geological Survey Bulletin 1405-B) 

Babliography: p. 

Supt. of Docs. no.: I 19.1405-B 

l. Geology, Stratigraphic-Tertiary. 2. Volcanism-The West. 

I. Anderson, John Jerome, 1930- joint author. II. Williams, Paul Lincoln, 1932- joint 

author. III. Title: A summary of Tertiary volcanic stratigraphy of the southwestern 

high plateaus ... IV. Series. V. Series: United States Geological Survey Bulletin 

1405-B. 

QE75.B9 no. 1405-B (QE691) 557.3'08s (551.2'1] 75-619290 

For sale by the Sup~rintendent of Documents, U.S. Government Printing Office 

Washington, D. C. 20402 

Stock Number 024-001-02752-6 
CONTENTS 

Page 

Metric-English equivalents........................................................................................ IV 

Abstract....................................................................................................................... BI 

Introduction ............................................................................................................... . 

Acknowledgments................................................................................................ 4 

Geologic setting.......................................................................................................... 4 

Lower 1"ertiary sequence............................................................................................ 5 

Claron Formation................................................................................................ 5 

Local unit............................................................................................................ 9 

Needles Range Formation................................................................................... 9 

Middle Tertiary sequence........................................................................................... 9 

Rocks of the eastern Great Basin volcanic province adjacent to the High 

Plateaus................................................................................................. 9 

Isom Formation............................................................................................ 9 

Quichapa Group.......................................................................................... 12 

Leach Canyon Formation............................................................................ 12 

Condor Canyon Formation.......................................................................... 13 

Harmony Hills Tuff..................................................................................... 13 

Rocks of the Marysvale volcanic province.......................................................... 13 

Mount Dutton Formation............................................................................ 13 

Buckskin Breccia.......................................................................................... 15 

Bear Valley Formation................................................................................. 15 

Older basalt flows......................................................................................... 15 

Osiris Tuff.............................................. ..................................................... 16 

Dry Hollow Formation................................................................................ 16 

Horse Valley Formation............................................................................... 16 

Mount Belknap Rhyolite............................................................................. 17 

joe Lott Tuff................................................................................................. 17 

Upper Tertiary and Quaternary sequence................................................................. 17 

Sevier River Formation ........................................ ....... ........................................ 17 

Younger basalt flows........................................................................................... 18 

References cited........................................................................................................... 18 

ILLUSTRATIONS 

Page 

FIGURE 1. Index map of southwestern Utah............................................................. B2 

2. Correlation chart o1 Cenozoic stratigraphy of the southwestern High 

Plateaus and adjacent Great Basin....................................................... 10 

TABLE 

TABLE 1. Summary of petrologic and stratigraphic characteristics of volcanic 

rocks exposed in the southwestern High Plateaus and adjacent Great 

Page 

Basin...................................................................................................... B6 

III 
Metric unit 

millimetre (mm) metre (m) 

kilometre (km) 

square metre (m2) 

square kilometre (km2) 

hectare (ha) 

cubic centimetre (cm3 ) 

litre (1) 

cubic metre (m3) 

cubic metre cubic hectometre (hm::) 

litre 

litre 

litre 

cubic metre 

cubic metre 

gram (g) 

gram 

tonne (t) tonne 

kilogram per square centimetre (kg/cm2) 

kilogram per square centimetre 

cubic metre per second 

(ma;s) 

METRIC-ENGLISH EQUIVALENTS 

English equivalent 

Length 

0.03937 inch (in) 

3.28 feet (ft) 

.62 mile (mi) 

Area 

10.76 

.386 

2.47 

Volume 

square feet (ft2) 

square mile (mi2) acres 

0.061 cubic inch (ina) 

61.03 cubic inches 

35.31 cubic feet (ft3) 

.00081 acre-foot (acre-ft) = 810.7 acre-feet 

2.113 pints (pt) 1.06 quarts (qt) .26 gallon (gal) .00026 million gallons (Mgal or 10a gal) 6.290 barrels (bbl) (1 bbl=42 ~al) 

Weight 

0.035 

.0022 

1.1 

.98 

ounce, avoirdupois (oz uvdp) pound, avoirdupois (lb avdp) 

tons, short (2,000 lb) 

ton, long (2,240 lb)· 

Specific combinations 

0.96 

.98 

35.3 

atmosphere (atm) 

bar (0.9869 atm) 

cubic feet per second (fta/s) 

Metric unit English equivalent 

Specific combinations-Continued 

litre per second (1/s) = .0353 cubic foot per second 

cubic metre per second 

per square kilometre 

[ (ma;s) /km2] 

metre per day (m/d) 

metre per kilometre 

(m/km) 

kilometre per hour 

(km/h) metre per second (m/s) metre squared per day (m2/d) 

cubic metre per second 

(ma;s) 

cubic metre per minute 

(m3/min) 

litre per second (1/s) 

litre per second per metre [ (1/s) /m] 

kilometre per hour 

(km/h) metre per second (m/s) 

gram per cubic 

centimetre (g/cma) 

gram per square centimetre (g/cm2) 

gram per square 

centimetre 

degree Celsius (°C) 

degrees Celsius 

(temperature) 

91.47 

= 3.28 

- 5.28 

= .9113 

= 3.28 

= 10.764 

= 22.826 

=264.2 

= 15.85 

= 4.83 

= .62 

= 2.237 

= 62.4::1 

= 2.048 

= .0142 

cubic feet per second per 

square mile [ (ft3/s)/mi2) 

feet per day (hydraulic conductivity) (ft/d) 

feet per mile (ft/mi) 

foot per second (ft/s) 

feet per second 

feet squared per day (ft2/d) 

(transmissivity) 

million gallons per day (Mgal/d) 

gallons per minute (gal/min) 

gallons per minute 

gallons per minute per foot 

[(gal/min) /ft] 

mile per hour (mi/h) 

miles per hour 

pounds per cubic foot (lb/ft3 ) 

pounds per square foot (lb/ft2) 

pound per square inch (lb/in2) 

Temperature 

1.8 degrees Fahrenheit (°F) 

= [ (1.8 X °C) +32] degrees Fahrenheit 

< 

C") 

0 

z 

~ 

tTl 

z 

~ 
CONTRIBUTIONS TO STRATIGRAPHY 

A SUMMARY OF TERTIARY VOLCANIC 

STRATIGRAPHY OF THE SOUTHWESTERN 

HIGH PLATEAUS AND 

ADJACENT GREAT BASIN, UTAH 

By PETER D. RowLEY, joHN J. ANDERSON, and PAULL. WILLIAMS 

ABSTRACT 

Recent geologic mapping of the southern flank of the volcanic pile centered at Marysvale, 

Utah, as well as the eastern edge of the Great Basin ash-flow tuff province, has necessitated 

changes and additions in nomenclature of Tertiary rocks. Nine formation names are retained, and five formation names are adopted: Mount Dutton (Oligocene and Miocene), 

Buckskin (Miocene), Bear Valley (Miocene), Osiris (Miocene), and Horse Valley (Miocene). 

The Dry Hollow Formation (Miocene) is redefined. Six new formal members are adopted: 

the Blue Meadows Member of the Isom Formation; the Narrows and Table Butte Members of 

the Leach Canyon Formation; and the Beaver, Kingston Canyon, and Antimony Members of 

the Mount Dutton Formation. The Baldhills Member of the Isom Formation is redefined. In 

our area the Leach Canyon Formation, Condor Canyon Formation, and Harmony Hills 

Tuff are lumped together as the Quichapa Group, in accord with the usage of Williams 

( 1967). The Sevier River Formation and overlying younger basalt flows are demonstrated to 

be older (Miocene) than previously thought. The name Wasatch Formation is not used in the 

area that we have mapped. The names Brian Head Formation and Parunuweap Formation 

arc abandoned. 

INTRODUCTION 

Changes in stratigraphic nomenclature of Tertiary volcanic rocks in 

southwestern Utah are necessitated by the results of a detailed mapping 

program, from 1963 to 1975, of 5,000 km2 of the southwestern flank of the 

volcanic pile centered at Marysvale (fig. 1 ). Stratigraphic revisions summarized herein are from a more detailed discussion by Anderson and Rowley (1975). 

Most published work on the Marysvale volcanic center is by Callaghan 

and his associates (Callaghan, 1938, 1939, 1973; Callaghan and Parker, 

1961a, 1961 b, 1962a, 1962b; Willard and Callaghan, 1962) and by Kerr and 

his students (for example, Kerr, 1963, 1968; Kerr and others, 1957). These 

studies concentrated on the Marysvale mining district in the center of the 

large Marysvale pile and on the north flank of the pile. Gregory (1945, 

1949, 1950, 1951) conducted numerous reconnaissance studies south of the 

Marysvale area. BI 
B2 CONTRIBUTIONS TO STRATIGRAPHY 

FIGURE 1.-The geography of southwestern Utah. Stippled pattern shows present 

present distribution of rocks of the Great Basin tuff province. Locations of type 

1, Blue Meadows Tuff Member; 2, Narrows Tuff Member; 3, Table Butte Tuff 

Tuff Member; 7, Antimony Tuff Member; 8, Buckskin Breccia; 9, Bear Valley 
TERTIARY VOLCANIC STRATIGRAPHY, UTAH 

0 20 40 60 Ml LES 

0 20 40 60 Kl LOMETRES 

---------- L_ --------- _L_-

distribution of rocks of the Marysvale volcanic pile; cross-hatched pattern shows 

sections for new suatigraphic units are identified by the following numbers: 

Member; 4, Mount Dutton Formation; 5, Beaver Member; 6, Kingston Canyon 

Formation; 10, Osiris Tuff; 11, Horse Valley Formation. 

B3 
B4 CONTRIBUTIONS TO STRATIGRAPHY 

Our work is an extension of the investigations by J. Hoover Mackin and 

his students (among them, Mackin, 1960, 1968), who mapped in and near 

the Iron Springs mining district to the southwest. Most of our work has 

been on the southern flank of the Marysvale pile; specifically, we mapped 

the southern Sevier Plateau, southern Tushar Mountains, and northern 

Markagunt Plateau-all in the High Plateaus-and the Black Mountains in the adjacent Great Basin (Anderson, 1965, 1971; Rowley, 1968, 

1972). Paleomagnetic investigations and K-Ar dating were an important 

part of the investigation (Nairn and others, 1975; Fleck and others, 1975). 

Reconnaissance mapping has been carried out on the eastern flank of the 

Marysvale pile (Williams and Hackman, 1971; Hackman and Wyant, 

1973). Williams (1960, 1967) also conducted regional stratigraphic studies 

on the Great Basin ash-flow tuffs of the Quichapa Group, and Rowley recently has filled in some gaps in the detailed mapping of Mackin in the 

Iron Springs district. 

This paper discusses only those stratigraphic units that occur in part or 

wholly within the southwestern High Plateaus and the Black Mountains. Thus, Great Basin volcanic units that occur adjacent to, but 

outside, these areas-such as the Hiko Tuff (Dolgoff, 1963; Cook, 1965) 

and the Rencher Formation, Kane Point, and Ox Valley Tuffs (Blank, 

1959; Mackin, 1960; Cook, 1965 )-are beyond the scope of this report. 

ACKNOWLEDGMENTS 

The late J. H. Mackin aided and encouraged us early in the study, as did 

R. L. Folk, R. E. Boyer, and D. S. Barker of the University of Texas at 

Austin. A. E. M. Nairn of the University of South Carolina supplied 

paleomagnetic data, and R. J. Fleck determined K-Ar ages on the volcanic 

rocks. We also are grateful for assistance during the study to Eugene 

Callaghan of the Utah Geological and Mineralogical Survey, P. E. 

Damon of the University of Arizona, James Judy, Thomas Iivari, and 

Douglas Kohout of Kent State University, as well as Paul Averitt, R. L. 

Parker, and W. E. Bowers. The manuscript was reviewed by D. H. 

Mcintyre and P. W. Lipman. The study was aided by support from the 

National Science Foundation (Grants GA-1098 and GA-11081), Penrose 

Bequest to the Geological Society of America, University of Texas at. 

Austin, Alfred P. Sloan Foundation, Shell Oil Company, Society of 

Sigma Xi, and Utah Geological and Mineralogical Survey. 

GEOLOGIC SETTING 

Between about 26 m.y. and about 20 m.y. ago (Miocene of Harland and 

others, 1964), volcanism that was centered near Marysvale inundated an 

area nearly 200 km in diameter to a thickness of at least 3,000 m. This 

complex of stratovolcanoes consisted in large part of locally derived 

andesitic to dacitic lava flows and volcanic breccia, with lesser silicic ash-
TERTIARY VOLCANIC STRATIGRAPHY, UTAH B5 

flow tuff and intrusive rock. Dacitic lava flows were deposited on top of 

these rocks and in turn were capped by basaltic lava flows and thick 

overlying rhyolite lava flows and poorly welded ash-flow tuff; the basaltic 

and rhyolitic rocks were deposited about 20 m.y. ago. 

Synchronous with the buildup of this Marysvale pile was emplacement of thin ash-flow tuff sheets of regional extent, derived from sources 

within the Great Basin. Representative sections of this ash-flow sequence 

are well exposed in the Iron Springs mining district (Mackin, 1960). 

These tuff sheets lap against and interfinger with the thick local rocks of 

the Marysvale pile; intertonguing relations are best seen in the Black 

Mountains and Markagunt Plateau. Table 1 summarizes petrologic and 

stratigraphic information on the volcanic units exposed in the southwestern High Plateaus and Black Mountains. 

On the basis of our mapping in these two overlapping volcanic. 

provinces, we subdivide the Cenozoic rocks into three stratigraphic 

sequences: lower Tertiary (includes rocks perhaps as old as Cretaceous), 

middle Tertiary, and upper Tertiary and Quaternary (Anderson and 

Rowley, 1975; fig. 2, this report). The lower Tertiary sequence consists of 

lacustrine-fluvial sedimentary rock (Claron Formation), unnamed local 

volcanic and sedimentary rock, and ash-flow tuff (Needles Range Formation); these units are continuous through the southern High Plateaus and 

eastern Great Basin. The middle Tertiary sequence is composed of the 

intertonguing volcanic rocks of the Marysvale pile and Great Basin province. Toward the close of and following deposition of the middle Tertiary volcanic rocks, block faulting began in the High Plateaus and Great 

Basin; erosion of upfaulted areas and deposition in downfaulted areas 

produced thick fluvial-lacustrine sedimentary rocks (Sevier River Formation). These rocks plus intercalated olivine basalt flows and perhaps rhyolite flows, as well as Quaternary surficial deposits, are in the upper Tertiary and Quaternary sequence. 

LOWER TERTIARY SEQUENCE 

CLARON FORMATION 

The Claron Formation consists mostly of fluvial and lacustrine conglomerate, sandstone, and limestone that unconformably overlie Upper 

Cretaceous and older rocks. Defined by Leith and Harder ( 1908), the 

Claron Formation has been mapped throughout the Iron Springs district 

and adjacent parts of the Great Basin as well as throughout the southwestern High Plateaus; usage of the name Wasatch Formation in these 

areas is abandoned in favor of Claron Formation (Mackin, 1960). In most 

places the Claron Formation is 400-700 m thick. Following Mackin 

(1960), we informally subdivide the unit into a lower, red part and an 

upper, white part. The Claron Formation is Eocene and Oligocene 

(Gregory, 1951; Mackin, 1960), but basal strata possibly are latest Creta-
TABLE I.-Summary of petrologzc and stratzgraphzc characteristics of volcanzc rocks exposed in the southwestern Hzgh Plateaus and adjacent 

Great Basm 

Name 

(Max1mum 

thiCkness 

mmetres) 

Needles Range 

Formation 

(200) 0 

lsom Formation, 

Blue Meadows 

Member (15). 

Isom Formauon, 

Baldhills 

Member (100). 

Isom Formation, 

Hole-In-The-Wall 

Member (30) 

Leach Canyon · 

Formation, 

Narrows Member 

(100) 0 

Leach Canyon 

Formation, 

Table Butte 

Member (200) 

Candor Canyon 

Formation, 

Swett Member (15). 

Candor Canyon 

Formation, 

Bauers Member 

(35+) 0 

Harmony Hills 

Tuff (30). 

Dommant 

color 

Pink, pale 

purple, light 

gray. 

Pale red, 

pale purple. 

Medium brown, 

purple, tan, 

gray. 

Pale red. 

Salmon, white, 

medium brown. 

Salmon, white. 

Medium brown. 

Pale red, pale 

purple, reddish 

brown tan. hght 

gray. 

Pink, tan. 

[Names for chemtcal composition are those of Nockholds (1954, p 1012-1021)) 

Average mode (percent) 

Groundmass, 62; plagioclase, 24; amphibole, 7; quartz, 

3; biotite, 2; opaque minerals, l; pyroxene, 

xenoliths, and K-feldspar, trace. 

Groundmass, 92; plagioclase, 5; pyroxene, 1; opaque 

minerals, l; xenoliths, l; K-feldspar, quartz, 

and amphibole, trace. 

Groundmass, 89; plagioclase, 8; pyroxene, l; opaque 

minerals, 1; xenoliths, l; quartz and amphibole, 

trace. 

Groundmass, 92; plagioclase, 7; pyroxene, 1; opaque 

minerals, xenoliths, trace. 

Groundmass, 80; plagioclase, 6; quartz, 6; K-feldspar, 

5; xenoliths, 2; biotite, l; opaque minerals, 

amphibole, and pyroxene, trace. 

Groundmass, 77; plagioclase, 8, xenoliths, 6; quartz, 

4; K-feldspar 4; biotite, 1; opaque minerals, 

amphibole, and pyroxene, trace. 

Groundmass, 92; plagioclase, 6; biotite, l; xenoliths, 

opaque minerals, quartz, trace. 

Groundmass, 86; plagioclase, 8; K-feldspar, 4; biotite, 

1; xenoliths, l; opaque minerals and pyroxene, trace. 

Groundmass, 58; plagioclase; 26; biotite, 6; amphibole, 

5; pyroxene, 2; quartz, 1; opaque minerals, l 

Groundmass 

character 

Moderately welded 

tuff, mostly 

devitrified. 

Densely welded 

tuff, mostly 

devitrified. 

Densely welded 

tuff, mostly 

devitrified. 

Vesicular densely 

welded tuff, 

mostly devitrified. 

Moderately 

welded tuff, 

mostly devitrified. 

Slightly welded 

tuff, mostly 

devitrified. 

Densely welded 

tuff, mostly 

devitrified. 

Densely welded 

tuff, mostly 

devitrified. 

Moderately welded 

tuff, mostly 

devitrified. 

Chem1cal or modal(-) 

compostuon 

Dacite. 

Dellenite. 

Dellenite, 

rhyodacite. 

Calc-alkali 

rhyolite. 

Dellenite. 

Dellenite. 

Dellenite, 

calc-alkali 

rhyolite. 

Dacite. 

Cd 

O"l 

(') 

0 

z 

~ 

:;tl 

; 

c 

~ 

0 

z 

V'J 

~ 

0 

V'J 

~ 

C') 

~ :;tl 

> 'i:l 

:r: 

>< 
Moum Duuon 

Formation, 

vem and 

alluvial facies 

(1,500+). 

Moum Duuon 

Formation, 

Beaver Member 

(250). 

Moulll Duuon 

Formation, 

Kingston Canyon 

Member (15) 

Mount Dutton· 

Formation, 

Antimony 

Member (20). 

Buckskm 

Breccia ( 170). 

Older basalt 

flows (200). 

Osins Tuff 

(60). 

Dry Hollow 

Formation 

(350). 

Horse Valley 

FormatiOn 

(350+). 

Gray, brown, 

tan, black, 

dark green. 

Pink, gray. 

Pink, pale 

purple. 

Medium brown. 

Pink, tan, 

light gray. 

Black, dark 

to medium 

gray. 

Reddish brown, 

light gray. 

Browmsh red, 

gray, pale 

red. 

Pink, light 

gray. 

Several phases, with average modes in the following 

ranges: groundmass, 38-75; plagioclase, 17-50; 

pyroxene, 0-9; amphibole, 0-7; opaque minerals, 0-4. 

Groundmass, 60; plagioclase," 25; amphibole, II; 

opaque minerals, 2; biotite, I; pyroxene, trace. 

Groundmass, 91; plagioclase, 5; xenoliths, I; opaque 

minerals, I; biotite, I: pyroxene, K-feldspar, 

quartz, and amphibole, trace. 

"Flow" groundmass 

of microlites or glass and 

microlites. 

"Flow" groundmass 

of glass and 

microlites. 

Densely welded 

tuff, mostly 

devitrified. 

Groundmass, 89; plagioclase, 6; K-feldspar, 2; xenoliths, Densely welded 

I; pyroxene, I; opaque minerals, I; quartz, tuff, mostly 

biotite, and amphibole, trace. devitrified. 

Groundmass with clasts of several phases, with average 

modes in the following ranges: groundmass (finely 

holocrystalline or of glass and microlites), 53-59; 

plagioclase, 21-28; amphibole, trace-12; 

K-feldspar, trace-9; opaque minerals, tr<.He-9; biollte, 

trace-7; pyroxene, trace-1; quartz, trace. 

Several phases, with average modes in the following 

ranges: groundmass, 78-89; plagioclase, 0-7; olivine, 

0-ll; pyroxene, 0-6; opaque minerals, 0-2. 

Groundmass, 78; plagioclase, 14; K-feldspar, 4; biotite, 

I; opaque minerals, I; pyroxene, I; xenoliths, 

I; quartz and amphibole, trace. 

Several phases, with average modes in the following 

ranges: groundmass, 69-78; plagioclase, 7-15; 

amphibole, 1-3; K-feldspar, 0-20; pyroxene, 0-10; 

opaque minerals, l-3; biotite, I; quartz, trace. 

Several phases, with average modes in the following 

ranges: groundmass, 78-94; plagioclase, 5-11; 

amphibole, 0-9;'pyroxene, 0-6; opaque minerals, 0-2; 

biotite, trace. ' 

Slightly welded 

to nonwelded 

tuff, mostly 

devitrified. 

"Flow" groundmass 

of microlites 

or glass and 

microlites. 

Densely welded 

tuff, mostly 

devmified. 

"Flow" groundmass 

of glass and 

microlites. 

"Flow" groundmass 

of glass and 

microlites. 

Andesite, 

doreite, 

dacite. 

Dacite. 

Dacite. 

Dacite. 

Grandiorite, 

tonalite, 

monzonite 

porphryry•, 

tonalite 

porphryry•. 

Andesite, 

doreite, basalt•. 

Rhyodacite. 

Rhyodacite, 

dacite. 

Rhyodacite, 

dellenite. 

...., 

~ 

:::0 

...., 

> :::0 

..-:: 

~ 

0 

t'"" 

Q 

z 

rs 

V'J 

...., 

:::0 

>- ...., 

(3 

:::0 

>-

""0 

l: 

_..-:: 

c::: 

...., 

> l: 

t:7j 

-J 
TABLE I.-Summary of petrologzc and stratzgraphzc characterzstzcs of volcanic rocks exposed in the southwestern Hzgh Plateaus and adjacent 

Great Basin-Continued 

Name (Maximum 

thickness 

m metres) 

Mount Belknap 

Rhyolite 

(350). 

joe Lott Tuff 

(35). 

Younger basalt 

flows (35). 

Dommant 

color 

White, black. 

White, tan. 

Black, dark 

to medium 

gray. 

Average mode (percent) 

Several phases with average modes in the following 

ranges: groundmass, 97; plagioclase, 1-3; K-feldspar, 

trace-1; quartz, trace-1; biotite, pyroxene, and 

amphibole, trace. 

Groundmass, 94; xenoliths, 5; quartz, plagioclase, and 

opaque minerals, trace. 

Several phases with average modes in the following 

ranges: groundmass, 69-78; plagioclase, 9-23; olivine, 

0-11; pyroxene, 2-6; opaque minerals, 0-4; 

amphibole, trace. 

Groundmass 

character 

Glassy "flow" 

groundmass, 

partly 

devitrified. 

Poorly welded 

to nonwelded 

tuff, mostly 

devitrified. 

"Flow" groundmass 

ot mtcrohtes 

or glass and 

microlites. 

Chemical or modal(•) 

composition 

Alkali 

rhyolite. 

Calc-alkali 

rhyolite. 

Mostly alkali 

basalt. 

~ 

00 

n 

0 

z 

...., 

~ 

; 

c::: 

...., 

0 

z 

IJ) 

...., 

0 

IJ) 

...., 

s 

(;=) 

?; 

"t:j 

::r:: 

>< 
TERTIARY VOLCANIC STRATIGRAPHY, UTAH B9 

ceo us(?) or Paleocene(?) if they are correlative with the Canaan Peak, Pine 

Hollow, and Wasatch Formations (Bowers, 1972) of the extreme southeastern High Plateaus (Anderson and Rowley, 1975). 

The upper part of the white part of the Claron Formation, tog~ther 

with the featheredges of several overlying named units (Needles Range, 

Isom, Leach Canyon, and Mount Dutton), was designated Brian Head 

Formation by Gregory (1945, 1949, 1950, 1951). Primarily for this reason 

(Threet, 1952; Anderson, 1971; Anderson and Rowley, 1975) the name 

Brian Head Formation is abandoned. 

LOCAL UNIT 

At scattered places in the southwestern High Plateaus and adjacent 

Great Basin, the Needles Range Formation is separated from the Claron 

Formation by an unnamed local unit composed of volcanic rocks and 

lesser interbedded sedimentary rocks that rarely total more than 100m in 

thickness. A single K-Ar determination on one of the volcanic units is 31.1 

m.y. (Fleck and others, 1975). We mapped these deposits as local volcanic 

and sedimentary rock of Oligocene age. 

NEEDLES RANGE FORMATION 

The Needles Range Formation consists of at least two mostly pink, 

pale-purple, or light-gray, silicic crystal-rich ash-flow tuff cooling units 

and local interbedded thin sedimentary or volcanic strata. It was defined 

by Mackin ( 1960) at a type locality in the east-central part of the Mountain 

Home Range (formerly called the Needle Range) of western Utah. The 

formation has been found over at least 50,000 km2 of Utah and Nevada 

(Mackin, 1963; Cook, 1965 ); its source is presumed to be in the Great 

Basin. We have mapped the formation through much of the southwestern High Plateaus and adjacent Great Basin. The Needles Range 

Formation is Oligocene, according to numerous K-Ar age determinations that clusteraround29 m.y. (Armstrong, 1970; Fleck and others, 

1975 ). 

Mackin (1960) defined two members of the Needles Range Formation: 

the lower member, the Wah Wah Springs Tuff Member, and the upper 

member, the Minersville Tuff Member. Recently Best and others ( 1973) 

proposed that Minersville be abandoned; we believe that the reasons given 

do not warrant such action. We therefore retain Mackin's names. 

MIDDLE TERTIARY SEQUENCE 

ROCKS OF THE EASTERN GREAT BASIN VOLCANIC PROVINCE ADJACENT 

TO THE HIGH PLATEAUS 

ISOM FORMATION 

Mackin (1960) defined the Isom Formation from exposures of silicic 

crystal-poor ash-flow tuff characterized by secondary plastic flowage and 

of true lava flows in the Iron Springs district. There, where the Isom 
SEQUENCE [ AGE 

MIDDLE 

TERTIARY 

Holocene 

Q) Q) 

c c 

Q) Q) 

u u 

B~ .!!! ll.. Q) 

a:: 

Miocene 

BLACK MOUNTAINS 

SOUTHWEST 

Younger 

basalt flows 

Sevier River 

Formation 

NORTH 

Younger 

basalt flows 

Sevier River 

Formation 

Mount Belknap 

Rhyolite 

Horse Valley 

Formation 

2; ~ .... c g Bauers 7 

~ c BauersTuff .g~ Tuff <0~ .. ·.· 

::J ~ Member g ~ g I Mbr 

0 c uuo <0 ~ 

u 

0 

-a 

~ 

Swett Tuff 

Member 

Volcanic 

breccia 

member 

SOUTHERN 

TUSHAR 

MOUNTAINS 

Younger 

basalt flows 

Sevier River 

Formation 

Mount Belknap 

Rhyolite 

Older basalt flows 

Dry Hollow 

Formation 

E_ 

Osiris 

Tuff 

~VI 

~~ :Jt: u._ 

C 

E en 

~ B·~ ...., :J ...., m C- ::J'+-

:Jitj o ... 

~- ::~ ::l_ 

0 

member 

Flowvolcanic 

breccia 

member 

~ > c :J 

:J = .2 ~ 

MARKAGUNT 

PLATEAU 

Younger 

basalt flows 

Older 

basalt flows 

Volcanic 

breccia 

member 

SEVIER, AWAPA, 

AND FISH LAKE 

PLATEAUS 

Younger 

basalt flows 

Mount Belknap 

Rhyolite 

Older 

basalt flows 

breccia 

member 

Antimony Tuff Mbr\ 

O:i 

0 -

(") 

0 

z 

..., 

::0 

; 

c:: 

..., 

0 

z 

en 

..., 

0 

en 

..., 

..., 

~ 

0 

~ '"d 

::r: 

><:: 
I

. .. ,_, ____ 

I! !YI.._,._.,, .. .._..._. .... ..., •• I Ill V VII,.,C:IIII'-' 

Group/ (alluvial facies) ~"V"Y breccia Tuff Condor Canyon Fm F'TtOr"Y"\hor Mbr 

Bear Valley "' Q) >c Formation ·u .!!! 0 "' Q) ·:; ~ ro ·~ ·u ::J ..... > ro Volcanic ro a. E Table Butte -ro c .... E .... Q) ro ._ Miocene l::l u.. -ro Tuff Volcanic ~ 2. Flow- Q) 0 breccia 0 c breccia E cau.. member ·:; .... 0 Member c volcanic ::J l'J > member u.. 0 

ro c c ·;::; breccia ~ MIDDLE I 1: ro 0 ro u member 

Narrows t E c E TERTIARY .s: ::J 0 .s: 0 u.. 

::J u Tuff 0 ro u.. ~>E c QlCU.. d Q) Member ..... c ..J ro 0 _J c ..... ::J g u ..... ..... 0 ::J ~ Hole-In-The- ~ ::J 0 !;1:: 0 ..... c Wall Tuff Mbr c ..... Miocene 0 ..... ::J 

and (or) E s: ·;::; c 0 oro ::J E Baldhills E ··'7 0 Kingston ~ :;o 

Oligo- "'E u.. Tuff ~ 

~ u.. -< -0 Tuff E E Blue Canyon cene u.. Member Mbr Meadows Tuff < ~ r ~ Ss Mbr s Tuff 

Mbr (; 

>- Needles Range ~ Formation ("; 

Oligocene ':F. 

..... c Upper white c :;d LOWER I ·;::; 

0 0 Upper white >-

part ·;::; ..... TERTIARY ro ro part ....... E E :-; 0 0 :::0 u.. u.. > 

I c Lower red c Lower red c Lower red Eocene :s e part e part e part ro ro ro -< u u u 

c: 

..... 

;...: 

:::c: 

FIGURE 2.-Correlation chart of the Cenozoic stratigraphy of the southern High Plateaus and adjacent Great Basin, Utah. The absence of strata 

is shown by stippled pattern, but local unconformities arc not shown. Abc;ence of information is shown by cross-hatched pattern. ~ 

~ 
B12 CONTRIBUTIONS TO STRATIGRAPHY 

Formation is about 150m thick, he recognized three members but named 

only the upper two, the mostly medium-brown or gray Baldhills Tuff 

Member and the pale-red Hole-In-The-Wall Tuff Member. The Isom 

Formation is exposed through much of southwestern Utah (Mackin, 

1960); we mapped it in most of the Black Mountains and much of the 

northern Markagunt Plateau. We have redefined the Baldhills Member to 

include Mackin's lower unnamed member because locally his lower 

member includes ash-flow tuff that is indistinguishable from some ashflow tuff in his Baldhills Member. The Baldhills Member consists of at 

least six cooling units, but the Hole-In-The-Wall Member is a single 

cooling unit. We also have defined a new member, the Blue Meadows Tu££ 

Member, which is a single pale-red or pale-purplish ash-flow tuff cooling 

unit cropping out through the northern Markagunt Plateau, where it 

underlies the Baldhills Member. The type locality of the Blue Meadows 

Tu££ Member is in the northern Markagunt Plateau (SEJA NEJA sec. 31, T. 

33 S., R. 6 W.; fig. 1, loc. 1) about 11 km northwest of Panguitch (Anderson and Rowley, 1975). The source of the Isom Formation is probably the 

Great Basin of southwestern Utah. On the basis of numerous K-Ar dates 

that cluster around 25 m.y. (Armstrong, 1970; Fleck and others, 1975), the 

Isom Formation is considered to be latest Oligocene or earliest Miocene. 

QUICHAPA GROUP 

Mackin (1960) designated as the Quichapa Formation four distinctive 

silicic ash-flow tuffs that occur together over much of southwestern Utah 

and southeastern Nevada; they were named the Leach Canyon, Swett, 

Bauers, and Harmony Hills Tu££ Members from exposures in and near the 

Iron Springs district. As a result of his work in Nevada, Cook (1965) 

elevated Leach Canyon and Harmony Hills to formations and defined 

the new name Condor Canyon Formation to embrace the Swett and 

Bauers Tuff Members; Quichapa was not used. Williams (1967) carried 

out regional stratigraphic studies of these same tuffs; he used Cook's terminology except that he reinstated Quichapa by elevating it to group 

status. We follow Williams' terminology. Williams suggested that the 

source of the tuffs of Leach Canyon and Condor Canyon Formations is 

the Caliente, Nev., area; the source of the Harmony Hills Tu££ is probably 

the Bull Valley Mountains (Blank, 1959). 

LEACH CANYON FORMATION 

The Leach Canyon Member of Mackin ( 1960) consists of white, salmon, 

or rarely medium-brown, slightly to moderately welded ash-flow tuff. 

The unit was elevated to formation rank by Cook (1965). Williams (1967) 

divided the Leach Canyon into a Narrows Tuff Member and the overlying less-welded fragment-rich and petrographically di££erent Table 

Butte Tuff Member. The type localities he proposed are (1) for the 

Narrows Member: the White River Narrows (fig. 1, loc. 2), T. IS., R. 62 E. 
TERTIARY VOLCANIC STRATIGRAPHY, UTAH Bl3 

(unsurveyed), Lincoln County, Nev., and (2) for the Table Butte Member: 

Table Butte (NE~ NE~ sec. 5, T. 34 S., R. 14 W.; fig. 1, loc. 3) in the 

Escalante Desert of Utah. We accept these nom.enclature additions. 

Mackin, Cook, and Williams mapped th'e Leach Canyon Formation 

over large areas of Utah and Nevada. Our detailed mapping carries the 

formation as far east as the Black Mountains and several scattered 

locations in the western Markagunt Plateau. The Narrows Member 

consists of one or two cooling units, and the more poorly exposed Table 

Butte Member apparently consists of one cooling unit. The Narrows Tuff 

Member has an age of about 24 m.y. (Armstrong, 1970; Fleck and others, 

1975). 

CONDOR CANYON FORMATION 

The Condor Canyon Formation was defined by Cook ( 1965) from exposures at Condor Canyon, T. 1 S., R. 68 E. (unsurveyed), Lincoln County, 

Nev. It consists of the Swett and Bauers Tuff Members of Mackin (1960). 

Both are densely welded crystal-poor ash-flow tuff compound cooling 

units; the Swett Member is medium brown, and the Bauers Member, wellzoned, is mostly pale red, pale purple, and light gray. Williams (1960, 

1967) traced both members over parts of Utah and Nevada. They are 

exposed at scattered places in the Black Mountains and western Markagunt Plateau. Numerous K-Ar age determinations (Armstrong, 1970; 

Fleck and others, 1975) indicate that the Swett Member is about 23 m.y. 

old and the Bauers Member is about 22 m.y. old, both early Miocene. 

HARMONY HILLS TUFF 

The Harmony Hills Member (Mackin, 1960) is a pink or tan crystal-rich 

ash-flow tuff cooling unit; it was elevated to formation status by Cook 

(1965 ). It is similar in phenocryst composition and general appearance to 

the tuffs of the Needles Range Formation. Williams (1960, 1967) mapped 

it in Utah and Nevada. It apparently never was deposited in the Black 

Mountains and High Pia tea us; its northeasternmost known occurrence is 

in the Red Hills. Armstrong (1970) published four K-Ar age determina· 

tions of about 20 to 21 m.y., or middle Miocene. 

ROCKS OF THE MARYSVALE VOLCANIC PROVINCE 

MOUNT DUTTON FORMATION 

The Mount Dutton Formation, as defined by Anderson and Rowley 

(1975), contains most of the rock on the southern flank of the Marysvale 

volcanic pile. Like the other volcanic units described below, the source of 

the Mount Dutton Formation was within the Marysvale pile. To the west 

it intertongues with many units of the Great Basin volcanic province. The 

type section (NE~ NE~ sec. 9 to center sec. 15, T. 32 S., R. 4 W.; fig. 1, loc. 

4), about 950 m thick, is at Mount Dutton in the southern Sevier Plateau 

(Anderson and Rowley, 1975). Near the center of the pile the main rock 
B14 CONTRIBUTIONS TO STRATIGRAPHY 

types are andesitic lava flows and autoclastic flow breccia, with lesser 

volcanic mudflow breccia; this material is mapped separately as the vent 

facies of the Mount Dutton Formation, following the concepts of Parsons 

(1965, 1969) and Smedes and Prostka (1973). Rocks of the vent facies are 

confined mostly to the Tushar Mountains; there the base of the section is 

not exposed but the rocks must be over 1,500 m thick. Anderson and 

Rowley (1975) have designated and described a reference section (SW~ 

SE~ sec. 31, T. 29 S., R. 3 W. toNE~ NE~ sec. 1, T. 30 S., R. 4 W.) for the 

vent facies about 1.5 km northwest of Junction. 

On ·the flanks of the pile the main rock type is volcanic mudflow 

breccia, with minor autoclastic flow breccia and lava flows; this is 

mapped as the laterally correlative alluvial facies of the Mount Dutton 

Formation, again following the concepts of Parsons and Smedes and 

Prostka. Rocks of the alluvial facies occur in the Awapa Plateau, Fish 

Lake Plateau, Sevier Plateau, Markagunt Plateau, and Black Mountains, 

where they attain thicknesses of about 1,000 m; they thin and pinch out 

away from the center. The features of the alluvial facies may be examined 

at the type section of the Mount Dutton Formation (Anderson and 

Rowley, 1974) or at a reference section (S~ sec. 17, T. 30 S., R. 2~ W.) east of 

Kingston, designated and described by Anderson ~nd Rowley (1975). 

Distinctive beds within the thick vent and alluvial facies are formally 

named. One such unit, defined by Anderson and Rowley (1975) as the 

Beaver Member of the Mount Dutton Formation, occurs near the 

presumed base of the vent facies. This pink or gray dacitic porphyry crops 

out over about 50 km2 of the northeastern Black Mountains and southwestern Tushar Mountains; the type section (SW~ sec. 12, T. 30 S., R. 7 

W.) is about 8 km south of Beaver (fig. 1, loc. 5). At most places the 

member is a lava flow and (or) ash-flow tuff about 100m thick, but near its 

western and southern outcrop limit, where the base is not exposed, it is 

more than 250m thick and may be intrusive. 

An informal sandstone member of the Mount Dutton Formation occurs 

at the top of the vent facies. This member crops out over 40 km2 or less in 

the southern Tushar Mountains, and it attains a thickness of about 70 m 

(Anderson and Rowley, 1975). 

Two silicic ash-flow members were defined within alluvial facies rocks 

in the southern Sevier Plateau. The Kingston Canyon Tuff Member, 

made up of two cooling units of pink or pale-purple crystal-poor ash-flow 

tuff, occurs near the base of the alluvial facies. We have mapped it over 

more than I ,300 km2 of the Sevier Plateau; its type section (NW~ NE~ sec. 

16, T. 30 S., R. 2~ W.) is in Kingston Canyon east of Kingston (fig. I, loc. 

6). The other new member is the Antimony Tuff Member of the Mount 

Dutton Formation, which occurs higher in the alluvial facies in the Kingston Canyon area and has its type section (center sec. 29, T. 30 S., R. 2 W.) 

northeast of Antimony (fig. 1, loc. 7). It consists of two cooling units of 

medium-brown, densely welded crystal-poor ash-flow tuff. 
TERTIARY VOLCANIC STRATIGRAPHY, UTAH B15 

The Mount Dutton Formation is latest Oligocene and early Miocene, 

according to K-Ar age determinations by Fleck, Anderson, and Rowley 

(1975). Lava flows near the base of the formation have been dated at 25.1 

and 26.0 m. y ., whereas ones from high in the formation have been dated at 

20.7 and 22.9 m.y. The age of the Beaver Member and of the Kingston 

Canyon Member has been determined to be about 25 m.y. 

BUCKSKIN BRECCIA 

The Buckskin Breccia, defined by Anderson and Rowley (1975), 

consists of volcanic mudflow breccia, probable autoclastic flow breccia, 

and (or) ash-flow tuff. All beds are characterized by the presence of abundant clasts of a distinctive local porphyry intrusion (Spry intrusion of 

Anderson and Rowley, 1975), which we have mapped about 25 km north 

of Panguitch; the source of the Buckskin Breccia is probably the vicinity 

of the Spry intrusion. The type section (SW~ NE~ sec. 26, T. 32 S., R. 6 W.) 

is just east of Buckskin Valley in the northern Markagunt Plateau (fig. 1, 

loc. 8); the unit is exposed through much of the northern Markagunt 

Plateau and part of the southern Sevier Plateau. The formation is most 

likely early Miocene because it is underlain by the Isom Formation of 

Oligocene or Miocene age and overlain by the Bear Valley Formation of 

Miocene age. 

BEAR VALLEY FORMATION 

The Bear Valley Formation was defined by Anderson ( 1971) from a type 

section (from SW~NW~ sec. 5, T. 33 S., R. 5 W. to NE~SE~ sec. 32, T. 32 

S., R. 5 W.; fig. 1, loc. 9) in the northern Markagunt Plateau; the formation is primarily a green, yellow, or gray sandstone exposed through the 

northern Markagunt Plateau, northern Red Hills, and part of the Black 

Mountains. The sandstone, a volcanic arenite largely of eolian origin, 

attains a thickness of at least 330 m; locally it contains thin intercalated 

beds of volcanic mudflow breccia, conglomerate, lava flow, and air-fall 

and ash-flow tuff. Potassium-argon ages of about 24 m.y. have been 

determined for several interbedded volcanic units within the formation 

(Fleck and others, 1975 ). 

OLDER BASALT FLOWS 

From his work in the Marysvale area, Callaghan ( 1939) recognized 

basaltic lava flows at two stratigraphic levels. The older sequence was 

later included within the Dry Hollow Formation (Callaghan and Parker, 

1962b). Our mapping confirms the presence of an old series of basaltic 

rocks. In the Sevier Plateau, Markagunt Plateau, and Tushar Mountains 

these black to medium-gray rocks are older than the Mount Belknap 

Rhyolite and mostly younger than the Osiris Tuff; some flows are characterized by olivine, pyroxene and (or) plagioclase phenocrysts. In the 

Awapa, Fish Lake, and Aquarius Plateaus, Williams and Hackman 

( 1971) mapped basaltic andesite that is mostly older than the Osiris Tuff; 
B16 CONTRIBUTIONS TO STRATIGRAPHY 

these dark porphyritic lava flows are characterized by plagioclase phenocrysts up to 2 em in length. All these basalts are included in the older 

basalt flows (Anderson and Row ley, 197 5 ). Although some of the rocks are 

classified petrographically as olivine basalt, the few chemical analyses so 

far determined are andesite and doreite, according to the chemical classification by Nockolds (1954). We have mapped older basalt flows at 

scattered places in the southern Tushar Mountains and southern Sevier 

Plateau; thicknesses of at least 150m have been recorded. Samples from 

the unit have received K-Ar age determinations of about 22 m. y. (Fleck 

and others, 1975 ). 

OSIRIS TUFF 

The Osiris Tuff is a reddish-brown or light-gray, densely welded, silicic 

compound ash-flow tuff cooling unit exposed at numerous scattered 

places through the High Plateaus. It displays conspicuous features of 

secondary plastic flow and is strongly zoned. Informally designated the 

tuff of Osiris by Williams and Hackman (1971), this unit was named 

Osiris Tuff by Anderson and Rowley (1975); the type section (SW~ NW~ 

sec. 2, T. 32 S., R. 2 W.; fig. 1, loc. 10) is near the abandoned community of 

Osiris in the southeastern High Plateaus. The unit has been dated at 

about 22 m.y. by Fleck, Anderson, and Rowley (1975). 

DRY HOLLOW FORMATION 

The Dry Hollow Latite (Callaghan, 1939) consists of mostly brownishred and gray porphyritic lava flows exposed through most of the Tushar 

Mountains and in several places in the southern Sevier Plateau. 

Callaghan and Parker ( 1962b) redefined the Dry Hollow Formation to 

include ash-flow tuff and basaltic lava flows. In our mapping, mostly 

south of the areas examined by Callaghan and Parker, we are able to map 

the ash-flow tuff and basaltic andesite lava flows as separate, named units, 

specifically the Osiris Tuff, Needles Range Formation and older basalt 

flows of this report. Thus, for our purposes we return to the original 

definition (Callaghan, 1939) for the Dry Hollow Formation. The age of 

the Dry Hollow Formation has been determined by K-Ar methods to be 

about 21.7 m.y. (Fleck and others, 1975). 

HORSE VALLEY FORMATION 

The northwestern Black Mountains are underlain by a thick sequence 

of pink or light-gray, crystal-poor silicic lava flows, intrusive plugs, and 

related volcanic mudflow breccia. These were defined by Anderson and 

Rowley (1975) as the Horse Valley Formation. The type section (sees. 20, 

21, T. 31 S., R. 12 W.; fig. 1, loc. 11) is 10 km west of Horse Valley, which is 

about 21 km southwest of Minersville. There an incomplete section of 

the unit is more than 350m thick; the base is faulted out. Fleck, Anderson, 

and Rowley (1975) give K-Ar ages of 19.0, 20.6, and 21.9 m.y. for the formation. 
TERTIARY VOLCANIC STRATIGRAPHY, UTAH B17 

MOUNT BELKNAP RHYOLITE 

The Mount Belknap Rhyolite, defined by Callaghan (1939), consists of 

white, black, or reddish-brown rhyolite lava flows and interbedded ashflow tuffs. Callaghan, Kerr, and their coworkers mapped the Mount Belknap in the Tushar Mountains and recorded maximum thicknesses of 

1,400 and 1,700 m. Anderson and Rowley (1975) have mapped scattered 

thin patches of rhyolite flows similar to the Mount Belknap in the 

northern Black Mountains and southern Sevier Plateau; these flows are 

correlated tentatively with the Mount Belknap but may be younger than 

the Mount Belknap and, therefore, may belong to the upper Tertiary and 

Quaternary sequence. The Mount Belknap is the uppermost formation in 

the Marysvale pile for which radiometric age determinations were made 

(Bassett and others, 1963); these ages cluster around 20 m.y., middle Miocene. Kerr (1963, 1969), however, apparently favors an age of about 18 

m.y., based upon a reinterpretation of the data. 

JOE LOTT TUFF 

The Joe Lott Tuff (Callaghan, 1939) comprises several cooling units of 

pink, white, and tan, slightly welded, very crystal-poor, pumice-rich 

rhyolite ash-flow tuff; it is the youngest formation of the Marysvale pile. 

Callaghan recorded thicknesses of nearly 250m for the unit. The Joe Lott 

Tuff is exposed through much of the Tushar Mountains, southern Pavant 

Range, and central Sevier Plateau. Although the tuff has not been dated 

by radiometric methods, similarities in outcrop distribution and chemical composition argue strongly for a genetic tie between it and the Mount 

Belknap Rhyolite, as noted by Callaghan ( 1939). 

UPPER TERTIARY AND QUATERNARY SEQUENCE 

SEVIER RIVER FORMATION 

The Sevier River Formation (Callaghan, 1938) consists of white, gray, 

or pink, poorly to moderately consolidated, fluvial and lesser lacustrine 

sedimentary rocks deposited in low downfaulted areas throughout much 

of the High Plateaus and adjacent Great Basin. Although exposures of the 

Sevier River Formation rarely exceed a few hundred metres, most of the 

downfaulted valleys in the High Plateaus and nearby Great Basin may be 

in large part filled with Sevier River rocks; if so, the formation may be 

many hundreds of metres thick. 

CalJaghan (1939) designated the Sevier River Formation as late Pliocene or early Pleistocene on the basis of diatoms and freshwater gastropods. Corroboration that some parts of the formation are as young as 

Pleistocene comes from K-Ar ages (Condie and Barsky, 1972; Hoover, 

1974) ranging from 855,000 to 987,000 years for basalt flows interbedded 

with the Sevier River Formation just west of the Pavant Range. However, 

a K-Ar age determination of 12.6 m.y. (Damon, 1969) for a younger basalt 
Bl8 CONTRIBUTIONS TO STRATIGRAPHY 

flow (see below) that overlies a section of the Sevier River Formation in 

the Sevier Plateau demonstrates that at least part of the unit is Miocene as 

well. We believe that the Sevier River Formation is Miocene, Pliocene, 

and Pleistocene. 

Gregory (1945, 1950) named scattered older gravel deposits in the 

southern High Plateaus as the Parunuweap Formation. These deposits 

are correlative with the Sevier River Formation, as Gregory apparently 

realized in some of his other publications (Gregory, 1944, 1949, 1951). We 

propose that Parunuweap Formation be abandoned in favor of the Sevier 

River Formation. 

YOUNGER BASALT FLOWS 

Basalt lava flow caprocks have been mapped through the Basin and 

Range and parts of the Colorado Plateau. Callaghan ( 1939) recognized 

those in the Marysvale area as being distinct and younger fro"m similarappearing lava flows that predate the Mount Belknap Rhyolite. We 

mapped scattered lava flows of olivine basalt in the Sevier Plateau, 

Markagunt Plateau, Tushar Mountains, and Black Mountains, and we 

have designated them as younger basalt flows (Anderson and Rowley, 

1975). Olivine basalt flows and related cinder-and-lava cones are widespread in the Awapa and Aquarius Plateaus and probably range from 

early to late Pleistocene in age. The younger basalt flows overlie and 

interfinger with the Sevier River Formation. 

The oldest known flow of this unit in the map area occurs in the 

southern Sevier Plateau; Damon (1969, p. 47) determined a K-Ar age 

of 12.6 m.y. for it. Numerous other K-Ar ages of basalts in and near 

our map area range from 31,000 years to 1.2 m.y. (Condie and Barsky, 

1972; Hoover, 1974; Fleck and others, 1975); some basalt lava flows on 

the Markagunt Plateau (Wilson and Thomas, 1964) have not been revegetated and are probably Holocene. The Sevier River Formation and 

younger basalt flows are believed to be associated with the Miocene 

through Holocene episode of block faulting of the southwestern High 

Plateaus and eastern Great Basin. 

REFERENCES CITED 

Anderson, ]. ]., 1965, Geology of northern Markagunt Plateau, Utah: Austin, Texas 

Univ. Ph. D. thesis, 194 p. 

__ 1971, Geology of the southwestern High Plateaus of Utah-Bear Valley Formation, 

an Oligocene-Miocene volcanic arenite: Geol. Soc. America Bull., v. 82, no. 5, p. 

1179-1205. 

Anderson, J. ]., and Rowley, P. D., 1975, Cenozoic stratigraphy of southwestern High 

Plateaus of Utah, m Anderson, ]. ]., Rowley, P. D., Fleck, R. J., and Nairn, A. 

E. M; Cenozoic geology of southwestern High Plateaus at Utah: Geol. Soc. America 

Spec. Paper 160, p. l-52. 

Armstrong, R. L., 1970, Geochronology of Tertiary igneous rocks, eastern Basin and 

Range Province, western Utah, eastern Nevada, and vicinity, U.S.A.: Geochim. et 

Cosmochim. Acta, v. 34, no. 2, p. 203-232. 
TERTIARY VOLCANIC STRATIGRAPHY, UTAH Bl9 

Basset!, W. A., Kerr, P. F., Schaeffer, 0. A., and Stoenner, R. W., 1963, Potassiumargon daring of the late Tertiary volcanic rocks and mineralization of Marysvale, 

Utah: Geol. Soc. America Bull., v. 74, no. 2, p. 213-220. 

Best, M. G., Shuey, R. T., Caskey, C. F., and Grant, S. K., 1973, Stratigraphic relations 

of members of the Needles Range Formation at type localities in southwestern Utah: 

Gcol. Soc. America Bull., v. 84, no. 10, p. 3269-3278. 

Blank, H. R., Jr., 1959, Geology of the Bull Valley district, Washington County, Utah: 

Seattle, Washington Univ. Ph. D. thesis, 177 p. 

Bowers, W. E., 1972, The Canaan Peak, Pine Hollow, and Wasatch Formations in the 

Table Cliff region, Garfield County, Utah: U.S. Geol. Survey Bull. 133J.:..B, 39 p. 

Callaghan, Eugene, 1938, Preliminary report on the alunite deposits of the Marysvale 

region, Utah: U.S. Geol. Survey Bull. 886-D, p. 91-134. 

___ 1939, Volcanic sequence in the Marysvale region in southwest-central Utah: Am. 

Geophys. Union Trans., 20th Ann. Mtg., Washington, D. C., 1939, pt. 3, p. 438-452. 

___ 1973, Mineral resources potential of Piute County, Utah and adjoining area: Utah 

Geol. Mineral. Survey Bull. 102, 135 p. 

Callaghan, Eugene, and Parker, R. L., 196Ia, Geology of the Monroe quadrangle, Utah: 

U.S. Geol. Survey Geol. Quad. Map GQ-155. 

___ l96lb, Geologic map of part of the Beaver quadrangle, Utah: U.S. Geol. Survey 

Mineral Inv. Field Studies Map MF-202. 

___ l962a, Geology of the Delano Peak quadrangle, Utah: U.S. Geol. Survey Geol. 

Quad. Map GQ-153. 

___ l962b, Geology of the Sevier quadrangle, Utah: U.S. Geol. Survey Geol. Quad. 

Map GQ-156. 

Condie, K. C., and Barsky, C. K., 1972, Origin of Quaternary basalts from the Black 

Rock Desert region, Utah: Geol. Soc. America Bull., v. 83, no. 2, p. 333-352. 

Cook, E. F., 1965, Stratigraphy of Tertiary volcanic rocks in eastern Nevada: Nevada 

Bur. Mines Rept. 11, 61 p. 

Damon, P. E., 1969, Correlation and chronology of ore deposits and volcanic rocksU.S. Atomic Energy Comm. Contract AT(ll-1) -689, Ann. Prog. Rept. C00-689-120: 

Tucson, Ariz., Arizona Univ., Geochronology Dept., 90 p. and appendices. 

Dolgoff, Abraham, 1963, Volcanic stratigraphy of the Pahranagat area, Lincoln County, 

southeastern Nevada: Geol. Soc. America Bull., v. 74, p. 875-900. 

Fleck, R. J., Anderson, J. J., and Rowley, P. D., 1975, Chronology of mid-Tertiary 

volcanism in High Plateaus region of Utah, in Anderson, J. J., Rowley, P. D., 

Fleck, R. J., and Nairn, A. E. M., Cenozoic geology of southwestern High Plateaus 

of Utah: Geol. Soc. America Spec. Paper 160, p. 53-62. 

Gregory, H. E., 1944, Geologic observations in the upper Sevier River Valley, Utah: 

Am. Jour. Sci., v. 242, no. II, p. 577-606. 

___ 1945, Post-Wasatch Tertiary formations in southwestern Utah: Jour. Geology, 

v. 53, no. 2, p. 105-115. 

___ 1949, Geologic and geographic reconnaissance of eastern Markagunt Plateau, Utah: 

Geol. Soc. America Bull., v. 60, no. 6, p. 969-998. 

___ 1950, Geology of eastern Iron County, Utah: Utah Geol. and Mineralog. Survey 

Bull. 37, 153 p. 

___ 1951, The geology and geography of the Paunsaugunt region, Utah: U.S. Geol. 

Survey Prof. Paper 226, 116 p. 

Hackman, R. J., and Wyant, D. G., 1973, Geology, structure, and uranium deposits 

of the Escalante quadrangle, Utah and Arizona: U.S. Geol. Survey Misc. Geol. Inv. 

Map I-744. 

Harland, W. B., Smith, A. G., and Wilcock, B., eds., 1964, The Phanerozoic time-scaleA symposium dedicated to Professor Arthur Holmes: Geol. Soc. London Quart. 

Jour., v. 120, supp., p. 260-262. 
B20 CONTRIBUTIONS TO STRATIGRAPHY 

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