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Figure 1 The relationship between Lundy's (1978) informal members of the Casper
Formation and the Casper limestones (1-10) as defined by Benniran
(1970) in the vicinity of Laramie,Wyoming. Map area falls within diagram.
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Re fe re nc e s Ben n ira n , M.M., 1970, Casper Form ation lim eston es, southwestern L ara m ie Moun ta in s, Alba n y Coun ty, W yom in g: M.S. T hesis, U n iversity of W yom in g, L ara m ie, m ap sca le 1:24,000. Houston, R.H., a n d Marlatt, 1997, Proterozoic geology of the Gra n ite Villa ge area, Alba n y a n d L ara m ie Coun ties, W yom in g, com pared with that of the Sierra Ma dre a n d Medicin e Bow Moun ta in s of southeastern W yom in g: U .S. Geologica l Survey Bulletin 2159, 25p., plate 1, sca le 1:24,000. Kirn, D.J., 1972, Sa n dston e Petrology of the Casper Form ation, Southern L ara m ie Basin, W yom in g a n d Colora do: U n iversity of W yom in g, Master’s T hesis. L un dy, D.A., 1978, Hydrology a n d geochem istry of the Casper aquifer in the vicin ity of L ara m ie, Alba n y Coun ty, W yom in g: M.S. T hesis, U n iversity of W yom in g, L ara m ie, m ap sca le 1:24,000. Ra m arathn a m , S., 1962, Geology a n d petrology of the southern portion of the L ara m ie a n orthosite m ass, Alba n y Coun ty, W yom in g: M.S. thesis, Colora do School of Min es, Golden , sca le 1:24,000 Ver Ploeg, A.J., a n d Boyd, C.S., 1999, Prelim in ary Geologic Map of the L ara m ie 30’ X 60’ Qua dra n gle, Alba n y a n d L ara m ie Coun ties, Southeastern W yom in g: W yom in g State Geologica l Survey Prelim in ary Geologic Map Series, PGM 99-1. Ver Ploeg, A.J., 1999, Recon n a issa n ce/photogeologic m ap of the Pilot Hill Qua dra n gle, Alba n y Coun ty, W yom in g: W yom in g State Geologica l Survey files (unpublished), sca le 1:24,000.
Caspe r/Fountain subd ivisions-this un it has been subdivided in to separate in form a l m em bers based on 10 distin ct lim eston e un its (10 bein g the youn gest lim eston e, 1 bein g the oldest) that are separated by sa n dston es (Figure 1). T he sa n dston e un its a ct as loca l aquifers. L un dy, 1978, com bin ed the lim eston e un its in to 5 in form a l m em bers (Epsilon, Delta, Ga m m a, Beta, a n d Alpha) based upon loca l, con fin ed aquifer pa cka ges (Figure 1).
Epsilon Me m be r--T he Epsilon m em ber represen ts the youn gest Casper Form ation m em ber a n d it is capped by lim eston e 10 in the south (which does not appear in the m apped area) a n d a sa n dston e un it that gra des in to the Sata n ka Sha le. It consists of red to pin k, m edium to fin e-gra in ed sa n dston e, m ostly covered in the L ara m ie area. Overa ll thickn ess 22 to 30 ft.
De lta Me m be r--In cludes lim eston es 9 a n d 8 a n d two separate sa n dston e un its. L im eston e 9 is a white-gra y to pin k, m assive, fra ctured lim e that caps the Delta Mem ber (thickn ess of 8 to10 feet). A reddish-brown to buff, thin ly la m in ated fin e-gra in ed cross-bedded suba n gular to subroun ded sa n dston e separates the lim eston es of the Delta Mem ber (thickn ess 20-35 feet). L im eston e 8 is a pin k to light-gra y m assive, fra ctured lim e that outcrops m ostly at the base of the L ara m ie Moun ta in s (thickn ess 12 feet). A light ta n to red ca lcareous cross-la m in a ted porous sa n dston e lies ben ea th lim eston e 8 (thickn ess 40 to 55 feet). Overa ll thickn ess 80 to 112 feet
Gam m a Me m be r--In cludes lim eston es 7 a n d 6 a n d two separate sa n dston e un its. L im eston e 7 is a n exten sive un it that form s prom in en t ridges a n d the m a in dip-slope of the western L ara m ie Moun ta in s, as well as cappin g the Ga m m a m em ber. It has a ta n to buff dolom itic base overla in by a sa n dy gra yish lim eston e (thickn ess 17-18 feet). L im eston e 6 is a den se, fossiliferous lim eston e that is on ly presen t on the northern portion of the m ap area (thickn ess 6 to 8 feet). A pin k to red, fin e to m edium gra de, fria ble, ca lcareous sa n dston e exten ds from the base of lim eston e 7 to the top of lim eston e 5. It is divided by lim eston e 6 to the north (thickn ess 50 to 60 feet). Overa ll thickn ess 73 to 86 feet.
Beta Me m be r--In cludes lim eston es 5 a n d 4 a n d two separate sa n dston e un its. L im eston e 5 is a fin ely crysta llin e, purple to pin k, den se, highly fra ctured lim eston e that wea thers to dark grey a n d caps the Beta Mem ber. It is thickest slightly north of Pilot Hill (thickn ess 8 to 12 feet). A light brown to ta n -red, ca lcareous, fin e-gra in ed, fria ble sa n dston e separates lim eston es 5 a n d 4 (thickn ess 25 to 30 feet). L im eston e 4 has a buff to ta n dolom itic base that gra des upward in to light gra y to purple, den se, ridge form in g lim eston e (thickn ess 18 to 26 feet). Below lim eston e 4, a red to buff, m oderately resistive, extrem ely ca lcareous, thick, m oderately sorted sa n dston e la yer form s the base of the Beta Mem ber (thickn ess 90 feet). Overa ll thickn ess 141 to 158 feet.
Alpha Me m be r--T he Alpha Mem ber represen ts the oldest m em ber of the Casper Form ation a n d in cludes lim eston e 3, 2, a n d 1 a n d three separate sa n dston e un its, the lower un it gra din g in to the Foun ta in Form ation, which form s the base of this m em ber. L im eston e 3 form s the top of the Alpha Mem ber a n d is on e of the m ore prom in en t lim eston es in this section of the Casper Form ation. T he base is light ta n to brown sa n dy dolom ite, fin in g upwards in to a purple-pin k carbon a te that weathers gra y a n d form s ridges (thickn ess 29 to 40 feet). A light-brown to reddish brown, poorly sorted, fin e-gra in ed sa n dston e un it separates lim eston e 3 a n d lim eston e 2 (thickn ess 75 to 80 feet). L im eston e 2 is a thin , pin k to purple, sa n dy un it that is m ostly covered in the m ap area (thickn ess 8 to 12 feet). A pin k to brown, ca lcareous, cross-la m in a ted, m edium -sorted, fin e-gra in sa n dston e separates lim eston es 2 a n d 1 (thickn ess 65 to 80 feet). L im eston e 1 is a purple to pin k, m assive, fossiliferous, sa n dy un it (thickn ess 9 to 13 feet). T he bottom sa n dston e is a ta n , pin k, a n d red, cross-bedded, m edium gra in ed sa n d that in terfin gers with thin , sa n dy lim eston es (up to 1 in ch) that is slightly arkosic; m ore so as it gra des in to the Foun ta in Form ation (thickn ess 80 to 150 feet). Overa ll thickn ess 266 to 375 feet.
Fountain Form ation (P e nnsylvanian)--Coarse-gra in ed pin k to red to purple sa n dston e a n d arkose, with som e con glom erates, siltston es a n d sha les. In terfin gers with a n d un derlies Casper Form ation, thin n in g to the north a n d pin chin g out n ear Rogers Ca n yon. For m appin g purposes, the Foun ta in Form ation was in cluded with the Alpha Mem ber. T he Foun ta in Form a tion lies un con form a bly on top of Preca m bria n basem en t rock. Possibly deposited by a n a lluvia l pla in or a series of coa lescin g fa n s at the base of the An cestra l Rockies. Approxim a tely 30 ft. thick at Pilot Hill (Ben n ira n , 1970).
Unc onform ity
MIDDLE P ROTEROZ OIC ROCKS SHERMAN GRANITE (MIDDLE P ROTEROZ OIC)--Medium to coarse gra in ed, pin k to ora n ge, biotite horn blen de gra n ite, syen ogra n ite, quartz m on zon ite a n d gra n odiorite. T he Sherm a n Gra n ite is gra da tion a l with or in terfin gers with the syen ite of the L ara m ie Moun ta in s. T he Sherm a n Gra n ite has been dated at 1,430 +20 MA (m illion years a go) by a Rb-Sr whole rock isochron (Z ielin ski a n d others, 1981).
LARAMIE MOUNTAINS ANORTHOSITE AND NORITE (MIDDLE P ROTEROZ OIC)--W hite to light bluish gra y, m edium to coarse gra in ed, gen era lly leucocratic a n orthosite that is m assive to la yered to brecciated. A m in or gra y m a fic a n orthosite or norite com m on ly form s a gra da tion a l phase between syen ites a n d the leucocratic a n orthosite, or form s less resista n t, m ore m a fic la yers in la yered a n orthosite. T his un it com m on ly occurs as sharply boun ded a n gular in clusions in the syen ite, but as noted a bove is gra da tion a l in to the syen ite. T his a n orthosite is the bulk of what som e geologists ca ll the L ara m ie Anorthosite Com plex.
EARLY P ROTEROZ OIC ROCKS OLDER P ROTEROZ OIC METASEDIMENTARY AND METAVOLCANIC ROCKS Laram ie Mountains--Pelitic schist, m arble, gra n ite gn eiss, la yered a m phibolite, a n d felsic gn eiss (Houston a n d Marlatt, 1997).
MAP SY MBOL S
Form ation c ontact Dashed where approxim a tely located.
Fault Dashed where approxim a tely located, dotted where con cea led. Bar a n d ba ll on down thrown block; arrows in dicate relative direction of oblique-slip m ovem en t.
Antic line T ra ce of axia l pla n e as determ in ed by field m easurem en ts a n d by photo in terpretation. Dashed where approxim a tely located. Short arrow denotes steeper dippin g lim b.
Strike and d ip of be d s, showing angle of d ip.
Strike and d ip m easure m e nts from Lundy (1978).
DESCRIPT ION OF MAP U NIT S
HOLOCENE AND P LEISTOCENE SURFICIAL DEP OSITS
ALLUVIAL DEP OSITS (HOLOCENE)--U n con solidated a n d poorly consolidated cla y, silt, sa n d, a n d gravel, m a in ly in floodpla in s a n d lowest strea m terra ces. T hickn ess approxim a tely 0 to 50 feet
COLLUVIUM (HOLOCENE/P LEISTOCENE)--U n consolidated m asses of rock fra gm en ts a n d soil m ateria l on relatively steep slopes with thickest a ccum ulations at the bases of slopes.
MIXED ALLUVIUM AND COLLUVIUM (HOLOCENE/P LEISTOCENE)--Sa n d, silt, cla y, a n d gravel deposited m a in ly a lon g in term itten t strea m s; in cludes slope wash a n d sm a ller a lluvia l fa n deposits that coa lesce with a lluvium . T hickn ess approxim a tely 0 to 50 feet.
LANDSLIDE DEP OSITS (HOLOCENE/P LEISTOCENE)--Blocks of bedrock or loose slope debris; arrows on the m ap show the in ferred direction of m ovem en t. Ma n y occur in the Alpha Mem ber of the Casper Form ation, deta chin g at the con ta ct with the un derlyin g Preca m bria n rocks.
WINDBLOWN SAND DEP OSITS (HOLOCENE)—Active a n d sta bilized dun es, m a de up of fin e-to fin e-gra in ed sa n d, sourced by Casper Form a tion sa n dston es. T hickn ess approxim a tely 0 to 15 feet.
Unc onform ity
P ERMIAN AND P ENNSY LVANIAN ROCKS CASP ER AND FOUNTAIN FORMATIONS UNDIVIDED Caspe r Form ation (P e rm ian and P e nnsylvanian)--Buff to reddish, ca lcareous to quartzitic, very fin e- to coarse-gra in ed, well cem en ted subarkosic sa n dston e in terbedded with buff to purplish-gra y lim eston e a n d dolom ite beds, usua lly m icritic a n d loca lly fossiliferous. Sa n dston e often exhibits large-sca le festoon cross-beddin g, in creasin g toward the south. T he Casper Form ation thin s to the south a n d west as the Foun ta in Form ation in creases in thickn ess. Also, lim eston e un its thin a n d even tua lly disappear southward a n d westward in the L ara m ie Basin, suggestin g a northwest-southeast tren din g shorelin e durin g deposition. As m a n y as 10 distin ct lim eston e or dolom ite beds, which are loca lly quarried for cem en t or gravel uses, ha ve been iden tified in the Casper form ation (Ben n ira n , 1970), in the L ara m ie area. T he Casper Form ation serves as the prim e aquifer for the city of L ara m ie. T hickn ess 690-735 feet (Ben n ira n , 1970, a n d Kirn, 1972)
EXP LANATION
CORRELATION OF MAP UNITS
U n con form ity
QU AT ERNARY
PENNSY L VANIAN
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WY OMING STATE GEOLOGICAL SURVEYRonald Surdam , State Ge ologist
Laram ie, Wyom ing(Howell) Geology - Interpreting the past to provide for the future(King Mountain)
P re pare d in c oope ration with theU.S. GEOLOGICAL SURVEY
(Ragged Top
Mountain)
(Gree
n Top
Mou
ntain)
(Sherman Mountains East)
(Sherman Mountains West)
(Red Buttes)
(Laram
ie)
PREL IMINARY GEOL OGIC MAP OF T HE PIL OT HIL L QU ADRANGL E, AL BANY COU NT Y , W Y OMINGby
Ala n J. Ver Ploeg a n d J. Fred McL a ughlin2006
UTM GRID CONVERGENCE (GN)1995 MAGNETIC DECLINATION (MN) AT CENTER OF SHEETDIAGRAM IS APPROXIMATE
MNGN
11196 MILS
2 MILS0 08'o
o
Projection: Universal Transverse Mercator (UTM), zone 13North American Datum of 1927 (NAD 27)10,000-foot grid ticks:Wyoming State Plane CoordinateSystem, East zone
A digital version of this map is also available on CD-ROM.Wyoming State Geological SurveyP.O. Box 1347 - Laramie, WY 82073-1347Phone: (307) 766-2286 - Fax: (307) 766-2605Email: [email protected]
People with disabilities who require an alternative formof communication in order to use this publication shouldcontact the Editor, Wyoming State Geological Survey.TTY Relay Operator 1 (800) 877-9975.
Digital cartography by J. Fred McLaughlin
Ope n File re port OFR 06-5P ilot Hill 1:24,000 - scale Ge ologic Map
1 0 10.5 Miles
1,000 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 Feet
1 0 10.5 Kilometers
CONTOUR INTERVAL 20 FEETNATIONAL GEODETIC VERTICAL DATUM OF 1929
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CROSS SECTION A-A'Vertical exaggeration at 2X
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Prepared in cooperation with and research supported by the U.S.\Geological Survey,
National Cooperative Geologic Mapping Program,\under USGS award Number 05HQAG0062.\
The views and conclusions contained in this document are those\of the authors and should not
be interpreted as necessarily\representin the official policies, either expressed or implied,\of the
U.S. Government.
Minor corrections and revisions to original compiled map by R.W. Jones\2005-2006.
Base map: Pilot ButteInterior, Geological Survey, Reston, Virginia, 1995
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