DEPARTMENT OF THE INTERIORUNITED STATES GEOLOGICAL SURVEY MISCELLANEOUS FIELD STUDIES

MAP MF-788 SHEET 1 OF 2COLORADO

"1

O K A 0 M A

Scale 1:500,0001 inch equals approximately 8 miles

109°Base from U . S . Geological Survey, 1969Lambert conformed conic projection basedon standard parallels 33° and 45°

See sheet 2 for explanation and list of sources

INTERIOR—GEOLOGICAL SURVEY. RESTON. V IRGIN l»—1976

For sale by Branch of Distribution. U.S. Geological Survey,Box 25286, Federal Center, Denver, CO 80225

DEPARTMENT OF THE INTERIORUNITED STATES GEOLOGICAL SURVEY

E X P L A N A T I O N

MISCELLANEOUS FIELD STUDIESMAP MF-788 SHEET 2 OF 2

COLORADO

Qa

Qg

Qgo

Qe

Qeo

Qd

Qdo

Ql Qb

Holoc.ene

Pleistocene

PlioceneUNCONSOLIDATED SURFICIAL DEPOSITS

AND ROCKS OF QUATERNARY AGE

Qa Modern alluvium—Includes Piney Creek Allu-vium and younger deposits

Qg Gravels and alluviums (Pinedale and Bull Lakeage)—Includes Broadway and LouviersAlluviums

Qgo Older gravels and alluviums (pre-Bull Lake age)—Includes Slocum, Verdos, Rocky Flats, andNussbaum Alluviums in east, and Florida,Bridgetimber, and Bayfield Gravels in south-west

Qe Eolian deposits—Includes dune sand and silt andPeorian Loess

Qeo Older eolian deposits—Includes Love land LoessQd Glacial drift of Pinedale and Bull Lake Glacia-

t ions—includes some unclassified glacialdeposits

Qdo Older glacial drift (pre-Bull Lake age)Ql Landslide deposits—Locally includes talus,

rock-glacier, and thick colluvial depositsQb Basalt flows (age <1.8 m.y.1)

QTsa

EAST NORTHWEST AND WEST-CENTRAL SOUTHWEST

QTa

QUATERNARY

^TERTIARY

UNCONSOLIDATED DEPOSITS OFQUATERNARY AND LATE TERTIARY AGE

QTsa Unclassified surficial deposits and underlyingAlamosa Formation (gravel, sand, and silt)in San Luis Valley

QTa Ancient alluvium—In isolated patches that maynot all be of the same age

Upper

Cretaceous

EAST NORTHWEST SOUTH-CENTRAL SOUTHWEST

Pliocenef?^)

Miocene

Oligocene

To

Ta

Twr

Tgv

Eocene

Paleocene

Th

Tcu

Tpc Tdu

Td Ts

Tos

Te

Tsp

Tip

Tos

Te

Tn

TERTIARY

SEDIMENTARY ROCKS OF TERTIARY AGE

EastTo

Tgv

Ta

Twr

Th

TcuTpc

Tdu

Tbp

Tt

Tnp

Tos

Twr

Tb

Tu

Tg

Tgp

Tgl

Tglm

Tgt

Tglu

Tglw

Tw

Tbb

Tbbi

Tbr

Tbrt

Taf

Ogallala Formation—Loose to well-cemented sandand gravel

Bouldery gravel on old erosion surfaces inFront Range and Never Summer Mountains

Arikaree Formation—Sandstone; contains abun-dant volcanically derived material

White River Formation or Group—Ashy claystoneand sandstone. Includes Castle Rock Con-glomerate in region southeast of Denver

Huerfano Formation—Shale and sandstone. In-cludes Farisita Conglomerate in northwest-ern Huerfano County

Cuchara Format ion—Sandstone and shalePoison Canyon Formation—Arkosic conglomerate,

sandstone, and shaleUpper part of Dawson Arkose—Arkosic sandstone,

conglomerate, and shale. Includes GreenMountain Conglomerate

NorthwestBrowns Park Formation—Sandstone and siltstone;

west of Park RangeTroublesome Formation—Sandstone and siltstone;

in Middle ParkNorth Park Formation—Sandstone, siltstone, and

conglomerate; in North Park and Laramiebasin

Oligocene sedimentary rocks—Includes DuchesneRiver Formation (sandstone and shale) andBishop Conglomerate near Utah border

White River Formation—Ashy claystone and sand-stone; in North Park

Bridger Formation—Claystone and raudstone; inSand Wash basin

Uinta Formation—Sandstone and siltstone; inPiceance basin. Formerly Evacuation CreekMember of Green River Formation

Green River Formation—MarIstone, sandstone,and oil shale

Parachute Creek Member—Oil shale, marl-stone, and siltstone; in Piceance basin

Lower part—Shale, sandstone, marlstone,and limestone in Anvil Points, GardenGulch, and Douglas Creek Members; inPiceance basin

Laney Member—Claystone, oil shale, andsandstone; in Sand Wash basin

Tipton Tongue—Claystone and oil shale; inSand Wash basin. In extreme northwestincludes rocks of Wilkins Peak Member

Luman Tongue—Carbonaceous shale and marl-stone; in Sand Wash basin

Lower part of Green River Formation and Wa-satch Formation—Shale and sandstone

Wasatch Formation—Claystone, shale, andsandstone

Pliocene

Miocene

Oligocene

Eocene

IGNEOUS ROCKS

Basalt flows and associated tuff, breccia, andconglomerate of late-volcanic bimodalsuite (age 3.5-26 m.y.)—Includes basaltsof Hinsdale Formation in San Juan Mountains,Servilleta Formation in San Luis Valley,and many other occurrences

Basaltic intrusive rocks related to basalt flows(Tbb)—In dikes and plugs

Rhyoli tic intrusive rocks and flows of late-volcanic bimodal suite

Ash-flow tuff of late-volcanic bimodal suite(age 22-23 m.y.)

Ash-flow tuff of main volcanic sequence (agein San Juan Mountains 26-30 m.y.; in SouthPark 29-32 m.y.)—Includes many named units

Northwest (Cont inued)Twc Cathedral Bluffs Tongue—Claystone, mud-

stone, and sandstone; in Sand Wash basinTwn Niland Tongue—Mudstone, sandstone, and

carbonaceous shale; in Sand Wash basinTwo Wasatch Formation (including Fort Union equiv-

alent at base) and Ohio Creek Formation—Claystone, mudstone, sandstone, and con-glomerate

Tf Fort Union Formation—Shale, sandstone, andlocal coal beds

Tc Coalmont Formation—Arkosic sandstone, con-glomerate, and shale; coal in lower part;in North Park

Tm Middle Park Formation exclusive of Windy GapMember—Arkosic sandstone and conglomeratecontaining abundant volcanic materials.Arbitrary line between Middle Park andCoalmont Formations is at ContinentalDivide

South-centralTd Dry Union Formation—Siltstone, sandstone, and

conglomerate. Includes Wagontongue Forma-tion (Miocene) in South Park

Ts Santa Fe Formation—Siltstone, sandstone, andconglomerate

Tos Oligocene sedimentary rocks—Includes Floris-sant Lake Beds (tuffaceous shale and tuff)and Antero Formation (limestone, tuff,tuffaceous sandstone, and conglomerate)

Te Eocene prevolcanic sedimentary rocks—Arkosicsand and bouldery gravel of Echo ParkAlluvium

Tsp South Park Formation—Arkosic sandstone andshale, volcaniclastic conglomerate, andandesite flows and breccia

SouthwestTip Los Pinos Formation—Volcaniclastic conglom-

erate interbedded with basalt flows ofHinsdale Formation (Tbb) on east flankof San Juan Mountains. Grades laterallyinto Santa Fe Formation of San Luis Valley

Tos Oligocene sedimentary rocks—Includes CreedeFormation (tuffaceous siltstone, sandstone,and conglomerate) and gravels interbeddedwith volcanic rocks northeast and south-east of Gunnison

Tsj San Jose Formation--Siltstone, shale, andsandstone

Te Eocene prevolcanic sedimentary rocks—IncludesTelluride Conglomerate and Blanco BasinFormation (arkosic mudstone, sandstone,and conglomerate)

Tn Nacimiento Formation—Shale and sandstone

' TbbL

Taf

Tpl

Twm

*****Tbbi

Tial

H *

Tbr

Tiql

TbrtTV

^**Tui

*****Tmi

TERTIARY

Eocene -I

Paleocene J

Upper /Cretaceous L

TKda CZldv TKdl TKr TKaTKec TKi

OF TERTIARY AGE

Tial Intra-ash-flow andesitic lavasTiql Intra-ash-flow quartz latitic lavasTpl Pre-ash-flow andesitic lavas, breccias, tuffs,

and conglomerates (general age 30-35 m.y.)—Includes several named units

Twm Wall Mountain Tuff (older than tuffs of SanJuan provenance; age 35-36 m.y.)—Earlyash-flow tuff of Sawatch Range provenance

TV Volcanic rocks In northwestern Colorado (age<-'7-33 m.y.)—Mainly of intermediate compo-sitions

Tui Upper Tertiary intrusive rocks (age <20 m.y.)Intermediate to felsic compositions

Tmi Middle Tertiary intrusive rocks (age 20-40m.y.)—Intermediate to felsic compositions

>TERTIARY

| CRETACEOUS

SEDIMENTARY AND IGNEOUS ROCKS OF EARLY TERTIARYAND LATE CRETACEOUS AGE

TKda

Tdv

TKdl

TKr

Denver and Arapahoe Formations--Sandstone,mudstone, claystone, and conglomerate;Denver is characterized by andesiticmaterials

Basaltic flows in Denver Formation nearGolden (age 62-64 m.y.)

Denver Formation or lower part of DawsonArkose—Arkosic sandstone, shale, mud-stone, conglomerate, and local coal beds

Raton Formation—Arkosic sandstone, siltstone,and shale; contains major coal depositsin Raton Basin

TKa Animas Formation—Arkosic sandstone, shale,and conglomerate; contains abundant vol-canic materials; Upper Cretaceous volcan-iclastic McDermott Member at base

TKec Telluride Conglomerate of Eocene prevolcanicsedimentary rocks (Te) and Cimarron RidgeFormation (Upper Cretaceous, volcanicbreccia and conglomerate, age about 66m.y.)—In northwestern San Juan Mountains

TKi Laramide intrusive rocks (age 40-72? m.y.)—Mainly intermediate to felsic compositions;some mafic

Million years.oAge of upper parts of uppermost Tertiary

units is problematic. These parts have his-torically been assigned to the Pliocene.Successive reductions in radiometric age ofthe base of the Pliocene in Europe to 7 m.y.(Lambert, 1971) or 5 m.y. (Berggren, 1972)places a Pliocene age in question, though topbeds of the formations have not been dated.

LowerCretaceous

Kl

Kf

Kp

Kn

Keg

Kdp

Kpu

Kpm

Kpl

Kc

Kd

Kvt

Kpg

Kl

Kl*

Kmw

Km

Kmfm

KdKfd

Kdb

Kkf

Kpcl

KchKmp

Km

Kdb

Kmv

Kmj

BP1 ^Pc U P I L 'SPjs liPcs TJFcp IPrIPdc

TiPmcRPlf

CRETACEOUS

SEDIMENTARY ROCKS OF CRETACEOUS AGE

EastKl Laramie Formation—Shale, claystone, sandstone,

and major coal bedsKf Fox Hills SandstoneK I f Laramie Formation and Fox Hills SandstoneKvt Vermej o Formation (shale, sandstone, and

major coal beds) and Trinidad SandstoneKp Pierre Shale, undividedKpu Upper unitKpm Middle unit—In Boulder-Fort Collins area,

contains Richard, Larimer, Rocky Ridge,Terry, and Hygiene Sandstone Members;elsewhere, shale between zones of B_aculi_t_esreesidei and 13. s co 11 i

Kpl Lower unit—Sharon Springs Member (organic-rich shale and numerous bentonite beds) inlower part

Kn Niobrara Formation—Calcareous shale andlimestone

Keg Carlile Shale, Greenhorn Limestone, andGraneros Shale

Kc Colorado Group—Consists of Niobrara Formation(Kn) and either Benton Shale or Carlile,Greenhorn and Graneros Formations (Keg)

Kpg Pierre Shale (Kp), Niobrara (Kn), and Carlile,

Greenhorn, and Graneros (Keg) Formations,undivided

Kdp Dakota Sandstone and Purgatoire Formation—Sandstone and shale

Kd Dakota Sandstone or Group

Northwest and west-centralKl Lance Formation—Shale, sandstone, and minor

coal beds; Fox Hills equivalent at baseKmw Windy Gap Member (Upper Cretaceous?) of Middle

Park Format ion—Andesitic breccia and con-glomerate

Kls Lewis ShaleKmv Mesaverde Formation, undivided—Maj or coal beds

in lower part; Rollins Sandstone Member atbase in Delta, Gunnison, and Pitkin Counties

Mesaverde Group or FormationKmvu Upper part—In Moffat and Rio Blanco Counties,

sandstone, shale, and coal beds above SegoSandstone. Along Grand Hogback south ofColorado River, sandstone and shale abovecoal-bearing sequence

Kmvl Lower part — Sandstone, shale, and maj or coalbeds

Northwest and west-central (continued)Kw Williams Fork Format ion—Sandstone, shale, and

maj or coal bedsKi lies Formation—Sandstone and shale. Trout

Creek Sandstone Member at top; coal bedsin upper half

Ksc Sego Sandstone, Buck Tongue of Mancos Shale,and Castlegate Sandstone

Kh Hunter Canyon Formation—Sandstone and shaleKmgs Mount Garfield Formation and Sego Sandstone—

Sandstone and shale; major coal beds inlower part of Mount Garfield

Km Mancos Shale—Intertongues complexly with units

of overlying Mesaverde Group or Formation;.1 ower part consists of a calcareous Niobraraequivalent and Frontier Sandstone and MowryShale Members; in areas where the Frontierand Mowry Members (Kmfm), or these and theDakota Sandstone (Kfd) are distinguished,map unit (Km) consists of shale above Fron-tier Member

Kmfm Frontier Sandstone and Mowry Shale Members andintervening shale zone

Kd Dakota SandstoneKfd Frontier Sandstone and Mowry Shale Members of

Mancos Shale and Dakota Sandstone—Locallyincludes, at base, Burro Canyon Format ion(shale and sandstone) or, in western MoffatCounty, Cedar Mountain Formation (conglom-erate and shale)

Kdb Dakota Sandstone and Burro Canyon Formation—Sandstone, shale, and conglomerate

SouthwestKkf Kirtland Shale and Fruitland Formation—Shale,

sandstone, and major coal bedsKpcl Pictured Cliffs Sandstone and Lewis ShaleKch Cliff House SandstoneKmp Menefee Formation (sandstone, shale, and coal)

and Point Lookout SandstoneKrnv Mesaverde Group, undivided—Sandstone and shaleKm Mancos Shale—Lower part contains Juana Lopez

Member (Kmj)Kmj Juana Lopez Member—Calcareous sandstone; a

thin but persistent unit distinguishedonly locally

Kdb Dakota Sandstone and Burro Canyon Format ion--Sandstone, shale, and conglomerate

UpperTriassic

LowerTriassicUpperPermianLower

PermianUpper andMiddle

Pennsylvanian

SEDIMENTARY ROCKS OF TRIASSTC,

1 PI Lykins Formation—Red silts tone, shale, andlimestone

IPs State Bridge Formation—Red and orange silt-stone and sandstone

'SP11 Lykins Format ion and Lyons Sandstone'EPj s Jelm, Lykins, Lyons, and Satanka Formations

—Red si Itstone, shale and sandstone'SPcs Chinle and State Bridge Formations—Red

siltstonc and sandstoner£Pop Chinl e, Mocnkopi, and Park City Formations

—Red and gray siltstone, shale andsandstone

TRIASSIC

PERMIAN

PENNSYLVANIAN

PERMIAN, AND PENNSYLVANIAN AGESrfiPr Triassic and Permian rocks—Red siltstone,

shale, and sandstone. Includes variouscombinations of Nugget, Jelm, Popo Agie,Chugwater, Red Peak, Forelle, Satanka,and Goose Egg Formations near Wyomingborder

"KPdc Dolores Formation (Upper Triassic) and CutlerFormation (Lower Permian)—Red siltstone,sandstone, and conglomerate

"PPmc Moenkopi Formation (Lower Triassic} and Cutler

Formation (Lower Permian)—Red siltstoneand sandstone

"S IPlf Lykins, Lyons, and Fountain Formations—Redsiltstone, sandstone, and conglomerate

Upper rPermian )Lower JPermian L

PP Pu

PC

Pp

Pu

PC

^PERMIAN

SEDIMENTARY ROCKS OF PERMIAN AGE

Park City Formation—Calcareous siltstoneand sandstone

Upper Permian rocks, undivided—Siltstone,dolomite, and sandstone; in southeast

Cutler Formation—Arkosic sandstone, silt-stone, and conglomerate

LowerPermian

Upper andM i d d l e

Pennsylvanian

MzMzPz

i MESOZOIC

> PALEOZOIC

Plf P£cf PPif Pis PPm\PPw

PPwm\

SEDIMENTARY ROCKS BROADLY CLASSIFIEDShown in small areas of complex structure

Mz Mesozoic rocks—Mainly Lower Cretaceous,Jurassic, and Triassic formations

MzPz Mesozoic and Paleozoic rocks—Mainly asin Mesozoic unit (Mz) plus Permianand Pennsylvanian formations

PERMIAN

PENNSYLVANIAN

SEDIMENTARY ROCKS OF PERMIAN AND PENNSYLVANIAN AGE

P2f Fountain Formation—Arkosic sandstone andconglomerate

PPcf Casper Formation (sandstone) and lower partof Fountain Formation

PPif Ingleside Formation (limestone and calcareoussandstone) and Fountain Formation

UpperPennsylvanian

MiddlePennsylvanian

LowerPennsylvanian

Pm

Pb

^-\ Smbe Ph

Frh

Pmr

PPs Sangre de Cristo Formation—Arkosic conglom-erate, sandstone, and siltstone

PPm Maroon Forma tion—Arkosic sandstone, silt-stone, conglomerate, and local limestone

PPw Weber SandstonePPwm Weber Sandstone and Maroon Formation

PENNSYLVANIAN

SEDIMENTARY ROCKS OF PENNSYLVANIAN AGE

KJdm- KJdj KJdw KJdr KJde KJds

> CRETACEOUS

I JURASSIC

Eb

PmbPe

SeeSEDIMENTARY ROCKS OF CRETACEOUS AND JURASSIC AGESSee under headings immediately above and below forcompositions and age designations of formations

KJdmKJdj

KJdw

KJdr

Dakota and Morrison Formations KJdeDakota, Burro Canyon, Morrison, and Junction

Creek Formations—Burro Canyon is locallyabsent

Dakota, Burro Canyon, Morrison, and WanakahFormations

Dakota Group and Morrison and Ralston CreekFormations at mountain front betweenBoulder and Colorado Springs KJds

Dakota, Purgatoire, Morrison, and Ralston CreekFormations in Canon City area

Dakota, Purgatoire, Morrison, Ralston Creek,and Entrada Formations in southeast

Dakota, Morrison, and Entrada Formationsin central mountains

Dakota, Burro Canyon, Morrison, Wanakah, andEntrada Formations in Gunnison River area

Dakota, Morrison, Curtis, and Entrada Formationsin northwest

Dakota, Morrison, and Sundance Formations

Minturn Formation in west-central and south- Smbecentral and other units of Middle Penn-sylvanian age—Arkosic sandstone, con-glomerate, shale, and limestone. Includes ffhMadera Formation and Sharpsdale Formationof Chronic (1958) in Sangre de CristoRange and Gothic Formation of Langenheim(1952) in Elk Mountains TPrh

BeIden Formation—Shale, limestone, and sand-stone. Includes Kerber Formation insouth-central

Minturn and Belden FormationsEagle Valley Formation—Siltstone, shale, and Pmr

local, gypsumEvaporitic fades—Gypsum, siltstone, and

shale; salt present in deep borings.Intertongues with Minturn and lower MaroonFormations. Diapiric structure in manyplaces

Evaporitic facies of Minturn and Belden For-mations in South Park and southward—Gypsum, siltstone, and shale

Hcrmosa Formation—Arkosi c sandstone, conglom-erate, shale, and limestone; gypsum andsalt in Paradox Member present in saltanticlines near Utah border

Rico and Hermosa Formations—Arkosic sand-stone, conglomerate, shale, and limestone.Includes at base in some areas siltstoneand shale of Molas Formation, or LarsenQuartzite

Morgan Formation (limestone, sandstone, andshale.) and Round Valley Limestone—Infar northwest

SOUTHERN FRONT RANGEAND WET MOUNTAINS

WEST-CENTRAL ANDSOUTH-CENTRAL

UINTAMOUNTAINS

Upper fDevonian \.

Upper fCambrian \

MCMDO

DOC0€

Or

MD

OC

MC MDCMDO

-Cs

DO

Mm

-Cl

M€ml

FARSOUTHWEST

MBC

MDMISSISSIPPIAN

DEVONIAN

ORDOVICIAN

CAMBRIAN

SEDIMENTARY ROCKS OF PRE-PENNSYLVANIAN PALEOZOIC AGE

UpperJurassic

Jm Jmj Jmc Jmw Jmr Jme Jms Jmse Jmce Jmre Jmwe JURASSIC

SEDIMENTARY ROCKS OF JURASSIC AGE

Jm

Jmj

Jmc

Jmw

Jmr

Morrison Formation—Variegated claystone, mud-stone, sandstone, and local beds of lime-stone

Morrison Formation and Junction Creek Sandstone—In Gunnison River area east of wedgeoutof all units of Wanakah Formation (Jmw)except the Junction Creek Member

Morrison Formation and Curtis Formation(glauconitic sands tone and limestone)

Morrison Formation and Wanakah Formation(sandstone, shale, limestone, and localgypsum; Junction Creek Sandstone Memberat or near top; Pony Express LimestoneMember at base)

Morrison Formation and Ralston Creek Formation(claystone, sandstone, limestone, andgypsum)

Jme Morrison Formation and Entrada SandstoneJms Morrison Formation and Sundance Formation

(sandstone, shale, claystone, and limestone)Jmse Morrison Format ion, Summerville Formation

(shale and siltstone), and Entrada SandstoneJmce Morrison, Curtis, and Entrada Formations—In

extreme southwestern Moffat County, includesthin wedge of Carmel Formation (red silt-stone and sandstone) beneath Entrada

Jmre Morrison, Ralston Creek, and Entrada (or Exeter)Formations

Jmwe Morrison, Wanakah, and Entrada Formations

MDO

DOC

O€Or

MD

0€

Upper JJurassic 1Lower f

Jurassic 1

Upper JTriassic |

J3gJ'Sgc

JlmgJBmc

JURASSIC

TRIASSIC

SEDIMENTARY ROCKS OF JURASSIC AND TRIASSIC AGE

Southern Front Range and Wet Mountains

Leadville Limestone (Mississippiau), WilliamsCanyon Limestone (Devonian), ManitouLimestone (Ordovician), and SawatchQuartzite (Cambrian)

Leadville Limestone, Williams Canyon Limestone,and one. or more Ordovic ian formations:Fremont Limestone, Harding Sandstone, andManitou Limestone

Wi Lliams Canyon Limestone, Manitou Limestone,and Sawatch Quartzite

Manitou Limestone and Sawatch QuartziteOne or more Ordovician formations—Fremont

Limestone, Harding Sandstone, and ManitouLimestone

West-central and south-central

Leadville Limestone (Mississippian), GilmanSandstone (Mississippian or Devonian),Dyer Dolomite (MississippianV and Devonian),and Parting Formation (Devonian, quartziteand shale)

One or more Ordovician formations (FremontLimestone, Harding Sandstone, and ManitouDolomite), Dotsero Formation (Cambrian,dolomite; in White River Plateau only),Peerless Formation (Cambrian, sandstoneand dolomite), and Sawatch Quartzite(Cambrian)

West-central and south-central (continued)

M€ Leadville, Gilman, Dyer, Parting, Fremont,Harding, Manitou, Dotsero, Peerless, andSawatch Formations

MDC Leadville, Gilman, Dyer, Parting, and SawatchFormations

MDO Leadville, Gilman, Dyer, Parting, Fremont,Harding, and Manitou Formations

DO Parting, Fremont, and Harding Formations-Cs Sawatch Quartzite—Locally includes Peerless

Formation

Uinta Mountains

Mm Madison Limestone (Mississippian)—Upper partincludes equivalents of Upper Mississip-pian Doughnut and Humbug Formations(shal e., limestone , and sandstone)

-Cl Lodore Formation (Cambrian)—Sandstone, shale,and conglomerate

MCml Madison Limestone and Lodore Formation

Far southwest

MDC Leadville Limestone (Mississippian), OurayLimestone (Devonian), Elbert Formation(Devonian, shale and sandstone), andIgnacio Quartzite (Cambrian)

MD Leadville, Ouray, and Elbert Formations

JT?gcGlen Canyon Sandstone — In northwestGlen Canyon Group and Chinle Formation — In

southwest. Glen Canyon Group consistsof Navajo Sandstone, Kayenta Formation(red siltstone, shale, and sandstone) ,and Wingate Sandstone; Chinle is redsiltstone

Upper JTriassic |

Lower JTriassic L

"Skc

Em

"Ewe

"fich"B cc

f t c Jtd *dg

Iwc

Hch

SEDIMENTARY ROCKS

Kayenta Formation (red siltstone, shale, andsandstone), Winga te Sandstone, and ChinleFormation (red siltstone and sandstone)

Wingate Sandstone and Chinle FormationMoenkopi Formation—Red siltstone, mudstone,

sandstone, and local gypsumChugwater Formation—Red sandstone, siltstone,

shale, and local limestone and gypsum

SYMBOLS

- ContactFault—Dotted where concealed. Bar and ball

on downthrown sideLow-angle thrust fault—Dotted where concealed.

Sawteeth on upper plateInferred fault in and beneath valley-fill

deposits—Bar and ball on downthrown sidePrecambrian shear zoneFold lines—General locations of major folds

shown where space allows. Dotted whereconcealed

AnticlineSynclineOverturned synclineMonocline

Volcanic cinder cone or crater (age <"!. 8 m.y.)—In Costilla and Eagle Counties

Volcanic neck (age 7-10 m.y.)—In southernRoutt County

Diatreme (pre-Upper Devonian, post-MiddleSilurian)—In northern Larimer County

Water body—Lake or reservoir

'Edg

JTJmg Morrison, Curtis, Entrada, and Glen CanyonFormations—Curtis is absent along GrandHogback

J"Smc Morrison, Entrada, and Chinle Formations—Along southern Grand Hogback, Chinle isrepresented only by basal Gartra Sand-stone Member

TRIASSIC

OF TRIASSIC AGE

Chinle and Chugwater FormationsChinle Formation — Red siltstone, sandstone,

and limestone-pellet conglomerateDolores Formation — Red siltstone , shale ,

sandstone , and 1 imestone-pellet conglom-erate

Dockum Group — Red sandstone, siltstone, andlocal 1 imestone

REFERENCES

Berggren, W. A. , 1972, A Cenozoic time-scale — someimpl ications for regional geology and paleo-biogeography: Lethia, v. 5, no. 2, p. 195-215

Boyer , R. E. , 1962 , Petrology and structure of thesouthern Wet Mountains, Colorado: Geol. Soc.America Bull., v. 73, no. 9, p. 1047-1070.

Chronic, B. J., Jr., 1958, Pennsylvanian rocks incentral Colorado, in Rocky Mtn. Assoc. Geolo-gists, Symposium on Pennsylvanian rocks ofColorado and adjacent areas, p. 59-63.

Lambert, R. S. J., 1971, The pre-Pleistocene Phan-erozoic time-scale — A review, in Part I ofthe Phanerozoic time-scale — A supplement :Geol . Soc . London Spec. Pub. no. 5, p. 9-34.

Langenheim, R. L., Jr., 1952, Pennsylvanian andPermian stratigraphy in Crested Butte quad-rangle, Gunnison County , Colorado: Am. Assoc.Petroleum Geologists Bull., v. 36, no. 4,p. 543-574.

-Cam

^CAMBRIAN

IGNEOUS ROCKS OF CAMBRIAN AGE

Alkalic and mafic intrusive rocks in smallplutons, and diabase dikes (age 510-570 m.y.)

SEDIMENTARY ROCKS IGNEOUS ROCKS

Yp

Yg

Yam

Xm

YXg

METAMORPHIC ROCKS

Xb X f h Xq

Wr

PRECAMBRIAN Y

PRECAMBRIAN X

PRECAMBRIAN W

SEDIMENTARY, METAMORPHIC, AND IGNEOUS ROCKS OF PRECAMBRIAN AGE

Yu

YXu

Xb

Xfh

Xq

Wr

Sedimentary rocks

Uinta Mountain Group (age 950-1,400 m.y.)--Quartzite, conglomerate, and shale

Uncompahgre Formation (older than granitesof 1,400-m.y. age group and younger thangranites of 1,700-m.y. age group)—Quartzite, slate, and phyllite

Metamorphic rocksAge 1,700-1,800 m.y.

Biotitic gneiss, schist, and migmatite—Locally contains minor hornblende gneiss,calc-silicate rock, quartzite, and marble.Derived principally from sedimentary rocks

Felsic and hornblendic. gneisses, either sepa-rate or Inter layered—Includes metabasalt,metatuff, and interbedded metagraywacke;locally contains interlayered biotitegneiss. Derived principally from volcanicrocks

Quartzite, conglomerate, and interlayered micaschist

Age probably >2,500 m.y.

Red Creek Quartzite—Metaquartzite, amphibo-lite, and mica schist. Present only insmall area at Utah border in UintaMountains

Igneous rocks

Yp Rocks of Pikes Peak batholith (1,000-m.y. agegroup)—Includes Pikes Peak, Mount Rosa,Windy Point, and Redskin Granites andunnamed rocks

Yg Granitic rocks of 1,400-m.y. age group (age1,350-1,480 m.y.)—Includes Silver Plume,Sherman, Cripple Creek, St. Kevin, VernalMesa, Curecanti, Eolus, and Trimble Granitesor Quartz Monzonites; also, San IsabelGranite of Boyer (1962) and unnamed graniticrocks

Yam Alkalic and mafic rocks in small plutons,and diabase and gabbro dikes

Xg Granitic rocks of 1,700-m.y. age group (age1,650-1,730 m.y.)—Includes Boulder Creek,Cross Creek, Denny Creek, Kroenke, BrownsPass, Powderhorn, Pitts Meadow, BakersBridge, and Tenmile Granites, QuartzMonzonites, or Granodiorites; also, unnamedgranitic rocks

Xm Mafic rocks of 1,700-m.y. age group—Gabbro andmafic diorite and monzonite

YXg Granitic rocks of 1,400- and 1,700-m.y. agegroups, undivided

P R E L I M I N A R Y G E O L O G I C M A P O F C O L O R A D OCompiled by Ogden Tweto

1976

0 50 100 150 KILOMETERS

INDEX MAP OF COLORADO SHOWING PRINCIPAL SOURCESOF GEOLOGIC DATA

PRINCIPAL SOURCES OF GEOLOGIC DATA

Geologic data for the Colorado map were de-rived principally from compilations of I°x2°quadrangles, references to which are given below.The individual I°x2° quadrangle maps in turnincorporate many other maps, references to whichmay be found on the I°x2° quadrangle maps. Allquadrangle maps have been generalized as necessaryto fit requirements of scale, and some have beenmodified or amplified from sources indicated underthe quadrangle headings.

1. Vernal quadrangleTweto, Ogden, 1975, Preliminary geologic map

of east half of Vernal I°x2° quadrangle,Colorado: U.S. Geol. Survey Open-fileRept. 75-588.

Supplementary data from:Rowley, P. D., and Hansen, W. R., U.S. Geo-

logical Survey unpub. maps of parts ofquadrangle.

2. Craig quadrangleTweto, Ogden, 1976, Geologic map of the CraigI°x2° quadrangle, northwestern Colorado:U.S. Geol. Survey Misc. Inv. Series Map I-972.

Supplementary data from:Snyder, G. L., U.S. Geol. Survey unpub. map

of Steamboat Springs-Oak Creek-Rabbit EarsPeak area.

3. Greeley quadrangleInterim compilation by Ogden Tweto from:Beckwith, R. H., 1942, Structure of the upperLaramie River valley, Colorado-Wyoming:Geol. Soc. America Bull., v. 53, no. 10,p. 1491-1532.

Bjorklund, L. J., and Brown, R. F., 1957,Geology and ground-water resources of thelower South Platte River Valley betweenHardin, Colorado, and Paxton, Nebraska,with^ a section on Chemical quality of theground water, by H. A. Swenson: U.S. Geol.Survey Water-Supply Paper 1378, 431 p.

Braddock, W. A., Calvert, R. H., Gawarecki,

S. J., and Nuta.laya, Prinya, 1970, Geologicmap of the Masonvilie quadrangle, LarimerCounty, Colorado: U.S. Geol. Survey Geol.Quad. Map GQ-832.

Braddock, W. A., Calvert, R. H., O'Conner,J. T., and Swann, G. A., 1973, Geologic mapand sections of the Horsetooth Reservoirquadrangle, Larimer County, Colorado: U.S.Geol. Survey open-file map.

Braddock, W. A., Conner, J. J., Swann, G. A. ,and Wohlford, D. D., 1973, Geologic map andsections of the Laporte quadrangle, LarimerCounty, Colorado: U.S. Geol. Survey open-file map.

Braddock, W. A., Nutalaya, Prinya, Gawarecki,S. J., and Curtin, G. C., 1970, Geologicmap of the Drake quadrangle, Larimer County,Colorado: U.S. Geol. Survey Geol. Quad. MapGQ-829.

Colton, R. B., and Lowrie, R. L., 1973, Mapshowing mined areas of the Boulder-Weld coalfield, Colorado: U.S. Geol. Survey Misc.Field Studies Map MF-513.

EggLer, D. H. , 1968, Virginia Dale ring-dikecomplex , Colorado-Wyoming : Geol, Soc..America Bull., v. 79, no. 11, p. 1545-1564.

Gable, D. J., and Madole, R. F., 1976, Geologicmap of the Ward quadrangle, Boulder County,Colorado: U.S. Geol. Survey Geol. Quad. MapGQ-1277.

Hershey, L. A., and Schneider, P. A., Jr., 1972,Geologic map of the lower Cache la PoudreRiver basin, north-central Colorado: U.S.Geol. Survey Misc. Ceol. Tnv. Map 1-687.

Hunter, Z. M., 1955, Geology of the foothillsof the Front Range in northern Colorado:Rocky Mtn. Assoc. Geologists, Denver, Colo-rado, 2 map sheets.

Izett, G. A., 1974, Geologic map of the TrailMountain quadrangle, Grand County, Colorado:U.S. Geol. Survey Geol. Quad. Map GQ-1156.

Lovering, T. S., and Goddard, E. N., 1950,Geology and ore deposits of the Front Range,Colorado: U.S. Geol. Survey Prof. Paper 223,319 p. [1951].

O'Neil, J. M., Colorado Univ., unpublished mapof Mount Richthofen quadrangle, Grand andJackson Counties, Colorado.

Pearson, R. C., and Speltz, C. N., 1975, Min-eral resources of the Indian Peaks studyarea, Boulder and Grand Counties, Colorado,w i t h a s e c t i o n o n Interpretation of aeromag-netic data, by Gordon Johnson: U.S. Geol.Survey Open-file Rept. 75-500.

Scott, G. R., and Cobban, W. A., 1965, Geologicand biostratigraphic map of the Pierre Shalebetween Jarre Creek and Loveland, Colorado:U.S. Geol. Survey Misc. Geol. Inv. Map 1-439.

Smith, R. 0., Schneider, P. A., Jr., and Petrie,L. R., 1964, Ground-water resources of theSouth Platte River basin in western Adams andsouthwestern Weld Counties, Colorado: U.S.Geol. Survey Water-Supply Paper 1658, 132 p.

Soister, P. E., 1965, Geologic map of the FortLupton quadrangle, Weld and Adams Counties,Colorado: U.S. Geol. Survey Geol. Quad. MapGQ-397.

1965, Geologic map of the Hudson quadran-gle, Weld and Adams Counties, Colorado:U.S. Geol. Survey Geol. Quad. Map GQ-398.

1965, Geologic map of the Platteville quad-rangle, Weld County, Colorado: U.S. Geol.Survey Geol. Quad. Map GQ-399.

Trimble, D. E., 1975, Geologic map of the Niwotquadrangle, Boulder County, Colorado: U.S.Geol. Survey Geol. Quad. Map GQ-1229.

Weist, W. G., Jr., 1965, Reconnaissance of theground-water resources in parts of Larimer,Logan, Morgan, Sedgwick, and Weld Counties,Colorado, with a sectlor^ ori The chemicalquality of the water, by Robert Brennan:U.S. Geol. Survey Water Supply Paper 1809-L,24 p.

Wrucke, C. T., and Wilson, R. F., 1964, Geo-logic map of the Boulder quadrangle, Boulder,County, Colorado: U.S. Geol. Survey open-file map.

U.S. Geol. Survey unpub, maps by W. A. Braddock,R. B. Colton, D. J. Gable, N. M. Denson,D. M. Kinney, M. E. McCallum, R. C. Pearson,G. R. Scott, and Ogden Tweto.

4. Sterling quadrangleScott, G. R., U.S. Geol, Survey unpub. map of

quadrangle.5. Grand Junction quadrangle

Cashion, W. B., 1973, Geologic and structuremap of the Grand Junction quadrangle, Colo-rado and Utah: U.S. Geol. Survey Misc.Geol. Inv. Map 1-736.

10,

11

12

13

14,

15,

16,

I50KILOMETERS

LOCATION MAP OF MAJOR TECTONICAND GEOGRAPHIC FEATURES

Leadville quadrangleTweto, Ogden, Moench, R. H., and Reed, J. C.,

Jr., 1976, Preliminary geologic map of theLeadville I°x2° quadrangle, northwesternColorado: U.S. Geol. Survey Misc. FieldStudies Map MF-760.

Denver quadrangleBryant, Bruce, U.S. Geol, Survey unpub. compi-

lation of northwest part of quadrangle.Bryant, Bruce, and Wobus, R. A., 1975, Prelimi-nary geologic map of the southwestern quarterof the Denver I°x2° quadrangle, Colorado: U.S.Geol. Survey Open-file Rept. 75-340.

McGrew, L. W., U.S. Geol. Survey unpub. map ofeastern part of quadrangle.

Soister, P. E., U.S. Geol. Survey unpub. map ofDenver and Dawson Formations.

Trimble, D. E., U.S. Geol. Survey unpub. maps of

Front Range Urban Corridor, Greater Denver andColorado Springs-Castle Rock areas.

Limon quadrangleSharps, J. A., U.S. Geol. Survey unpub. map of

quadrangle.Moab quadrangleWilliams, P. L., 1964, Geology, structure, and

uranium deposits of the Moab quadrangle, Colo-rado and Utah: U.S. Geol. Survey Misc. Geol.Tnv. Map 1-360.

Supplementary data on Precambrian rocks from:Case, J. E., 1966, Geophysical anomalies overPrecambrian rocks, northwestern UncompahgrePlateau, Utah and Colorado: Am. Assoc. Pe-troleum Geologists Bull., v. 50, no. 7, p.1423-1443.

Hedge, C. E., Peterman, Z. E., Case, J. E., andObradovich, J. D., 1968, Precambrian geochron-ology of the northwestern Uncompahgre Plateau,Utah and Colorado, in Geological Survey Re-search 1968: U.S. Geol. Survey Prof. Paper600-C, p. C91-C96.

Mose, D. G., and Bickford, M. E., 1969, Precam-brian geochronology in the Unaweep Canyon,west-central Colorado: Jour. Geophysical Re-search, v. 74, no. 6, p. 1677-1687,

Montrose quadrangleTweto, Ogden, Steven, T. A., Hail, W. J., Jr.,

and Moench, R. H., 1976, Preliminary geologicmap of the Montrose I°x2° quadrangle, south-western Colorado : U.S. Geol. Survey Misc.Field Studies Map MF-761.

Pueblo quadrangleScott, G. R., Taylor, R. B., Epis, R. C., andWobus, R. A., 1976, Geologic map of the Pueb-lo I°x2° quadrangle, south-central Colorado:U.S. Geol. Survey Misc. Field Studies Map MF-775.

Lamar quadrangleSharps, J. A., 1976, Geologic map of the Lamar

quadrangle, Colorado and Kansas: U.S. Geol.Survey Misc. Inv. Series Map 1-944.

Supplementary data on bedrock from:

Boettcher, A. J. 1964, Geology and ground-waterresources in eastern Cheyenne and Kiowa Coun-ties, Colorado, with a section on Chemicalquality of

and Wyant, D. G.,

he ground water, by C. A. Horr:U.S. Geol. Survey Watrer-Supply Paper 1779-N,32 p.

Coffin, D. L., 1967, Geology and ground-waterresources of the Big Sandy Creek valley,Lincoln, Cheyenne, and Kiowa Counties, Colo-rado, with a section on Chemical quality ofground water, by C. A. Horr: U.S. Geol. Sur-vey Water Supply Paper 1843, 49 p.

Voegeli, P. T., Sr., and Hershey, L. A., 1965,Geology and ground-water resources of ProwersCounty, Colorado: U.S. Geol. Survey Water-Supply Paper 1772, 101 p.

Weist, W. G., Jr., 1965, Geology and occurrenceof ground water in Otero County and thesouthern part of Crowley County, Colorado,with_sections on Hydrology of the ArkansasRiver valley in the project area, by W. G.Weist, Jr., and E. D. Jenkins; Hydraulicproperties of the water-bearing materials,by E. D. Jenkins; and Quality of the groundwater, by C. A. Horr: U.S. Geol. SurveyWater-Supply Paper 1799, 90 p.

Cortez quadrangleHaynes, D. D., Vogel, J. D

1972, Geology, structure, and uranium depo-si ts of the Cortez quadrangle, Colorado andUtah: U.S. Geol. Survey Misc. Geol, Inv. Map1-629.

Durango quadrangleSteven, T. A., Lipman, P. W., Hail, W. J., Jr.,

Barker, Fred, and Luedke, R. G., 1974, Geolo-gic map of the Durango quadrangle, southwest-ern Colorado: U.S. Geol. Survey Misc. Inv.Series Map 1-764.

Supplementary data on surficial deposits from:Atwood, W. W., and Mather, K. F., 1932, Physi-

ography and Quaternary geology of the SanJuan Mountains, Colorado: U.S. Geol. SurveyProf. Paper 166, 176 p.

Richmond, G. M., 1965, Quaternary stratigraphyof the Durango area, San Juan Mountains, Colo-rado, JLTI Geological Survey Research 1965:U.S. Geol. Survey Prof. Paper 525-C, p. C137-C143.

Trinidad quadrangleJohnson, R. B., 1969, Geologic map of the Trin-

idad quadrangle, south-central Colorado: U.S.Geol. Survey Misc. Geol. Inv. Map 1-558.

Supplementary data from:Boyer, R. E., 1962, Petrology and structure of

the southern Wet Mountains, Colorado: Geol.Soc. America Bull., v. 73, no. 9, p. 1047-1070.

Burroughs, R. L., 1971, Geology of the San LuisHills, south-central Colorado, _in New MexicoGeol. Soc. Guidebook 22d Field Conf., SanLuis Basin, Colorado, 1971: p. 277-287. Also,unpub. geologic map of San Luis Hills area.

Cochran, D. M., 1974, Charles S. Robinson andAssociates, Inc., unpub. geologic map ofForbes Trinchera Ranch.

Gaca, J. R., and Karig, D. E., 1966, Gravitysurvey in the San Luis Valley area, Colorado:U.S. Geol. Survey open-file report, 22 p.

Kleinkopf, M. D., Peterson, D. L., and Johnson,R. B., 1970, Reconnaissance geophysical stud-ies of the Trinidad quadrangle, south-centralColorado, in. Geological Survey Research, 1970:U.S. Geol. Survey Prof. Paper 700-B, p. B78-B85.

McCulloch, D. S., 1963, Late Cenozoic historyof Huerfano Park, Colorado: Michigan Univ.Ph. D. thesis, 158 p.

Scott, G. R., and Taylor, R. B., 1975, Post-Paleocene Tertiary rocks and Quaternary vol-canic ash of the Wet Mountain Valley, Colo-rado: U.S. Geol. Survey Prof. Paper 868,15 P.

Tweto, Ogden, U.S. Geol. Survey reconnaissancemapping.

Vine, J. D., 1974, Geologic map and cross sec-tions of the LaVeta Pass, LaVeta, and RitterArroyo quadrangles, Huerfano and CostillaCounties, Colorado: U.S. Geol. Survey Misc.Inv. Series Map 1-833.

LaJunta quadrangleScott, G. R., 1968, Geologic and structure con-

tour map of the LaJunta quadrangle, Coloradoand Kansas: U.S. Geol. Survey Misc. Geol.Inv. Map 1-560.

INTERIOR —GEOLOGICAL SURVEY, RESTON. VI RG IN [A—1976

For sale by Branch of Distribution, U.S. Geological Survey,Box 25286, Federal Center, Denver, CO 80225