Sawtooth Mountain, 12,147 ft

Mount Ouray,

13,971'

Antora Peak, 

13,365'

(west rim, 

Bonanza caldera)

Razor Creek Dome

11,530'

NORTHEAST

SOUTHWEST

Cochetopa Dome, 11,132'

Cochetopa Creek

Agency Peak, 11,179'

 San Luis caldera complex

(high peaks are postcaldera lava flows)

La Garita Mountains

(resurgent uplift within caldera)

Mesa Mountain, 12,944'

(on east rim, La Garita caldera)

Los Pinos Creek

W Pass Creek

NE-trending lobe of Nelson Mountain Tuff, erupted from within San Luis caldera complex

North Pass Cochetopa Hills (Continental Divide) Green Mountain

Panoramic view of Cochetopa Park caldera, looking east and south from summit of Sawtooth Mountain. Sawtooth Mountain, Razor Creek Dome, Green Mountain, Cochetopa Hills, and Agency Peak are surviving erosional remnants of the topographic rim of Cochetopa Park caldera. Nelson 

Mountain Tuff, a large ignimbrite erupted at 26.90 Ma from eruptive vents within the San Luis caldera complex, flowed to northeast along a pre-existing graben (partly defined by the drainage of Los Pinos Creek), into Cochetopa Park caldera as it subsided concurrently with this eruption. Cochetopa 

Dome is a postcaldera sequence of rhyolitic lava flows erupted from within the Cochetopa Park caldera after it subsided. West Pass and Cochetopa Creeks have eroded soft caldera-filling tuffaceous sedimentary rocks, exhuming the Oligocene caldera morphology. In distance to south is northern segment 

of La Garita caldera, source of the Fish Canyon Tuff at 28.02 Ma; the north rim of this 75-km-long subsidence structure is the Continental Divide along the Cochetopa Hills, which form a ridge between Cochetopa Park and La Garita calderas. Digital photograph by Andreas Sbisa, July 2009.

5

5

5

5 5

5

5 5

5

5

5

5

5

5

5

5

5 5

5

5

5

5

5

5

5

5

5

5

5

5

5

5

5

5

5 5

5

5 5

5

5

5

5

15

25

25

20 60

20

10

15 20

20

30

10

15

30 30

15 40

25 15 35

35

25 15

25

20 15

70

30

40 15

10

50

20

45 10 65

10

25

60

10 35 10

30

20

10 20

10 25

50

15

60 25 15 20 20

50 25

45 35 20

50

80 80

70 50

60

75

50

20 20

50

30

10 20

70 30

40

25 20 45

30

85

15

80

30

50

45 40 25 25

65

20

60

60

20 10

65 15 20 40 50 45

75

20 20 50

45

15

40

45 30

35

45

20 50 50

45

60

20 20

40 75

60

40

65 20 70

80

75

10

15 35

10

10 10

60 35 10 40

25 20

60 60 80 10 45

25

40

50 75 25 40

25

50

15 20 30

10

55 15 55 30

60 10 35

15 25

10 50

35

15 30 60

75 20

10 55

30 20 40 25 30 15 60 20 60 25 25 60 25

35

10

35 30 15

15 25

15

15

10

20

45 10 35

25

20

15

10

50

10 20 25

60 25

50 20

25 20 20

15 10

20

25

20

60

5

25

25

50

55

55

10

20

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25 30

20

40

80

70

50

35 10 75

65

10

25

25

65 25

40

35

45

45

30

25

10

381

±60

33.18

±.06

33.98

±0.08

34.61

±16h

32.00+0.09b

32.27±

0.05

32.29±0.05

29.85±0.04

29.63±0.06

29.79±0.05 27.14

±0.05

27.08±0.05

33.19

±0.05

34.10±0.05

30.08

±0.09

29.83

±0.05

32.26

±0.07

27.07±0.06

32.40±0.05

32.55

±0.05

32.48±0.05

32.14±0.05

27.48

±0.05

32.10

±0.30

32.44

±0.08 26.90±0.04

33.17±0.06

26.81

±0.04

26.99±0.14

26.88±0.05

26.88±0.06

27.59±0.05

26.83±0.05

32.15

±0.10

27.53±0.04,

27.60±0.06

32.15

±0.06

32.22

±0.05 27.35

±0.05

27.35

±0.05

29.98±

31gm 27.44

±0.05 27.41

±0.04

26.93±0.08

32.49

±0.07

27.57±0.21

32.15

±0.05

33.60±

0.09b

34.28±0.18h

33.67±

0.19b

34.39±0.23h

34.42

±0.21h

32.07±0.17b

26.95±0.06,

26.93±0.04

32.31±

0.13b

32.22±0.12b

30.41±

0.79h

27.92±0.19h

30.47±

0.08b

32.75±0.08b, 

32.82±0.18h

37.13

±0.09

26.91±0.20ob

32.45

±0.05

30.20±

0.14gm

30.31±

0.17gm

30.54±0.29gm

30.16±0.23gm

30.17±

0.11gm

32.19±0.13

32.17

±0.06

27.64±0.12gm,

28.32±0.31gm

27.96±

0.11gm

27.50±

0.11gm

27.81±

0.16gm

27.51.±

0.16gm, 

27.46±

0.11gm

36.95±0.15gs,

36.85±0.07

32.48±0.17,

32.21±0.07 

33.01±0.10b

32.98±0.21h

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Tbt

Tci

Tca

Tscn

Tscl

Tpba

Tca

Tcr

Tsc

Tbrl

Tscn

Tcv

Tfc

Tsc

Tcv

Tfc

Tsc

Tpbf

Tfc

Qc

Km

p_g

QTg

Tpcf?

Qc

Tbpv

Tcv

Tcv

Qfo

Tfcn

Tfc

Twsn

Tcrn

Tbd

Tcrn

Qc

p_g

Tpcf

Tcfr

Tca

Tcd

Tnpd?

Tcv

Tcuv

Tpbm

Tfcb

Tca

Tcfr

Tca

Tcfr

Tbt

Qc

Jj

Ql

Tbd

Tscn

Tscn

Tci

Tcv

Tcd

Tcd

Tpba

Tci

p_g

Tbfa

QTg?

p_g

Tid

Tca

Qc

Tcv

Tfc

Twsn

Jj

Tbrl

Tcrn

Tbt

Tscc

Tci

Tcv

Qgo

QTg

Tcd

Tnpd

Tscn

Tbd

Jj

Tsa

Tca

Tcr

Qt

Tpbf

Tld

Tdbm

Tws?

Tcv

Tsc

Tnn

Tsc

Tws

Tcfr

Tcrn

Tcfr

Tcr

Tdb

Tbd

Tws

Tfcb

Jm

Tsc

Tdc

Tnpd

Tfc

Tsc

Tct

Tev

Tdb

Tcv

Tsc

Tca

Tcv

Tpt

Thb?

Tld

Tfc

Tscn

Tscn

Tfc

Tpff

Tcfr

Twsn

Qfo

Tbd

Tbg

Tcc

Km

Tsc

Tsc

Tcd

Tcfr

Tdb

Tdb

Tfc

p_g

Tbd

Tpbr?

Twm

QTg?

Tnpr

Tw

Tcht

Tcrn

Tpt

Km

Tcr

Tbt

Trdn?

Tscn

Tst?

Tw

Tdc

Tst

Tbd

Tcv

Tdb

QTl

Tci

Twsn

Tfc

Tpba?

Tst?

Tfc

Tbg

Tfcb

Tpbf

Tca

Tsc Jj

Jj

Tcd

Thu

Tsc

Tscl

Tcv

Tfc

Tsc

Tbd

Tct

Tscn

Tdb

Tfc

Tca

Tcap

Tscn

Tws

Tbfa

Tca?

Tbt

Tcd

Tca

Tpbm

Qc

Tdb

Tws

Tst

Tci

Tdb

Tca

Km

Tfcn

Thb?

Tpba

Tfcn

Tcv

Twsn

Tsc

Tfc

Tfcn

Thu

Tcv

Twsn

Tcv

Tca

Tscn

|l

Tbg

Twsn

Tcdi

p_g

QTg?

Tca

Tws

Tsc

Tpbf

Tir

Tpbm

Tcd

Tcd

Tbt

Tsa

Tdb

Tcfr

Tbd

Tst

Tpt

Tbrl

Tsc

Tcfr

Tfc

Tscn

Tpt

Tfcn

Twsn

Tcfr

Tca

Kd

Tcv

Qc

Tab

Qc

Tci

Tscn

Qlo

Tpt

Tca

Tsc

Tsc

Tca

Qc

Tcv

Km

Tpba

Qc

Tca

Tcv

Twm

Tbfa

Tcap

Tfc

Kd

Tcfr

Qt

Ql

Tcv?

Kd

Tpba

Twsn

p_m

Tld

Tct

Qc

Tcd

Tcv

Qc

Qc

Km

Tnpr

Tcr

Tca

Qm

Tca

Qc

Qc

Tdb

Tev

Qc

Qt

Tcv

Ql

Qc

Qt

Qc

Tca

Kd

Qt

Tfc

Tbc

Qt

Qt

Kd

Tcv

Jj

Jj

Km

Tca

Tpbf

Tcr

Qc

Tlr

Tca

Jm

Twsn

Qc

Tca

Tca

Tcr

Tsc

Tcd

Jm

Tdb

Tnpr

Jj

Qc

Tws

Tcd

Qc

Qc

Tfc

Jj

Tcd

Qc

Kd

Tcv

Tcd

Ql

Tab

Km

Tcv

Tpcf

Tca

Tsd

Tcsa

Tcv Qc

Qg

Tct

Ql

Tfc

Tfc

Tbd

Km

Tcv

Tfc

Qc

Qc

Tba

Tfc

Qt

Ql

Tfc

Tca

Qc

Qt

Tct

Twm

Tca

QTl

Tca

Ql

Qc

Tcd

Tpff?

Qc

Tca

Tpcf

Qc

Twsn

Qm

Tsc

Tcv

Qc

QTl

Qf

Qc

Qt

Tdb

Tsc

Ql

Qc

Qc

Ql

Tscn

Tbfa

Qc

Tfc

Km

Qc

Qc

Qc

Tcfr

Jm

Tcht

Jm

Tcfr

Tcv

Tfc

Tfc

Tcv

Tca

Tfc

Tpbs

Ql

Ql

Qc

Tcfr

Tld

Tnpr

p_g

Qc

Ql

Ql

Tnpd

Qc

Ql

Qc

Km

Tca

Tca

Tcr

Tca

Tcdm

Ql

Tpcf

Jm

Tca

Tws

Tcfr

Tba?

Tcv

Tcr

Km

Tca

Tbfc

Tct

Tcv

Tca

Tnr

Tfc

Jm

Qc

Ql

Tcv

Tcr

Ql

Tws

Tcfr

Tpba

Tfc

Tfc

Tcfr

Tcfr?

Qc

Kd

Tcv

Jm

QTf

Km

Twm

Tpba

Kd

p_m

Tfc

Tca

Tws

Qc

Tcv

Qc

Tcfr

Tcd

Tca

Tsa

Tcfr

Km

Ql

Tcfr

Qc

Tca

Tsc

Tcd

Tca

Kd

Tcr

Tcd

Qc

Tca

Qc

Tfc

Tcv

Tcdi

Tcv

Tcfr

Qt

Tcr

Tsa

Tbt

Tcd

Tbfa

Tca

Tcv

Jm

Tcd

Tfc

Tw

Tcd

Tca

Trdn?

Tcv

Ql

Ql

Tcv

Tcd

Tfc

Qc

Kd

Tcfr

Tcd

Qc

Tcr

Tnpr

Tfc

Tfc

Thb?

Ttsn?

Tev

Tca?

Tsc

Tia

Tnn

Tbfa

Tfcb

Tia

Tpbr

Twm

Tscn

Tcd

Tia

Tsc

Tnpa?

p_g

Tid

Tcfr

Twsn

Tcap

Tfc

Exposed Tfc-Tcr contact

SHEEP

CREEK

 ZONE

FAULT 

NEEDLE CREEK INTRUSION

COCHETOPA CREEK GRABEN

RALSTON CREEK FAULT ZONE

LOS PINOS GRABEN

Mesa-capping 

Tsc, at higher 

elevations than 

younger Tfc

Modern canyon at 

right angle to 

volcanic-filled 

paleovalley

Thick mesa cap of 

Tsc, previously 

mapped as tuff of 

Cochetopa Creek

Gunnison River follows old paleovalley 

that localized Tws deposition

N-trending postTws paleovalley, 

filled with Tfc

Steep 

unconformity, 

Tfc against Tws

High-standing 

paleohill of Tsc, 

abutted by Tfc

Paleohill capped 

by Tsc, abutted 

by Tfc

Complex slumping 

on underlying 

Mancos Shale (Km)

N-trending dikes, 

similar in composition 

and age to Needle Cr 

intrusion

In-place Tbc 

directly on Pzl, 

just east of map

Concentrated 

boulder float of 

Pzl; no outcrop

Ridge-capping 

andesite; tentatively 

Thb (Olson and others, 1975)

Poorly exposed 

Tsc, seemingly 

overlain by Tca?

Deposition of 

thick-welded 

Tws controlled 

by N-trending 

paleovalley

Large (to 0.5 m) 

pumice blocks 

in Tscn

Rheomorphic ramp 

structures in mesacapping Twn

Outer caldera 

fault(?); only 

modest 

displacements

Slumped 

brecciated slabs 

of andesite

SAWTOOTH 

MOUNTAIN 

INTRUSION

Slumped 

brecciated 

slabs of 

andesite

Abundant basalt 

fragments in 

rhyolite plug

Alternatively, thick 

valley-filling lava 

dome?

Coherent outer 

caldera floor, and 

(or) downsagged 

caldera margin?

Conspicuous knob: unclear 

whether Tpbf or in-place 

brecciated Tfc?

Clasts of 

Precambrian 

rocks to 

0.5 m, in 

unit Tcht

Multiple ages 

(29.8, >34 Ma) 

of Tcfr?

Deep 

paleovalleys 

fill of Tbd

Broad paleovalley 

fill (Tfc, Tcr)

May include 

some slumped 

Tfc

 Rheomorphic 

Tts, banked 

against steep 

paleotopography

Scabs of Tbd, 

banked high 

on paleovalley 

wall

Angular 

andesite 

breccia Angular 

andesite 

breccia

Coarse 

conglomerate, 

=g and Tca 

boulders

Large blocks 

(to 10 m), both 

Tbd and Tsc

Long Branch 

intrusion (at roof 

level)

Slumped 

Tbd

Low 

paleovalley 

fill of Tbd

Faults that displace 

Tfc unconformably 

covered by Tcr

Thick Tcr, 

ponded within 

graben

Thick Tfc, ponded 

steeply against Tca 

lavas: early caldera 

wall?

Densely welded Tfc, 

banked steeply 

against fault scarp, 

no apparent offsets

Dipping Tcr, depositional 

against graben margin

BLUE 

CREEK 

INTRUSION

Vapor-phase 

crystallized 

nonwelded 

dacite tuff

Megablock 

slabs of 

dacite

Abundant clasts 

of Tnd, Tnr

Compaction(?) faults, 

along buried caldera wall

Black obsidian 

nodules (Apache 

tears) in Tcdu 

basal perlite

Near-vertical 

ramp structures, 

near top of 

Tcdm flow

Near-vertical ramp 

structures, near top of 

Tcdl flow

Angular clasts of 

dacitic ignimbrite 

(Tnd or Tld?) in 

unit Tpt

Brecciated sequence 

of andesite-dacite; 

incipient caldera 

landslides?

No obvious structural 

control for NE 

topographic grain

Abrupt change 

upward from 

crystal-poor to 

crystal-rich Tnr

Meter-size 

blocks of Tcr 

in landslide 

deposit Tpbm

Topographically 

irregular scabs of 

Tsc, high on 

caldera rim

Jumbled precaldera units (caldera 

megabreccia?)

Sparse clasts 

of gray crystalrich ignimbrite 

(Tts?)

Vitrophyre along 

flow contact

Inclined columnar 

cooling joints near flow 

base

Odd closed basin; possible 

maar of Hinsdale Fm.?

Flow-layered 

lava, Tsc 

composition

Complexly 

slumped/rotated 

Tld blocks

Sparse clasts of Tsc 

in conglomeratic Tsv

Abundant clasts of Tsc 

in conglomeratic Tsv

Megablocks 

(to 20 m) of 

Tld 

Massive finely 

brecciated rhyolite

Transitional, 

Tlr-Tld

Paleovalley fill of 

Tbd, parallel 

present drainage

Maximum late fault 

displacement where

 aligned with 

caldera wall

Paleolandslide of Tsc 

into same valley as 

earlier localized Tbd

Large inclined 

columnar joints, 

against caldera 

wall

Large coherent 

early Quaternary 

slump block

Sparse probable 

clasts of Tsc in 

conglomeratic Tsv

Tws could lie 

within caldera

Uncertain location 

of caldera margin; 

age of Tnpd too 

old?

Slumped fill from 

La Garita caldera

Uncertain 

boundary 

between 

Tsa and Tcv Alternatively, 

Tcd?

Silicifiedwood 

logs (to 1 

m long)

Paleovalley fill of 

Tw, oblique to 

present valley

Massive chaotic 

breccia of uncertain 

origin

Good exposure, 

section between 

Tsc and Tfc

Sparse clasts of Tld in 

distal conglomeratic Tdc

Tcr unambiguously 

overlies andesite flows 

(Thu equivalent)

Dark dacite 

flow with large 

sanidine 

phenocrysts 

(to 2 cm)

Resembles 

Tca, but 

overlies Tsc

Scientific Investigations Map 3123

Sheet 1 of 2

Pamphlet and CD-ROM accompany map

Base from U.S. Geological Survey in cooperation 

with Colorado Division of Planning, Department of 

local affairs, 1:50,000 county map series 

(topographic): Chaffee; Gunnison, sheets 4,5; 

Saguache, sheets 1–4.

Lambert Conformal Conic projection

Geology mapped by P.W. Lipman 2000–2006; 

assisted by J. Robinson (2000) and P. Christe (2001)

Digital database by Joel Robinson

Edited by J.L. Zigler

Digital cartographic production by Kathryn Nimz

Manuscript approved for publication April 28, 2010

APPROXIMATE MEAN

DECLINATION, 2012

9 / ° 1 2

MAGNETIC NORTH

TRUE NORTH

CONTOUR INTERVAL 80 FEET

Geologic Map of the Cochetopa Park and North Pass Calderas, Northeastern San Juan Mountains, Colorado

By

Peter W. Lipman

2012 Printed on recycled paper

COLORADO

AREA OF MAP

U.S. Department of the Interior

U.S. Geological Survey

Any use of trade, product, or firm names in this publication is for descriptive 

purposes only and does not imply endorsement by the U.S. Government

For sale by U.S. Geological Survey, Information Services, Box 25286, 

Federal Center, Denver, CO 80225, 1–888–ASK–USGS

Digital files available at http://pubs.usgs.gov/sim/3123/

Suggested Citation: Lipman, P.W., 2012, Geologic map of the Cochetopa 

Park and North Pass calderas, northeastern San Juan Mountains, Colorado: 

U.S. Geological Survey Scientific Investigations Map 3123, 48 p., 2 sheets, 

scale 1:50,000. (Available at http://pubs.usgs.gov/sim/3123/.) Lake Mountain (LM) Grouse Creek (GC)

Lake Mountain (LM) Trickle Mountain (TM) Sargents Mesa (SM) Sargents (SS)

Rock Creek Park (RC)

Spring Hill Creek (SH)

Iris NW (IW)

Iris NW (IW)

Iris (IR) Houston Gulch (HG) Doyleville (DV) Sargents (SS)

Rock Creek Park (RC) Elk Park (EP) Saguache Park (SA)

Grouse Creek (GC)

 38°07'30"

38°30'

107°

106°45'

106°37'30"

106°30'

38°30'

106°22'30"

38°22'30"

38°15'30"

38°07'30"

106°22'30"

106°30' 38°00' 106°37'30"

38°00'

106°45'

106°52'30"

107°

 38°15'30"

 38°22'30"

106°52'30"

P. Lipman,

1986–89, 1995–99

MAPPING CREDIT

P. Lipman,

2000–2007

Pre-Tertiary geology modified

from published USGS maps

(J. Olson and others, 1974–76)

COCHETOPA-NORTH PASS CALDERA MAP AREA BONANZA CALDERA STUDY AREA

CENTRAL SAN JUAN MAP AREA

(Lipman, 2006)

Cochetopa Park

Caldera

NP 

Caldera 

Bonanza

Caldera

Saguache, sheet 3

Saguache, sheet 1

Saguache, sheet 4

Saguache, sheet 2

Gunnison,

sheet 4 Gunnison, sheet 5 Chaffee

Figure 3. Northeastern San Juan region, showing areas of geologic mapping responsibilities, 7.5' topographic quadrangles (black lines), abbreviations 

used on maps and in text, and 1:50,000-scale county maps (blue dashed lines and labels). Published USGS 7.5' geologic map quadrangles indicated by 

citation below quadrangle name and abbreviation. In-progress study of the Bonanza caldera, east of this map area, provides documentation for some 

features referenced in this report.

Iris

(IR)

Houston Gulch

(HG)

Doyleville

(DV)

Sawtooth

Mountain (ST)

Razor Creek

Dome (RD) West Baldy

(WB)

Sargents Mesa

(SM)

Cold Spring

Park

(CS)

Grouse Creek

(GC)

North

Pass

(NP)

Trickle

Mountain

(TM)

Rock Creek

Park

(RC)

Spring Hill

Creek (SH)

Iris NW

(IW)

Cochetopa

Park

(CP)

Stewart Peak

(SP)

Elk Park

(EP)

Saguache Park

(SA)

Lake Mountain

(LM)

Lake Mountain

Northeast

(LMNE)

Laughlin Gulch

(LG)

Klondike Mine

(KM)

Saguache

(SG)

Hickey Bridge

(HB)

Chester

(CH)

Bonanza

(BZ)

Graveyard Gulch

(GG)

Whale Hill

(WH)

Sargents

(SS)

Pahlone Peak

(PP)

Mount Ouray

(MO)

Poncha Pass

(PO)

Olson and

Steven, 1976a

Hedland and

Olsen, 1974

Olson and

Steven, 1976b

Olson, 1976c Olson, 1976b Olson, 1976a

38°30’

38°

107° 106°