U.S. Department of the Interior Scientific Investigations Map 3394 U.S. Geological Survey Sheet 1 of 2 Pamphlet accompanies map 106°22'30" Pahlone Peak (PP) 38°30' 10800 106°15' 14 13 10800 Mount Ouray (MO) Old Monarch 106°07'30" Poncha Pass (PO) 18 Pass 17 106° 16 15 9200 Monarch Pass 10800 14 13 18 38°30' 10400 108° 106° 104° 10400 17 16 Poncha Hot 15 14 13 8800 8000 11600 10400 11600 10000 18 17 Springs 8400 40° 9600 9200 16 15 Hunter 14 13 18 17 Figure 16. Panoramic view 0 10 20 30 40 50 MILES 23 24 Porphyry Gulch Dry Lake 8800 10800 Round Mountain Gulch Wicker PikesPark Peak 10800 across crest of Whale Hill (dacitic Bonanza Tuff) 11600 Hayden Peak Creek Spring Creek 19 20 11200 Whale Hill Elkhorn resurgent dome, eastward 0 25 50 75 KILOMETERS 21 Peak (late lava flows) San Luis Valley Denver Porphyry 11200 22 Dacitic Creek 23 24 (RioRedman Grande rift) toward San Luis Valley (Rio 9600 SangreCreek de Cristo Mountains 19 Rhyolitic Porphyry Peak Bonanza Tuff 20 Creek F 10800 21 22 Grande rift), from west rim of r Bonanza Tuff 23 24 19 o 11200 20 Cleveland n Bonanza caldera. Intracaldera 21 22 23 t 11200 8000 24 19 8400 12400 Mountain 8800 20 10000 Bonanza Tuff is as much as 2.5 8400 Agate Creek Pahlone 9600 8400 Park Caldera-floor lavas c r Peak km thick, dips 45–55° on flank ni ocks Mount 12000 Creek Southeast a R 25 Peck lc a 26 12000 of resurgent dome. Photo n caldera rim 10000 o 11200 Spruce v g 30 Creek location shown on fig. 10. e 29 Creek Poncha 28 9200 f 11200 12000 o 27 Fooses Dacitic 26 Mountain Postcollapse rhyolite 25 Green 10800 Fork Bonanza Tuff 8800 t 30 10000 29 Creek i 10400 l 28 l 27 m l South 10800 Pass 26 25 30 i l 29 l GP l Browns 9200 28 27 Postcollapse lavas l 26 25 30 l Park 29 l l S North 10800 11600 8800 a l Morraine and landslide SAN ISABEL n a Creek w South i 10800 Con Colorado Peelcealed ring fa NATIONAL FOREST g a 9200 i Stumpy 10400 r t BP Point ult o c Springs 35 36 h Thirtynine Mile . 31 Pass Creek Lake Sand Creek 10400 32 11600 x volcanic area 10400 10000 Loggie 33 Gulch King o Timber 34 10000 r Andesite lavas 11200 Andesite lavas Gulch Gulch 35 36 p Brier 10000 Silverheels MP 31 p (on west caldera wall) (on west caldera wall) UAV Morraine and landslide 11600 32 Creek Gulch A l 10800 Agate 33 MA unmapped West Elk l Burned 34 Cochetopa 35 12000 36 31 32 l 33 34 l 9200 9600 35 locus R Creek 11600 10400 36 31 a 12000 32 9200 11600 n 10400 g Little e AREA OF 10400 Bonanza Tuff, on west caldera rim 10400 Columbine Gunnison 9600 Methodist MAP Tdu Mountain Gulch M W 10000 Bz 12800 l 13200 Camp Rock Gulch l e 2 l 1 l 6 5 8800 l t 4 l 12400 9600 Creek l 3 2 10800 Tcd l M 10800 l 10000 l l 1 l 11200 Droz C o 6 11200 5 20 l l NP u Treasure Chipeta l 4 3 l l n 11600 l l l l l 2 l 3 l 1 11200 l l l l 4 l 11600 l t l 5 l l 9200 Mountain 6 10800 l l 50 l l a l Linear contact l Tdua : 2 l l l l Qc l i l l l S l unconformity 1 l n 6 l l l Saguache l l or fault? l a s 38° l l l Tcv? 104005 l l l n SL l l l l l l Creek Tcap l l l l g m l l LO l l l l LGN l l l l l l l r 11200 Tev l l l l l e l SK l l l Lime l l l Precambrian l l Pahlone Peak (PP) l S l l B l l Ridge boulders l l l l l l l to 1 m Difficult distinction l l l l l l Tcv? l l 33.46 l between l l SC 11200 Grays ±0.11b l Tdu Tcv and Tdua l l l l Poncha Pass (PO) Cr l 11 12 l Tcv Creek l l l 7 8 9 10 11600 l l l San Luis Lime Creek 11 San Juan 12 l 7 8 9 Little/no offset of 9 l 10 10 l SR 11 Tia l l Tdup across major 12 8 11 l Devils l volcanic Valley Ql l l l l l Ql basement fault O'Haver 7 12 l de Oh Armchair l Om 9200 7 l locus 13600 Lake l LGS l l l l Tcap l 12000 m 8 l l l l u 8800 Tca 285 l l Mount 10400 l l 20 l Ouray Poncha Pass l Qc Creek l Oh Qc Tdup l l l Tbc l Pl 30 Qc l l Tbc 35 11200 SAN ISABEL Beaver 30 Qal Tcd Creek Dorsey l l 15 l Concentrated angular u 13200 NATIONAL FOREST 9200 A 15 k float; bedrock m, Tdua 13 Creek 9600 p 14 13 12800 p Spanish r 18 17 10800 12000 or facies of Tdup? o 16 15 Tcd x Of 14 13 . C 18 17 12400 16 Creek Peaks Tcap 10 u 15 14 20 16 15 o r Ml 13 17 14 ri i 15 Qc Paleovalley fills Qt 18 13 g s 20 11600 Ouray Tree 18 i Om t 9600 along Poncha Creek; 20 n ADO 17 a o COLOR Tev 10 15 l 20 Box Tbfr, Tbfd, Tbdk Tbfr? 10400 Tbfr? 15 34.09 32.27 33.05 l CO 30 Tent Tca Paleovalley fills im NEW MEXI 16 ±0.11 Tbfd? ±0.31b ±0.09 T 9200 Dc 25 34.11 Poncha along Silver i u 25 t 30 25 25 Larkspur Creek ±0.11 s 20 Tcab Creek: Tbfr, Tbfd a 32.79 o l l 5 20 s l s 45 f 5 ±0.05 Questa-Latir v l 5 Tdu M 10000 Creek o 33.06 Best exposures, Mine Wastewater Tbc Creek l 9200 Tbfd Tbfd? o 10 Tcv ±0.12b Remnant of c l Treatment Reservoir Harry Creek 35 Intracaldera Tbd against a u volcanic locus Tbc 10 40 65 Bonanza n n M 23 l 24 1019 Qm Mlb Dc Bonanza wall (or downfaulted ic t 20 21 45 caldera wall? a l l l Bulls 22 23 Ql proximal outflow?) i l o D Laramide-age 24 19 20 25 Tbfr 24 m Round ro n A 10800 Ditch 21 35.04 33.05 c u 34.18 22 Lone s reverse fault ±0.11b 23 ±0.04 40 Hill 22 23 k RO ±0.19 33.15 Qc 20 21 24 s n Tmd 5 E 32.49 19 33.02 19 t a IN 10800 Tbdk Silver ±0.08 i 10 M 10800 ±0.05gm ±0.01 Tcd Ttra m 20 ns Creek Cobbles of Tbd 30 9600 9600 H Creek Om 40 Creek Lakes Murphys 33.20 Tev C 33.83 and Tbc, along Ql San ±0.07 Creek Ql 15 T Ml I ±0.13 contact with u Tbrb? Hole Creek Tbc? 10400 9200 Round Hill EXPLANATION P 32.94 Sawmill Swidinski 10 l 33.06 Of 24 9600 g 10 Ttmb? ±0.13 Ttmb? Good roadcut 35.28 Ttr? g Tcap Tca ±0.13 Gulch Gulch 15 ±0.55 Qal 35 Luis Nelson Qc exposures, 33.81 Ttmc 70 33.06 Mid-Tertiary volcanic areas Granitic intrusion Regional structural attitude 33.91 Ttr vitrophyre ±0.10 Ttma Tcd 30 25 ±0.07 Creek 10 ±0.32 10 33.09 33.72 9600 34.29 ±0.04 & megabreccia Marshall m 9200 9200 9200 33.74 33.04 ±0.12 9600 Creek ±0.59 33.93 Pass Tma 30 20 Trap Sedimentary fill of Rio Grande Rift MP Mount Princeton batholith Major bounding faults of asymmetrical 33.54 ±0.11 ±0.61 ±0.22 Creek Ttma 60 Tbfd? Tbfd? Tbd 26 25 ±0.17 g Tra Tca rift grabens 30 29 Tma 28 Marshall 33.91 Oh 25 27 26 25 Tcd 10000 Qc Qf Tdu? Late rift basalts Trend of Colorado Mineral Belt Ml 30 Qc 29 ±0.09 28 25 Tbd Decker l 27 l 26 Of? l GUNNISON 10800 Creek 25 15 Tmp 10800 28 Trd 27 Merkt Diffuse structural-transition boundary 20 26 l Qc 35 30 Creek 30 29 25 30 NATIONAL FOREST OA Oh? 29 l l Caldera 34.11 Ttmc D 11200 15 Tra m l l ±0.21 Qt S SR Ttrn 15 Irregular Creek D Tmp A Paleovalley fills O A P Tbr Qc North R Ttr Ttmb Millswitch 35 fault, or steep 10000 TCH E L along Silver I Tmap 34.02 P M IN L A ±0.13 unconformity? Creek; Tbfr, Tbfd s Tmd H Creek Trfr S 15 Tdu? a 30 R 10400 Trd 38°22'30" A 10000 Starvation Figure 1. Map of Southern Rocky Mountain Volcanic Field (SRMVF), showing ignimbrite calderas, major erosional remnants and inferred original 25 Ttr Trap 20 Tbmc l M 10400 Trap Tdu? 8800 8800 Chester Tbma 40 Tbdn extent of middle Tertiary volcanic cover, caldera-related granitic intrusions, and later sedimentary fill in asymmetric grabens of the Rio Grande rift.