MAGNETIC NORTH 







































































































































































































































ELKHORN

THR

S

T

39 

SCIENTIFIC INVESTIGATIONS MAP 3043 

Version 1.0

105°52’30” 

U

Kenosha Pass 

Milligan 

Elkhorn 

Hartsel 

U.S. DEPARTMENT OF THE INTERIOR
 

U.S. GEOLOGICAL SURVEY
 

CORRELATION OF MAP UNITS 105°45’

54 Qal 50 Qal Holocene 

56 Xbg Qpl Qac 

39 Qa2 Late Pleistocene 55 Georgia Pass 38 

Kp 50 Tsa 51 Yqm 62 Qa1 

48 QUATERNARY Tsc 72 36 Middle Pleistocene

31 Tsc 40 Qal
 

75 Qp
 47 

Boreas Pass Jefferson 

44 45 18 A' Early Pleistocene 35 

Tsr Xfg
 27 Qal
 

49 Qac
 

66 15 Unconformity
 39°22’30” 

54 48 24
 

58
 Txc Tsa 

51 Tsa
 

Qac 26 

30
 Xfg 

Tsl Paleocene TERTIARY 

38 27 Tsr Tsc A 13 22

Tsl 53 Qac 

Kfh 54 Tsr Como Tsc Lakes 

Kfh 

Kp 

Upper Cretaceous CRETACEOUS 

Kp 

Qp 

Qa1 

Qal 

Qp 

Kfh 

33 

Kfh 

Qa1 

52 38 

61 

29 

31 

Txc 

50 

Yqm YXmr 

Unconformity 

MIDDLE 

PROTEROZOIC 

39°15’ 

34 Tsc 

Qal 

Qal Xbg Xfg EARLY 

PROTEROZOIC 

Qp 

Qa2 

Qac 35 

Yqm 

Fairplay East 

Fault—Dashed where 

approximately located or 

inferred. Bar and ball on 

downthrown side. 

Thrust Fault—Dashed where 

approximately located or 

inferred. Teeth on hanging 

Garo 

4 MILES 

5 KILOMETERS 

Xbg DESCRIPTION OF MAP UNITS Qac Txc 

Qa1 [Soil nomenclature from Birkeland (1999) and Machettte (1985). Oxygen isotope stages 

35 15 from Lisiecki and Raymo (2005) and Ralph Shroba (USGS, written commun).] 

Qac Tsc 

29 Qac Qal Stream alluvium (Holocene)—Light-brown to dark-brown, organic-rich silt Qal 23 interbedded with light-tan to light-gray, fine-grained sand and lenticular Qa1 Qp 39 Xbg beds of pebble-size gravel. Gravel contains locally derived clasts of 

Kp Tertiary to Precambrian rock. Mapped within and adjacent to active 

Qal Tsl Qp stream channels and dry gulches and deposited within a low-energy 34 wall. 

fluvial system as channel and overbank deposits. On western edge of 39°07’30”

Qa1 38 37 map unit locally consist of reworked South Park Formation conglomer­ 25 Qa1 Qpl ate (Tsc). Unit has very weak soil development. Thickess less than 3 m 

Tsc Qa2 Younger stream and fan alluvium undifferentiated (late Pleistocene)— 51 Interbedded silt, sand, and pebble-size gravel mainly deposited during the 0 

Figure 1. Structural setting of the Elkhorn thrust and location of quadrangle 

boundaries. Elkhorn quadrangle shown by yellow box. Adjacent 7.5-minute 

quadrangles shown in red. Faults shown on the Como and Fairplay East, Colo., 

7.5-minute maps are compiled from Widmann and others (2005) and Kirkham and 

others (2006), respectively. Faults extending south of the map area modified from 

Bryant and others (1981). The northern extension of the Elkhorn thrust is 

compiled from Wyant and Barker (1976) and Barker and Wyant (1976) and new 

30 Pinedale glacial cycle (oxygen isotope stage 2, 14–24 ka) (Lisiecki and 

Qpl Kfh Raymo, 2005; Shroba, written commun.). Depositional surface of Qp 0 deposits has well expressed bar-and-swale morphology with less than 1 37 Qac B' m of relief. Gravel clasts are subrounded to well rounded and well sorted 

and comprised of locally derived clasts from the Paleocene South Park Tsc Qa2 36 Xbg Formation and Precambrian igneous and metamorphic rocks. Soils Qa1 31 EH 2006–1 formed on unit have weak and thin (less than 20 cm) Bt horizons. Unit 

is commonly inset into units Qp and Qa1 as much as 15 meters. 80 Qpl 

Kp 29 Maximum thickness less than 5 m 36 46 Qa1 Older stream and fan alluvium, undifferentiated (late middle 

Pleistocene)—Moderately sorted to well-sorted sandy pebble-size gravel Tsc 36 Qac deposited during the Bull Lake glacial cycle (marine oxygen isotope stage mapping through Georgia Pass by Bohannon and Ruleman (unpublished mapping). 

STRUCTURAL SETTING 

The Elkhorn thrust is defined by the juxtaposition of Early and Middle Proterozoic 

metamorphic and igneous rocks against Mesozoic and Tertiary rocks. Within the mapped 

area, an imbricate frontal thrust system juxtaposes Upper Cretaceous rocks against Paleocene rocks of the South Park Formation. In the southeastern section of the quadrangle, 

Middle Proterozoic igneous rocks are thrust over the South Park Formation. Syntectonic 

conglomerates (Txc) are preserved both on the hanging wall and footwall of the Elkhorn 

thrust. North of the map area we have identified normal faulting of probable Quaternary 

REFERENCES 

Barker, Fred, and Wyant, D.G., 1976, Geologic map of the Jefferson quadrangle, Park and 

Qac Tsc Summit Counties, Colorado: U.S. Geological Survey Geological Quadrangle Map

Yqm 25 Qpl Playa deposits (Holocene and late Pleistocene)—Brown to light brown GQ–1345, scale 1:24,000. 

34 6, 130–150 ka) (Lisiecki and Raymo, 2005; Shroba, written commun.). B
 Depositional surface of deposits is characterized by a smooth surface 

29 underlain by an eolian silt cap of varying thickness. Soils formed on this 58 39 Qp 40 unit are primarily moderately developed having a Bt horizon with blocky Tsc Qac Qp 

Qal 38 to prismatic structure and reddish hues. Localized pedogenic Bk horizons Txc with stage II-III morphology are developed in soil. Average thickness 24 

Qpl 25 20 varies from 3 m to 5 m 

Kp Qa1 41 Qp Piedmont deposits (middle and early Pleistocene)—Poor to moderately 

10 sorted sandy pebble- to cobble-size gravel deposited on gently sloping 35 YXmr aprons adjacent strike ridges and bedrock-cored upland surfaces. Within Qa2 15 43 

Qac Qpl the quadrangle, clasts are sub-angular to sub-rounded and locally derived

Tsc from Tsc, within an eolian silt matrix (greater than 20 percent). Clasts 15 Yqm show well developed angular facets from ventification processes. Most age. Qac bedrock units beneath Qp are deeply weathered in most places. Soils 

10 20 formed on unit are similar to those found on Qal, but show more 

Tsc 39 development with strong stage II to weak stage III Bk horizons. Where 

Qpl 20 25 Qac unit is mapped adjacent to Yqm, deposits consist of deeply grussified 

25 orthogneissic rocks and have weak and discontinuous soil development. Qa2 31 

Qac Thickness averages 4–6 m 25 Txc 

Birkeland, P.W., 1999, Soils and Geomorphology, New York, Oxford University Press, 430 p. 

Bryant, Bruce, McGrew, L.W., and Wobus, R.A., 1981, Geologic map of the Denver 1°× 

2° quadrangle, north-central Colorado: U.S. Geological Survey Map I–1163, scale 

Qa1 25 15 44 Thickness less than 2 m 1:250,000, 2 pls. 

and white, fine-grained silt deposited in shallow depressions of probable 

Tsc 43 

27 

22 eolian deflation origin. Unit is locally overlain by and interbedded with 

Qal thin gravel deposited as slopewash from strike ridges and older alluvium. 

Kirkham, R.M., Keller, J.W., Houck, K.J., and Lindsay, N.R., 2006, Geologic map of the 

Fairplay East quadrangle, Park County, Colorado: Colorado Geological Survey OpenQac 34 11 Pleistocene)—Poorly to moderately well sorted, fine- to coarse-grained File Report 06–9, scale 1:24,000, 1 CD-ROM. Txc Lisiecki, L.E., and Raymo, M.E., 2005, A Pliocene-Pleistocene stack of 57 globally distrib20 36 

30 25 24 Qac Alluvium and colluvium, undifferentiated (Holocene and late Qp Qac 

15 20 silt and sand interbedded with pebble- to cobble-size gravel. Unit Qa2 36 includes slopewash deposits; forms low- to moderately-sloping surfaces uted benthic δ18O records, Paleoceanography, v. 20, PA1003, Qp adjacent to strike ridges and other bedrock-cored hills. Soils on unit vary doi:10.1029/2004PA001071. 19 50 35 20 in development from very weak A horizons to moderate Bt horizons. Machette, M.N., 1985, Calcic soils of the southwestern United States, in Weide, D.L., ed., 15 YXmr Locally, unit is capped by silty loess deposits as much as 0.5 m thick. Soils and Quaternary geology of the southwestern United States: Geological 

Approximate thickness ranges from less than 1 m to 10 m of America Special Paper 203, p. 1–21. 

21 Society 15 Tsc 20 

Qpl 25 Qa1 Sawatzky, D.L., 1967, Tectonic style along the Elkhorn Thrust, eastern South Park and 

western Front Range, Park County, Colorado: Golden, Colorado School of Mines, 

Ph.D. dissertation, 206 p. 

20 Qal 62 Txc Elkhorn thrust conglomerate (Paleocene)—Poorly sorted, sub-angular to Tsc Qac 41 17 sub-rounded, boulder- to cobble-size conglomerate with interbedded, Qa1 21 Qpl 21 coarse grained sandy lenses of varying thickness (that is, 0.5–2.0 m). Widmann, B.L., Kirkham, R.M., Keller, J.W., Poppert, J.T., and Price, J.B., 2005, Geologic 

map of the Como quadrangle, Park County, Colorado: Colorado Geological Survey 

Open-File Report 05–4, scale 1:24,000, 1 CD-ROM. 

Wyant, D.G., and Barker, Fred, 1976, Geologic map of the Milligan Lakes quadrangle, Park 

County, Colorado: U.S. Geological Survey Geological Quadrangle Map, GQ–1343, 1 unconformably overlies east-dipping beds of the South Park Formation. Qac plate. 25 Thickness varies but generally less than 100 m 

Txc
 

Qac South Park Formation (Paleocene)
 44 Tsc 

Qpl Qac 20 Qac 

31 Tsa Arkosic member—Light brown to yellowish brown, interbedded 

sandstone, siltstone, mudstone and minor conglomeratic lenses; where Qa2 Tsc 25 30 Qpl eroded forms swales and subtle strike ridges. Predominantly composed 

of and derived from Precambrian igneous and metamorphic rocks to the 

Qal 55 east (Sawatzky, 1967). Thickness as much as 1,050 meters 

Qal 20 

55 Tsc Tsl Link Spring Tuff Member—Gray to brown, laminated tuff interbedded 

41 with tuffaceous sandstone and lenticular pebble-cobble conglomerate Qa1 35 Txc Tsc Txc having a tuffaceous matrix. Locally contains leaf impressions (Wyant and Qa2 Qal Qal 

Barker, 1976). This is a resistant unit within the South Park Formation; 

68 forms strike ridges. Member thins to the south and pinches out near the 

Tsc 15 Most igneous clasts in unit are deeply weathered to grus. Clasts primarily derived from Yqm. Unit is interpreted as a syntectonic conglomerate Qa1 15 

Kp Kfh 15 deposited coeval with movement along the Elkhorn thrust. In the 

19 northeast corner of the Hartsel, Colo., 7.5-minute quadrangle, unit 

Qa 68 Bailey 30 × 60-minute sheet 2 15 51 C' vicinity of Elkhorn Ranch near sample location EH-2006-01. Maximum 39°30 Qal Qpl Tsc 20 Qac thickness 230–262 m (Wyant and Barker, 1976) Map area 40 39° 105° 106° Tsc Conglomeratic member—Light brown, gray, and brown interbedded Qa1 20 conglomerate, sandstone, and tuffaceous silty mudstone. Conglomerate COLORADO 

MAP LOCATION 

Qpl 30 20 Qa contains clasts of quartzites, chert, and red siltstone, all of Paleozoic age, 1 46 and abundant clasts of silicified wood. Forms rounded strike ridges with Qa1 47 20 81 poor exposure. Thickness approximately 1,400 m (Wyant and Barker, Tsc 

Qac 48 1976)

20 Yqm 15 38 Tsr Reinecker Ridge Volcanic Member—Upper part consists of interbedded 

well rounded conglomerate and gray-brown, platy tuffaceous sandstone. 48 61 Lower part consists of interlayered, alternating porphyritic, hornblende Qac Qa1 

15 

5 30 20 andesite flows and poorly sorted, angular, lahar deposits. Colors range Tsc Qa1 Tsc from purple, brown, green, and gray depending on degree of hydro- Tsc Qal 33 Tsc C
 39 thermal and chemical alteration. Maximum thickness approximately 300 

meters (Wyant and Barker, 1976) 105°45’ 

Base from U.S. Geological Survey, Elkhorn, 1956 (revised 1980) 10° SCALE 1:24 000 Geology mapped by C.A. Ruleman and R.G. Bohannon Kfh Fox Hills Sandstone (Upper Cretaceous)—Yellowish-brown to grayishCOLORADO JEFFERSON 

105°52’30” 

39°30’ 

1 1/ 2 0 1 MILE during the 2005–2006 field season. brown, well sorted, fine- to medium-grained, crossbedded sandstone

Polyconic projection 

North American Datum of 1927 (NAD 27) 

10,000-foot grid based on Colorado coordinate system, 

central zone 

TRUE NORTH

Digital database prepared by C. A. Ruleman and J.B. grading down into a parallel bedded calcareous (marine) sandstone. 

Within map area, exposures vary from deeply weathered to well consoli­ GQ–1345 1 .5 0 1 KILOMETER Workman 

(Wyant and MAP LOCATION Manuscript approved for publication August 24, 2008 dated, particularly well-exposed outcrop at Mexican Ridge within the Barker, 1976) CONTOUR INTERVAL 20 FEET Edited and digital cartography by L.J. Binder north-central part of the quadrangle. Maximum thickness 110 m (Wyant 106° 105°37’30” 

OBSERVATORY 

1000-meter Univeral Transverse Mercator grid ticks, zone 13 APPROXIMATE MEAN 

DECLINATION, 2006 NATIONAL GEODETIC VERTICAL DATUM OF 1929 Denver Publishing Service Center and Barker, 1976) 39°22’30”

Kp Pierre Shale (Upper Cretaceous)—Interbedded, brown, gray, and yellowish COMO MILLIGAN

LAKES ROCK marine shale, siltstone, and sandstone that locally contain calcareous 

nodules. Poorly exposed owing to easy erodibility and surface cover. (Widmann, GQ–1343 

Kirkham, and (Wyant and Elsewhere within the Front Range, the complete section of Pierre Shale Poppert, 2005) Barker, 1976) exceeds 1,800 m A
 A'

West 

ELKHORN THRUST

ELKHORN THRUST 

39°15’ 

Yqm Monzogranite (Middle Proterozoic)—Pale orange, brown orange, and pink, East FAIRPLAY ELKHORN EAGLE ROCK equigranular, garnet-bearing, biotite monzogranite. Unit is deeply 11,000 EAST 3,350 weathered to grus in most places; however, eroded clasts locally have 

weak foliation. Locally contains pegmatite and aplite veins and diffuse (Kirkham, 

xenoliths of Xbg and Xfg. Unit dated at 1,377 Ma ± 35 Ma (sample Keller, and 

10,000 Tsr Houck, 2006) Kfh EH-2006-01, at UTM coordinates: 13N, E431568, N4337945) Kp Yqm 

2,750 

METERS (asl)

Kfh Tsr Tsl 39°7’30” Tsc Tsa YXmr Mixed metamorphic and igneous rocks, undivided (Middle and Early 

9,000 Proterozoic)—Unit consists of equal amounts of at least two of the GARO HARTSEL SULPHUR

following units: monzogranite (Yqm), biotite gneiss (Xbg), and felsic MOUNTAIN 

gneiss (Xfg). Xenoliths in the gneisses show diffuse boundaries and 

represent intense intrusion and initial assimilation of the metamorphic 8,000 rock into the monzogranite (Yqm) 

39° Xbg Biotite gneiss (Early Proterozoic)—Gray, black, and white, layered and well Index map showing Elkhorn quadrangle and 7,000 2,130 foliated, fine- to coarse-grained gneiss comprised of biotite-plagioclase­ adjacent 7.5-minute quadrangles. For U.S. 

Geological Survey publications, number, authors, 

and date of publication are shown for 

quadrangle; for non-U.S. Geological Survey 

publications, authors and year of publication are 

Xfg Felsic gneiss (Early Proterozoic)—Light-gray to white, fine- to medium- shown. 

NO VERTICAL EXAGGERATION quartz gneiss. Unit is locally interlayered with hornblende gneiss and 

sillimanite-biotite-quartz gneiss and contains garnetiferous zones. 

Leucocratic, plagioclase-quartz rich layers of gneiss comprise 5 to 50 

percent of the unit 

B
 

West B'
 grained, leucocratic, moderately to strongly foliated plagioclase-quartzbiotite gneiss of apparent granitic origin 11,000 

10,000 

East 

3,350 

Contact 

Yqm Thrust Fault—Solid where well located, dashed where approximately located or 

Kfh 

Tsc 

Kp Tsc Kp Kfh 

2,750 

METERS (asl)

inferred; dotted where concealed. Teeth on hanging wall of fault. 

Tear Fault—Solid where well located, dashed where approximately located or 

inferred; dotted where concealed. Arrows indicate sense of displacement Suggested citation:
 

along fault. Ruleman, C.A., and Bohannon, R.G., 2008, Geologic map of the Elkhorn 


Kfh 9,000 

8,000 quadrangle, Park County, Colorado: U.S. Geological Survey Scientific 

Anticline—Solid where well located, dashed where approximately located or Investigations Map 3043, 1 sheet, scale 1:24,000. YXmr inferred; dotted where concealed 

7,000 

NO VERTICAL EXAGGERATION 2,130 Syncline—Solid where well located, dashed where approximately located or 

inferred; dotted where concealed Publishing support provided by: 

Denver Publishing Service center Strike and dip of bedding 

FEET (asl) FEET (asl) FEET (asl)

ELKHORN THRUST

C For more information concerning this publication, contact: ' 30 

West 

Inclined Team Chief Scientist, USGS Earth Surface Processes 

East 

3,350 

Box 25046, Mail Stop 980

11,000 Vertical Denver, CO 80225 

10,000 

(303) 236-5344 80 Overturned 

Any use of trade, product, or firm names is for descriptive purposes only and does not imly endorsement by the 

U.S. Government. 

Txc Txc Strike and dip of foliation 

2,750 

METERS (asl)

Tsc 15 Foliation attitude for metamorphic rocks 

Vertical foliation attitude for metamorphic rocks 

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. 

Tsc Kfh Kp Yqm 9,000 

Foliation attitude for igneous rocks 50 For sale by U.S. Geolgical Survey Information Services 

8,000 

7,000 

Kfh 

NO VERTICAL EXAGGERATION 

Kfh Kp 

2,130 

EH 2006–1 Sample collection location for SHRIMP U-Pb dating 

Water body 

Bedding plane—Shown in cross-sections only 

Box 25286, Federal Center, Denver, CO 80225 

1-888-ASK-USGS 

A .pdf of this report is available at: 

http:// pubs.usgs.gov/sim/3043 

GEOLOGIC MAP OF THE ELKHORN QUADRANGLE, PARK COUNTY, COLORADO 

By 

Chester A. Ruleman and Robert G. Bohannon 

2008 

C