U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

Base from U.S. Geological Survey digital data, 1:24,000, 2008

Bowen Mountain, 1957, photorevised 1977 

Universal transverse Mercator projection 1927 (NAD27)

Zone 13 North

Vertical coordinate information is referenced to the National 

Geodetic Veritcal Datum of 1929 (NGVD29)

PRELIMINARY GEOLOGIC MAP OF THE BOWEN MOUNTAIN 7.5 MINUTE QUADRANGLE,

GRAND AND JACKSON COUNTIES, COLORADO

By

James C. Cole, William A. Braddock, and Theodore R. Brandt

2011

Suggested citation:

Cole, J.C., Braddock, W.A., and Brandt, T.R., 2011,

Preliminary geologic map of the Bowen Mountain

quadrangle, Grand and Jackson Counties, Colorado:

Geological Survey Open-File Report 2011–1111,

scale 1:24,000.

Any use of trade, product, or firm names is for descriptive purposed only

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

Although this information product, for the most part, is in the public

domain, it also contains copyrighted materials as noted in the text.

Permission to reproduce copyrighted items for other than personal use 

must be secured from the copyright owner.

For sale by U.S. Geological Survey Information Services

Box 25286, Federal Center, Denver, CO 80225

1-888-ASK-USGS

A PDF of this report is available at:

http://pubs.usgs.gov/of/2011/1111

Geology mapped in 1985–1990 (WAB) using aerial 

photographs, supplemented by 2006–2008 field 

reconnaissance (JCC). Geology compiled on 

1:24,000-scale topographic base map 

GIS database by T.R. Brandt

Manuscript approved for publication April 28, 2011

OPEN-FILE REPORT 2011–1111

MAP UNITS

MAP SYMBOLS

LIST OF MAP UNITS

[Due to the addition of a shaded-relief base, colors in the list of

map units may not exactly match unit colors on the map]

EXPLANATION

ALLUVIAL UNITS

Mountain valley alluvium (Holocene and upper Pleistocene)

Stream-terrace gravel deposit (Holocene and upper Pleistocene)

Contact—Identity and existence certain, location accurate

Contact approximate—Identity and existence certain, location approximate

Contact concealed—Identity and existence certain, location concealed

Contact questionable—Identity and existence questionable, location approximate

Crest line of moraine

Shoreline

Landside scarp approximate—Approximately located. Hachures point down scarp

Fault—Identity and existence certain, location accurate

Fault approximate—Identity and existence certain, location approximate

Fault concealed—Identity and existence certain, location concealed

Thrust fault—Identity and existence certain, location accurate. Sawteeth on

 upper plate

Thrust fault concealed—Identity and existence certain, location concealed.

 Sawteeth on upper plate

Dike—Identity and existence certain, location approximate

Anticline approximate—Identity and existence certain, location approximate

Anticline concealed—Identity and existence certain, location concealed

Syncline approximate—Identity and existence certain, location approximate

Syncline concealed—Identity and existence certain, location concealed

Horizontal bedding

Inclined bedding—Showing strike and dip value

Vertical bedding—Showing strike

Overturned bedding—Showing strike and dip value

Vertical or near-vertical flow foliation or layering in ingeous rock—

 Showing strike

Inclined foliation in layered gneiss or schist—Showing strike

 and dip value

Vertical or near-vertical foliation in metamorphic rock—Showing strike

Crinkled foliation—Showing strike and dip value

Average foliation with minor folds—Showing strike and dip value

Minor fold axis—Showing bearing and plunge

Mineral lineation—Showing bearing and plunge

Crinkled fold axis—Showing bearing and plunge

Adit

Radiometric-age sample site

Oil/gas exploration hole, dry

POST-LARAMIDE SEDIMENTARY ROCKS

Fluvial gravel (Miocene and upper Oligocene?)

Troublesome Formation (lower Miocene and upper Oligocene)

POST-LARAMIDE VOLCANIC ROCKS

Volcanic rocks, undivided (upper Oligocene)

Basalt and trachyandesite (upper Oligocene)

LARAMIDE SEDIMENTARY AND VOLCANIC ROCKS

Middle Park Formation (Paleocene and Upper Cretaceous?)

Arkosic unit (Paleocene)

 Volcanic unit (Paleocene)

 Windy Gap Volcanic Member (Upper Cretaceous?) 

PRE-LARAMIDE SEDIMENTARY ROCKS

Pierre Shale (Upper Cretaceous)

Upper shale unit

 Middle sandy unit

 Lower shale unit

Niobrara Formation (Upper Cretaceous)

Dakota Sandstone (Lower Cretaceous)

Morrison Formation (Upper Jurassic)

Chugwater Formation and older units (Lower Triassic and Upper

 Permian)

GLACIAL UNITS

Rock glacier deposit (Holocene and upper Pleistocene)

Organic-rich sediment (Holocene and upper Pleistocene)

Till of Pinedale age (upper Pleistocene)

Till of Bull Lake age (upper and middle Pleistocene)

MASS-MOVEMENT UNITS

Colluvium (Holocene and upper Pleistocene)

Talus deposits (Holocene and upper Pleistocene)

Landslide deposits (Holocene and upper Pleistocene) 

Debris-flow deposit (Holocene)

POST-LARAMIDE INTRUSIVE ROCKS

Intrusive rocks, undivided (Miocene to Oligocene)

Rhyolite porphyry (late Oligocene)

Intrusive basalt (late Oligocene)

Intrusive tuff-breccia (late Oligocene)

Quartz latite of Apiatan Mountain (late Oligocene)

PALEOPROTEROZOIC METAMORPHIC ROCKS

Quartzofeldspathic biotite schist and gneiss 

Biotite granofels 

Hornblende gneiss and amphibolite 

Granitic gneiss 

EOLIAN DEPOSIT

Loess (Holocene and upper Pleistocene)

MESOPROTEROZOIC INTRUSIVE ROCKS

Granite of Longs Peak batholith 

MESOPROTEROZOIC AND (OR) PALEOPROTEROZOIC

 INTRUSIVE ROCKS

Pegmatite

Qva

Qgy

Qr

Qo

Qtp

Qtb

Qc

Qta

Qls

Qdf

Qlo

N$g

N$t

N$i

$rp

$bi

$lx

$qla

$ba

$ma

$mv

Kmw

Kpu

Kps

Kpl

$v Xbq

Xfb

Xh

Xf

Kn

Kd

Jm

^Pc

YgLP

YXp

Open water

?

15

80

75

30

10

10

65

65

Qva

N$t N$i

YXp

Qr Qo

Qc Qta Qls Qlo

Qdf

Qgy

Qtp

Qtb

Kpu

Kps

Kpl

Kn

Kd

Jm

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$rp

$bi

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$mv

Kmw

$lx

Xbq Xfb Xh Xf

YgLP

$qla

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N$g

Holocene

JURASSIC

TRIASSIC

AND

PERMIAN

PALEOPROTEROZOIC

MESOPROTEROZOIC

Upper

Jurassic

Lower

Cretaceous

Upper

Cretaceous

Lower

Triassic to

Lower(?)

Permian

QUATERNARY

PALEOGENE

CRETACEOUS

upper

Oligocene

Paleocene

Miocene NEOGENE

upper

Pleistocene

middle

Pleistocene

PRE-LARAMIDE UNITS

LARAMIDE UNITS

INTRUSIVE

ROCKS

METAMORPHIC ROCKS

Unconformity

Unconformity

Unconformity

Unconformity

Unconformity

Unconformity

Unconformity

ALLUVIAL UNITS GLACIAL UNITS

CORRELATION OF MAP UNITS

MASS-MOVEMENT UNITS

POST-LARAMIDE UNITS

INTRUSIVE

ROCKS

SEDIMENTARY

ROCKS

VOLCANIC

ROCKS

COLORADO

106° 

Map area

MAP LOCATION

Estes Park 30 ́ × 60 ́

quadrangle

Steamboat Springs

30 ́ × 60 ́quadrangle

40°15‘

1 .5 0 1 KILOMETER

1 1/ 2 0 1 MILE

SCALE 1:24,000

CONTOUR INTERVAL 40 FEET

NATIONAL GEODETIC VERTICAL DATUM OF 1929

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72N7

25.6 plus or

minus 2.0 Ma

72N6

26.2 plus or

minus 2.3 Ma

a

a

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Sunray

DX # 1-D

Brooks

EB # 1

Voyager

# 1

50

40

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50

22 25

45

26

35 54

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75

53

37

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65

55

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55 70 46

54 50

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38

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32

37

13°

231 MILS

11 MILS

0°36‘

UTM GRID AND 1977 MAGNETIC NORTH

DECLINATION AT CENTER OF SHEET

MN

GN