Chapter 4 Geologic Setting Martin C. Larsen

4-35 he Snake/Salt River Basin comprises approxi- to Snake/Salt River Basin groundwater resources mately 5,500 square miles (16.80 million begins with the nonconformable deposition of Tacres) in western Wyoming and extends into south- transgressive marine sediments onto underlying eastern Idaho. In Wyoming, the Snake/Salt River Precambrian basement rocks. From that time Basin encompasses nearly all of Teton County and forward, a general geologic history that describes portions of Lincoln, Sublette, and Fremont coun- the development of the stratigraphic, structural, ties. The basin is bounded by the Overthrust Belt and volcanic elements the Snake/Salt River Basin is to the west and south, the Green River Basin to as follows: the southeast, the Wind River Range to the east- southeast, the Bighorn Basin to the east, and the 1. Paleozoic strata in the Snake/Salt River Yellowstone River Drainage to the north. Of all Basin were deposited in numerous Wyoming basins, the Snake/Salt River Basin has marine and nonmarine environments the most complex geology. The geologic settings related to periodic transgressive and for this drainage encompass: regressive environments. Sandstone, shale, conglomerate, and limestone • The Overthrust Belt, which includes three are the dominant lithologies, with less major mountain chains (Salt River, Wyo- extensive dolomite. Deposition in the ming, and Snake River Ranges) related to Paleozoic Era was broken by long periods the Sevier Orogeny; of erosion, as indicated by several regional • Two structural basins (Jackson Hole and unconformities in the geologic record. Hoback) and three mountain ranges (Gros Ventre, Teton, and Absaroka) associated 2. The Mesozic Era was a time of shallow with the Laramide Orogeny; seas with deposition of interbedded layers • Range-front normal faulting and two (in decreasing abundance) of sandstone, structural basins associated with the Basin siltstone, shale, carbonates, and evaporites. and Range Province; and An emergent transition to terrestrial • The Yellowstone Plateau, and the Absaroka environments during the Late Triassic and Volcanic province. Early Jurassic epochs deposited marginal marine, eolian, fluvial, and paludal An extensive set of figures, maps and plates are sandstone and shale. included in this report to depict the basin’s complex geologic settings. Plate 1 illustrates the bedrock 3. Sevier and Laramide deformation affected geology of the Snake/Salt River Basin in Wyoming the Southwest Cordillera between earliest and a small portion of southeastern Idaho overlain Cretaceous and Early Eocene time on a base map that shows highway, township, state (approximately 140 - 35 million years and county data. Inset maps present the elevations ago). The Sevier Orogeny is defined by of the Precambrian basement and lineaments. “thin-skinned” deformation, characterized Appendix A contains detailed descriptions of the by shallow thrusts faults. Parallel north- geologic units shown in plate 1. Six cross-sections, south trending Sevier-aged faults in the figures 4-1through 4-6, show typical subsurface Overthrust Belt are generally younger structure in the Snake/Salt River Basin. Isopach to the east. Laramide deformation was maps of the major aquifers in the Snake/Salt River a period of intense folding and faulting Basin are unavailable. with large-scale reverse and thrust faults 4.1 General geologic history and asymmetric folds. The “thick- skinned” deformation of the Laramide The correlation between the major structural and Orogeny included Precambrian basement- lithologic elements significantly influences the cored mountain ranges and uplifts that availability of groundwater within the Snake/ surrounded and partitioned the Snake/ Salt River Basin. The geologic history relevant Salt River Basin structural basins. During

4-36 the Middle Eocene, massive eruptions Teton and Gros Ventre ranges consist of basement related to the Absaroka Volcanic Province core, broad, asymmetrical anticlines, northeast emplaced rhyolitic and basaltic volcanic dipping thrust faults, and parallel folds. The material along the northern side of the initial stages of forming Teton and Gros Ventre Snake/Salt River Basin. structures were concurrent with the early phases of the Laramide deformation. These major structures 4. Late Tertiary Basin and Range normal controlled the character and trend of the later, faulting, coupled with volcanic activity Snake, and Salt River structures in Wyoming. from the Yellowstone hotspot, has The structural architecture of the Salt River, and overprinted many of the Sevier and Snake River Ranges are also the result of the Sevier Laramide geologic relationships. Uplift “thin-skinned” deformation. The Overthrust Belt during the past five million years resulted located in southwestern Wyoming and neighboring in erosion of Tertiary strata, stripping areas of Idaho and Utah, is a north-south trending, the Laramide and Sevier structures, and elongate fold and thrust belt that encompasses shaping the present day landscape of structurally deformed Paleozoic and Mesozoic the Snake/Salt River Basin. Tertiary-age units. The complex structural deformation in this rocks include volcanic deposits and an region includes folding, imbricated thrust faults, assortment of sedimentary units, including and reverses faulting. During the Sevier Orogeny, conglomerates, sandstone, limestone, and thrust sheets were pushed eastward, resulting in the mudstone. Some of the Tertiary volcanics parallel thrust faults with the younger thrust belts include andesitic flows, breccias, and to the east. porphyries that resemble breccias of the Yellowstone and the Absaroka volcanic Beginning in the Tertiary and continuing to the regions. present day, some Laramide and Sevier structural features have been overprinted or transected by 5. The youngest units in the Snake/Salt River north-south tending, high-angle normal faults due Basin are unconsolidated Quaternary to Neogene Basin and Range extension. Normal alluvial, colluvial, lacustrine, and glacial faults are coincident with north-northwest tending deposits of varying thicknesses. These folds and thrust fault bounded uplifts that define deposits, some several hundreds of feet a complex set of half-grabens. Holocene-age thick, consist of interbedded mixtures displacement is apparent on some of the normal of clay, silt, sand and gravel, landslide faults. deposits, glacial deposits, and lacustrine sediments. Quaternary glacial deposits The topography of the Snake/Salt River Basin is correlate to the advance and retreat of the reflected by major structural features that uplifted, Bear Lake and Pinedale glaciations (15,000 folded, faulted, and eroded Precambrian basement years before present). and the Phanerozoic sedimentary and volcanic deposits. The insert map in plate 1 is a structural 4.2 Structural geology contour map of the Precambrian basement surface in the Snake/Salt River Basin that shows a general The Snake/Salt River Basin encompasses three northwest-southeast lineament trend. The geologic characteristic structural provinces: 1) the cross-sections on figures 4-2 through 4-7 continental shelf deposits, which includes the Teton show Precambrian basement rocks overlain by and Gros Ventre ranges; 2) west of the shelf zone, varying thicknesses of Phanerozoic formations, all structurally deformed passive margin Paleozoic deformed by large-scale folding and faulting. and Mesozoic units that include the Wyoming, Salt and Snake River ranges (i.e., the Overthrust The major structural elements of the Snake/Salt Belt); and 3) the volcanism of the Yellowstone River Basin (fig. 4-1) comprise: Plateau and Absaroka Province. The dominant structural features that form the backbone of the

4-37 Index Map ¤£20 Lake_

¤£20 ¤£89 ¤£16 _ ¤£14 Old Faithful ¤£191 ¤£287 Yellowstone Lake Yellowstone I D A H O

W Y O M I N G Shoshone Lewis Lake Lake Heart

r Lake P A R K e Plateau v Ri

r

s Absaroka e

v Ri

w i v

e e Ri ak er T N l L Sn Fal U T A H N O 0 25 50 100 Miles M Mountains E T47N R R115W Jackson R110W R108W

Explanation F ¤£89 Geologic Features Base Data ¤£191

¤£287 Overthrust Belt _ City or town Hole Jackson State or U.S. highway Lake Structural Basins Teton lo rk Buffa Fo River or creek T45N Precambrian Teton_ia N

Lake or reservoir O

Quarternary T Township boundary Jackson Volcanic E T E T O N Basin T Range Tertiary Volcanic County boundary Jenny Lake ¤£26 State boundary ¤£287 Jackson Valley ¤£26 Yellowstone National e F R E M O N T ¤£89 ntr The Rim Park boundary s Ve Victor Gro Major Quaternary _ ¤£191 Ri Fault «¬33 ve Valley Gros r Data Sources: WSGS 2014 G Projection: NAD 1983 Wilson Wyoming State Geological «¬22 _ N

UTM Zone 12N O Survey, 2008 _Jackson Ventre

I S

H n ¤£26 a T01N k T40N _ S e R39E R45E M Irwin na Snake Range Ri ke A Ri ve v r Palisades er 0 5 10 20 Miles _ O W D River H T01S i o l b N l a Y o I c Ri k w

v Range e r

B O N N E V I L L E W Hoback

Cr Ri Palisades ¤£89 ve e Alpine ¤£26 r e k Reservoir _ Little G Wyoming Basin B I N G H A M r e G y ¤£189 n s e S r e a e r l y Ri t ve £ s r ¤191 Bl G a ¤£89 ck fo o Range 3«¬52 t Star Valley T35N Ri Green T05S «¬34 _Ranch v Ri e

r v e _ r Blackfoot Thayne Salt _Pinedale Reservoir Star River Ri L I N C O L N v ¤£191 er S U B L E T T E «¬237 Valley River _ C A R I B O U 2«¬38 Afton Basin

Soda Springs _ ¤£189 ¤£30 Range «¬34

r T30N 3«¬51 a _ Marbleton T30N

K Be T10S Grace Ri R119W R109W v T10S R115W _ C R39E e 3«¬50 _ r R45E Big Piney O B E A R L A K E N _ ¤£89 «¬235 Georgetown N ¤£189

A ¤£30 B

«¬36 Figure 4-1. Geologic features, Snake/Salt River¤£89 Basin.

F R A N K L I N k

r

Fo

4-38 Cross Section A - A'

Huckleberry Ridge Big Game Ridge

A Wolverine A' FEET FEET Anticline WASHAKIE RANGE Bend in Section Hancock 10,000 Ta 10,000 Jsg Anticline Pp 9,000 Pp KJm Qlg Qlg Buffalo Fork Thrust Ta 9,000 Crooked Creek *Mta Jsg Snake River Dd ^cd Qlg Kh East Sheridan Fault Qa Qlg 8,000 8,000 Snake River Ob 

West Sheridan Fault West Qa ^cd  Qa  Snake River Jsg Mm  Snake River _r 7,000 Mm Ta 7,000   Dd Kb Kh *Mta  6,000 6,000   Buffalo Fork

 5,000 Ob _r  Kc Kb Thrust Fault =r 5,000 4,000 4,000 Kf Kc 3,000 Kh 3,000 Kmt KJm 2,000 Kf  2,000 KJm Kmt  1,000 =r Jsg ^cd 1,000 *Mta Pp Jsg Sea Level ^cd Pp Sea Level -1,000 Ob Mm Dd -1,000 *Mta Mm -2,000 -2,000 No Vertical Exaggeration

Index Map and Line of Section Geologic Units

CENOZOIC MESOZOIC (cont.) PALEOZOIC (cont.) Quaternary Cretaceous-Jurassic Mississippian

Qa Alluvium and terrace deposits KJm Cloverly and Morrison Formations Mm Madison Limestone Qlg Landslide and glacial deposits Jurassic Devonian

Snake River Tertiary Jsg Sundance and Gypsum Spring Formations Dd Darby Formation Lewis River Ta Absaroka Volcanic Supergroup Triassic Ordovician WYOMING A' ^cd Chugwater and Dinwoody Formations Ob A MESOZOIC Bighorn Dolomite PALEOZOIC T48N £¤89 Cretaceous Cambrian Permian Kh Harebell Formation _r Cambrian rocks R116W R115W R114W R113W R112W R111W Pp Phosphoria Formation Kb Bacon Ridge Sandstone T47N PRECAMBRIAN Teton Kc Cody Shale Pennsylvanian-Mississippian p_r Precambrian rocks Kf Frontier Formation *Mta Tensleep Sandstone and Amsden Formation Jackson T46N Lake Kmt Mowry and Thermopolis Shales Fault

Surface Geology Base Data Quaternary _ City or town Township boundary

Tertiary River or creek County boundary Mesozoic State or U.S. highway Paleozoic Fault Precambrian Love, J.D., and Keefer, W.R., 1975, Geology of sedimentary rocks in southern Yellowstone National Park, Wyoming: U.S. Geological Survey, Professional Paper 729-D, scale 1:62,500. Figure 4-2. Geologic cross section A-A’.

4-39 Cross Section B - B' B B'

FEET FEET Middle Leidy Peak 2 10,000 10,000 1 Kt Kmr Tp 9,000 Leidy Creek 9,000 Spread Creek

8,000 KJm Kws Qlgu Ju Slate Creek Kc 8,000 Gros Ventre River Gros Ventre Kf  Kccs Kb 7,000 KJm Zone of squeezing and possible thrusting ^c Kccs Kmr Kccs 7,000 Ju KJm 6,000 *ta Kf 6,000 ^c Mm ^d Kb 5,000 ^d Pp  5,000 Pp Kt Kmr Kc 4,000 *ta Ob 4,000 3,000 Mm _u Dd Dd 3,000 2,000 Ob =  KJm 2,000 Kmr 1,000 _u Kt 1,000 Kt Ju Sea Level = Sea Level KJm ^d ^c -1,000 Pp -1,000 -2,000 Kmr Kt -2,000 KJm *ta -3,000 Ju Mm -3,000 Dd -4,000 ^c Ob -4,000 -5,000 1 Carter Oil Co., Treglown No.1 Pp ^d -5,000 *ta _u -6,000 2 Stanolind Oil & Gas Co., Unit No. 1 -6,000 Mm = -7,000 Dd -7,000 Ob -8,000 -8,000 _u -9,000 -9,000 = No Vertical Exaggeration Index Map and Line of Section Geologic Units

CENOZOIC MESOZOIC (cont.) PALEOZOIC (cont.) Jackson Lake £¤287 Quaternary Cretaceous (cont.) Pennsylvanian-Mississippian R115W R114W R113W R112W R111W Qal – Alluvium Kf – Frontier Formation *ta – Tensleep and Amsden Formations B' Qlsd Kmr Snake River£¤191 T44N – Landslide debris – Mowry Shale Mississippian Qlgu – Landslide and glacial debris Kt – Thermopolis shale and Muddy sandstone Mm – Madison Limestone Tertiary Cretaceous-Jurassic Devonian Tp – Pinyon Conglomerate and greenish-gray KJm – Cloverly and Morrison Formations Dd – Darby Formation T43N and brown sandstone and shale Jurassic Ordovician sequence undivided Ju –Jurassic rocks undivided Ob – Bighorn Dolomite MESOZOIC Triassic Cambrian Teton B Cretaceous ^c – Chugwater Formation _u – Cambrian rocks undivided Gros Ventre River T42N Kws – White sandstone sequence ^d – Dinwoody Formation PRECAMBRIAN Kccs – Lenticular sandstone and shale PALEOZOIC p_ – Precambrian igneous and metamorphic sequence and coaly sequence, undivided Permian rocks Surface Geology Base Data Kb – Bacon Ridge Sandstone Pp – Phosphoria Formation Quaternary _ City or town Township boundary Fault Tertiary River or creek State boundary Kc – Cody Shale Mesozoic State or U.S. highway County boundary Paleozoic Fault Love, J.D., Keefer, W.R., Duncan, D.C., Bergquist, H.R., and Hose, R.K., 1951, Geologic map of the Spread Creek-Gros Ventre Precambrian River area, Teton County, Wyoming: U.S. Geological Survey, Oil and Gas Investigations Map OM-118, scale 1:48,000.

Figure 4-3. Geologic cross section B-B’. 4-40

Cross Section C - C'

Snow King J A C K S O N H O L E Mountain C' C Bend in Section FEET FEET South Park Mad *Mw Pp P*w *Mw 8,000 Mmb *Mw Thrust Fault Game Creek J^n P*w 8,000

Pp Ql  ^a Qc Qg2 Mmb 

 Mad Jackson Thrust Fault

Qg2 Fault of Teton  Qls 7,000 Snake River

Hoback Fault 7,000 Qg2  Postulated position Mm Channel Ways Mm Ka Qtg Qta Ql Mm Mm Mmb

Qsb Qal Flat Creek Qfp Qf Jt ^p ^r ^d   6,000  Qb Dd 6,000 Kbr  Kpb Ka Ob _g Mmb Kg   Mad 5,000 Kbr  Kb 5,000 Jsp Kg Jt Jsp Kc 4,000 4,000 No Vertical Exaggeration

Index Map and Line of Section Geologic Units CENOZOIC MESOZOIC (cont.) PALEOZOIC (cont.) Wilson Quaternary Cretaceous (cont.) Permian-Pennsylvanian T41N Qal Alluvium Ka Aspen Shale P*w Wells Formation upper unit Jackson C' Qfp Floodplain deposits Kbr Bear River Formation Pennsylvanian-Mississippian

Qtg Terrace deposits undifferentiated Kg Gannett Group *Mw Wells Formation lower unit

Qc Colluvium Jurassic Mississippian Teton Snake River Qls Landslide debris Jsp Stump and Preuss Sandstones Mad Darwin Sandstone Member (Amsden Formation) T40N Qta Talus Jt Twin Creek Limestone Mmb Bull Ridge Member (Madison Limestone)

Qf Alluvial fan deposits Jurassic-Triassic Mm Main body Madison Limestone 191 £¤ J^n Nugget Sandstone Qsb Slump block Devonian Dd Darby Formation Ql Loess Triassic R117W R116W R115W C ^p Popo Agie Member (Chugwater Formation) Ordovician Qg2 Glacial deposits and related outwash gravels ^a Alcova Limestone Member (Chugwater Formation) Ob Bighorn Dolomite T39N Qb Lithified talus breccia ^r Red Peak Member (Chugwater Formation) Cambrian MESOZOIC Surface Geology Base Data Cretaceous ^d Dinwoody Formation _g Gallatin Limestone Quaternary _ City or town Township boundary Tertiary River or creek State boundary Kpb Post-Bacon Ridge rocks PALEOZOIC Mesozoic State or U.S. highway County boundary Permian Paleozoic Fault Kb Bacon Ridge Sandstone Precambrian Pp Phosphoria Formation Fault Kc Cody Shale

Love, J.D., and Albee, H.F., 1972, Geologic map of the Jackson quadrangle, Teton County, Wyoming: Figure 4-4. Geologic cross section C-C’. U.S. Geological Survey, Miscellaneous Geologic Investigations Map I-769-A, scale 1:24,000.

4-41 4-41 Cross Section D - D'

D D' FEET FEET 10,000 10,000

Mm 9,000 *Mw 9,000 Ppu  St.Thrust John 8,000 ^w Jt South Fork Fall Creek *Mw 8,000 ^t North Fork Indian Creek

Ppm St.Thrust John Qc J^n P*w South Fork Fall Creek Kau Absaroka Thrust Big Basin Canyon Ppu ^d *Mw Ke Qg Qal 7,000 ^a   Kb 7,000 Ppm Kgu Kal ^d ^t Jt Kal P*w Js Kb 6,000  Ppu ^w 6,000 P*w J^n ^a Jp *Mw 

*Mw Ppm  5,000 ^w ^t  5,000 Js Jp Ke Kgu 4,000 4,000 No Vertical Exaggeration

Index Map and Line of Section Geologic Units

Snake River CENOZOIC MESOZOIC (cont.) PALEOZOIC Lincoln Quaternary Jurassic Permian R118W Qal Alluvium Js Stump Sandstone Ppu Phosphoria Formation R117W R116W Qc Colluvium Jp Preuss Formation Ppm Mead Peak Member (Phosphoria Formation) D' Qg Glacial deposits Jt Twin Creek Limestone Permian-Pennsylvanian T39N P*w Upper Wells Formation MESOZOIC Jurassic-Triassic J^n Cretaceous Nugget Sandstone Pennsylvanian-Mississippian *Mw Lower Wells Formation IDAHO Kau Upper Aspen Formation Triassic

WYOMING £¤89 Kal Lower Aspen Formation ^a Ankareh Formation Mississippian D Kb Bear River Formation ^t Thaynes Formation Mm Mission Canyon Limestone Snake River Kgu Gannett Group ^w Woodside Formation T38N Teton Ke Ephraim Conglomerate ^d Dinwoody Formation Fault

Palisades Reservoir

Surface Geology Base Data Quaternary _ City or town Township boundary Tertiary River or creek State boundary Mesozoic State or U.S. highway County boundary Paleozoic Fault Love, J.D., and Keefer, W.R., 1975, Geology of sedimentary rocks in southern Yellowstone National Park, Precambrian Wyoming: U.S. Geological Survey, Professional Paper 729-D, scale 1:62,500.

Figure 4-5. Geologic cross section D-D’.

4-42 Cross Section E - E'

SALT RIVER RANGE WYOMING RANGE GREEN RIVER BASIN E GREYS RIVER VALLEY E' FEET FEET 12,000 STAR VALLEY Prater Mountain Jsp Ke 12,000 Ke Mm J^n Kdp P*w *Ma Kdp 10,000 MDd Murphy Creek _g

Telephone Hollow Telephone Jsp 10,000

Qd Ob Js Beaver Creek

Ob _g  Ke Qd Qd Little Elk Creek

 Ke Jt

Greys River  Qd _g  Kbr White Creek Kdp Js 8,000 Ob  Kdp Kbb Qtg Kdp  Twl 8,000  Jp Qtg Qal Ka ^a ^a Qtg  Jt  Kbr  Jt J^n _gv _gvs _gvs Jt Jp 6,000 Absaroka Thrust Jp Ke Jt ^t  Jsp 6,000 _gv Kbb Tsl  Js Ka Thrust Twc Th Ka Jt pect J^n Kbr Pros 4,000 J^n 4,000 ^a ^a Kmv   2,000 ^t ^t Th 2,000 Kbr ^w  Kh P*w ^d Pp Sea Level Sea Level Vertical Exaggeration 1.5x Love, J.D., and Keefer, W.R., 1975, Geology of sedimentary rocks in southern Yellowstone National Park, Wyoming: U.S. Geological Survey, Professional Paper 729-D, scale 1:62,500.

Index Map and Line of Section Geologic Units

CENOZOIC MESOZOIC (cont.) PALEOZOIC Quaternary Cretaceous (cont.) Permian Gannett Group from top to base Qal Floodplain and alluvial fan deposits Kdp Pp Phosphoria Formation Little Greys of Peterson T36N Permian-Pennsylvanian River Qd Rock debris and colluvium Ke Ephraim Conglomerate 89 P*w Wells Formation £¤ Qtg Terrace gravels and older alluvium Greys River Jurassic Js Stump Sandstone Pennsylvanian-Mississippian T35N Tertiary *Ma Amsden Formation Salt River Tsl Salt Lake Formation Jp Preuss Redbeds E E' Twl La Barge Member (Wasatch Formation) Jsp Mississippian R119W Thayne Stump Sandstone and Preuss Redbeds T34N Mm Twc Chappo Member (Wasatch Formation) Jt Twin Creek Limestone Madison Limestone Sublette Th Hoback Formation Jurassic-Triassic Mississippian-Devonian Lincoln MDd Darby Formation MESOZOIC J^n Nugget Sandstone T33N Cretaceous Triassic Ordovician R115W R114W R118W IDAHO R116W Ob R117W Kbb Blind Bull Formation ^a Ankareh Redbeds Bighorn Dolomite WYOMING

Kmv Mesaverde Sandstone ^t Thaynes Limestone Cambrian Surface Geology Base Data _g Gallatin Limestone Quaternary _ City or town Township boundary Kh Hillard Shale ^w Woodside Redbeds Tertiary River or creek State boundary Ka Aspen Formation _gvs Gros Ventre Shale Mesozoic State or U.S. highway County boundary ^d Dinwoody Formation Gros Ventre Formation Paleozoic Fault Kbr Bear River Formation _gv Precambrian middle limestone member

Fault Figure 4-6. Geologic cross section E-E’.

4-43 4-43 Cross Section F - F'

F F' FEET Red FEET 12,000 Mountain 12,000 Box Canyon Creek Mount J^n Jt Qm

J^n Qd Apperson Creek Bald Mountain Jt ^a ^w Qd Schidler North Piney Creek 10,000 Pp J^n Qm Qm North Piney Creek Qd 10,000 ^d QTf ^a Qm Qal Qd Qal Qm ^a Qal Qal Qm Qd ^t Qtg ^t Qal Jp Pp Kbb Twl 8,000 Qal ^w Mm J^n 8,000 ^a _g J^n ^d

Salt River Qal Spring Creek Qd Jsp ^a P*w Ka Jt P*w Ke Th 6,000 ^a Pp Twc 6,000 Tsl *Ma *Ma Ka Ke ^t  J^n Jt Mm ^t ^w  4,000 Js  *Ma Mm Kbr   4,000 ^a ^w J^n  ^d Kmv Jp P*w MDd Kdp Jt ^t ^a MDd Ke P*w P*w Js Kbb 2,000 Jt Pp ^t Ob *Ma 2,000 Mm Jp Pp Kh ^d Mm  Pp ^w ^a J^n ^d  Sea Level  Sea Level ^t Mm *Ma Ob _gvs _g _gv Kbr Kdp Vertical Exaggeration 1.5x Love, J.D., and Keefer, W.R., 1975, Geology of sedimentary rocks in southern Yellowstone National Park, Wyoming: U.S. Geological Survey, Professional Paper 729-D, scale 1:62,500.

R119W Index Map and Line of Section Geologic Units

CENOZOIC MESOZOIC (cont.) PALEOZOIC Quaternary Cretaceous (cont.) Permian T33N Qal Floodplain and alluvial fan deposits Kh Hillard Shale Pp Phosphoria Formation Qd Rock debris and colluvium Ka Aspen Formation Permian-Pennsylvanian

Salt River Swift Kbr P*w Wells Formation IDAHO Qtg Terrace gravels and older alluvium Bear River Formation Creek T32N WYOMING Afton Qm Glacial till and moraine Kdp Gannett Group from top to base of Peterson Pennsylvanian-Mississippian

Greys River *Ma Amsden Formation T31N QUATERNARY-CENOZOIC Ke Ephraim Conglomerate F F' Quaternary-Tertiary Lincoln Jurassic Mississippian QTf Fanglomerate or till Js Stump Sandstone Mm Madison Limestone £¤89 Sublette Jp T30N CENOZOIC Preuss Redbeds Mississippian-Devonian Tertiary Jsp Stump Sandstone and Preuss Redbeds MDd Darby Formation Tsl Salt Lake Formation R119W R118W R117W R116W R115W R114W Jt Twin Creek Limestone Ordovician Twl La Barge Member (Wasatch Formation) T29N Jurassic-Triassic Ob Bighorn Dolomite Twc Chappo Member (Wasatch Formation) J^n Nugget Sandstone Cambrian Surface Geology Base Data Th Hoback Formation Triassic _g Quaternary _ City or town Township boundary Gallatin Limestone Tertiary River or creek State boundary ^a Ankareh Redbeds MESOZOIC _gvs Gros Ventre Shale Mesozoic State or U.S. highway County boundary Cretaceous ^t Thaynes Limestone Paleozoic Fault _gv Gros Ventre middle limestone member Precambrian Kbb Blind Bull Formation ^w Woodside Redbeds Fault Figure 4-7. Geologic cross section F-F’. Kmv Mesaverde Sandstone ^d Dinwoody Formation

4-44 4-44 Figure 4-8. Geothermal features, Snake/Salt River Basin.

4-45 • Multiple phases of folding and faulting that involved Precambrian basement Volcanic material derived from the Absaroka rocks. Volcanic Province and Yellowstone hotspot that • Folding and faulting of the Overthrust sculpted and formed the Absaroka Mountains Belt during the Sevier Orogeny. and Yellowstone Plateau are composed primarily • Extension of the Basin and Range of basalt and rhyolite flows, tuffs, re-worked Province. volcaniclastic material, and igneous intrusions. • Volcanism that created the Yellowstone Plateau and the Absaroka Range. Late Tertiary to Quaternary unconsolidated • Uplifted mountain ranges that surround hydrogeologic units in the Snake/Salt River Basin and separate the basins, including the include alluvial, fluvial, paludal, lacustrine and Gros Ventre, Teton, Wyoming, Salt River colluvial sediments; landslide deposits; glacial and Snake River mountains. Subsidence of deposits; gravel pediment and fan deposits; and structural basins including Jackson Hole, terrace gravels. The Quaternary-aged glacial Hoback Basin, and Star Valley. deposits consist of poorly sorted clay, silt, sand, gravel. and boulders. Glacial deposits are present 4.3 Geologic units in the Snake/Salt in the Overthrust Belt and Jackson Hole. River Basin 4.3.1 Teton Range (Smith, 1993) Geologic units within the Snake/Salt River Basin vary widely in lithology and distribution, and range The Teton Range, situated within the Middle in age from Precambrian crystalline rocks to recent Rocky Mountain physiographic province, is the alluvial and terrace deposits. The legend on plate youngest mountain range in the Rockies. The 1 identifies the geologic units present in Snake/ Neogene age Teton Range is superimposed over Salt River Basin; the individual geologic units are the northwest portion of the ancestral Gros Ventre described in appendix A. The distribution of Range. The Tetons are an upthrown, titled fault- geologic units throughout the basin reflects several block of Precambrian basement rocks and more periods of deposition, uplift, faulting, folding, than 5,000 feet of overlying Paleozoic sedimentary erosion, volcanism, and reworking/re-deposition of strata, including significant carbonates. The range older units as younger units. has a vertical uplift of over 25,000 feet, inferred from the depth to basement, about 16,400 feet, Precambrian basement rocks are exposed in the underneath Jackson Hole. The Precambrian rocks cores of the Tetons, Gros Ventre, and Absaroka exposed in the Teton Range consist predominantly mountains and are bounded by Paleozoic to of gneiss and schist, with intrusions of pegmatite Cenozoic sedimentary strata and volcanic material. granite. Exposures of metaconglomerates and The sedimentary succession of the Overthrust Belt, metaquartzites also occur throughout the range. predominately the Wyoming, Salt, and Snake River ranges, can be divided into two main classifications: The remarkable front of the Teton Range is a 1) a passive margin sequence ranging in age from product of one of the most active normal faults Middle Cambrian to Late Jurassic that consists of in the Intermountain Seismic Belt (ISB) and the carbonates and fine-grained clastic sedimentary eastern extent of the Basin and Range Province. strata, and 2) a clastic wedge ranging in age from The Teton fault system originated as early as 5 Early Cretaceous to Late Tertiary strata comprised to 13 million years ago and has been active ever of marine and terrestrial clastic detritus. The since. Quaternary fault scarps, ranging from 9 passive margin deposits derived from successive to approximately 150 feet high, are exposed over transgressive-regressive sequences, and the clastic 25 miles along the 33 mile length of the Teton wedge resulted from material shedding off orogenic fault. The youngest fault scarps offset Pinedale-age highlands to the west.

4-46 (approximately 14,000 years) glacial deposits and consisting of a broad asymmetrical anticline with younger alluvial and fluvial deposits. a steep and locally faulted southwest limb (fig. 4-1). The western portion of the range is bounded 4.3.2 Absaroka Mountains (Sundell, by the Jackson Hole valley and is transected by 1993) Tertiary faults. Older structures extend to the north beneath Jackson Hole and into the Teton The Absaroka Range is a remnant of thick volcanic fault block. The range is subdivided into two and volcanic-derived accumulations erupted along asymmetric uplifts, or blocks of basement core, a belt of andesitic stratovolcanoes. Today, the separated by the Granite Creek syncline: the remaining deposits cover approximately 9,000 eastern Shoal Creek block and the western Skyline square miles in northwestern Wyoming and Trail block. Maximum displacement occurred southwestern Montana. In the Snake/Salt River along the southwestern margin of the Gros Ventre Basin, the Absaroka Range is bordered by the Range where offset in Precambrian basement rocks Bighorn Basin to the east, the Beartooth Mountains indicates the greatest relative uplift. to the northeast, the Yellowstone Plateau to the north-northwest, and the Gros Ventre Range to 4.3.4 Wyoming Range (Ross, 1960) the south. Volcanism occurred between 53 to 35 million years ago (53-35 Ma). Volcanic materials The Wyoming Range is bounded by the Hoback superimpose Phanerozoic sedimentary strata in Basin to the east, the Green River Basin to the the shallow foreland topographic and Laramide South, and the Gros Ventre Range to the north structural basin. The Absaroka Volcanic Province (fig. 4-1). The range is structurally bounded to signifies the largest Eocene volcanic field in the west with the Salt River Range by the Absaroka Rocky Mountains. The Absaroka volcanic suite Thrust sheet. Exposed shale, sandstone, is composed of andesite, dacite, breccia, tuff, and conglomerate, and limestone units range in age re-worked volcaniclastic material (conglomerates, from Middle Cambrian to Tertiary. The Wyoming sandstone, siltstone, and claystone), with a Range encompasses the Darby thrust system, the maximum, combined thickness of more than 6,000 easternmost and youngest thrust system of the feet. Overthrust Belt. The primary structural features of the Darby Thrust system are the Darby, Prospect, Deformation of the Absaroka volcanic rocks Jackson, and Hogsback thrust faults. Sections of occurred as a result of Laramide folding and the Darby Thrust sheet have been overprinted by faulting, intrusive igneous activity, slope processes, Basin and Range normal faults, predominantly, and post-volcanic extension and compaction. by the Hoback fault. The Hoback fault is a Mid- Tertiary high angle fault that is superimposed on Some of the largest landslides ever known in Earth’s previously folded and faulted Sevier structures. history consisted of transported reworked volcanic East of the Hoback fault, a series of imbricated material from the Absaroka Volcanic Province. thrust faults are structurally bounded by the Cache Creek thrust fault. 4.3.3 Gros Ventre Range (Horberg and others, 1949) 4.3.5 Salt River Range (Lageson, 1979 )

The Gros Ventre Range is a northwest trending, The Salt River Range is the structural culmination Laramide uplift that consists of a Precambrian-age of the Absaroka-St. Johns thrust complex and basement core underlying a generally continuous encompasses a complex array of imbricated thrust Paleozoic, Mesozoic, and Tertiary sedimentary faults and asymmetric folds associated with/ section. The range is situated just west of the related to the Overthrust Belt system. The range Wind River Range and south of the Absaroka is bounded by the Star Valley to the west, the Mountains and is bounded to the southwest by Wyoming Range to the east-northeast and the the northwest-striking Cache Creek thrust fault, Green River Basin to the east (fig. 4-1). The

4-47 Grand Valley fault bounds the range along the Cretaceous to Late Tertiary strata comprises of western margin where Tertiary-age units are marine and nonmarine clastic detritus. offset against Mesozoic and Paleozoic strata. The Tertiary-age Grand Valley fault, a basin and range 4.3.7 Yellowstone Plateau (Smith, bounding normal fault, runs along the western 1993) margin of the Salt River Range and along the eastern margin of Star Valley forming an 85 mile The Yellowstone-Snake River Plain (YSRP), a 16 long fault complex. Rock units within the Salt million-year old volcanic system that transects River Range vary from Middle Cambrian to upper Nevada, Idaho, Montana, and Wyoming is one Cretaceous and consisting of shale, sandstone, of the Earth’s largest silicia-rich volcanic systems. conglomerate, and limestones. The geology and hydrogeology is dominated by the Yellowstone hotspot. The Yellowstone-Snake A parallel series of faults associated with the River volcanic system in northwestern Wyoming Absaroka thrust system are the primary structural is a large, silicic, Pleistocene-age volcanic field features of this range. The Absaroka thrust system, distinguished by three large calderas with a total part of the Overthrust Belt, is a 150 mile thrust eruptive volume of about 2,050 cubic miles. The sheet extending from the Snake River Plain in Yellowstone Plateau, a relatively flat landscape with eastern Idaho to Salt Lake City, Utah. In the low, rolling mountains, accumulated from this Salt River Range, the Absaroka Thrust sheet is volcanic material, rises approximately 8,200 feet considered to be a large-scale duplex structure high above mean sea level. The volcanic rocks from bounded on the north and south by steep lateral the Yellowstone area range in age from 0.6 to 16 ramps in large footwall imbricated thrusts. million years old, with the oldest rocks outcropping in southwestern Idaho and northern Nevada. The 4.3.6 Snake River Range (Horberg, Yellowstone-Snake River volcanic material within 1949) the Snake/Salt River Basin consists predominantly of rhyolite with scattered basalt flows and minor The Snake River Range is the northern continuation igneous intrusions. of the Wyoming and Salt River ranges and is the northern arc of the Overthrust Belt. The range is 4.3.8 Hoback Basin (Spearing, 1969) bounded by the Teton Range to the north, Gros Ventre Range to the east, and the Caribou Range, During the early Tertiary, western Wyoming’s located in southeastern Idaho, to the southwest. overthrust region experienced numerous stages of The Snake River Range encompasses westward- uplift supplemented by synorogenic deposition dipping thrust faults and parallel folds. Although of thick sediments into subsiding intermontane the Snake River Range includes nine, imbricate basins. The Hoback structural basin is a prime sheets of the Absaroka system, which form an example of one of these sinking basins and the overlapping array, the Absaroka, Poison Creek, and Hoback Formation, confined within the basin, St. John thrust faults are the primary structural exhibits one of these thick, early Tertiary deposits. features of the range. The Absaroka thrust can be The Hoback Basin covers approximately 315 traced over the entire length of the Overthrust Belt. square miles and is bounded by the Wyoming The St. John overrides the Absaroka at the north Range to the west, the Gros Ventre Range to the end of the complex in the Snake River Range. Rock north north-east, and the Rim to the south (fig. units within the Overthrust Belt of the Snake River 4-1). The Rim is a drainage divide at the northern Range vary from Middle Cambrian to Late Tertiary. boundary of the Green River Basin. The Hoback Middle Cambrian to Late Triassic age units consists Formation ranges in age from Middle Paleocene of carbonates and fine grained clastics and Early to early Eocene. Structurally bounded along

4-48 the western portion of the basin, the Hoback 4.3.10 Star Valley (Walker, 1965) Formation is overridden by the Jackson-Prospect thrust sheet along the Prospect fault and is Star Valley consists of two half-grabens that folded along the Little Granite-Monument Ridge resulted from extensional processes along the anticline. Along the western margin of the basin, Grand Valley fault system during the Neogene. the Hoback Formation has a moderate eastward The valley is bounded by the Salt River Range to dip of 40 degrees that decreases to 10 degrees at the the east and the Gannett Hills in Idaho to the west. eastern margin. On the eastern side of the basin, Sedimentary strata exposed along the front of the the units are structurally truncated by the Cache Salt River Range and Gannett Hills consist of Creek Thrust fault and a small syncline along the Mesozoic age conglomerate, sandstone, limestone, southwestern flanks of the Gros Ventre Range. The and shale. Paleozoic limestone outcrops in a small Cache Creek thrust fault plane dips northeast, and butte located in the northern part of the valley. its asymmetrical trace indicates a relativity low dip The elevation of the valley floor ranges from 6,000- angle. The units dip towards the southwest along 7,000 feet and contains moderate slopes on the strike with the Cache Creek Thrust fault. alluvial fans derived from the Salt River Range and The Hoback Formation is characterized by three, Gannett Hills. The alluvial fans on the east side major environments of deposition: thick sandstone are steeper at their heads than the alluvial fans on facies; conglomerate facies; and thin, interbedded the west side of the valley, indicating that the east sandstone, shale, and limestone facies. The side of the valley is remains structurally active along formation is wedge-shaped with the maximum normal faults associated with the Grand Valley basin subsidence and sedimentary axis located in fault system. the central and northern portions of the Hoback Basin. The formation is thickest (~16,000 feet) Star Valley is divided into two basins because of in the center of the basin and thins southward the difference in sediment type and Quaternary to approximately 2,500 feet where the southern displacement rates on different segments of boundary of the Hoback Basin meets the north end the Grand Valley fault system. In the northern of the Green River Basin. section of the valley, the Salt River Range front, geomorphic relations indicate a lower rate 4.3.9 Jackson Hole (Smith, 1993) displacement along the Grand Valley fault than along the southern segment. The valley floor Jackson Hole, a 44 mile long Laramide structural sediments in the northern section include older basin, occupies the hanging wall of the Teton (early to late Pleistocene) alluvial fans and extensive fault and is covered by asymmetric, west dipping, Tertiary outcrops. In contrast, the southern Tertiary-Quaternary basin-fill stratigraphy. The section of the valley encompasses numerous fault valley is bounded by the Teton Range to the west scarps separating younger valley sediments from and the Gros Ventre Range to the east (fig. 4-1). deformed Mesozoic and Paleozoic strata in the Salt The Quaternary deposits in the valley consist of River Range. Additionally, steep walled canyons, fluvial, alluvial, glacial, and volcaniclastic facies apparent range-front triangular facet spurs, and and are underlain by Tertiary fluvial, lacustrine, young, faulted range front alluvial fans indicate and volcaniclastic deposits. The glacial deposits rapid basin subsidence. Pleistocene-age deposits in in the valley provide evidence for two periods of Star Valley consist of sand and gravel, which are the Pleistocene glaciation known as the Bull Lake (100 principal aquifers in the valley. to 150 thousand years ago) and the Pinedale (14 to 30 thousand years ago) periods. Several bedrock 4.4 Geothermal resources buttes, containing Paleozoic rocks, are exposed in the central and southern parts of the valley. The geothermal resources of the Snake/Salt Paleozoic units are also exposed on the eastern River Basin occur where groundwater exists at flank of the Teton Range. anomalously elevated temperatures relative to the average geothermal gradient. The hydrothermal

4-49 occurrences within the Snake/Salt River Basin Absaroka Mountains near the Gros Ventre River. are typically found at a depth that prohibits their A historical metal mine is sited on the western beneficial use. Hydrothermal resources within the flanks of the northern Teton Range. Currently, Snake/Salt River Basin are primarily suited to local, there is no active coal mining in the Snake/Salt small-scale projects that utilize low-temperature River Basin. Sand, gravel, and limestone have waters for space-heating, de-icing, and recreational/ been extensively mined within the Snake/Salt River therapeutic applications (e.g., Granite Hot Basin, and still are produced in some localities Springs). (figs. 5-7 through 5-9).

Generally, groundwater heats as it flows downdip into a structural basin in accord with the local geothermal gradient. Snake/Salt River Basin hydrothermal resources occur primarily where heated groundwater rises under artesian hydraulic pressures at velocities that preclude dissipation of the heat acquired at depth. This requires vigorous upward flow through permeable, up-folded strata or along faults, fracture systems, or wells. In general, the conditions that control hydrothermal resources occur only within the more productive Mesozoic and Paleozoic aquifers in the Snake/Salt River Basin. The locations of known and potential areas of hydrothermal resource development are shown on figure 4-1.

4.5 Mineral resources

Figures 5-4, 5-7, 5-8, and 5-9 show the distribution of petroleum operations and other active and historic mineral development locations within the Snake/Salt River Basin (section 5.7.2). Mineral development operations require the use of groundwater and may create potential avenues for groundwater contamination. Even in areas without mineral development, the presence of some naturally occurring minerals, such as those containing uranium, arsenic, and hydrocarbons, can, at significant concentrations, negatively impact groundwater quality.

Significant quantities of oil and gas have never been developed in the Snake/Salt River Basin.

Figure 5-7 shows abandoned coal, metal, uranium, phosphate, and sand and gravel mines in the Snake/Salt River Basin. Mapped coal, sand, and gravel mines are predominantly historic pit mines. A single, historic phosphate mine is located near Afton and a single uranium mine is located in the

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