GEOLOGIC INVESTIGATIONS SERIES I–2799 U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY SHEET 1 OF 4 Pamphlet and CD-ROM accompany map 107°15' (CA) 38°07'30'' 107°07'30'' Mineral Mtn (MM) 107° (SP) 106°52'30'' Elk Park (EP) 106°45' Saguache Peak (SA) 106°37'30'' 38°07'30''

Thick, densely welded Tnd, ponded in graben during subsidence of Cochetopa Caldera

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Photograph of , showing view toward northeast from ridge between East Willow and Whited Creeks (SL). These highlands, reaching 13,710 ft (4,180 m) at La Garita Peak in center of photo, are resurgently uplifted core of north segment of , associated with eruption of the Fish Canyon Tuff at 27.6 Ma. The resurgent La Garita block failed on its south side during collapse of the Bachelor caldera at 27.35 Ma. The entire south slope of La Garita Peak, downnot mapped to 10,200 ft (3,110 m) along East Willow Creek, consists of a single cooling unit of intracaldera Fish Canyon Tuff (La Garita Member) in an aggre- gate section more than 1 km thick, with no base (caldera floor) exposed. Looking south; north-central sheet 1.

Photograph showing Amethyst vein (Commodore 5 level), Creede mining district. Vein follows fault (arrows, mine workings) downdropping Campbell Mountain zone of intracaldera Carpenter Ridge Tuff (on west) against Willow Creek zone. Fault control of vein is inherited from keystone graben of resurgent dome within Bachelor caldera, but mineralization is younger than the Creede caldera. West Willow Creek (north margin, CR). View northwest; center join of sheets 1 and 2. Willow Creek zone

Campbell Mountain zone

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38°

West Willow Creek

Unconformity: andesite over variably altered dacite

Photograph showing outflow tuff sheets of San Luis caldera Tst Nelson Mtn Tuff complex, at Wheeler Geologic (dw caprock) Monument (HM). Weakly welded upper Rat Creek Tuff is EQUITY separated from densely welded BLOCK basal Cebolla Creek Tuff by 0.5 m of surge-bedded ash. Surge beds and accretionary lapilli also are present in the basal nonwelded (nw) rhyolitic ash of the Nelson Mountain Tuff. The densely weldednot mapped (dw) caprock of Nelson Mtn Tuff the Nelson Mountain is transi- (nw base) tional rhyolite-dacite that is more phenocryst rich than the basal rhyolite. View to north from Wheeler Monument trail; southeast sheet 1.

Cebolla Creek Tuff

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LT

AU F

Tmcb OMON-HOLES

SOL Rat Creek Tuff MOS (upper part)

37°52'30'' 107°15' Slumgullion Pass (SG) 107°07'30'' Baldy Cinco (BC) Base from U.S. Geological Survey in cooperation with 107° 1 10 /2 ° (SL) Division of Planning, Department of Local Affairs, 1:50,000 106°52'30'' Half Moon Pass (HM) county map series (topographic): Hinsdale County, sheet 1 106°45' 37°52'30'' Mesa Mtn (ME) (north, 1978); Mineral County, sheet 1 (north, 1978); Saguache 106°37'30'' SCALE 1:50 000 County, sheets 1 (northwest, 1979) and 3 (southwest, 1979) Geology mapped by P.W. Lipman (1986-89 and 1995-99; fig. 3); assisted 1 1/2 012 3 4 MILES by D.A. Sawyer (1986-89), D. Yager (1989), O. Bachmann (1995-97), Lambert Conformal Conic projection TRUE NORTH COLORADO MAGNETIC NORTH 30000 3000 6000 9000 12000 15000 18000 21000 FEET Christian Huber (1997), Olivier Roche (1998), and Charles Perring (1999) Note: 1:24,000-scale quadrangle boundaries, names, and MEAN DECLINATION, 2006 Digital database by Joel Robinson, with contributions by Dillon Dutton, (at center of map) 1 .5 0 1 2 3 4 5 KILOMETERS abbreviations (along map boundary) refer to areas of original AREA OF MAP Tracey Felger, and David Ramsey mapping included in database CONTOUR INTERVAL 80 FEET Edited by J.L. Zigler Digital cartography by Kathryn Nimz Manuscript approved for publication June 25, 2003 107°15' 107°07'30'' 107° 106°52'30'' 38°07'30'' 106°45' 106°37'30'' Saguache County, 38°07'30'' sheet 1

SOUTHEAST SOUTHWEST Cannibal Plateau (CA) Mineral Mtn (MM) Stewart Peak (SP) Elk Park (EP) Saguache Peak (SA)

Hinsdale County, sheet 1 Saguache County, sheet 3 38° 38° Postcollapse lavas within Resurgent block, intracaldera Fish Canyon Tuff Moat fill, Nelson Mtn Tuff San Luis caldera complex (La Garita Mountains) Slumgullion Pass (SG) Baldy Cinco (BC) San Luis Peak (SL) Half Moon Pass (HM) Mesa Mtn (ME) (Table Mountain) Moat fill, Nelson Mtn Tuff Mineral County, East caldera rim, mainly precaldera lavas (Sheep Mountain) sheet 1 (Mesa Mountain) 37°52'30'' 107°15' 37°52'30'' Panoramic view of north segment, La Garita caldera, 107°07'30'' 107° 106°52'30'' 106°45' 106°37'30'' caldera slope from north topographic rim (Saguache Park road, at avas, on inner Andesitic l Continental Divide), looking south across nearly entire extent of sheet 1 map. Snow covered La Garita Moun- tains on center skyline are 20 km distant. Old log building at left (Salt House) and grassy slopes in foreground are poorly exposed Carpenter Ridge Tuff (lowest regional tuff sheet of caldera fill), which laps out against andesitic lavas of the Conejos Formation along the inner caldera slope. (Photograph by Danielle Odette, May 2006.)

Geologic Map of the Central San Juan Caldera Cluster, Southwestern Colorado

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