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Sheet 2 of 2 U.S Scientific Investigations Map 3123 U.S. Department of the Interior Sheet 2 of 2 U.S. Geological Survey Pamphlet and CD-ROM accompany map CORRELATION OF MAP UNITS LIST OF MAP UNITS Debris-flow deposits of Buffalo Pass Campground [Dotted 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 Tdc Distal conglomerate 0 5 10 KM Some major formation names are labeled. Some units of a formation are divided by emplacement type] for unit identification. These units are labeled where possible; unlabeled units are 107° attributed in the database] Tdb Mesobreccia and conglomerate 38°15' 106°45’ SURFICIAL DEPOSITS SURFICIAL DEPOSITS Tdbm Megabreccia blocks Precambrian and Mesozoic GLACIAL DEPOSITS Qal Alluvium (Holocene) Qal Qc Qf Qt Holocene Andesite of hill 9519 Ql Qc Intermediate-composition Colluvium (Holocene) Taha Aphyric andesite RCD Qfo Qm Qg QUATERNARY lava and breccia Pleistocene Ql Landslide deposits (Holocene and Pleistocene) Qlo Qgo Tahh Hornblende andesite STM Topographic Qf Alluvial-fan deposits (Holocene) OLD SURFICIAL DEPOSITS CALDERA-RELATED ROCKS PREDATING THE WESTERN AND CENTRAL rim Qt Talus (Holocene) CALDERA CLUSTERS C. D. QTl QTf QTg QUATERNARY North Pass Caldera Cycle AND TERTIARY Qlo Older landslide deposits (Pleistocene) CALDERA Luders Creek Tuff Qfo Older alluvial-fan deposits (Pleistocene) FCT RELATIONS ASH-FLOW SHEETS AND Tld NP Welded dacite landslide 1 LAVAS AND RELATED ROCKS VOLCANIC SEDIMENTARY ROCKS INTRUSIONS CD (age) RELATED ROCKS Tfc & faults Cochetopa GLACIAL DEPOSITS Tlr Nonwelded to partly welded rhyolite Park Tuffaceous Thb Qm Moraine and till (Pleistocene; Pinedale glaciation) POSTCALDERA Volcanics of Cochetopa Hills caldera sediments ROCKS Miocene Hinsdale Formation Qg Glacial-outwash and other terrace gravels (Pleistocene; Pinedale Volcaniclastic deposits glaciation) Tst Bedded rhyolitic tuff Tpff Tpcf ? o Qgo Older glacial-outwash and other stream gravels (Pleistocene; 38° pre-Pinedale glaciation) Tsd Dacitic conglomerate Caldera-margin fanglomerate FCT landslide Los Pinos Graben ? Tfc Tcdu OLD SURFICIAL DEPOSITS Tsa Andesitic conglomerate QTl High-level landslide or debris-flow deposits (Quaternary and Tertiary?) Postcaldera lava flows Tcdc Cathedral Graben Tpt Tnpd Dacite of East Pass Creek Cochetopa Creek Tcdm Tcdx QTf Deeply dissected alluvial-fan deposits (Quaternary and Tertiary?) Nutras Creek C C SaP Tnpr Rhyolite of Taylor Canyon Dacite Tcdl QTg High-level gravel deposits (Quaternary and Tertiary?) C. D. COCHETOPA SP PARK Cochetopa Dome Rhyolite Intracaldera tuffaceous rocks Tnpa Andesite, undivided LA GARITA MIOCENE POSTCALDERA VOLCANIC ROCKS MM CALDERA Tcdi Saguache Creek Tuff (north) Tpbf Tpbm Tpbs Tpbr Tpbd Tpba Hinsdale Formation o Fill of the Cochetopa Park caldera Tscl Landslide breccia of hill 9943 SL Caldera-margin landslide breccia Thb Mafic flows R C N M Tfc and Tndn Tscc Densely welded crystal-rich rhyolite BC Nelson Mountain caldera cycle OLIGOCENE VOLCANIC ROCKS Resurgent Tnd Tsc Nonwelded to densely welded crystal-poor rhyolite dome SAN LUIS CALDERA Tnr ROCKS OF COCHETOPA PARK CALDERA AND SAN LUIS CALDERA COMPLEX La Garita Mtns Tscn Nonwelded crystal-poor rhyolite COMPLEX (26.9 Ma) Tnn Rocks of the Nelson Mountain Caldera Cycle MeM Tbt Bedded tuff Nelson Mountain Tuff Caldera-Fill Flows and Intrusions Tuff of Spanish Creek BACHELOR Tcc Cochetopa Dome Rhyolite Tcdu Upper lava flow Tts Welded tuff Cebolla Creek Tuff Figure 10. Generalized geologic map of San Luis complex in relation to Cochetopa Park caldera, showing present-day Tcdc Crystal-rich flow Ttsn Nonwelded tuff caldera margins (unconformities between precaldera and caldera-fill rocks; thick colored lines, dotted where concealed) Trdn and inferred topographic rim of Cochetopa Park caldera. Modified from Lipman (2006, fig. 5C). Calderas of the San Intrusions of Uncertain Affinity Trr Tcdm Middle lava flow Luis complex: CC, Cebolla Creek; NM, Nelson Mountain; RC, Rat Creek. Tfc, Fish Canyon Tuff; FCT, clasts of Fish BC CD MeM Tia Andesite Canyon Tuff in caldera-margin landslide deposits. Geographic names: , Baldy Cinco; , Cochetopa Dome; , Rat Creek Tuff Tcdx Glassy flow breccia Mesa Mountain; MM, Mineral Mountain; NP, North Pass; RCD, Razor Creek Dome; SaP, Saguache Park; SL, San Tid Dacite Luis Peak; SP, Stewart Peak; STM, Sawtooth Mountain. C. D., Continental Divide. SOUTH RIVER Tw Tcdl Lower lava flow CALDERA CYCLE Tir Rhyolite (27.4 Ma) Wason Park Tuff Tcdi Intrusions Bonanza Caldera Cycle Tal Caldera-Fill Volcaniclastic Rocks Postcaldera lavas and related rocks Andesite of Mountain Lion Creek Caldera-margin fanglomerate Tba Upper andesite Tpff Fanglomerate with clasts of Fish Canyon Tuff Tcrn Bonanza Tuff BACHELOR CALDERA Tpcf Fanglomerate and sandstone, with clasts of andesitic and rare dacitic Tcr CYCLE (27.5 Ma) lava derived from the Conejos Formation Tbd Lower dacite Carpenter Ridge Tuff Tpt Intracaldera tuffaceous sediments S.E. & W. SJ Tbrl Lower rhyolite, densely welded VOLCANIC Sawatch Range Trend Transition Loci Central SJ Latir Lake City Caldera-margin landslide breccias LOCI Thu VOLCANIC ROCKS PREDATING BONANZA CALDERA Tpbf Massive breccia with clasts solely of Fish Canyon Tuff Huerto Andesite FC Conejos Formation, Lower Units 3 Tpbm 5,000 km LA GARITA CALDERA Tfcb Breccia with sparse clasts of Carpenter Ridge Tuff Tci Intermediate-composition granitoid intrusions 3 2,000 km3/m.y. CYCLE (28.0 Ma) Tfc Tpbs Breccia with clasts of Saguache Creek Tuff 4,000 km /m.y. Lava flows and proximal breccias SP AT 16,000 Tfcn Tpbr Breccia with clasts of Conejos rhyolite lava Tca Andesite NM WM SM CR Fish Canyon Tuff 1,000 3 Tpbd Breccia with clasts of Conejos dacite lava Tcsa Andesite scoria 1,000 km /m.y. Twsb Tcap Plagioclase andesite 3 Tpba Breccia with clasts of Conejos andesite lava 250 km3/m.y. WESTERN SAN JUAN Tws Nelson Mountain Tuff Tcd Dacite 12,000 3 CALDERAS (28.3 Ma) LJ CP Twsn Tndn Nonwelded to partly welded dacite Tcfr Rhyolite Sapinero Mesa Tuff Tnd Welded silicic dacite and transitional rhyolite-dacite Tcv Volcaniclastic rocks Tbfc NM Tnr Welded to partly welded rhyolite Rhyolitic tuff GP SC 8,000 500 WP SMT AT Tbfa Tct Tan to light-gray rhyolitic tuff and tuffaceous sandstone Tnn Nonwelded to partly welded rhyolite and silicic dacite Rhyolite of Barret Creek Cumulative volume, km Rocks Erupted from the Cebolla Creek Caldera Tcht Pink tuff of Home Gulch SP Tcuv (individual tuff sheets), km Volume Tbpf Cebolla Creek Tuff Tev Early volcaniclastic sedimentary deposits Tbpi BC B 4,000 Tbpv Tcc Weakly welded mafic dacite EARLY IGNIMBRITES ERUPTED FROM SAWATCH RANGE CALDERAS SR Basalt of point Benny Rocks Erupted from the Rat Creek Caldera Tbc Badger Creek Tuff (Bcr) Tla Tlav Rat Creek Tuff Twm Wall Mountain Tuff Andesite of Lone Tree Gulch Trdn Weakly welded dacite 0 0 38 36 34 32 30 28 26 24 22 PREVOLCANIC ROCKS Trr Nonwelded rhyolite Age, in m.y. Tbg TERTIARY MESOZOIC SEDIMENTARY ROCKS Tuff of Big Dry Gulch Oligocene ROCKS ERUPTED FROM SOUTH RIVER CALDERA Km Mancos Shale (Cretaceous) Tw Wason Park Tuff Figure 7. Age-distance-volume plot, showing southward progression of Tertiary ignimbrite-caldera volcanism in the Southern Rocky Mountain Tab Volcanic Field. Ignimbrite abbreviations; AT, Amalia Tuff; B, Bonanza Tuff; BC, Badger Creek Tuff; Bcr, rhyolite of Barret Creek flow field; CP, Kd Dakota Sandstone (Cretaceous) Andesite of Big Dry Gulch YOUNGER INTERMEDIATE-COMPOSITION LAVA FLOWS Chiquito Peak Tuff; CR, Carpenter Ridge Tuff; FC, Fish Canyon Tuff; GP, Grizzly Peak Tuff; LJ, La Jara Canyon Tuff; NM, Nelson Mountain Upper volcaniclastic rocks Tuff; SC, Saguache Creek Tuff; SM, Sapinero Mesa Tuff; SMT, Snowshoe Mountain Tuff; SP, Sunshine Peak Tuff; SR, tuff of Stirrup Ranch; Tal Andesite of Mountain Lion Creek Jm Morrison Formation (Jurassic) WM, Wall Mountain Tuff; WP, Wason Park Tuff. SJ, San Juan. Tdc Tdb Tdbm Local lava flows and volcaniclastic rocks ROCKS ERUPTED FROM BACHELOR CALDERA Jj Junction Creek Sandstone (Jurassic) Debris-flow deposits of Buffalo Pass Campground Carpenter Ridge Tuff PALEOZOIC SEDIMENTARY ROCKS Taha Tcrn Nonwelded to partly welded tuff |l Paleozoic limestone (lower Paleozoic) Tahh Tcr Welded rhyolite tuff PRECAMBRIAN ROCKS Andesite of hill 9519 =g Granitic intrusive rocks, undivided Conejos Formation, upper units (~30 Ma) ROCKS OF LA GARITA CALDERA CYCLE Huerto Andesite =m Metamorphic rocks, undivided Tld Thu Olivine-bearing andesite and hornblende-bearing andesite-dacite, Age (Ma), before present Tlr undivided 29 28 27 26 25 Fish Canyon Tuff Contact—Dashed where approximately located; dotted where gradational. Luders Creek Tuff Internal contacts delineate some conspicuous lava flows or gradational Tfcb Fault-scarp breccia, with clasts of Fish Canyon Tuff Younger ash-flow cooling breaks within map units. No contact shown where CREEDEFisher Dacite (4) Tst (2) Tfc Widespread welded outflow ignimbrite sheet boundary between map units is uncertain or indefinite or where mapping Older Bedded rhyolitic tuff stops Snowshoe Mountain Tuff, Tfcn Nonwelded to partly welded tuff (2) Tnpd Tsd Fault—Dashed where approximately located; dotted where concealed or intracaldera (5) OLDER TUFFS RELATED TO WESTERN SAN JUAN CALDERAS occupied by intrusive rocks. Bar and ball on downthrown side Dacite of East Pass Creek Dacitic conglomerate Snowshoe Mountain Tuff, outflow (2) Sapinero Mesa Tuff Quaternary slump block—Approximately located; hachures on downthrown
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