PERMFILE44303 - Laserfiche WebLink

Home Browse Search

T. r T. 660C FE I3 43) 39 °37'30" 1( DEPARTMENT OF THE INTERIOR UNITED STATES GEOLOGICAL SURVEY Photorevised in 1971 10,000 -foot grid based on Colorado coordinate system, central zone 1000 -meter Universal Transverse Mercator grid ticks, zone 13, shown in blue —x1111 I1d IIII I I� — IIIaIV lull a II SCALE 1:24000 1 Yz 0 -� 1 MILE 11 0 1 KILOMETER CONTOUR INTERVAL 40 FEET DA UM IS MEAN SEA LEVEL Vn ul3u' Geology mapped during 1966 -72. Geology of the western part of the quadrangle has in part been revised from COLORADO Gable (1968). Geology of sedimentary rocks in part adapted from Smith ( 19 64) . Geology of surficial Deposits in part adapted from Pearl (1968). Contact between sedimentary and crystalline QUADRANGLE LOCATION rocks in part mapped in 1966 by C. T. Wrucke. Assistance on photogrammetric plotting by C. L. Pillmore and R. R. Beins. Assistance In the field by Juanita M. Scott GEOLOGIC MAP OF THE MORRISON QUADRANGLE, JEFFERSON COUNTY, COLORADO By Glenn R. Scott 1972 3 °45' f J 3S 4 S. u CORRELATION OF MAP UNITS Unconformity Qe Un conformity Qb Unconformity Qlo Unconformity s 0Qs7 Q QS1 Unconformity Unconformity Unconformity Qn Unconformity and local major uplift Unconformity and local uplift fish ti Td its Unconformity and local uplift Tt3 TKcI Tt2 Ka Unconformity and local major uplift Unconformity Kc Kcgg Kgh Kg Kty .' Unconformity Jm Unconformity Jr Unconformity Plb PI Plf I Unconformity PPf Major inconformity and uplift YbV NYI Xgnm Xgng XgrtIS Q. Pleistocene Pleistocene to Eocene (?) Lower Cretaceous Upper Jurassic Precambrian Y ( ?)' X' TERNARY JURASSIC TRIASSIC ( ?) PERMIAN PENNSYLVANIAN PRECAMBRIAN IGS °22'30" 15' 7.30" 40°07,30 "i T 103 °00 - 52'30" 104.45' ;"74 o� Fe JQ4fld 4o•ca' 0flJ R °IILUEK Ofl T— .,P, c. - c. 1WELD' —�- a'• 5230^ 45'1 "`* 37'30.. 39.30' 0 10 lG Mllis INDEX SHOWING LOCATION OF MORRISON QUADRANGLE DESCRIPTION OF MAP UNITS Surficial deposits, where mapped, generally are 5 feet or more thick ARTIFICIAL FILL - Includes uncompacted rubbish, uncompacted dumped fill, and compacted select fill. Rubbish is unsuitable for most foundations and is a source of pollution to shallow water supplies. Dumped fill commonly contains large blocks of concrete or other debris and voids that make it unsuitable for most founda- tions. Compacted fill generally is placed under highways and in small earth dams at optimum moisture and maximum density ACTIVE LANDSLIDE (UPPER HOLOCENE) - Earthflows on north- east and southwest sides of Green Mountain and in northern part of Red Rocks Park. Slides were moving in 1971 Qpp POST -PINEY CREEK ALLUVIUM (UPPER HOLOCENE) - Dark - gay humic sandy to gravelly alluvium containing sticks and roots. Only along major streams where it forms flood plain and one or rarely two terraces less than ten feet above stream level. Lies within channels cut into Piney Creek Alluvium along arroyos and valleys, but overlies Piney Creek Alluvium where arroyos are not cut. Underlain by older gravelly alluvium along large valleys. Thickness about 5.15 feet. Most seasonal floods cover this unit Qn PINEY CREEK ALLUVIUM (UPPER HOLOCENE) - Dark -gay to F reddish -brown humic clayey silt and sand containing layers of pebbles, generally in lower part. Underlain by older gravelly allu- vium or bedrock. Grades upslope into cofluvium. Contains upper Holocene weak Brown soil in upper part. Thickness 5 -20 feet. Terrace is 10.20 feet above modem streams. Generally not covered by seasonal floods YOUNG LANDSLIDE (HOLOCENE) - Earthflows obviously younger than nearby landslides. All are on or near Green Mountain TALUS (UPPER HOLOCENE) - Block rubble of Precambrian rock types on steep unstable slopes along Bear Creek ® LANDSLIDE (UPPER HOLOCENE TO PLEISTOCENE) - Land- slides in the Precambrian rocks; earthflows mostly on Green Moun- tain near top of Denver Formation and in Green Mountain Con- glomerate but also below the middle Shoshonite flow (of the Table Mountain Shoshonite) in Denver Formation on South Table Moun- tain and on north flank of pediment on Denver Formation east of Youngfield Avenue and north of Colfax Avenue. Most steep slopes in Denver Formation and Green Mountain Conglomerate � are potentially unstable. Some slides are as old as Pleistocene �J COLLUVIUM (UPPER HOLOCENE TO PLEISTOCENE) - Dark -gay to reddish -brown bouldery to sandy silt and clay on slopes in mountains and plains where it was deposited by gravity and sheet wash. Grades downslope into Piney Creek Alluvium. Locally con- tains some alluvium. Generally thicker than 5 feet. Ranges in age from Holocene to pre-Bufl lake; most is Piney Creek or Louviers in age. Contains soil in upper part r Qe EOLIAN SAND (LOWER HOLOCENE AND UPPER PART OF PINEDALE GLACIATION) - Light -brown well- sorted medium sand in two small patches on high areas, one on U.S. Highway 6 2 miles south of Golden and the other one mile north of Bear Creek new the east edge of the quadrangle. Brown soil of early Holo- cene age (Altithermal) in upper part. Blown from bedrock during early Holocene aid climate BROADWAY ALLUVIUM (PLEISTOCENE - PINEDALE GLA- CIATION) - Yellowish-orange to light -brown sandy to clayey alluvium along small intermittent streams or cobbly alluvium along major streams. Contains fossil mollusks. Thickness prob- ably about 25 feet. Brown soil of early Holocene age (AltithermaU in upper part. Terrace is 25-40 feet above modern streams Qlo LOUVIERS ALLUVIUM (PLEISTOCENE - BULL LAKE GLA- CIATION) - Reddish -brown pebbly to bouldery alluvium along permanent streams and sandy to clayey alluvium along intermit- tent streams. Coarse alluvium is stained by manganese and iron. Thickness probably more than 25 feet. Terrace is about 65 feet above modern streams. Strong Brown soil of post -Bull Lake pre - Pinedale age in upper part. Alluvium contains fossil mollusks. Six -foot boulders in torrential flood deposit between Bear Creek and Turkey Creek resulted from flash flood during capture of Turkey Creek by small tributary of Bear Creek. Turkey Creek in pre - Louviers time flowed southeast from gap in Dakota hogback SLOCUM ALLUVIUM (PLEISTOCENE - SANGAMON INTERGLA- CIATION) OR ILLINOIAN GLACIATION - Moderate-reddish- brown pebbly silt and clay interlayered with gravel. Gravel con- tains larger and more abundant boulders new mountains than to east. Stones are altered by weathering and are coated by calcium carbonate, Thickness probably averages about 15 feet. Contains fossil mollusks. Upper part of most deposits is overbank silt on which a very strong Brown soil of pre -Bull Lake (Sangamon?) age is developed. The B t(clayenriched) horizon of this soil commonly has a high swell potential a: Lower of two terraces or pediments lies about 100 feet above mod- ern stream Upper terrace or pediment lies about 120 feet above modern stream VERDOS ALLUVIUM (PLEISTOCENE - YARMOUTH INTERGLA- CIATION) OR KANSAN GLACIATION - Yellowish -brown pebbly silt and clay interlayered with gravel. Gravel contains larger and more abundant boulders near mountains than to east. Stones are altered by weathering and are coated by calcium car- bonate. Thin beds of sand are crudely interlayered with thick beds of gavel. Upper part of most deposits is overbank silt oh which is a very strong Brown soil of pre -Bull Lake (Yarmouth ?) age. B horizon commonly has high swell potential. Cos (white calcium carbonate-enriched horizon) underlies B horizon and has abrupt upper boundary but has stringers that fade out downward at about 4 or more feet. Thickness of alluvium averages IS feet Lower of two terraces or pediments lies about 200 feet above mod- ern stream Upper terrace or pediment lies about 250 feet above stream. ABU- ®vium in upper terrace contains ash layer (Qva) in lower part Pearlette -like volcanic ash layer type 0 of Izett and others CI 970) - a white water -laid ash that chemically and mineralogically re- sembles the ash of the Cudahy pit, Meade County, Kansas ROCKY FLATS ALLUVIUM (PLEISTOCENE - AFTONIAN INTER - GLACIATION) OR NEBRASKAN GLACIATION - Reddish - brown pebbly silt and clay interlayered with gavel. Gravel in Rocky Flats y Alluvium from Green Mountain is finer than from mountains. Stones deeply weathered, and, in upper part of de- posit, coated by calcium carbonate. Very strong Brown soil of pre -Bull Lake (Aftonian ?) age developed in upper part. Pediment lies about 350 feet above modern streams. Inferred Rocky Flats erosion channel preserved in Mount Vernon Canyon and in wind - gap through Dakota hogback west of Green Mountain. Thickness of alluvium 10-15 feet _ ROCKSLIDE (PLEISTOCENE - NEBRASKAN GLACIATION) - Urge volume of Fountain Formation that slid down dip slope along east side of Mount Morrison. Slide possibly was caused when stream flowing parallel to mountain front between Nussbaum and Rocky Flats time undercut Fountain Formation NUSSBAUMU) ALLUVIUM (PLEISTOCENE) - Yellowish -brown bouldery alluvium in northeast comer of quadrangle. Thickness probably about 10 fcet. Strong soil of pre -Bull Lake age lies in the upper part of alluvium. Pediment is about 450 feet above modern streams SAPROLITIC WEATHERED ZONE (PLEISTOCENE to EOCENE ?) - Approximate extent of deeply weathered zone more than 8 feet thick over much of nearly level upland on lookout Mountain. Up- land surface probably cut in Eocene( ?) time and then weathered for past 38 million years. Remnants of surface are preserved on Precambrian rocks between Mount Morrison and Ralston Creek north of area _ SHONKINITE ( TERTIARW) - Dark -brown to black medium - grained rock in a small igneous Plug northwest of Mount Falcon. Chief minerals are sanidine, clinopyroxene, and biotite. Weathers to rounded boulders _ DIABASE (TERTIARY) - Dark -gray dense rock in narrow igneous dikes. Principal minerals are labradorite, pyroxene, and magnetite. _ GREEN MOUNTAIN CONGLOMERATE' (PALEOCENE) - Upper 200 feet is mainly conglomerate, but contains some sandstone and claystone; next 250 feet is thin- bedded claystone, siltstone, sandstone, and conglomerate; next 150 feet is conglomerate and sandstone; in lowermost 50 feet is yellowish -brown cobble -and- boulder conglomerate. Grain size of conglomerate increases up- ward. Andesite pebbles make up small part of lower conglomerate and decrease upward. Other stones are gneiss, pegmatite, quart- zite, and sandstone. Contains pollen and plant fossils of Paleocene age in lower 450 feet. Thickness 650 feet. East - trending erosion channel inferred in mountains west of thick pile of coarse Green Mountain Conglomerate TABLE MOUNTAIN SHOSHONITE'(PALEOCENE) - Dark -gray porphyritic flow rock crops out as two flows interlayered with andesitic sedimentary rock above middle of Denver Formation on South Table Mountain. Lowest of three flows crops out north of area (Van Horn, 1972, unit Tv 1). Shoshonite is potassium -rich basalt and contains augite, plagioclase, olivine, and magnetite set in a fine- grained groundmass. Cavities contain wolite minerals. Total thickness of both flows is about 150 feet Upper flow Tt2 Middle flow TKd DENVER FORMATION (PALEOCENE AND UPPER CRETA- CEOUS) - Yellowish -brown to grayish -olive fluvial claystone, siltstone, friable sandstone, and conglomerate, and interlayered olive -gray mudflows ranging from clay containing a few small volcanic pebbles to clay containing a preponderance of boulder - sized angular volcanic blocks or rounded boulders. Sandstone and finer grained fluvial rocks gre tuffaceous and commonly weather to montmorRlonitic clay having low to high swell poten- tial. Fluvial conglomerate is composed of about 95 percent an- desitic volcanic rocks and 5 percent granitic igneous and metamor- phic rocks. Although quite altered, conglomerate has high pene- tration resistance. Clayey matrix in mudflows also weathers to montmorillonite having high swell potential. Blocks of potassium - rich Shoshonite in mudflows are only slightly weathered. Heu- landite and chabazite partly fill cavities in the pebbles and sand- stone. Some fine -gamed layers are unstable on slopes as gentle as 8 °; many earthflows were mapped on slopes steeper than 150 Denver Formation contains fossil leaves, dinosaur and mammal bones, and silicified wood. Thickness 950 feet ARAPAHOE FORMATION (UPPER CRETACEOUS) - Coarse -and fine -grained sandstone, siltstone, claystone, and thin pebble beds in upper part; white, yellowish -gray, and yellowish- orange coarse - grained sandstone and poorly sorted pebble-and-cobble conglom- erate in lower part. Stones from sedimentary rocks make up about 60 percent and igneous and metamorphic rocks about 40 percent of basal conglomerate° but proportions reverse upward. Sandstone composed of quartz, feldspar, and mica. Conglomerate contains shale blocks 4 by 2 feet, sandstone blocks 1 by 1 foot, chert, and petrified wood. Cut- and -fill structure in conglomerate. Contains concretions and layered concentrations of ironstone and ®dinosaur bones. Thickness 400 feet LARAMIE FORMATION (UPPER CRETACEOUS) - Upper part is light -gray micaceous siltstone stained yellowish orange, light -, olive -, and pinkish -gay silty claystone, grayish -brown Bgnitic claystone, minor white and yellowish- orange friable ridge - forming sandstone, and near top thin layers of conglomerate composed of pebbles of sedimentary rocks. Sand gains are quartz and chert. Yellowish- orange sandy ironstone concretions. Lower part is almost entirely yellowish -gray iron-stained and white "salt -and- pepper" friable sandstone composed of quartz, biotite mica, and kaolinized feldspar. Sandstone 110 feet thick at base is considered Fox Hills Sandstone by one authority. Gray sandstone contains gay shale chips. Contains thin ironstone layers and shale layers near base. Subbituminous coal beds as thick as 8 feet lie in lower 200 feet above basal sandstone. Abandoned coal mines are areas of potential subsidence, as in the valley south of Alameda Park- way. Gray or white claystone in beds more than 10 feet thick is used for manufacture of brick and tile. Contains fossil leaves, wood, and other plant remains. Thickness 550 feet FOX HILLS SANDSTONE (UPPER CRETACEOUS) - Upper 105 feet is olive -gay to dark - yellowish -brown silty shale and inter- bedded wavy- banded friable micaceous sandstone. Shale contains flattened gray limestone concretions 12 inches in diameter. Lower 75 feet is yellowish- orange massive to thin- bedded, locally cross - bedded, friable fine- gained ridge - forming sandstone and inter- bedded dark-olive-gray shale and claystone. Contains large reddish - brown hard calcareous iron- stained sandstone concretions about 65 feet above base. Shale beds are abundant new base. Contains large flow casts about 20 feet above base. Contains fossil Pricey - pods in lower part of upper shale and at top of lower sandstone. Thickness 180 feet. Entire mapped formation is considered Pierre Shale by one authority PIERRE SHALE (UPPER CRETACEOUS) - Thin bentonite (clay) layers common in formation. Shale and bentonite beds have potential of swelling when wetted and shrinking when dried. Con - cretions contain marine fossils. Thickness 6.200 feet Upper transition member - Olive -gray shale, fine -grained brown sandstone layers containing hard 4 -fool brown sandstone con- cretions, and interbedded yellowish -brown to olive -gay silty sandstone and sandy shale containing limestone and ironstone concretions. Underlying olive -gray claystone contains ironstone and limestone concretions. Large limestone masses called Tepee Butte limestone, an informal name, lie between zone of Bamlites ehasi and zone of Baculites Seoul. Thin sandstone bed in zone of Didymoceras cheyennense. At base is yellowish -brown sandy silt- stone equivalent to upper part of type Hygiene Sandstone Member Hygiene Sandstone Member - Yellowish -gay or olive -brown Sand- _ stone Lower par[ - Oljve -gray clayey shale containing ironstone and limestone concretions _ NIOBRARA FORMATION (UPPER CRETACEOUS) Smoky Hill Shale Member - Pale- to yellowish -brown soft thin - bedded calcareous shale and interbedded thin layers of limestone. Three ridge - forming beds: yellowish - orange chalk at top, yellowish - gay chalky limestone in middle, and gray soft platy limestone in lower third. Contains many bentonite beds. Contains marine Fossils. Thickness 410 feet Fort Hays Limestone Member - Yellowish -gray dense hard lime- stone in beds 1 -7 feet thick. Thin shale beds make up only about 5 percent of the member. Contains marine fossils. Thickness 35 feet Kcgg CARLILE SHALE, GREENHORN LIMESTONE, AND GRANEROS SHALE - Fossils FKin many parts. Total thickness 530 feet CA Ke. RLILE SHALE (UPPER CRETACEOUS) - In descending order, Juana Lopez Member, grayish -brown hard calcarenite (sandy lime- stone composed of shell fragments); Blue Hill Shale Member, gay silty sandstone; Fairport Chalky Shale Member, yellowish -gray soft calcareous shale GREENHORN LIMESTONE (UPPER CRETACEOUS) - In descend- ing order, Bridge Creek Limestone Member, gay dense limestone beds and hard gray calcareous shale; Hartland Shale Member, gay shaly calcarenile; Lincoln Limestone Member, grayish -brown thin beds of hard calcarenite and shaly calcarentte containing marker bentonite at base GRANEROS SHALE (UPPER AND LOWER CRETACEOUS) - Dark - gray hard clayey shale; at base dark -gray hard platy siltstone equivalent to Mowry Shale DAKOTA GROUP (LOWER CRETACEOUS) - Thickness 300 feet SOUTH PLATTE FORMATION (LOWER CRETACEOUS) - Con- tains three sandstone members separated b two o shale members. embers. Sandstone yellowish gray, well sorted, cross stratified, porous; composed of well- rounded to subrounded fine to medium quartz sand. Shale dark gray, silty, hard, parallel bedded; interbedded with thin gray sandstone layers; contains gray or white refractory clay or porceltanite layers. Asphalt occurs in a seep and with py- rite in uranium prospects near Turkey Creek_ Dinosaur footprints ®along Alameda Parkway. Thickness about 220 feet LYTLE FORMATION (LOWER CRETACEOUS) - Yellowish -gray or yellowish -brown medium- to fine- grained )ronstained sandstone and conglomerate. Conglomerate generally near base composed of quartz, quartzite, chert, and some petrified wood. Silicified tree trunks in upper part of the formation. Thickness about 80 feet MORRISON FORMATION (UPPER JURASSIC) - Red siltstone and thin brown sandstone beds in upper part; green siltstone and clay- stone, some varicolored maroon and green beds, and interbedded sandstone and limestone layers in middle; several brown lentic- ular sandstone beds containing clay balls and red jasper in lower part. Dense gray limestone beds in middle part contain charo- phytes (algae). Dinosaur bones occur in middle green siltstone beds and in lower sandstone. Thickness 300 feet Jr RALSTON CREEK FORMATION (UPPER JURASSIC) - Purplish - gay sandstone and siltstone, underlain by grayish -yellow silty Sandstone containing crystalline clayey limestone having red jasper and calcite crystals; thin layers of vermilion and white sandstone lie above base of formation. South of Turkey Creek, formation contains thick bed of gypsum. Thickness 90 feet LYKINS FORMATION (TRIASSIC? AND PERMIAN) - Thickness 450 fee[ Strain Shale Member of LeRoy (1946) - Maroon stratified mica- ceous fine - grained silty sandstone and siltstone containing some ®green siltstone layers. Thickness about 300 feet Forelle Limestone Member - Pink Wavy - laminated sandy marine limestone 130 feet above base of formation; contains algal stro- matolites. Thickness about 17 feet Mb Bergen Shale, Falcon Limestone and Harriman Shale Members of LeRoy (1946) - Maroon and green siltstone containing laminated red - weathering gray crystalline sandy limestone (Falcon) 75 feet above base and yellow crystalline limestone 2 feet above base. Thickness about 133 feet noLYONS SANDSTONE (PERMIAN) - Yellowish -gay conglomerate composed of Precambrian detritus as large as 2 inches, which grades downward into yellowish -gray and yellowish-orange iron - stained fine - grained cross - stratifted sandstone that also contains conglomerate a few feet above base. Thickness about 190 feet PIPF FOUNTAIN FORMATION (PERMIAN AND PENNSYLVANIAN) - Maroon arkosic thick- bedded coarse- grained sandstone and con- glomerate containing thin layers of dark- maroon micaceous silty fine - grained sandstone that are more abundant in lower part. Characterized by festooned and torrential crossbedding. Com- posed primarily of Precambrian detritus, but contains rare frag- ments of lower Paleozoic rocks in lower part. Conglomerate near base contains boulders as large as 10 inches in diameter. Thickness 1,650 feet Permit# M 7 111-1-0 D I i Date: Doc Name See Map Origin: '� ) � i'1' I s 1 i I FOLIO OF THE MORRISON QUADRANGLE, COLORADO MAP I -790 -A Ybl / BIOTITE LATITE (PRECAMBRIAN Y ?') - Reddish -gray porphy- title dike rock with aphanitic groundmass; along Lariat Loop road and northwest of Mount Falcon. Chief minerals are microper- thite, oligoclase, biotite, quartz, and muscovite. Possible correla. live of dikes related to Pikes Peak Granite (R. B. Taylor, oral common., 1972) Yl LAMPROPHYRE (PRECAMBRIAN Y ?) - Dark -gray porphyritic dike rocks composed of potassic and sodic feldspar and either biotite or hornblende. Possible correlative of dikes emplaced near age of Silver Plume Quartz Monzonite or Pikes Peak Granite ( R. B. Taylor, oral common., 1972) GNEISSIC QUARTZ MONZONITE AND GRANODIORITE (PRE- CAMBRIAN X' ) - Medium- to coarse - grained foliated biotite quartz monzonite and granodiorite, locally prophyritic and con- taining laths of potassic feldspar as much as 4 mm in length. Equivalent to the Boulder Creek Granodimite _ QUARTZ DIORITE (PRECAMBRIAN X) - Black and white massive medium to coarsely crystalline bodies composed chiefly of horn- _blende, plagioclase, biotite, and minor quartz HORNBLENDITE (PRECAMBRIAN X) - Greenish -black medium to coarsely crystalline bodies composed chiefly of hornblende, quartz, and accessory minerals MIGMATITIC QUARTZO - FELDSPATHIC GNEISS (PRECAMBRIAN X) - Grayish - orange to gay fine- to coarse- gained gneiss that locally may be nearly nonfoliated owing to intensive migmatiza. tion and intrusion of granitic material. Contains gray cordierite- bearing biotite - quartz gneiss near mouth of Bear Creek and to west and southwest. Contains reddish- orange to white sifirowitie muscovite-quartz- plagioclase gneiss (fluorine metasomatized to rutile- and topaz- bearing gneiss) from Strain Gulch southward to border of quadrangle. Contains dark -gay hornblende gneiss in wide east- trending layers from about I mile north to I mile south of Mount Vernon Canyon. Migmatitic gneiss also contains many ®small dikes and irregular bodies of granite pegmatite GARNETIFEROUS BIOTITE- QUARTZ - PLAGIOCLASE GNEISS (PRECAMBRIAN X) - Gray fine- to medium- grained gneiss com- posed chiefly of quartz, plagioclase, biotite, and minor garnet BIOTITE- QUARTZ - PLAGIOCLASE GNEISS (PRECAMBRIAN X) - Gray medium - grained gneiss consisting of quartz, plagioclase, and biotite Contact - Dashed where approximately located; dotted where con- cealed; concealed bedrock contacts shown only in critical areas u -4 D = Fault, showing dip - Dashed where approximately located; short dashed where inferred; dotted where concealed; queried where doubtfuLU, upthrown side; D, downthrown side. Arrows show direction of relative movement. Many beds are thinned by faults that are not shown -' Brecciated fault zone —�--- Syncline - - -- Ammonite zone - Dashed where approximately located; dotted where concealed. Zone line is drawn through principal collections of ammonites in faunal assemblage zones. The collections through which a zone line is drawn are not always at the same horizon; therefore the line may rise or fall within that ammonite zone 25 Strike and dip of beds - i Inclined r-� Overturned I Vertical 30 -60 Average strike and range of dip of many foliation attitudes - Placed on map to give well drillers, contractors, and planners an indication of the attitude of layering in the metamorphic rocks in the moun- tains; original attitudes are shown in U. S. Geological Survey Bul- letin 1251 -E (Gable, 1968) X Prospect pit Adit e Shaft 7Z Quarry or open -pit mine X Gravel pit Fossil mollusk locality x 02409 USGS Mesozoic invertebrate fossil locality *1 Rohlas- Dry hole Wallen 'An interim scheme for subdivision of Precambrian time recently adopted by the U.S. Geological Survey: Precambrian Z - base of Cambrian to goo m.y. Precambrian Y - 800 m.y. to 1,600 m.y, Precambrian X - 1,600 m.y. to 2,500 m.y. Precambrian W - older than 2,500 m.y. 2 The Green Mountain Conglomerate was named ( "Green Moun. tain Conglomerate series ") in an unpublished report by Mart (1929) for Green Mountain, 3 miles northeast of Morrison in the Morrison quadrangle. The first published use of the name and description of the rock were by LeRoy (1946). The formation consists of conglom- erate, sandstone, siltstone, and claystone, as described in more detail above. It was deposited as coarse, basin -fill material from a through. going stream emerging from the rising Front Range to the west. The formation is restricted to Green Mountain, where it is 650 feet thick. It disconformably overlies the Denver Formation; the upper contact is an erosional one. On the basis of fossil leaves and pollen of Paleocene age, the Green Mountain possibly correlates with the uppermost part of the Dawson Formation in the Denver basin. 3 The Table Mountain Shoshonite was named and described as the Table Mountain basalt by Cross (1896) for North and South Table Mountains near Golden, Colo. Although assigned 76 years ago, his name was never formally adopted for use in the U.S. Geological Survey. Two flows were described by Cross; a third and lower, less- extensive flow was later disco and was mapped b Van an Horn Y 1957 197 Six analyses f ( 2. y o the rock -two reported by Cross (1896, p. 306, 308) and four recent analyses - show it to be a potassium -rich basalt (sho- shonite) that chiefly contains augite, plagioclase, olivine, and mag- netite set in a fine - gained groundmass. Although the rock was called castle latite by W. T. Pecora (Van Horn, 1957), its silica content, according to these analyses, averages 51.73 percent, ranging only from 49.69 to 53.8 percent; its potash content ranges from 3.83 to 4.8 percent, and clearly lies in the range of Shoshonite compositions. Thicknesses of the three Bows are: lower, 60 feet; middle, 90 feet and upper, 60-90 feet (Van Horn, 1957). The source of the flows was suspected by Cross to have been the Ralston dike about 4 miles north of Golden; this dike still is favored as the source. In 1964 (Evernden and others), a cobble from soft dacitic pumice in the Denver Forma- tion 225 feet below the middle flow in the SW%NWy4 sec. 31, T. 3 S., R. 69 W., was dated by the K -Ar technique at 64.8 m.y. (million years); a sample of the middle flow about 10 feet above its base at the same locality was dated by the K -Ar method at 58.7 M.Y. In 1970, John D. Obradovich, Glen A. Izett, and I examined this local- ity and collected material from a volcaniclastic dacitic pumice bed from Denver Formation about 35 feet above the level of the lower sample dated by Evernden and others. This new sample was recently dated by Obradovich using the K -Ar method at 64.3 m.y. An age of the Ralston dike was recently announced by Edwin E. Larson, Uni- versity of Colorado (oral common., 1972), by the K -Ar method at 63 + 2.5 m.g., or early Paleocene in age. This leads us to believe that the age of the middle flow is more likely to be 63 -64 m.y., rather than 59 my. REFERENCES CITED Cross, Whitman, 1896, Igneous formations, Chap. 5 in Emmons, S. F., Cross, C. W., and Eldridge, G. H., Geology of the Denver Basin in Colorado: U.S. Geol. Survey Mon. 27, p. 279 -315. Evernden, J. F., Savage, D. E., Curtis, G. H., and lames, G. T., 1964, Potassium -argon dates and the Cenozoic mammalian chronology of North America: Am. lour. Sci., v. 262, p. 145 -198. Gable, D. J., 1968, Geology of the crystalline rocks in the western part of the Morrison quadrangle, Jefferson County, Colorado: U.S. Geol. Survey Bull. 1251 -E, P. EI -E45. Izett, G. A., Wilcox, R. E., Obradovich, J. D., and Reynolds, R. L., 1971, Evidence for two Pearlette4ike ash beds in Nebraska and adjoining areas: Gent. Sec. America Abs. with Programs, v. 3, no. 4, p. 265 -266. LeRoy, L. W., 1946, Stratigraphy of the Golden- Morrison area, Jeffer- son County, Colorado: Colorado School Mines Quart., v. 4l, no. 2,115 p. Marr, J. D., 1929, Stratigraphy of the post - Laramie sediments of the Green Mountain area, Jefferson County, Colorado: Colorado School Mines, Golden, Colorado, unpub. undergraduate report. Pearl. R. H., 1968, Quaternary geology of the Morrison quadrangle, Colorado: Mtn. Geologist, v. 5, no. 4, p. 197 -206. Smith, J. H., 1964, Geology of the sedimentary rocks of the Morrison quadrangle, Colorado: U.S. Geol. Survey Misc. Geoff. Inv. Map Id28. Van Horn, Richard, 1957, Bedrock geology of the Golden quadrangle, Colorado: U.S. Geol. Survey Gent. Quad. Map GQ -1.03. -- 1972 Su rficial and bedrock geologic map of the Golden quad - tangle, Jefferson County, Colorado: U.S. Geed. Survey Misc. Geol. Inv. Map 1- 761 -A. IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII 0016970 SPECIFICATION AGGREGATES, INC. P.O. Box 10775 Edgemont Branch GOLDEN, COLORADO 80401 (303) 279.4514 Forsale. by U. S. Geological Survey Denver. Colo, 80225 and Reston, Va. 22092, price 75 cents 40 i • • C I