COLORADO • - . . . : • • ; , » . ,M SUMu1313 SHERMAN ST. POCM735

DENVER. CO

DEPARTMENT OF THE INTERIORUNITED STATES GEOLOGICAL SURVEY

57'SO"

MISCELLANEOUS FIELD STUDIESMAP MF-482SHEET I OF 2

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SEE SHEET 2 FOR CORRELATIONAND DESCRIPTION OF MAP UNITS

Base from U.S .Geological Survey1:24,000 quadrangles.Editions of 1948-1961; photorevised1969.

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Geology mapped in 1971 as a part of the Pueblo 1:250,000-scale geologic mapping program. Map compiled in part byR. B. Taylor. Mapping of units within Pikes Peak batholithin part by Fred Barker and W. N. Sharp. Some contacts nearCheyenne Mountain adapted from unpublished thesis map byJohn C. Harms (1959). John E. Rovik assisted in geologicmapping of the area near the Louisiana State Universityfield camp. Contacts near the Garden of the Gods adaptedfrom Grose (1960). Bedrock contacts near Palmer Park fromFinlay (1916). Contacts in Air Force Academy from Varnesand Scott (1967).

SS'JO" R. 67*. 30' R.66W, 47'30" 4S' K. 66*. R.65W. 42'30"

RECONNAISSANCE GEOLOGIC MAP OF COLORADO SPRINGS AND VICINITY, COLORADOBy

Glenn R.Scott and Reinhard A. Wobus

1973 Far tali by U.S. Geological Surviy, price SI.00 per ser

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DEPARTMENT OF THE INTERIORUNITED STATES GEOLOGICAL SURVEY

CORRELATION OF MAP UNITS

MISCELLANEOUS FIELD STUDIESMAP MF-482SHEET 2 OF 2

- • Holoc«n«

•Pleistocene

Unconformity and major uplift| Tda | "1 Middl« PHoe*n«(?) tol_ B | / Upper Mloc.n.(?)

Unconformity and major upliftPaltoetne

Upper Cretaceous

TKd

Kflo

rm y and

Kl

Kl

Kp

Kn

noJQ

Kpl

Kp.

Kn,

Knl

Udconform

Kcgg

ly

f uplift

Kn.

Lower Cretaceous

QUATERNARY

} Upl

Intruiivi rackt of J*Bauldvr Crook aga \ 1.72 billion years

-•tj? billion yeare

} JURASSIC

TRIASSICC?)

PERMIAN

PENNSYLVANIAN

JMISSISSIPPIAN

j ORDOVICIAN} CAMBRIAN

PRECAMBRIAN Y

PRECAMBRIAN X

DESCRIPTION AND ENGINEERING GEOLOGY PROPERTIES OFTHE MAI' UNITS

of ARTIFICIAL FILL—Trash, dumped fill, and ellty mill Callings,Ranges in thickness from 10 to 100 feet

Uncompacted, easily excavated. Foundation stability gener-ally poor; footings or piers set on suitable underlyingmaterial probably are necessary for heavy structures.Generally readily eroded

Qp PINEY CREEK ALLUVIUM (UPPER HOLOCENE)—Gray to brown humic-rich, f irmly compacted clayey silt and sand. Containspebble lenses in lower part. Unmapped deposits alongsmaller streams are subject to flooding. Thickness asmuch as 20 feet . Top of terrace alluvium is about 20feet above major streams

Permeability is medium to .low- Easily excavated. Com-pressible where rich in humus; however, compaction gen-erally is easy where humus Is lacking. Foundation sta-bility fair to poor for heavy structures; clayey partsof this unit may have low to medium swelling propertieswhen wetted. Foundation stability poor where close toarroyos and water courses. Slope stability poor tomedium. Cut slopes stand vertically along deep arroyoawhen dry, but slump when the base Is wet ted . Check damsnecessary to prevent erosion. Source of sand and gravelalong large streams

Topographically lowest part of unit mapped adjacent Colarger streams is called post-Piney Creek alluvium, butIt is undifferentiated here. It is sandier and lesscompacted than Piney Creek Alluvium. Thickness more than10 feet. Post-Piney Creek alluvium is subject to season-al flooding; also, shallow water table locally mighthinder the use of basements. Source of sand and gravelalong large streams

Qc COLLUVIUM (UPPER HOLOCENE)—Reddish-brown bouldery, clayeycoarse sand containing cobbles and pebbles, chiefly ofPikes Peak Granite south of Hast Monument Creek. Occurson steep slopes

Permeability high. Excavation and compaction moderatelyd i f f i cu l t for small power equipment because of steepslopes and large boulders. Foundation stability fair Cogood. Deposits on steep slopes may be subject to land-sliding if overloaded or wetted excessively. Resistanceto erosion good owing to boulders and vegetative cover

Qfa FAN ALLUVIUM (UPPER HOLOCENE)—Reddish-brown bouldery, cobbly,pebbly coarse sand on steep slopes along mountain frontand Fountain Creek

Permeability high. Excavation moderately d i f f icul t forsmall power equipment because of steep slopes and largeboulders. Compaction moderately d i f f i c u l t because oflarge boulders and lack of fines. Foundation sta-bility fair co good; deposits on steep slopes may besubject to landslidlng if underlying clayey shale iswetted excessively. Resistance to erosion fair

Qls LANDSLIDE DEPOSITS (UPPER HOLQCBNK TO KANSAN CLACIATION)—Reddish- to yellowish-brown debris slides and earthflowschiefly on steep slopes along mountain front , on eastflank of Dakoca hogback, along edges of pediments, andalong valley of FounCain Creek. All deposits boulderyand sandy, but clay and silc content varies from abun-dant, where slides involve shaly bedrock, to absent,where slides are derived from Pikes Peak Granite. Uppersurface humraocky. Probably as much as 30 feet thick

Permeability low to high depending on clay content. Exca-vation moderately diff icul t for small power e q u i p m e n tbecause of steep slopes and boulders. Compaction moder-ately d i f f icu l t because of boulders. Foundation stabili-ty very poor to good, depending on moisture conditions,slope, and load imposed. Some deposits may be subjectco further sliding depending on above three factors. Inaddition, some slopes chat have not slid, but that aresimilar to thoae that have, may be potentially unstableunder adverse load and moisture condi t ions and warrantinvestigation before any excavation or construction takesplace. Earthquake stability for both existing slides andpotentially unscable areas probably is very poor. Resis-tance to erosion good if covered by boulders and vegeta-tion; fair if vegecacion lacking

Ql LOESS (LOWER HOLOCENE AND UPPER PART OF PINEDALE GLACIATION)—Light-yellowish-brown silt and some very fine sand.

Has columnar structure and slightly sticky firm consis-tence when moist; hard when dry. Calcareous soil isdeveloped in upper part. Thickness possibly as much as10 feet

Permeability low. Excavation and compaction easy. Wallsof trenches may collapse If not Supnorced by shoring.Foundation s tabi l i ty generally good if excessive wateris not introduced around foundations

Qes EOLIAN SAND (LOWER HOLOCENE AND U P P E R PART OF PINEDALE GLA-CIATION)—Yellowish-brown coarse to fine slightly com-pact sand; silty and clayey in southern part of area.Thickness possibly as much as 20 feet

Permeability medium to high depending on clay content.Clayey soil in upper part slows infiltration of water.Excavation easy. Some compaction under static load;vibratory equipment probably needed for proper compac-t ion. Walls of trenches may collapse if not suppor tedby shoring. Foundation stability generally good, butheavy loads may cause settlement, possibly owing topoor original consolidation. Readily eroded by wind orwater if lacking plant cover. Source of commercialsand

Qb BROADWAY ALLUVIUM (PLEISTOCENE—PINEDALE GLACIATION) —Yellowish-brown gravelly alluvium containing pebbles,cobbles, and boulders along Fountain and Monument Creeksand drainages joining them from the wese; yellowish-brown coarse sand along drainages j o i n i n g from the eaat.Alluvium 1,8 slightly compacted, poorly sorted (nonuni-form-sized particles), and well s t ra t i f ied. Thicknesspossibly as much as 50 feet . Top of alluvial terrace isabout 40 feet above major streams

Permeability is high. Excavacion generally easy wi th lighcpower equipment. Ease of compaction IB variable depend-ing on amounc of fines; mosc of alluvium lacks fines.Foundation stability good. Slope stability probably poor;shoring probably necessary in trenches. Erosion resis-tance good except in coarse sand fades. Source of sandand gravel

Qpt PINEDALE TILL (PLEISTOCENE—PINEDALE GLACIATION)—Gray non-sorted, nonst ra t i f led firmly compacted bouldery sandytill on steep east flank of Almagre Mountain. Thicknessmore than 20 feet

Medium permeability. Excavation and compaction probablymoderately d i f f icu l t for light power equipment becauseof coarseness and steep slopes. Foundation stabilityprobably poor. Erosion resistance probably poor t£vegetation removed. Potential hazard from dams foundedon till

Qlo LOUVIERS ALLUVIUM (PLEISTOCENE—BULL LAKE GLACIATION)—Yellowish-brown gravelly alluvium containing pebbles,cobbles, and boulders along Fountain and Monument Creeksand tributaries joining them from the west; yellowish-brown coarse sand along tributaries joining them f romthe east. Alluvium is weakly compacted, poorly sorted,and well stratified. Thickness probably as much as 40feet. Top of alluvial terrace is about 70 feet abovemajor streams

Permeability generally Is high; however, infiltration maybe slow owing to a clayey soil in the upper part of Chealluvium. Excavation generally easy with light powerequipment. Compaction is moderately easy using vibra-tory compaccors and rubber-tired rollers. Foundationstability generally good. Slope stability fairly good,but shoring probably necessary in trenches. Resistanceto erosion good except in coarse sand facias. Sourceof sand and gravel

Qlo0 Pebbly alluvium similar to above but in slightly youngerterrace about 50 feet above Monument Creek

BULL LAKE TILL (PLEISTOCENE—BULL LAKE GLACIATION):Qbt,, Younger Clll—Gray nonsorted nons t ra t i f ted f i r m l y compact-

ed bouldery sandy till forming low inner ridge aroundLake Moraine. Overlies weathered Pikes Peak Granite,Thickness more than 40 feet

O . b t j Older till—Yellowish-gray nonsorted nonstra t i f led f i rmlycompacted bouldery sandy till forming high outer ridgearound Lake Moraine. Overlies weathered Pikes PeakGranite. Thickness more than 100 feet

Engineering geologic characteris tics of both tills similar.Permeability medium. Excavation and compaction probablysomewhat d i f f i cu l t owing to some large boulders . Foun-dation stability probably poor owing to poor consolida-tion. Slope s tabi l i ty fairly good. Fairly resistant toerosion because of boulders. Potential flood hazardfrom dams founded on till

Qs SLOCUM A L L U V I U M (PLEISTOCENE—SANCAMON 1NTERGLACIATION ORILLINOIAN GLACIATION)—Moderate-reddlsh-brown poorlysorted, moderately compacted, stratified gravel contain-ing layers of clay, si l t , and sand, and clay balls de-rived from shaly bedrock. Near mountains, gravel con-tains larger and more abundant boulders than to ease.Alluvium east of Monument Creek consists of coarsearkosic sand derived f rom Dawson Formation. Stones areweathered and are coated by calcium carbonate. Upperpart of most deposits contains a calcareous soil.Thickness as much as 40 feet. Top of alluvial terraceor pediment gravel is 80-120 feet above major streams

Permeability high in gravel, but generally low in clayeyand silty layers. Excavation and compaction generallyeasy except in bouldery deposi ts . Foundation stabilitygood. Material in vertical cuts generally slumps a f c e ra shore Cime to a slope of 25 degrees or less. Gener-ally resistant to erosion. Source of sand and gravel

Qrof ROCKFALL DEPOSIT (PLEISTOCENE—YARMOUTH? INTERGLACIATIQN)—Extensive deposit of granodiorite boulders formed bylarge catastrophic rockfal l off cast face of CheyenneMountain. Rockfall may have been caused by an earth-quake, and rocks probably moved rapidly downslopc on acushion of air. Boulders are as large as 20 feet indiameter. Most of those below the soil line are deeplyweathered. Deposi t contains little fine-grained mate-rial, in eastern part of area a Chin layer of grano-dlorice boulders overlies; the Pierre Shale. Thicknessprobably more than 20 feet

Permeability high. Excavation and compaction di f f icul twhere boulders ;tre large. Foundation stabil i ty goodunless foundation projects down InCo Pierre Shale,VerClcal cuts subject to small rockfalls. Resistant toerosion. Earthquakes could trigger additional rockfallson most steep slopes.

Qv VERDOS ALLUVIUM (PLEISTOCENE—YARMOUTH INTERCLACIATION ORKANSAN GLACIATION) —Brown poorly sorted, moderatelycompacted, s t rat i f ied gravel containing lenses of sand,silt, and clay. Deposits near the mountains containlargest stones. Stones are weathered and are coated bycalcium carbonate. Upper part of most deposits containsa calcareous soil. Thickness locally nearly 100 feet .Top of alluvial terrace ar pediment gravel is 160-200feet above major streams, Locally divided;

Ojv_ Lower terraceQv. Upper terrace

Permeability high in grave], but generally low in clayand silt lenses. Excavation and compaction generallyeasy except in bouldery deposits. Foundation stabilitygood for small structures but subject to collapse ofs t ruc tu re when wetted under heavy loads. Material invertical cuts generally slumps a f t e r a short time to aslope of 25 degrees or less. Resistant to erosion.Source of sand and gravel

Qrf ROCKY FLATS ALLUVIUM (PLEISTOCENE—AFTONIAN INTERGLACUTTONOR NEKRASKAN GIACTATION)—Reddish-brown pebble, cobble,and boulder gravel In western part of area. Largestboulders are near mountains. Clayey coarse sand ineastern pare of area. Alluvium poorly sorted, firmlycompacted, and stratified. Scones altered and coatedby calcium carbonate. Upper part of most deposits con-tains a calcareous soil. Thickness locally more than50 feet . Top of alluvial terrace or pediment gravellies 260-280 feet above modern streams

Permeabi l i ty moderately high. Excavarion and compactioneasy except where boulders are large. Foundation sta-bility good. Slope stab'.lity good; excavations standIn vertical walls for mo .ths, but eventually slump to2S-do8'-«(i sitnpcs. RPSi'-ant to aroeHon. £ouro*> ofSand and gravel

Qn NUSSBAUM ALLUVIUM (PLEISTOCENE—NEBRASKAN? GLACIATION)—Brownish-gray poorly sorted, firmly compacted, strati-fied bouldery alluvium south of Little Fountain Creekwhere gravel is composed of granite, porphyry, andgneiss. Brown well-stratified, fairly well sorted,weakly compacted coarse sand and pebble gravel becweenWilliams Canyon and Queens Canyon, where gravel is com-posed of fragments of Pikes Peak Granite, Precambrianbiotite gneiss, and lower Paleozoic sandstone and lime-stone. Large boulders abundant near mountain front .Stones altered by weathering and coaced by calcium car-bonate. Upper part of mosc deposits concains a calcar-eous soil; another soil horizon lies near middle ofgravel south of Little Fountain Creek. Thickness morethan 80 feet. Top of pediment gravel in this area is550 to 700 feet above modern streams

Permeability good. Excavation and compaction easy exceptfor some large boulders. Dusts badly when used as roadmetal. Foundation s tabi l i ty good. Slope stabilityfairly good; vertical cuts stand for a long time, thenslump to a slope of 25 degrees or less. Fiiirly resis-tant to erosion. Source of sand and gravel

Tdg GRAVEL AT DIVIDE (MIDDLE PLIOCENE? TO UPPER MIOCENE?) —Brownclayey, si l ty, sandy gravel In extensive paleovalley online with West Monument Creek. Poorly sorted, poorlys t r a t i f i e d , f i rmly compacted. Covered almost exclusivelyby grass. Contains boulders as large as 3 feet in lowergray part of channel f i l l , which possibly is Oligocene inage (Chadron—equivalent Co Cascle Kock(? ) Conglomerate).Finer part of gravel composed chiefly of Pikes PeakGran i t e , but contains metased tmentary rocks and othergranitic rocks. Most of larger stones consist of vol-canic rocks derived f rom Thir tynine Mile volcanic 'fieldand from Cripple Creek volcanic field. Thickness nearly100 feet

Permeability probably low, Excavation and compaction easy.Foundation stability good. Vertical cuts are stable forshort time, then slump to slope of 40 degrees. Erosionchecks probably required. Source of road metal or fill,but not of concrete aggregate

DAWSON FORMATION (PALEOCENE AND UPPER CRETACEOUS)—Containsarkosic and andesitic (minor) units, in part occurringIn separate beds. Total thickness of format ion Is about2,000 feet

TKd Upper part—Highest arkosic uni t , covering greatest area,contains white and yellowish-gray coarse sand, orangehard thin Lronscone layers, and light-green claystone.Next lower unit conCalns mixed yellowish-gray arkosicand olive-brown andesi t ic material composed of sand-sCone, siltscone, claysCone, and thin layers of ande-site pebbles. Next lower unit concains c l i f f - fo rm ingarkosic coarse sandsCone cropping out in an arc markedpartly by Pulpit Rock, Austin B lu f f s , and Palmer Park.Thickness about 1,800 feet

Kda Lower part—Olive-brown andasitic sandstone, siltstone,and claystone containing andcst te pebbles. Thicknessabout 200 feet

Permeabi l i ty probably is medium In the arkosic sandstoneand low in the siltstone and claystone and in the ande-sitic beds. Availability of ground water is discussedby Cardwell and Jenkins (1967). Excavation is moder-ately diff icul t in unweathered claystone and siltatoneand moderately d i f f i c u l t to d i f f i cu l t In the sandstonebeds; blasting'may be necessary in the cliff-formingarkosic sandstone. Compac t ion is moderate ly d i f f i cu l tin the claystone and siltstone to very d i f f i cu l t In thesandstone. Foundation stability is good in the sand-stone, but probably poor In the claystone and siltstone,which may have low to high swelling properties—espe-cially the andesitic claystone. Some beds slake rapid-ly on exposure co ale, and caissons should be pouredsoon after holes are drilled. Slope stability is goodin sandstone beds but poor in claystone and siltstonebeds. Most beds, except hard sandstone, erode easily

Kl LARAMIE FORMATION (UPPER CRETACEOUS)— Dark-grayish-brown oryellowish-gray fine-grained iron-stained sandstone,olive-gray claystono, and subbituminous coal bods.Thickness about 250 feet

Permeability medium. Availability of ground waCer :t<t dis-cussed by Cardwell and Jenkins (1967)• Excavation mod-erately d i f f icu l t In che harder sandscone beds whererippers and Che largest tracked vehicles or, locally,even blasting may be necessary. Compact ion also diff i -cult except in the softer more shaly beds. Founda t ionstability excellent on the sandstone beds but poor inthe olive-gray claystone beds, which may have low tovery high swelling potential. Subsidence is takingplace above mined-out ar,eas where coal was extracted(mines not shown). Slope stability good except in shalyand coaly beds. Resistance to erosion moderate to ex-cellent. Source of coal and clay

Kf FOX HILLS SANDSTONE (UPPER CRETACEOUS)—Light-olive-graythin-bedded friable sandy shale in upper 100 feet andolive-brown massive friable fine-grained sandstone inlower 150 feet . Concains phospliatlc pebbles throughout.Thickness 250 feat or more

Permeability medium. Availability of ground water is rttfl-cussed by Cardwell and Jenkins (1967). Excavation ofsandstone moderately difficult ; rippers and large trackedvehicles probably are necessary. Compaction d i f f i c u l t ifsandstone breaks in angular blocks. Foundation stabilitygood to excellent. Slope stability good except in shale,which slumps somewhat from a vertical cu t . Erosion re-sistance good

P f K R R E SHALE (UPPER CRETACEOUS)—Marine shale containing ben-tonite bads and wcll-prtserved fossils. Ranges in thick-ness from 3,750 to 5,200 .feet

Upper transition member—Predominantly sandy beds. Thick-ness 400 co 590 feac

Kpt Upper part—Yellowish-gray shale, siltstone, and sand-stone; only mapped locally. Thickness 400 feet

Kps Lower pa r t—Sof t olive-brown sandsCone; concains layersof phosphacic nodules; only mapped locally. Thickness190 feec

Kp Main pare of formation—Predominantly shaly beds. Upperpart Is clayey shale containing fibrous aragonite andcone-in-cone structure, underlain by dark-gray shalysandstone above middle of fo rmat ion . Under la in by clayeyshale containing large irregular gray limestone massesthat weather into conical mounds called tepee buttes.Under la in by s o f t shaly yellowish-brown sandstone belowmiddle of format ion. Underlain by silty noncalcareousshale containing ironstone nodules, then by a thin ridge-forming sli tstone, then, at the base, by olive-grayclayey calcareous shale. Thickness 3,150 to 4,800 feet

Permeability low. Excavation and compaction easy exceptfor tepee buttes. Foundation stabili ty poor; much ofshale has low to very h i g h swelling potential, especiallythe bentonite beds, Slope stability poor; vertical cutsmay collapse, Shale in slopes no steeper than 5 degrees

slide, if che coe of che slope is removed. Erosioncheck da

for brick and tile and of bloated clay for manufac-ture of light-weight aggregate

NIOBRARA FORMATION (UPPKIJ CHKTACEOUS)Smoky Hill Shale Member—Yellowish-brown s o f t thin-bedded

calcareous shale and incerhedded thinly layered lime-stone. Seven units from top to bottom: (1) yellowish-orange ridge-forming upper chalk u n i t ; (2) yellowish-orange upper chalky shale uni t ; (3) yellowish-grayridge-forming middle chalk or limestone unit; (4) dark-gray middle shale unit; (5) gray ridge-forming hardplaty lower limestone unit; (6) dark-gray fissile toplaty lower shale uni t ; and (7) gray shale and limestoneunit . Thickness probably more than 530 feet

Permeability low. Excavation fairly easy in che shale,buC moderaCely d i f f i cu lc in Che chalk and limestonebeds. A small backhoe can excavate only with greatdi f f icul ty Che lower limestone to a depth of 10 feet;the shalu and limestone uni t requires more powerful equip-ment. Compaction easy except where large blocks arepresenc. Foundat ion stability fairly good; however, theshale contains some swelling clay and bentoni te beds.Slope stabl-licy good- Erosion resisCance moderatelypoor; check tUnna probably are needed. Potential sourceof cement rock and smelter limestone

Fort Hays Limestone Member—Cray hard limestone beds,

1-26 inches thick, separated by thin shale part ings.Thickness about 30-40 feet

Permeability poor. Excavation and compact ion d i f f i c u l t .Foundation s tab i l i ty excellent. Slope s tabi l i ty excel-lent, except on an undercut dip slope. Erosion resis-cance good. Source of cement rock and smelter lime-stone

Knc NTOBKARA FORMATION, C A K L I L E SHALE, GREENHORN LIMESTONE, ANDCRANEROS SHALE UNDIVIDED (UPPER CRETACEOUS).

Kcgg CARLILE SHALE, GREENHORN LIMESTONE, AND GRANEROS SHALE(UPPER CRETACEOUS)—Total thickness about 300 feet

Carlile Shale—In descending order, Juana Lopez Member ,grayish-brown hard calcarentte (sandy limestone com-posed of shell fragments); Codell Sandstone M e m b e r ,yellowish-gray massive to thin-bedded sandstone; BlueHill Shale Member, dark-gray noncalcareous shale con-caining large sepCarian concreClans; Fa i rporc ChalkyShale Member, yellowish-gray sofc calcareous shale

Greenhorn Llmescone—In descending order. Bridge CreekLimestone Member, gray dense limestone beds and grayhard calcareous shale; Hartland Shale Member , gray shalycalcarenlcc; Lincoln Limestone Member, grayish-brownthin beds of hard caicarenite and shaly calcarenitecontaining marker bentonite at base

Graneros Shale—Dark-gray hard clayey shaleThe Carlile, Greenhorn, and Craneros Formations share

similar engineering properties as follows: Permeabilityis low except in the Codell. Excavacion and compactionare moderately easy excepc in the Juana Lopez, Codell,and Bridge Creek Members, where chey are d i f f i c u l t .Foundation s t ab i l i t y Ls f a i r Ui pi.mr, .mil the shalemembers have some swelling properties; however, CheJuana Lopes, Codell, and Bridge Creek Members have ex-cellenc scability. Only Che Juana Lopez, Codell, andBridge Creek scand well in vercical cues and resisterosion; all other units are stable only In slopes of5-10 degrees or less, and erode readily

Kdp DAKOTA SANDSTONE AND PURGATOIRE FORMATION (LOWER CRETACEOUS)Dakota Sandstone—Yellowish-brown fine-grained crossbedded

sandstone containing some shale (Dry Creek Canyon Member)In the upper middle part

Purgatolre Formation—Glencairn Shale Member, at top, con-tains shale, clay, and some gypsum; underlain by cheLytle Sandscone Member, which conCalns fine- co coarse-grained sandstone and pebbly beds

Permeability is medium. Excavation is d i f f i c u l t , andblasting may be required. Compaction is difficult .Foundation stability is excellent. Slope stability isexcellent except that rocks on dip slopes may slide ifundercut. Erosion resistance is excellent

Jmr MORRISON FORMATION AND RALSTON. CREEK FORMATION (UPPERJURASSIC)

Morrison Formation—Varicolored gray, maroon, and greensiltscone and claystone and th in beds of sandstone, lime-stone, and conglomerate. Thickness 225 feet

Ralston Creek Formation—Sandstone, siltstone, gypsum, andbeds of limestone containing red jasper grains. Thick-ness 20 feec

Permeability low. Excavation moderately diff icul t below a5- to 10-fcr^t weathered zone. Compaccion fairly easy.Foundation stability poor to fair. Slope stabilitymoderately good. Erosion resistance fair; erosionchecks probably needed

1 PI LYKINS FORMAT ION (TRIASSIC? AND PERMIAN)—Maroon and greensilty shale; white, maroon, and pink fine-grained sand-stone, limestone, and gypsum. Thickness 180 feet

Permeability low to medium. Excavation and compactiondiff icul t to impossible for small power equipment suchas a truck-mounted backhoe or a small tracked vehicle.Foundation stability good except on the gypsum. Slopeson most beds stand vertically for long time. Fairly

Ply LYONS SANDSTONE (PERMIAN)—Red and yellowish-gray fine-grainedsandstone consisting of resistant upper and lower ridge-forming units separated by less resistant sandstone, andlocally, conglomerate. Thickness 700-800 feet

Permeability medium. Excavation and compaction difficultto impossible for small power equipment. Foundationstability excellent. Slope stabil i ty and erosion resis-

PlPf FOUNTAIN FORMATION (PERMIAN AND PENNSYLVANIAN)—Moderate-reddish-brown arkosic conglomerate, yellowish-gray coarse-grained arkosic sandscone, and thin layers of pale-greenand dark-reddish-brown shale. Glen Eyrie Shale Member,at base, consists of gray sandscone, sandy shale, andblack shale about 100 feet thick. Thickness of formation4,400 feet

Permeabilicy medium Co low. Excavacion and compaction verydiff icult to Impossible for small power equinmenc. Foun-dation stability excellent. Slope stability and erosionresistance excellent

MCr MISSISSIPPIAN, ORDOViCIAN, AND CAMBRIAN ROCKS—Parts of thisunit locally are mapped separately. Includes in descend-ing order:

Leadville and Williams Canyon Limestones (Mississtppian)—Both are dark gray, hard, dense. Thickness about 130feet

Ohm Harding Sandti tone (Middle Ordovician)—Yellowish-gray andgreenish-white fine-grained Chin-bedded sandstone andreddish-brown sandy shale. Thickness about 65 feet

Manitou Limestone (Lower Ordovician)—Reddish-gray thlck-

chercy in upper pare. Limestone is deformed by solutionnear Manitou Springs. Thickness about 185 feet

Peerless Dolomite (Upper Cambrian)—Dark-red finely tocoarsely crystalline granular glauconitic thin-beddeddolomite. Thickness about 40 feet

6s Sawacch Sandscone (Upper Cambr ian)—Reddish-brown, white,and green fine- Co coarse-grained well-bedded sandscone.Clauconitic in upper part. Contains some dolomite beds.Thickness about 25 feet

-€sd Sandstone dike (Cambrian?)—Reddish-brown hard quartziticfine-grained sandstone filling parts of Ute Pass faultand subsidiary parallel fractures. Thickness locallymore than 30 feet

Engineering properties of above units are similar. Perme-ability low excepc in solucion cavities. Springs commonnear Manitou Springs. Excavation and compaction d i f f i -cult; blasting required. Foundacion stability and slopestability excellent, except where solution has madecaverns and loose breccia zones in limestone. Erosionresistance excellent. Leadville, Williams Canyon, Mani-cou, and Peerless Formations are sources of crushed stonefor use as concrete aggregate

PRECAMBRIAN ROCKS—Mapped separately, as described individu-ally below. All Precambrian rocks share similar engi-neering properties as follows:

Permeability low to nonexistent excepc along joints andother fractures, or where rocks are weathered or arecovered by chin veneers of alluvium or colluvium; thenpermeability Is medium to high, Weachered layer (grus)on Pikes Peak Granite locally exceeds 25 feet in thick-ness. Weathering in other units is thinner, especiallyin che porphyry ae che Keeton Ranch (Galloway, 1956),Windy Point Granite, and quartz monzonite. Excavationmust be preceded by drilling and blasting, except thatin the weathered zone excavation wi thout recourse toexplosives is easy to moderately difficult for smallpower equipment . Compaction probably is d i f f i c u l c acmosc sices because of a lack of fines and because oflarge blocks. Foundation stability generally is excel-lent except on steep slopes such as the canyon walls ofFountain Creek, where weathered Pikes Peak Granite issubject to landsliding, and on Che east flank of CheyenneMountain where che granodiorice is subjecc to rockfalls.Slope stability and resistance to erosion are excellentexcept in the deeply weathered grus. Potential floodhazard exists where dams are founded on weathered PikesPeak Granite,

n LAMPROPKYRE (PRECAMBRIAN Y)—Black f inely crystallinetabular masses in the Pikes Peak batholith interpretedas dikes chat are discontinuous at the surface, but

Yk PORPHYRY AT THE KEETON RANCH (GALLOWAY, 1956) (PRECAMBRIAN Y)—Reddish-brown quartz monzonite porphyry. Euhedral pla-

gloclase phcnocrysts form about one-third of the rock;bipyramidal quartz, opaque iron oxide, and mafic crystalsaltered to carbonate, chlorite, and nontronite form smallphenocrysts; groundmass is micrographic intergrowth ofquartz and perthitic potash feldspar

Ymr MOUNT ROSA G R A N I T E (PRECAMBRIAN Y)—Light-gray granice. Con-tains riebeckite in rosette clusters; generally mediumbut locally finely crystalline or pegmaCitic; age rela-tive Co Windy PoinC Granite unknown, but approximatelycorrelative

Ywp W I N D Y POINT GRANITE (PRECAMBRIAN Y)—Gray to pink finely crys-talline p o r p h y r i t i c granite or quartz monzonite. Con-tains biotite in rounded clusters; same as porphyriticgranite of Gross and Hainrtch (1965)

Ync GRANITE OF NELSON CAMP (PRECAMfiRIAN Y)—Tan to greenish-brownmedium-crystalline biotite granite. Contains minorastrophyllice and riebeckite

Yam GRANITE OF ALMAGRE MOUNTAIN (PRECAMBRIAN Y ) — P i n k oquigranu-lar medium-crystalline biotite granite. Contains inter-locking tabular microcline crystals and prominent roundedquartz grains

Ypp PIKES PEAK GRANITE (PRECAMBRIAN Y)—Pink to reddish-tanmedium to coarsely crystalline bioti te*or hornblende-bioti te granite or quartz monzonite. Encloses many peg-matites that locally contain crystal-lined miarolitic

broic or dtobasic dikesYfg FAYALITE GRANITE (PRECAMBRIAN Y)—Dark-green medium-crystal-

line bioti te granite. Contains small amounts of faya-lite or Its pseudomorphs. Occurs as xenolithic segre-gations in Pikes Peak Granite

Yqm QUARTZ MONZONTTti (PRECAMBRIAH Y)—Pinkish-gray bodies ofintrusive rock having numerous semi-alined tabular crys-tals of potash feldspar in a medium-crystalline matrix.Contains muscovite, biotite, feldspar, and quartz; cor-related wich Che Silver Plume Quartz Monaonite of thecentral Front Range

Xgd GRANODIORITE AND QUARTZ DIORITE ( P R E C A M B R t A N X)—Dark-graymedium to coarsely crystalline, biotitic; generallygnelsslc; minor amounts of quartz dioritc. Correlatedwith the Boulder Creek Granodiorite of the central FrontRange

Xgnb BIOTITE GNEISS (PRECAMBRIAN X)—Gray plagioclase-quartz-blotite gneiss. Locally contains muscovite, sillimanite,garnet; minor interlayers include hornblende gneiss andother variants

• CONTACT

5 FAULT U, upthrown side; D, downthrown side

REFERENCESCardwell, W. D. V.., and Jenkins, E. D . , 1967, Ground water ,

_in_Varnes, D. J., and Scott, G. R., General and engineer-ing geology of the United States Air Force Academy site,Colorado: U . S . Geological Survey Professional Paper 551,p. 81-89.

FInlay, G. I., 1916, Description of the Colorado Springsquadrangle, Colorado: U . S . Geological Survey GeologicAtlas, Folio 203, 17 P - , mans.

Galloway, J, D . , 1956, Petrology of the Keeton Porphyry, ElPaso County, Colorado: Iowa State College M.S . thesis.

Grose, L. T,, i960, Geologic formations and s t r u c t u r e of Colo-rado Springs area, Colorado, p, 188-195, in. Rocky MountainAssociat ion of Geologises, Guide to the geology of Colo-rado; Geological Society of America, Rocky Mountain Asso-ciation of Geologists, and Colorado Scientific Society,303 p.

Gross, E. H . , and H e i n r l c h , E. W. , 1965, Petrology and miner-alogy of the Mount Rosa area. El Paso and Teller Counties,Colorado—[E'c . l 1, The granites: American Mineralogist,v, 50, no. 9, p. 1273-1295.

Harms, J. C . , 1959, Structural geology of the eastern flankof the southern Front Range, Colorado: Colorado Univer-s i ty Ph .D. thesisJ available from Universicy M i c r o f i l m s ,Inc., Ann Arbor, Michigan, 165 p.

Varnes, D. J. , and Scocc, G. R., 1967, General and engineer-ing geology of Che UniCed States Air Force Academy site,Colorado, w l c l i a flirt ion on Ground wate r , by U. D. E.Cardwell and E, D. Jenkins: U . S . Geological SurveyProfess iona l Paper 551, 93 P.

RECONNAISSANCE GEOLOGIC MAP OF COLORADO SPRINGS AND VICINITY, COLORADOBy

Glenn R, Sco t t and Reinhard A, Wobus

1973