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~9°00'
<br />dOC L"~0
<br />~EiT
<br />52'30"
<br />T 135
<br />T la s
<br />350 000
<br />FFCi
<br />7155
<br />QV VEfiDUb ALLUVIUM IYLrJJt VI,uYGI tlOUWery motile gravel near muuniam>
<br />decreases in groin size away from mountains. Much calcium carbonate (CaC031 in
<br />upper pan when not removed by erosion. Contains many weathered stones.
<br />Elsewhere deposit locally contains bed of volcanic ash thought ro be 600,000 yrs old.
<br />Thickness averages about 4.5 m, Forms gently sloping surface 61 to 76 m above
<br />present streams
<br />ROCKY FLATS ALLUVIUM (PLEISTOCENE)-Bouldery cobble gravel near
<br />mountains; decreases in grain size away hom mountains. Much calcium carbonate
<br />(CaC03) in upper part where not removed by erosion. Contains many unsound
<br />stones. Commonly about 4.5 m thtck. Forms gently sloping surfaces about 110 m
<br />above present streams
<br />~n NUSSH4UM ALLUVIUM (PIFdSTOCENE)-Brownish-gray poorly sorted, firmly
<br />compacted, shatlfied boWdery alluvium south of Little Fountain Creek where gavel
<br />tr composed of partite, porphyry, and gneiss. Brown well-stratified, latrlycaell-sorted,
<br />weakly compacted coarse sand and pebble gravel between Williams Canyon and
<br />Queens Canyon where grovel u composed of fragments of Pikes Peak Granite.
<br />Precambrian biotite gneiss, and lower Paleozoic sandsone and limestone. Alluvium
<br />contains abundant large boulders nearmountain front. Stones altered by weathering
<br />and coated by calcium carbonate. Upper pan of most deposits contains a calcareous
<br />soil; bused soil horizon omurs near middle of gravel south of Little Fountain Creek.
<br />Thickness more than 24 m. Top of pediment gravel in this area is 167 to 213 m above
<br />modem streams
<br />.'.'~ HIGH-LEVEL GRAVEL DEPOSITS (PLIOCENE TO OLIGOCENE?)-Rounded to
<br />subangular pebbles, mbbtes, and boulders as much as 6 m ro diameter in sandy
<br />matrix. Age span uncertain. BoWders chiefly granite, but include Wall Mountain TuH,
<br />phonolite from Cripple Creek area, and Thinynine Mile Andesite IOLgocene) from
<br />the Th"vtynine Mile volcanic field. Nearly all types of [he Precambrian rocks are
<br />represented in the pebble-sized material. Caps spurs and ridges about 300 m above
<br />present streams along weri-central edge of mapped area
<br />~~TCr •. CASTLE ROCK CONGLOMERATE (LOWER OLIGOCENE(-Well indurated
<br />bouldery cobbly gravel composed morily of Precambrian rocks but also containing
<br />some then and Terdary volcanic rocks. Sandy matrix of the conglomerate is
<br />well-Cemented by sutra, but basal part Ls locally less cemented and softer. Generally
<br />less than 15 m thick. Includes mudrione, clayrione, siltstone, and sandstone in
<br />eariem part of area
<br />WALL MOUNTAIN TUFF (LOWER OLIGOCENE(-Lightyray fine-grained rhyoGtlc
<br />volcanic rock (74 percent sutra). Most of rock composed of devitrified glass shards.
<br />Part of once-continuous ash-Oow sheet Probably less than 15 m thick. Age about 35
<br />m.y. (Izen, Scott, and Obedovith, 19691
<br />DAWSON FORMATION
<br />de Upper pan (Paleocene and Upper Cretaceous)-Arkosic sandstone, siltstone,
<br />tlayrione, and minor conglomerate. Farms mori of bedrock between Coloedo
<br />Springs and Denuer. As much as 610 m thick (Stott and Wobus, 1973)
<br />Lower part (Cretaceous)-Olive-brown andesitic sandstone, siltstone, and daystone
<br />containing andesite pebbles. About 60 m thick (Scott and Wobus, 1973)
<br />K! LARAMIE FORMATION (UPPER CRETACEOUSI~Shale, dayrione, siltstone, and
<br />sandstone that contnlns coal beds, mainly in the lower part. Thickness about 76 m.
<br />Source of mat, brick day, and refectory clay
<br />Ki FOX HILLS SANDSTONE (UPPER CRETACEOUS)-Sandstone and interbedded
<br />shale that contains sparse marine mollusks. Along the mountain front generallyftirms
<br />sandsone edge that stands up between lower areas of Pierre Shale and Laemie
<br />Formation. Thickness 76 m or more. Source o! underground water
<br />_ PIERRE SHALE (UPPER CRETACEOUS)-Olive-gray shale and interbedded
<br />sandstone. Thickness 960 to 1,463 m. Ben[onite beds in Pierre Shale have
<br />undesirable swelling properties. Source of clay for bock and file and expanded
<br />aggregate
<br />® NIOBRARA FORMATION (UPPER CRETACEOUS(-consists of Smoky H01 Shale
<br />Member Composed d interbedded soh calcareous shale and thin layers of lmestone,
<br />probably more than 162 m thick, and the underlying Fon Hays Limestone Member
<br />composed o(grey hard dense limestone beds about 9 to 12 m thick. Source of cement
<br />and smelter limestone
<br />Kcgg CARLILE SHALE, GREENHORN LIMESTONE, AND GRANEROS SHALE
<br />(BFNTON GROUP), UNDIFFERENTIATED (UPPER CRETACEOUS)~onsists of
<br />interbedded shale, sandstone, and limestone that constitute the upper formation (the
<br />Car61e Shale), a middle kmerione fonnaHon (the Greenhorn Limestone), and a lower
<br />gray to black shale (the Graneros Shale). Total thickness i5about 91 m
<br />_ DAKOTA GROUP (LOWER CRETACEOUS(---Consists of pn upper interbedded
<br />sandstone and shale unit (the South Ratte Formation) about 61 to 91 m thick, and a
<br />lower conglomeefic sandsone (the Lytle Formation) about 12 to 24 m thick. The
<br />South Platte Formation contains refractory day. The Dakota Group forms the most
<br />prominent hogback ridge along mounain front
<br />Jmr MORRISON AND RALSTONCREFJCFORMAT(ONS(UPPER JURASSIC)-Redand
<br />variegated claystone, siltstone, and interbedded brown and ye0owish-gray
<br />sandrione; minor interbeds of fimerione and gyFs'um. Combined thickness about
<br />75 m
<br />LYKINS FORMATION (LOWER TRIASSIC AND UPPER PERMIAN(-Interbedded
<br />. .._ .~_,___,, ~:._,~~.,,,.,, Wars-laminated limestone about 4.5 rob m_
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