GEOLOGIC INVESTIGATIONS SERIES I–2799 U.S. DEPARTMENT OF THE INTERIOR SHEET 4 of 4 U.S. GEOLOGICAL SURVEY Pamphlet and CD-ROM accompany map

CORRELATION OF MAP UNITS LIST OF MAP UNITS Mineral Mountain Rhyolite Tcr Outflow rhyolite tuff Twa Local andesitic lava flow EXPLANATION 107° 106°45' Cochetopa [Short-dashed boundaries indicate gradational welding or other emplacement contacts within eruptive units. [Some unit exposures on the printed or plotted maps are too small to distinguish the color for unit Tmm Crystal-poor rhyolite flows and domes Intracaldera units ROCKS ERUPTED FROM THE PLATORO CALDERA COMPLEX ben Park Some major formation names are labeled. Some units of a formation are divided by emplacement type] identification. These units are labeled where possible; unlabeled units are attributed in the database] a Tmmt Crystal-poor tuff and tuffaceous sediments Intracaldera Bachelor Mountain Member os Pinosgra en Lower member of Summitville Andesite L b Caldera-related granitic top SURFICIAL DEPOSITS Tcbi Rheomorphic and intrusive tuff unit e ra Tmmi Dacitic-rhyolitic intrusion(?) Tsua Andesitic lava flows intrusions g SURFICIAL DEPOSITS Cathedral och k Alluvium (Holocene) C ee Qal Tcbg Windy Gulch welding zone Saguache Park GLACIAL DEPOSITS Tcma Local andesitic lava flows Tsup Porphyritic andesite flows CC Cr Qal Qc Qf Qt Holocene Qc Colluvium (Holocene) Campbell Mountain welding zone LA GARITA Ql Dacite of East Willow Creek Tsuv Volcaniclastic rocks Resurgently uplifted Stewart Stone Qfo Qr Qm Qg QUATERNARY Ql Landslide deposits (Holocene and Pleistocene) Tcbc Least altered tuff intracaldera tuff NM Peak (North) Cellar Pleistocene Twl Dacite lava Treasure Mountain Group Qlo Qmo Qgo Table Mtn Qf Alluvial fan deposits (Holocene) Tcbck Potassium-metasomatized tuff Tt Treasure Mountain Group, undivided Twlb Carapace breccia Fault—Bar and ball on Mineral SL 38° CALDERA downdropped block Mtn Qt Talus (Holocene) Cebolla Creek Tuff Tcbw Willow Creek welding zone Tts South Fork Tuff RELATIONS ASH-FLOW SHEETS AND RELATED ROCKS LAVAS AND RELATED ROCKS VOLCANIC SEDIMENTARY ROCKS INTRUSIONS 1 (age) Qlo Older landslide deposits (Pleistocene) Tccd Densely welded mafic dacite Tcsb Shallow Creek Breccia Member Ttr Ra Jadero Tuff La G ari Late faults (Rio Grande Baldy RC E Sheep Thb Thr Miocene Qfo Older alluvial fan deposits (Pleistocene) Tcc Partly welded mafic dacite Tcab Andesite breccia member ta M POSTCALDERA Thbi Ttm Middle tuff Cinco Mtn rift and slump) tns ROCKS Tlp Hinsdale Formation Tccn Nonwelded mafic dacite Tcwb Wagon Wheel Gap Breccia Member GLACIAL DEPOSITS Ttj La Jara Canyon Tuff Caldera-related faults Mesa Qr Rock glacier (Pleistocene) Rocks of the Rat Creek caldera cycle Phoenix Park Breccia Member Ttb Black Mountain Tuff Tcg Tct Tcaf Tcl Mtn Tcpl Landslide-breccia unit Qg Glacial outwash gravel (Pleistocene; Pinedale glaciation) Mineral Creek Dacite Ttl Lower rhyolite tuff Tfa Tc Early faults, associated CREEDE Tfl Tfb Tfv Tfi Tmix Crystal-rich rhyolite lava flows Tcpt Talus-breccia unit BACHELOR Qm Moraine and till (Pleistocene; Pinedale glaciation) with Pagosa Pk Dacite CALDERA ROCKS PREDATING CENTRAL CALDERA CLUSTER Pool Table CYCLE Tmid Silicic dacite lava flows Tmr Rhyolite of Miners Creek Clear Creede Tsl Tslw Tslc Tslf Tslm Tsld Tsla Fisher Dacite Creede Formation Qmo Older moraine and till (Pleistocene; pre-Pinedale glaciation) Tuff of Luders Creek Mtn (26.8 Ma?) Tsp Ts Boundaries of 7.5' Cre D Tmit Silicic dacite tuff Tld Welded dacite Qgo Older glacial outwash gravel (Pleistocene; pre-Pinedale glaciation) ROCKS ERUPTED FROM THE SILVERTON CALDERA quadrangles (fig. 3) ek CREEDE Snowshoe Mountain Tuff (western ) gra Cr Tmis Tuffaceous sediments Tln Nonwelded to partly welded rhyolite p ben Bristol en ee POSTCALDERA VOLCANIC ROCKS Tclt Crystal Lake Tuff Head D rab Rat Creek Tuff Tuff of Saguache Creek g Hinsdale Formation (Miocene) Tbir Tbi Tbia Snowshoe Wagon Tbf Tbv Trdn Nonwelded to partly welded dacite tuff ROCKS OF CYCLE Tscc Densely welded crystal-rich rhyolite Mtn Thb Basaltic flows Wheel Gap 37°45' Baldy Cinco Dacite Trd Welded dacite tuff Huerto Andesite Tsc Nonwelded to densely welded crystal-poor rhyolite Tsir Thr Rhyolite lava, tuff, and intrusion Tsd Tsa Tsi Thu Andesitic lava flows and volcaniclastic rocks, undivided Trr Nonwelded to partly welded rhyolite tuff Conejos Formation Basaltic intrusion Ruby Lake Tsdv Tsv Thbi Intrusions and vents R Trrl Lithic-rich zone in rhyolite tuff Tci Intrusions io Tss G South Stewart Peak Volcanics Tlp Los Pinos Formation (Miocene and Oligocene) Dacite Baldy Lake ran Thid Fisher Fork Lava flows and proximal breccias Mtn Humphreys d Lava flows premonitory(?) to San Luis Caldera complex Mtn e Tndn Andesitic dikes and other intrusions Red Lake g OLIGOCENE VOLCANIC ROCKS Thi Tcf Lava flows and breccias, undivided ra Trout b Dacite of Captive Inca e Tnde Tnlr Tnld Tnlf Trout Lake Mtn n ROCKS OF THE CREEDE CALDERA CYCLE Porphyritic andesitic dikes and other intrusions Tca Tcds Volcaniclastic sedimentary rocks Thip Andesite Tnd Creede Formation SOUTH Intrusions of hornblende andesite and mafic dacite Tcap Metroz Tcdf Dacite flow Thih Porphyritic andesite Tnr Tc Fine-grained sedimentary deposits Cimarrona lt LA GARITA RIVER Mtn Lava flows au Tcd Dacite Peak f S River Tnn Tcg Tcdb Flow breccia (South) Nelson Mountain caldera cycle Conglomerates Peak Table Mtn Thd Dacite s Cr Tnns Tcfr Rhyolite m Tct Travertine and calcareous tufa Tcdi Vent intrusion Tha Finely porphyritic and undivided andesite llia Tnxp Tcv Volcaniclastic rocks Wi Tcaf Dacitic ash-flow tuff Ttd Rhyolite of Table Mountain Mount Nelson Mountain Tuff Thah Hornblende-bearing andesite-dacite Tcs Volcanic sandstone Hope Tcl Landslide breccia Dacite of McKenzie Mountain Heart Thap Platy plagioclase andesite Mtn SAN Tmcd Dacite flow Tcas Arkosic sandstone Tst Fisher Dacite LUIS Ths Vent scoria 37°30' Wolf Cr CALDERA Tfl Dacite lava flows Tmcb Flow Breccia Tcst Tuff of Snowball Park Tmm Tmmt Tmmi Pass Cre Pass COMPLEX Volcaniclastic rocks Intrusions Saddle (27.0-26.9 Ma?) Tcma Tfb Flow breccia Tmci Intrusions of uncertain affinity Thv Bedded breccia and conglomerate Mtn e k Andesite fau Twl Twlb Dacite of Silver Park Tia Beaver Treasure Tfa Andesitic lava flows lt Thbf Landslide breccia with clasts of Fish Canyon Tuff Creek Mtn zo Tsf2 Flow 2 Dacite ne Tfv Volcaniclastic rocks Tid fault Thbp Landslide breccia with clasts of Pagosa Peak Dacite Tccd Tcc Tccn Tsf1 Flow 1 Intrusions PREVOLCANIC ROCKS Cebolla Creek Tuff Tfi Thc Conglomerate and sandstone with clasts of Fish Canyon Tuff

Cebolla Creek caldera cycle San Juan Basin Andesite of Bristol Head Tbb Blanco Basin Formation (Eocene) Snowshoe Mountain Tuff Tbd Mafic dacitic flow and breccia Tgs Intracaldera sedimentary rocks Ku Sedimentary rocks, undivided (Cretaceous) Tmix Tmid Tmit Tmis Tsp Partly welded tuff Tba Andesitic flows Tfnd Dacite of Nutras Creek 0 5 10 KILOMETERS Trdn Mineral Creek Dacite Ts Densely welded tuff p_q Quartzite (Precambrian) Tbav Andesitic volcaniclastic rocks Fish Canyon Tuff Trd Landslide breccia member Figure 6. Granitic intrusions (texturally variable granodiorite-andesite) and regional caldera-related and other faults, in relation to Tgfc Late intracaldera landslide breccia overall geometry of central San Juan caldera cluster. E, Equity block (fault-bounded triangular uplift). Abbreviated geographic Tsl Mixed lithologies ROCKS OF THE SOUTH RIVER CALDERA CYCLE Trr Trrl Contact—Dashed where approximately located; dotted where gradational. name: SL, . Calderas of San Luis complex: CC, Cebolla Creek; NM, Nelson Mountain; RC, Rat Creek. Tfc Outflow tuff sheet—Local welding zones Tfc1, Tfc2, Tfc3, Tfc4, Tfc5, Tfc6 Internal contacts delineate some conspicuous lava flows or gradational Tslw Breccia with clasts of Wason Park Tuff South River Volcanics ash-flow cooling breaks within map units. No contact shown where Rat Creek Tuff Intrusions Tfg La Garita Member Rat Creek caldera cycle Tslc Breccia with clasts of Carpenter Ridge Tuff Tsri boundary between map units is uncertain or indefinite Tcdi Tfgl Lithic-rich partly welded zone Tcdf Tcdb Tcds Tsf2 Tsrx Xenocrystic andesite lava flows Tslf Breccia with clasts of Fish Canyon Tuff Concealed intrusive contact Ttd Tmcb Tmcd Tsf1 Tmci Tsrb Biotite dacite lava flows Tgbf Intracaldera landslide breccia with clasts of Fish Canyon Tuff Tslm Breccia with clasts of Masonic Park Tuff Lava-flow vent boundary Tbd Tba Tbav Tsrh Mafic dacite lava flows Tgbp Intracaldera landslide breccia with clasts of Pagosa Peak Dacite Tsld Breccia with dominant clasts of dacitic lava Premonitory(?) lava flows Fault—Dashed where approximately located; dotted where concealed or Tsra Hornblende andesite lava flows Tgbm Intracaldera landslide breccia with clasts of Masonic Park Tuff Tsla Breccia with clasts of andesitic lava occupied by intrusive rocks. Bar and ball on downthrown side Tsrm Andesite lava flows Tgbs Intracaldera landslide breccia with clasts of Sheep Mountain Ramp structure—Sawteeth on upper side. Near tops of lava flows, domes, Lavas of Tsrx ROCKS OF THE SAN LUIS CALDERA COMPLEX Andesite Tsrv Volcaniclastic rocks and lava-like parts of Pagosa Peak Dacite Tgbw Intracaldera landslide breccia with clasts of western San Juan tuff Eroded topographic wall Tsrb Tsrh Tsra Tsrm Tsrv Tsrt Tsri Rocks of the Nelson Mountain caldera cycle sheets SOUTH Tsrt Caldera-wall talus South River Volcanics Baldy Cinco Dacite Quaternary slump block—Approximately located; hachures on RIVER Pagosa Peak Dacite downthrown side CALDERA Intrusions Wason Park Tuff COCHETOPA Twcd Tpl Massive lava-like rocks CYCLE (La Garita 4?) Tbir Rhyolite Twcd Intracaldera dacitic tuff Hinge line—Dashed where approximately located; dotted where concealed. Twn (27.1 Ma) Tpc Carapace breccia Marks north margin of resurgence within San Luis caldera complex. Tbi Porphyritic dacite Tw Twn Nonwelded to partly welded tuff Double hachures indicate direction of uplift Tpr Rheomorphically brecciated zone CC Wason Park Tuff Tbia Andesite Tw Densely welded tuff San Luis Unconformity along caldera wall—Dashed where approximately located; Tpbb Pyroclastic breccia NM Tbf Lava flows dotted where concealed. Listed younger to older LA GARITA 3 ROCKS OF THE BLUE CREEK CYCLE (caldera concealed) (Saguache) Tmd2 Tpab Lens of andesitic slide breccia RC Creede La Garita (27.6 Ma) Tmd Tbv Volcaniclastic rocks Lava flows of McClelland Mountain SL Tmd1 Tpb Blob-and-ash deposits Tmd Dacite, undivided San Luis Complex Bachelor Stewart Peak Volcanics BACHELOR ? Tma LG (27.3 Ma) ? Tsir Resurgent intrusions Tpbl Lithic-bearing blob-and-ash deposits Nelson Mountain and Cochetopa BLUE ? Lava flows of McClelland Mountain Tmd2 Dacite flow 2 CREEK Tpp Pyroclastic-flow deposits B Porphyritic dikes and sills Tmd1 Dacite flow 1 Cebolla Creek CYCLE Tbc Tsi CREEDE (27.2 Ma) Tbcn Mafic dacite Tma Andesite flow ROCKS ERUPTED FROM THE PLATORO CALDERA COMPLEX Rat Creek (26.8 Ma) Creede Blue Creek Tuff Tsd Lava flows Treasure Mountain Group ? Blue Creek Tuff South River Creede LA GARITA 2 Ttc Chiquito Peak Tuff LA GARITA 2 Tvbb Tvbh Tvba Tvbm Tvbv Tvbc Tvbs Tsdv Volcaniclastic rocks Tbc Densely welded tuff (central) (central) Volcanics of Beaver Creek Bachelor A Porphyritic to fine-grained andesite Tbcn Nonwelded to partly welded tuff ROCKS OF THE MASONIC PARK CYCLE (caldera concealed) 1965 SOUTH Tsa Lava flows Sheep Mountain Andesite La Garita RIVER Oligocene Volcanics of Beaver Creek (Steven and Ratté,1965) Mount Tscf Tsci Tsma Porphyritic andesite Hope TERTIARY Tsv Volcaniclastic rocks Tvbb Silicic dacite lava flows Depositional synclinal sag—In east moat of La Garita caldera (sheet 1) LA GARITA 1 Tbs Tsmd Hornblende dacite (south) Tss Tuffaceous sedimentary rocks Tvbh Dacitic lava flows Strike and dip of beds B C Tcm Tcpl Tsmv Volcaniclastic rocks 1995-2000 Nelson Mountain Tuff Tvba Andesitic lava flows Inclined 1969-1976 (this report) BACHELOR Tcrf Tcbg Tndn Nonwelded to partly welded dacite Tmp Masonic Park Tuff—Local welding zones Tmp1, Tmp2, Tmp3, Tmp4 (Lipman and others, 1970; CALDERA Tvbm Andesitic cone breccia Tcbi Horizontal Steven and Lipman, 1976) CYCLE Tcbc Tnde Welded mafic dacite (Equity facies) Tmpl Lower welding zone Tcsb Tcab Tcwb Tcpt Tvbv Dacitic volcaniclastic rocks (27.3 Ma) Tcr Tcbck Strike and dip of foliation Tnd Welded silicic dacite and transitional rhyolite-dacite Tmpb Brecciated tuff Tvbc Andesitic volcaniclastic rocks Tcbw Inclined Caldera-fill boundary—Dashed where approximately located; Tnr Welded to partly welded rhyolite dotted where concealed; queried where uncertain Outflow Intracaldera Tvbs Volcanic sedimentary rocks OLDER ROCKS RELATED TO WESTERN SAN JUAN CALDERAS Horizontal Inferred caldera structural margin Carpenter Ridge Tuff Tnn Nonwelded to partly welded rhyolite and silicic dacite Twbl Tertiary landslide breccia ROCKS OF THE BACHELOR CALDERA CYCLE Tmr Vertical Eroded topographic wall Tnns Nonwelded surge-bedded rhyolite Silverton Volcanics(?) Dacite of Shallow Creek SILVERTON Tsvl Andesitic lavas and breccias 25 Tnxp Nonwelded crystal-poor rhyolite Tscf Flow and flow breccia Lineation—Showing bearing and plunge. Defined by elongate pumice lenses CALDERA, Tclt or flow structures. May be combined with foliation symbol Tsvv Volcaniclastic rocks 010203040 KILOMETERS W. SAN JUAN Crystal Lake Tuff Landslide breccia lenses Tsci Intrusion (27.5 Ma) Hydrothermally altered rock—Areas of conspicuous supergene acid-sulfate Tnlr Breccia lenses with clasts of Mineral Mountain Rhyolite Western San Juan tuff sheets Tbs Intracaldera sedimentary rocks alteration, mainly due to dissolution of pyrite, in vicinity of Thd Breccia lenses with clasts of dacitic lavas Tws Sapinero Mesa Tuff subvolcanic intrusions Thid Tnld Figure 4. Maps showing successive interpretations (1965-2000) of central San Juan caldera geometry: B, Bachelor; CC, Cebolla Creek; LG, La Thu Thv Carpenter Ridge Tuff Tha Thah Thap Ths Thbf Thbp Thc Twd Dillon Mesa Tuff Garita; NM, Nelson Mountain; RC, Rat Creek; SL, San Luis. A. Initial caldera identifications. B. Revised geometries. C. Present interpretation. Thi Thip Thih Tnlf Breccia lenses with clasts of Fish Canyon Tuff Outflow tuff units Age determination—In Ma (table 1). Mostly 39Ar/40Ar (s, sanidine; b, Huerto Andesite biotite; p, plagioclase; h, hornblende), a few K-Ar whole rock (w) Rocks of the Cebolla Creek caldera cycle Tcm Mammoth Mountain Member Twb Blue Mesa Tuff Tgs Tst Tuff and travertine Tcrf Mafic fiamme zone Twu Ute Ridge Tuff Drill site—Creede Continental Scientific Drilling Program Tfnd

Tgfc LA GARITA CALDERA Tfc Tfgl 107°W EXPLANATION 106°45' EXPLANATION 107°W 106°45' CYCLE Tgbf Tgbp Tgbm Tgbs Tgbw C.D. C.D. Tfg (27. 6 Ma) Hinsdale Formation Hinsdale Formation EXPLANATION 107° 106°45' Fish Canyon Tuff ? ? Creede Formation Creede Formation Hinsdale Formation .D. Precambrian & Mesozoic 107°15'W 107°W 106°45'W C Fisher Dacite Fisher Dacite k Cathedral Creede Formation Tpbb Tpab S-n Cathedral Cree CREEDE CREEDE Sa CREEDE RCD Snowshoe Mtn Tuff Sa Snowshoe Mtn Tuff gua gua ch Fisher Dacite ch CC e P Tpl Tpc Tpr CC hetopa Creek e P Topographic Baldy Cinco Dacite; ark Baldy Cinco Dacite; hetopa ark STM Tpb i i CREEDE Snowshoe Mtn Tuff rim Cannibal Mineral Mtn Stewart Peak Elk Park Saguache i, intrusion Coc i, intrusion Coc Plateau (CA) (MM) (SP) (EP) Park (SA) Stewart Pk Volcanics Stewart Stewart Pk Volcanics Stewart Baldy Cinco Dacite; Tpbl . Tpp Pk Pk i i, intrusion C.D Nelson Mountain Tuff MM Nelson Mountain Tuff MM Stewart Pk Volcanics 38°15' Pagosa Peak Dacite H-n 38°N S-s Mineral Mtn Rhyolite 38°N Mineral Mtn Rhyolite 38°N SL SL Nelson Mountain Tuff FCT COCHETOPA NP landslide CD Cebolla Creek Tuff k Cebolla Creek Tuff RC eek & faults PARK RC NM ee NM Mineral Mtn Rhyolite Rhy. of PLATORO SHEET 1 Baldy Cr Baldy CALDERA Cochetopa

Ttc Mineral Creek Dacite Cinco LA GARITA LA GARITA Dome SAN LUIS COMPLEX SAN LUIS COMPLEX Mineral Creek Dacite Cinco CALDERA C.D. SAN LUIS COMPLEX Cebolla Creek Tuff Baldy Cinco San Luis Half Moon Mesa Mtn i he Cr Tuffaceous C.D. he C.D. en e COMPLEX uac sediments lid Chiquito Peak Tuff Slumgullion Rat Creek Tuff (North) rab s (BC) Peak (SL) Pass (HM) (ME) (North) Rat Creek Tuff Mineral Creek Dacite d (28.2 Ma) Sag SAN LUIS COMPLEX ? lan Pass (SG) Saguac La inos G South River Volcanics La South River Volcanics Garit Rat Creek Tuff s P FCT G Mesa a M o ? ari Mesa L eek Tsma Tsmd Tsmv CR, BC, WP Tuffs, ta M Mtn CR, BC, WP Tuffs, tns and assoc. lava flows tns and assoc. lava flows Mtn South River Volcanics MASONIC Wheeler etopa Cr Tmp Sheep Mountain Andesite Huerto Andesite BACHELOR Huerto Andesite BACHELOR CR, BC, WP Tuffs, och Wheeler Cathedral C Graben Monument PARK CYCLE Was and assoc. lava flows Nutras Creek Tmpb Was Monument CC SaP M-n Fish Canyon Tuff on P o (28.3 Ma) Tmpl ar Fish Canyon Tuff n Pa Huerto Andesite Dacite Hermit Lakes Bristol Head Creede Wagon Wheel Pool Table k rk C.D. Pagosa Peak Dacite SP LA GARITA

LA GARITA LA Pagosa Peak Dacite Masonic Park Tuff (HL) (BH) (CR) Gap (WW) Mtn (PT) GARITA LA Fish Canyon Tuff Silver MM Masonic Park Tuff and Pool Masonic Park Tuff and Silver Pool (north) Creede Park Table Creede Park Table Pagosa Peak Dacite 38°

Treasure Mountain Group GARITA LA Mtn Treasure Mountain Group SL Precaldera lavas Mtn H-s Precaldera lavas Gra Masonic Park Tuff and RC Twbl (Conejos Fm) Rio Grande (Conejos Fm) Rio 37°45'N nd Treasure Mountain Group BC Resurgent e Tsvl Tsvv Bristol C. D. dome Western SJ Tuffs NM WESTERN Head Bristol La Precaldera lavas G Tws Silverton Volcanics(?) Lake Head ari SAN JUAN (Conejos Fm) t MeM (Age relations Little Squaw Workman Spar City Humphreys South Fork CREEDE CREEDE a M Snowshoe Prevolcanic rocks tns CALDERAS Twd Creek (LS) Creek (WC) (SC) (LH) West (SF) Snowshoe with Chiquito Peak Mtn (Mesozoic, Precambrian) BACHELOR (28.0-28.4 Ma) Mtn Wagon Wagon C Wheel Gap Twb and Masonic Park .D. Wheel Gap Tuffs uncertain) Twa RG Twu Contact Creede PTM Uplifted M-s caldera floor ? Beaver Ruby Ruby Fault—Bar and ball on downthrown C le BH Cimarrona Creek Lake Baldy Lake side. Dashed where approximately ar Trout Baldy LH Trout Cr WWG Peak (CP) Palomino South River (MH) Reservoir Mtn LH located; dotted where concealed g Red Fisher Mtn South Red Mtn Mtn South ra CREEDE Fisher be Tts Mtn (PM) Peak (SR) Cr Fork SnM (BR) Lake Mtn Lake Cr Mtn Fork n 37°45' Ttr PLATORO Trout Lake C.D Trout Lake Boundaries of 7.5' quadrangles C.D Mtn Tsua Tsup Tsuv Mtn Metroz CALDERA 37°30'N . . (fig. 3) Ttm Cimarrona Mtn Red COMPLEX Tt Peak SOUTH Red SOUTH Tia Tid SHEET 3 SHEET 2 Ttj Metroz Mtn (SE. SAN JUAN) RIVER TM South C.D. RIVER Eroded topographic rim (28.5 - ~29.5 Ma) Intrusions of Pagosa Peak Saddle Mtn Wolf Creek FM Fork Ttb Cimarrona S River uncertain age and affinity S River Table Mtn (PP) (SM) Pass (WP) Pk Peak Table Mtn C.D Peak . Ttl Summitville Andesite (precaldera and caldera) r LA GARITA e Cr Me Goose C Goos SOUTH Treasure Mountain Group A-c A-e (South) RIVER LA GARITA (South) Mt Hope Mt Hope SRP TaM 1:50,000-scale county maps: A, Archuleta (c, central; e, east); H, Hinsdale (n, north; s, south); Tld M, Mineral (n, north; s, south); RG, Rio Grande; S, Saguache (n, northwest; s, southwest) La Garita (south) MH (Tuffs erupted from Tcfr Tci ROCKS Tln Tcd 37°30' MAPPING CREDIT k 37°30' k Sheep northeast sources: Tcf Tca Tcap Tcv Tcs Tcas r Sheep r PREDATING o o Precollapse Tscc F Mtn F Mtn lava dome 37°30' Cochetopa Park?) CENTRAL P. Lipman, 1986-89, Modified by P. Lipman, 1995-99, from e e l Wolf Cr l Wolf Cr SM d Treasure d Treasure d 1995-99 Steven and Ratté (1965, 1973), Steven d rk Tsc i CALDERA i Pass Contact Pass Contact Fo Pagosa Eagle Mtn C.D Fork Pagosa Eagle Mtn C.D WCP

M Conejos Formation (1967), Steven and others (1969), and M . . TrM CLUSTER P. Lipman and D. Sawyer, st Peak Mtn Peak Mtn C.D. Ea East PP EM SA 1986-89; P. Lipman, 1995-99 Steven and Lipman (1973) R Tcst Modified by P. Lipman, 1994-99, Fault—Bar and ball on downthrown Saddle Fault—Bar and ball on downthrown P. Lipman and O. Bachmann, Saddle side. Dashed where approximately Mtn side. Dashed where approximately San from Lipman and Steven (1976) Piedra R PREVOLCANIC ROCKS 1995-98 Piedra San Mtn located; dotted where concealed San located; dotted where concealed Jua n Jua Juan Bas Ba 0 5 10 KILOMETERS n 0 5 10 KILOMETERS C 0 5 10 KILOMETERS sin Figure 3. Map of central caldera cluster, showing areas of geologic mapping responsibilities, 7.5' Ba Tbb Eocene sin Boundaries of 7.5' quadrangles in Boundaries of 7.5' quadrangles topographic quadrangles (black lines; abbreviations used on maps and in text for files in database), A (fig. 3) B (fig. 3) and 1:50,000-scale county maps (blue dashed lines; used as base for printed maps). C.D., Continental Divide. Ku Cretaceous MESOZOIC Figure 5. Generalized geologic maps of the central San Juan caldera cluster. Abbreviated geographic names: BC, Baldy Cinco; BH, Bristol Head; CD, Cochetopa Dome; C.D., Continental Divide; EM, Eagle Mountain; FM, Fisher Mountain; LH, Lake Humphreys; MM, Mineral Mountain; Me, Metroz Mountain; MeM, Mesa Mountain; MH, Mount Hope; NP, North Pass; PP, Pagosa Peak; RCD, Razor Creek Dome; SA, Saddle Mountain; SaP, Saguache Park; SL, San Luis Peak; SM, Sheep Mountain; SnM, Snowshoe Mountain; SP, Stewart Peak; SRP, South River Peak; STM, Sawtooth Mountain; TaM, Table Mountain; TM, Trout Mountain; TrM, 1 Ar-Ar ages generalized from Lanphere (1988, 2000), Lipman and others (1996), Treasure Mountain; WCP, Wolf Creek Pass; WWG, Wagon Wheel Gap. Calderas of San Luis complex: CC, Cebolla Creek; NM, Nelson Mountain; RC, Rat Creek. Ash-flow sheets: BC, Blue Creek Tuff; CR, Carpenter Ridge Tuff; WP, Wason Park Tuff. A. Geometry of the San Luis caldera complex, Creede caldera, and associated Lipman (2000), and Bove and others (2001) p_q PRECAMBRIAN ash-flow sheets. B. Geometry of the Bachelor caldera, South River caldera, and associated ash-flow sheets. C. Geology of La Garita caldera and associated proximal eruptive deposits. FCT, Fish Canyon Tuff; SJ, San Juan. Geologic Map of the Central San Juan Caldera Cluster, Southwestern

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