Geology of the Dogskin Mountain Quadrangle, Northern Walker Lane

Text and references to accompany Nevada Bureau of Mines and Geology Map 164

Geologic Map of the Seven Lakes Mountain Quadrangle, Washoe County, Nevada and the Eastern Part of the Constantia Quadrangle, Lassen County, California

by

Christopher D. Henry, Alan R. Ramelli, and James E. Faulds Nevada Bureau of Mines and Geology

With a section on Gravity-Based Geologic Cross Sections

by

Michael C. Widmer Washoe County Department of Water Resources 4930 Energy Way Reno, Nevada 89502

2009

INTRODUCTION

The Seven Lakes Mountain quadrangle (SMQ) lies about 40 km (25 miles) north of the Reno-Sparks metropolitan area (fig. 1). Because Seven Lakes Mountain and its distinctive geology continue westward into the eastern part of the Constantia quadrangle in California, our geologic mapping was continued about 2 km into that quadrangle to depict the geology more completely. The acronym SMQ below refers to this complete map area. The SMQ encompasses all of the unusually west- trending Seven Lakes Mountain, the northern parts of the generally north-trending Petersen Mountain, Porcupine Mountain, and Sand Hills, the northwestern part of Dogskin Mountain, and the southern part of the Fort Sage Mountains. Long Valley, Red Rock Valley, and Lees Flat separate the north-trending ranges, and the west-trending Dry Valley separates Seven Lakes Mountain from the Fort Sage Mountains. Geologic mapping of the SMQ was undertaken for several applied and scientific reasons and is part of a broader investigation of the northern Walker Lane, a northwest-trending belt of active, right-lateral strike-slip faults (fig. 2). The Honey Lake fault system, a major strand of the northern Walker Lane, transects the SMQ. A region around the SMQ has experienced 13 earthquakes of magnitude 6 or greater since 1851 and two of magnitude 7 or more (dePolo et al., 1996). Geodetic data indicate the northern Walker Lane is undergoing about 10 mm/year of

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right-lateral motion, which represents 20–25% of Pacific flowed down and are mostly preserved in generally west- North American plate motion (Bennett et al., 1999, 2003; striking paleovalleys cut into Mesozoic rocks (figs. 2 and Thatcher et al., 1999). The combined Honey Lake, Warm 3; Henry et al., 2004; Faulds et al., 2005a, b; Brooks et al., Springs Valley, and Pyramid Lake fault systems may be 2008; Hinz et al., 2009). Because they trend nearly accommodating 6 to 8 mm/year (Dixon et al., 2000; perpendicular to the strike-slip faults, the paleovalleys are Hammond and Thatcher, 2007). However, the earthquake the best piercing points to measure strike-slip displacement hazard potential, as well as the Quaternary and late (Faulds et al., 2005a). Basins in and around the SMQ are Tertiary structural-tectonic origin and evolution of the being investigated as a source of groundwater for the northern Walker Lane, remain poorly understood. expanding Reno metropolitan area (Jewel et al., 2000; Important questions related to young faulting include: Sanger and Ponce, 2003; Berger et al., 2004; M. Widmer, (1) Which faults are taking up this motion? written commun., 2009). The geologic map should aid (2) Have all important faults been identified? exploration for groundwater and evaluation of the total and (3) What is the Pleistocene to Holocene displacement sustainable resource. Previous mapping of the SMQ history? and consisted of the 1:62,500-scale Chilcoot 15’ quadrangle (4) What is the earthquake potential of these faults? (Grose and Mergner, 2000), which includes the Constantia Furthermore, the SMQ contains a thick sequence of 7.5’ quadrangle, and 1:250,000-scale maps of Washoe Oligocene to lower Miocene ash-flow tuffs. Our new County, Nevada (Bonham and Papke, 1969), the Chico mapping and other recent research show that these tuffs 1°x2° quadrangle, California (Saucedo and Wagner, 1992),

3 and the Reno 1°x2° quadrangle, Nevada (Greene et al., metavolcanic rocks underlie much of Dry Valley and the 1991). Deino (1985) did a thesis map of the western part of alluvial fan area in the northeastern part of the SMQ. The Seven Lakes Mountain and established most of the gravity data also indicate the metavolcanic rocks are essential ash-flow tuff stratigraphy of the area. abruptly terminated along the Honey Lake fault zone Major rock types in the SMQ (fig. 2) are Mesozoic beneath Dry Valley. Similar metavolcanic rocks are widely metamorphic and plutonic rocks; a complex sequence of distributed in western Nevada (fig. 2; Grose, 1984; Oligocene to lower Miocene ash-flow tuffs, interbedded Garside, 1998; Henry et al., 2004). sedimentary deposits, and minor andesite that accumulated Parts of five Mesozoic plutons, four granodiorites and in west-draining paleovalleys; a relatively thin sequence of one quartz monzodiorite, and numerous aplite to pegmatite Miocene mafic lavas and clastic sedimentary rocks dikes crop out in the SMQ. None of these rocks are dated, (Pyramid sequence); a thick sequence of very coarse to and none of the major plutons contact each other; finely clastic sedimentary rocks that accumulated in therefore, absolute and relative ages are unknown. extensional basins; and a wide array of Quaternary, mostly Nevertheless, all are probably Cretaceous, about 90–100 alluvial fan, deposits (see pl.). Major structural elements of Ma, possibly to as old as 120 Ma, similar to other plutons the SMQ are dominantly north-striking, east-dipping in the region (John et al., 1993; Van Buer, 2008). All normal faults along the east sides of Petersen Mountain, plutons contain plagioclase, quartz, potassium feldspar, Porcupine Mountain, the Sand Hills, and the Fort Sage biotite, and hornblende and accessory titanomagnetite, Mountains; northwest-striking, right-lateral strike-slip apatite, sphene, and zircon; black tourmaline commonly faults of the Honey Lake fault system, which makes a coats fractures. They are distinguished by different mineral major left step of about 2.5 km around Seven Lakes abundances and character (table 1). For example, the Mountain; and a complex anticline (Seven Lakes quartz monzodiorite of Dogskin Mountain (Kqmd) has the Mountain)–syncline (Dry Valley) system that formed in lowest quartz content, has microcline as the potassium this left step. General characteristics of the rocks are feldspar, and is commonly weakly foliated. The pluton discussed in the ―Rock Descriptions‖ section. This text continues extensively east and southeastward into the focuses on regional geologic setting, especially on how the Dogskin Mountain and Bedell Flat quadrangles (Garside, rocks and structures of the SMQ fit into that setting. 1993; Henry et al., 2004). The granodiorites of Petersen Mountain (Kgp) and the Sand Hills (Kgs) have the highest quartz and lowest mafic MESOZOIC ROCKS mineral contents and have potassium feldspar as orthoclase. Differences are that biotite and hornblende are Mesozoic rocks consist of probably Jurassic euhedral in the Sand Hills body and anhedral in Petersen metavolcanic and metasedimentary rocks (Mmv) and five Mountain, and orthoclase makes prominent phenocrysts up spatially and petrographically distinct granitic rocks (table to 2 cm across in the Petersen Mountain body. Both 1). The metavolcanic rocks, which make up much of the intrusions continue southward into the Granite Peak southern Fort Sage Mountains, are variably porphyritic quadrangle (Garside, 1987). andesite and basaltic andesite lavas. Sedimentary rocks are The granodiorite and mafic granodiorite of the Fort a mix of coarse volcaniclastic rocks and finer sandstone Sage Mountains (Kgf, Kgm) contain abundant biotite and and siltstone. Metamorphism is to greenschist and lower hornblende, and quartz is commonly strained. Both amphibolite facies with the grade of metamorphism continue northward into the Fort Sage Mountains, where appearing to increase westward toward the contact with they were mapped as biotite granodiorite and hornblende granodiorite of the Fort Sage Mountains (Kgf). Detailed diorite, respectively (Grose, 1984). gravity data (Widmer, this report) indicate that the

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erupted from the same or similar sources. A caldera PALEOWEATHERED ZONE complex in the Clan Alpine Mountains (fig. 3; Riehle et al., 1972) about 190 km to the east is probably one source. A distinct paleoweathered zone (Kgw) is commonly A caldera in the Desatoya Mountains (McKee and Conrad, developed in the plutonic rocks along their contact with 1987) about 200 km to the east-southeast probably is the overlying Oligocene tuffs or sedimentary deposits. This source of the 28.9-Ma tuff of Campbell Creek (Tcc) and weathered zone is best developed and mapped as a distinct the petrographically and chemically similar, 29.0-Ma tuff unit in the granodiorite of the Sand Hills (Kgs), in the Sand E (Brooks et al., 2003, 2008). Our published and Hills and on Seven Lakes Mountain, and in the quartz unpublished petrographic, stratigraphic, and age data monzodiorite of Dogskin Mountain (Kqmd). The upper indicate that the tuff of Axehandle Canyon can be part of the granodiorite of Petersen Mountain (Kgp) also correlated 235 km eastward with a tuff in Reese River appears to be weathered in the small area where it is in Narrows in north-central Nevada (fig. 3; Henry et al., contact with tuff of Sutcliffe (Ts). The weathered zone is 2004; Faulds et al., 2005a). M.G. Best (personal commun., marked by alteration of biotite and reddening and 2001) correlates the tuff in Reese River Narrows with part disaggregation of the granitic rock. The disaggregated rock of the Windous Butte Formation. Further work is needed has been recemented by an unidentified ferruginous to evaluate possible correlation between the tuff of material into a hard, dark red rock in one area along the Axehandle Canyon and the Windous Butte Formation. southeastern flank of Seven Lakes Mountain. Weathering The middle, 25.3–24.9 Ma group of three tuffs occurred after 90–100 Ma, the presumed age of the includes the petrographically distinctive and easily granitic rocks, and dominantly, possibly entirely, before 31 correlated Nine Hill Tuff (Tnh) and tuff of Chimney Ma, the age of the oldest tuffs. Much of the weathering Spring (Tcs), which are recognized widely in western probably occurred during the Eocene, when the climate Nevada and the eastern Sierra Nevada (e.g., Deino, 1985, was warm and humid and intense weathering occurred in 1989; Best et al., 1989; John, 1995; Brooks et al., 2003, the Sierra Nevada gold belt (MacGinitie, 1941; Bateman 2008; Henry et al., 2004; Faulds et al., 2005a), and the and Wahrhaftig, 1966; Kelly et al., 2005; Mulch et al., lower tuff of Painted Hills (Tphl). The tuff of Chimney 2006). Spring correlates with the intracaldera tuff of Poco Canyon in the Stillwater Range (fig. 3; John, 1995; Hudson et al., CENOZOIC ROCKS 2000), about 140 km to the east, and the New Pass Tuff east from there (Deino, 1989). The tuff of Painted Hills Lower Miocene and Oligocene Ash-flow may correlate with the tuff of Elevenmile Canyon, which Tuffs also erupted from a caldera in the Stillwater Range (John, 1995; Hudson et al., 2000). The source of the extremely A thick sequence of at least 13 major ash-flow tuffs widespread Nine Hill Tuff (Deino, 1985, 1989; Best et al., ranging in age from 31.2 to ~23.7 Ma and interbedded 1989) is uncertain, but Deino (1985) proposed that it sedimentary deposits crops out in the SMQ. The tuffs are erupted from a caldera buried beneath Carson Sink (fig. 3), exposed mostly on Seven Lakes Mountain, the northern based in part on the distribution of the upper, more end of Petersen and Porcupine Mountains, and the abundantly porphyritic variety of Nine Hill Tuff (Tnhu). northwestern corner of Dogskin Mountain. The tuffs are The 23.7 Ma rhyolite-dacite ash-flow tuff (Trt), the part of a sequence of at least 18 ash-flow tuffs that are only representative of the youngest group, is probably widespread in western Nevada and the eastern Sierra related to a group of rhyolite to dacite intrusive domes that Nevada (Deino, 1985, 1989; Saucedo and Wagner, 1992; are concentrated in the southern parts of the Tule Peak and Brooks et al., 2003, 2008; Henry et al., 2004; Faulds et al., Sutcliffe quadrangles and northern parts of the Fraser Flat 2005a). Known and probable sources are located and Moses Rock quadrangles (figs. 1 and 2; Faulds et al., exclusively in central Nevada at least 140 km to the east 2003a, b; Garside et al., 2003). Both the tuff and domes (table 2; fig. 3). In western Nevada, the tuffs mostly contain abundant, large phenocrysts of plagioclase, biotite, flowed down and were deposited in paleovalleys cut into hornblende, minor quartz, ± sanidine. The best indication Mesozoic rocks. The tuffs in the SMQ fall into three age of the age of the rhyolite-dacite ash-flow tuff comes from 40 39 groups (tables 2 and 3). Most erupted between 31.2 and Ar/ Ar dates on sanidine from three domes of 28.9 Ma; three tuffs erupted between 25.3 and 24.9 Ma; 23.66±0.04, 23.77±0.06, and 23.82±0.06 Ma in the Tule the youngest tuff is about 23.7 Ma. Peak and Sutcliffe quadrangles (Faulds et al., 2003a, b). The oldest group of tuffs includes at least nine The tuff breccia (Tbt) near the top of the tuff sequence is mappable units. Many of these tuffs are petrographically composed of angular blocks of tuff of Chimney Spring up similar, with varying proportions of plagioclase, sanidine, to 3 m in diameter. It is similar to megabreccia generated and biotite and little quartz (table 2). Their narrow age by slumping of intruded tuffs and dome material off the range and petrographic similarities suggest that they

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6 flanks of the steep intrusive domes. However, no domes flank of the Fort Sage Mountains appears to mark the have been found in the SMQ. northern margin of a paleovalley. However, this area has Conglomerate, breccia, and some finer-grained been displaced about 4 to 10 km to the southeast relative to sedimentary rocks (Tcn, Tcy, Tts, Tcu, Tcr, Tck) underlie Seven Lakes Mountain along the Honey Lake fault system and are interbedded with the tuffs. A basal conglomerate (Faulds et al., 2005a; Hinz et al., 2009; this study), so its (Tck) containing only clasts of Mesozoic rocks up to 1.5 m original position relative to the Seven Lakes paleovalley is in diameter is exposed primarily in the western part of uncertain. Seven Lakes Mountain. Stratigraphically higher The complex interbedding of tuffs and sedimentary conglomerates are dominated by coarse clasts of ash-flow deposits is particularly well illustrated along the western tuff, locally with clasts of Mesozoic granitic rocks. Platy end of Seven Lakes Mountain (Faulds et al., 2005b). The tuffaceous sandstone and siltstone are present in most oldest tuffs rest on granodiorite of the Sand Hills (Kgs) sedimentary sections. along the top of the mountain, along the axis of the Poorly exposed hornblende andesite (Tha) appears to anticline, in what was originally the lowest part of the have formed one or more lavas in the upper part of the ash- paleovalley. Tuffs in the middle of the ash-flow sequence flow sequence, underlying the tuff breccia (Tbt), which rest directly on granodiorite of the Sand Hills on the north locally contains clasts of andesite. This andesite would be and south flanks. Pre-Nine Hills Tuff units were deeply the oldest locally derived Cenozoic volcanic rock and the eroded and the Nine Hill Tuff filled in a steep, narrow only andesite contemporaneous with ash-flow deposition paleocanyon at the southwest end of Seven Lakes near the SMQ. Other old intermediate volcanic rocks are Mountain. found in the northern part of Washoe County and in the southeastern Pah Rah Range (South Willow Formation of Pyramid Sequence Bonham and Papke, 1969, with a K/Ar age of 32 Ma) and

28 Ma andesite in the Carson Range (Garside et al., 2005; The informally named Pyramid sequence of mafic to Cousens et al., 2008). intermediate lavas and lesser silicic lavas and ash-flow tuff Both ash-flow tuffs and sedimentary deposits are is widespread from the Fort Sage Mountains eastward to laterally discontinuous because they were deposited almost the Lake, Nightingale, and Pah Rah Ranges (fig. 2; exclusively in deep paleovalleys throughout western Bonham and Papke, 1969; Grose et al., 1990; Ressel, Nevada and the Sierra Nevada (fig. 3) and were commonly 1996; Henry et al., 2004; Hinz, 2004). The Pyramid eroded to varying degrees before deposition of overlying sequence crops out extensively across Seven Lakes tuffs. In the SMQ, the basal conglomerate and oldest tuffs Mountain and in the northeastern part of the SMQ but is were deposited in and are largely restricted to the deeper thinner and shows less compositional diversity than in parts of the paleovalley along what is now the east-striking these other areas. The dominant rock type of the Pyramid anticline of Seven Lakes Mountain (see pl. and cross sequence in the SMQ is finely porphyritic basaltic andesite sections). The southern edge of the paleovalley is readily lava (Tpp’). Coarsely porphyritic basaltic andesite (Tpp) apparent where the tuffs thin and pinch out southward and aphyric basalt (Tpb) lavas are locally present. against Mesozoic granitic rocks on Petersen Mountain, Conglomerate, breccia, and sandstone (Tpc) dominated by Porcupine Mountain, and the Sand Hills. Wedging out of clasts of Pyramid lavas are also present locally and may be the tuff of Sutcliffe (Ts) is particularly well shown at the more extensive. However, many areas of Pyramid outcrop north end of Petersen Mountain (Faulds et al., 2005b). The consist of basaltic boulders that cannot be distinguished as northern paleovalley margin is largely buried beneath Dry lava or coarse sediment. Valley (cross sections A and B). A thin sequence of tuff of The Pyramid sequence in the SMQ is undated, but Cove Spring, tuff of Dogskin Mountain, and Nine Hill isotopic ages of lavas and tuffs in the sequence both in Tuff overlying Mesozoic metavolcanic rocks on the south

7 adjacent areas and regionally range from about 15.6 to conglomerate (Tfc), sandstone, and siltstone; to diatomite. 13.1 Ma (fig. 2; Grose et al., 1990; Ressel, 1996; Faulds et Although the basin fill probably generally fines upward, al., 2003a, b; Garside and Bonham, 2003; Hinz, 2004; extremely coarse and fine deposits are complexly Hinz et al., 2009; and see summary in Henry et al., 2004). interbedded. Locally, boulder beds are directly overlain or 40Ar/39Ar dates of 14.82±0.15 and 14.78±0.29 on lower underlain by diatomite and are abundant even in the and upper flows in the Fort Sage Mountains (Hinz et al., stratigraphically highest parts of the sequence observed in 2009) just to the north probably best indicate the age of the this study. Pyramid sequence in the SMQ. Based on isotopic and fossil data in Long Valley near A small intrusion of finely porphyritic basaltic the SMQ and more regionally, the sedimentary rocks are andesite (Tppi) is present near Porcupine Mountain, and late Miocene to Pliocene. A basaltic andesite interbedded feeders may underlie the flows on Seven Lakes Mountain. in the stratigraphically lowest part of the sequence along However, most source areas of the Pyramid sequence the west flank of Petersen Mountain, 5 km south of the appear to be outside the SMQ in the Fort Sage Mountains SMQ, is 11.66±0.25 Ma (Henry et al., 2007). Vertebrate (Grose, 1984; Grose et al., 1989, 1990; Hinz et al., 2009), fossils in the upper part of the sequence in the western part north-central Virginia Mountains (Faulds et al., 2003b; of Long Valley are Blancan (late Pliocene; Koehler, 1989; Henry et al., 2004), Pah Rah Range (Garside et al., 2003), Grose and Mergner, 2000), or between 4.75 and 1.81 Ma and Lake Range (Ressel, 1996). (Berggren et al., 1995; Gradstein et al., 2004; GeoWhenDatabase, 2005). 40Ar/39Ar dates on deposits Late Miocene Dacite or Andesite deformed along the Honey Lake fault in Honey Lake basin are 3.71±0.10 and 2.95±0.13 Ma (Henry et al., 2007). Minor plagioclase-hornblende dacite or andesite forms Basal parts of similar sedimentary deposits overlie or are a lava (Td) and dike (Tdi) in the northwestern part of the interbedded with volcanic rocks dated between 12 and 10.4 map area. The lava overlies conglomerate composed Ma near Reno (Trexler et al., 2000; Henry and Perkins, mostly of granitic clasts but with a few clasts from the 2001). Tephra in upper parts of the sequence near Reno 40 39 Pyramid sequence, which indicates the dacite is younger have Ar/ Ar and tephrochronologic dates as young as 3.1 40 39 than Pyramid sequence. The dacite may correlate with Ma (Henry and Perkins, 2001). Ar/ Ar dates on tephra in dacite and andesite that have 40Ar/39Ar dates between 9 and the Moses Rock and Tule Peak quadrangles are 8.77±0.16 11 Ma in the Diamond Mountains to the west (Grose et al., and 3.58±0.45 Ma, respectively (Garside et al., 2003; 1990; Hinz, 2004; Hinz et al., 2009). Henry et al., 2007). The deposits accumulated in extensional basins, similar to contemporaneous deposits regionally in western Late Miocene-Pliocene Basin Fill Nevada and northeastern California (Stewart, 1992; Trexler et al., 2000; Henry and Perkins, 2001). The size A thick sequence of very coarse to fine, late Miocene- and boundaries (i.e., basin-bounding faults) of the basin Pliocene sedimentary rocks (Tf, Tfc, Tfm, Tfk, and Tft) is around the SMQ are uncertain. Continuity of deposits in widespread through the SMQ. The most extensive deposits Long Valley well south of the SMQ indicates they were are in the northern part of Long Valley west of Petersen part of a single basin. Discontinuously exposed deposits Mountain and along the northwest flank of Seven Lakes northward and northeastward through the SMQ and into Mountain. The deposits are also extensive but poorly the Honey Lake basin suggest that the whole area may exposed in Dry Valley and beneath older fan deposits have been a single, contiguous basin. Major normal faults (Qfvo) north of the North Fork of Dry Valley Creek in the that truncate the deposits along the west side of Long northeastern part of the SMQ. Total thickness of the Valley and the Honey Lake basin may coincide with early sedimentary deposits and depth to ash-flow tuff or basin-bounding faults. Similar sedimentary deposits are Mesozoic rocks in these areas (e.g., along cross sections A not present in the Diamond Mountains west of Honey Lake and B) are speculative, but drilling data from water test basin (Grose et al., 1990; Saucedo and Wagner, 1992; wells confirmed the presence of the deposits and Hinz, 2004) but could underlie part of Sierra Valley west thicknesses of at least 200 m. Additional outcrops are of Long Valley (fig. 1). along the south flank of the Fort Sage Mountains and at the Other evidence for the location of bounding faults and northern end of Red Rock Valley along the south flank of fault scarps is equivocal. The boulder beds indicate nearby Seven Lakes Mountain. This distribution suggests the significant relief, but the general rounding of clasts suggest sedimentary deposits covered most or all of the SMQ they may not have been derived from immediately before latest Cenozoic–Quaternary faulting and folding. adjacent fault scarps. For example, the boulder beds The deposits range from boulder beds composed composed of granodiorite of Petersen Mountain (Tfk), just entirely or dominantly of clasts, commonly up to 4 m and west of Petersen Mountain, could have been derived from locally to 12 m in diameter, of granitic rocks (Tfk), ash- a topographic high in that area, although the full flow tuff (Tft), or metavolcanic rocks (Tfm); through finer

8 distribution of the granodiorite is not known. Several northeastern California and what is now the Sierra boulder beds composed of ash-flow tuff underlie Nevada–Basin and Range boundary indicates that little if granodiorite-bearing boulder beds and rest on tuff that any faulting or extension could have occurred for a rests on granodiorite along the west flank of Petersen considerable time before 31 Ma. These relationships and Mountain, both in the SMQ and more prominently several timing constraints are similar throughout much of the kilometers to the south. These relations are consistent with region north and south of the SMQ (Henry and Perkins, progressive stripping of a rising fault scarp but possibly of 2001; Henry et al., 2004, 2007; Faulds et al., 2005a, b; any topographic high. Moreover, no specific fault scarp Colgan et al., 2008). can be located in this area, and the complex interbedding Understanding of the overall structure and structural of boulder beds and diatomite argues against a proximal history is aided by dividing the SMQ into several domains alluvial fan environment typical of many extensional (pl. and fig. 4). The moderately west-dipping normal-fault- basins. bounded blocks of Long Valley–Petersen Mountain, Red Rock Valley–Porcupine Mountain, and Lees Flat–Sand Hills make up the southern domain. Along the north edge QUATERNARY FANS AND ALLUVIUM of the SMQ, the gently west-dipping fault-bounded block of the Fort Sage Mountains is structurally similar but less Quaternary deposits in the SMQ are mostly alluvial tilted. The northwest-striking, right-lateral Honey Lake fan deposits, but also include fluvial deposits and fine- fault system cuts northwest-southeast between the two tilt- grained basin fill. Ponded deposits, eolian deposits, and block domains. The northeastern part of the SMQ has spring deposits occur locally. In the north part of the several poorly exposed northeast-striking, possibly left- quadrangle, alluvial fan deposits consisting of gravel and lateral faults that may connect the Honey Lake fault sand form the piedmont areas flanking Fort Sage, Seven system with the Warm Springs Valley fault system (fig. 2), Lakes, and Dogskin Mountains, and fluvial deposits occur another right-lateral system that parallels the Honey Lake along Dry Valley Creek. In the south part of the SMQ, fan system to the northeast (Grose, 1984; Henry et al., 200, deposits dominated by granitic sand (grus) flank Petersen 2007; Faulds et al., 2005a). Mountain, Porcupine Mountain, Sand Hills, and Dogskin Mountain; fine-grained basin fill occurs in Lees Flat; and West-dipping Fault Blocks in the Southern fluvial deposits occur along the unnamed wash that Seven Lakes Mountain Quadrangle connects Bedell Flat, Lees Flat, Red Rock Valley, and Long Valley. Ponded gravel and fine-grained sediment Each of the three fault blocks in the southern SMQ (Qp) occur in closed depressions (mainly the ―Seven dips west and is bounded on the east by east-dipping Lakes‖) on Seven Lakes Mountain. Minor eolian sand normal faults; each block continues well south of the deposits (Qe) are delineated around Porcupine Mountain SMQ. The Petersen Mountain block is the longest, with a and Sand Hills. Minor spring deposits (Qs) occur total length of about 30 km, and most tilted (cross section throughout the SMQ. C; fig. 1). The Pliocene to late Miocene sedimentary Alluvial fan units are distinguished and labeled by deposits (Tf) in Long Valley dip 20° to 55° to the west; dominant lithology (―v‖ for volcanic or ―g‖ for granitic), dips average about 30° in the north increasing to about 40° and by relative age (older ―o‖ for early to middle at the south edge of the SMQ. The major, moderately east- Quaternary; intermediate age ―i‖ for middle to late dipping Petersen Mountain fault marks the eastern edge of Quaternary; and younger ―y‖, further subdivided into late the block, with a parallel fault strand covered by Pleistocene (―y2‖) and Holocene (―y1‖). In the west part of Quaternary deposits about 300 m into Red Rock Valley. the map (mainly on the Constantia quadrangle), dissection Total displacement on the Petersen Mountain fault zone is of Long Valley Creek has left the older fan deposits about 1 km at this latitude but decreases to the north, dying stranded tens of meters above younger surfaces. out within the Seven Lakes Mountain anticline, and probably increases to the south (Garside, 1987). Displacement appears to die out on the western fault to the CENOZOIC STRUCTURE south and to increase on the eastern fault, so that the range front steps eastward. Several down-to-the-east scarps cut Rocks in the SMQ are highly faulted and folded, and Quaternary fans in Red Rock Valley. all of this deformation must have occurred in the late The Porcupine Mountain block dips about 15° to 20° Cenozoic. Conformable dips within the Oligocene ash- westward based on attitudes in Oligocene ash-flow tuffs. flow tuff sequence and between the tuffs and rocks of the Basin-fill deposits are poorly exposed on the west side of Pyramid sequence indicate that no measurable tilting and Porcupine Mountain and at the north end of Red Rock therefore no major faulting or extension took place Valley and are covered in Red Rock Valley. Displacement between 31 Ma and at least 15 to 13 Ma. Further, the on the normal fault along the east side of Porcupine continuity of paleovalleys across western Nevada and Mountain is estimated at slightly less than 1 km. The fault

9 continues to the south out of the SMQ and has a total Regional data demonstrate that the Honey Lake fault length of about 15 km. system has undergone right-lateral displacement (Wagner The Sand Hills block is estimated to dip about 15° et al., 1989; Wills and Borchardt, 1993; Henry et al., 2004; westward also, but based only on the asymmetry of the Hinz, 2004; Faulds et al., 2005a, b; Hinz et al., 2009). For range. Oligocene ash-flow tuffs, the only preserved example, Hinz (2004), Hinz et al. (2009), and Faulds et al. Cenozoic rocks, dip gently eastward along a minor, west- (2005a) use offset paleovalleys to estimate about 10 km of dipping fault in the eastern part of the block. The bounding displacement between the Diamond and Fort Sage normal fault strikes northwest in the SMQ, curves to north- Mountains about 15 km northwest of the SMQ (figs. 1 and northeast to the south, and then probably joins the Petersen 2). Wills and Borchardt (1993) estimated a Holocene slip Mountain fault about 20 km to the south (fig. 2; Garside, rate of between 1.1 and 2.6 mm/year on the fault system 1993). Displacement on the Sand Hills fault is probably west of the Fort Sage Mountains. Turner et al. (2008) about 2 km, but overprinting by the Honey Lake fault narrowed that estimate to 1.7±0.6 mm/year for the same system precludes a precise estimate. location. One of the few examples of relatively young right-lateral displacement on a Honey Lake fault is found about 2 km southeast of the SMQ in the Dogskin Mountain West-dipping Fault Block of the Fort Sage quadrangle. At that location, three drainages show Mountains apparent right-lateral deflections of about 20 to 40 m on a

fault that also shows vertical displacement down to the The Fort Sage Mountains in the SMQ are also southwest (Henry et al., 2004). bounded on the east by an east-dipping normal fault, but Evidence for right-lateral displacement along the HLF volcanic rocks in the southern part dip gently to the south in the SMQ comes from two features. (1) The south edge and southwest. Volcanic rocks in the Fort Sage Mountains of the ash-flow-tuff-filled paleovalley is displaced about 2 in the Stateline Peak quadrangle to the north dip about 10° to 4 km between the southern part of the Dogskin to the west (Grose, 1984; Hinz, 2004; Hinz et al., 2009). Mountain quadrangle (Henry et al., 2004) and Porcupine The southerly dip in the SMQ probably reflects and Petersen Mountains (fig. 2). (2) The Seven Lakes downfolding into the Dry Valley syncline superposed on Mountain–Dry Valley folds are consistent with contraction the westward tilt. The preserved length of the Fort Sage in a left, restraining bend of a right-lateral fault zone. The boundary fault is about 6 km, but the Warm Springs Valley difference in displacement along the Honey Lake fault fault system truncates it to the north. Displacement is system, 10 km west of the Fort Sage Mountains and 2 to 4 probably about 1 km in the Stateline Peak quadrangle km in the SMQ, probably results from three factors. (1) (Grose, 1984) but decreases southward. Displacement may be dying out southward toward the

southern end of the fault system. (2) Some displacement Honey Lake Fault System may be transferred to active, north-striking faults along the west side of Long Valley (fig. 2). If so, the Long Valley The Honey Lake fault system (HLF) is a northwest- faults should be undergoing right-oblique slip. (3) Finally, striking right-lateral system of faults that extends about 80 some displacement may be taken up by contraction in the km from Honey Lake (Grose et al., 1990; Wills and Seven Lakes Mountain–Dry Valley folds. One problem Borchardt, 1993) at least to Warm Springs Valley (figs. 1 with the last possibility is that the folds mostly lie and 2; Garside et al., 2003; Henry et al., 2004, 2007). The southwest of the Honey Lake fault system, which would fault system consists of numerous, generally northwest- suggest the fault system south of the folds should have striking, discontinuously exposed faults in a 2- to 3-km- greater displacement than the fault system north of the wide belt over its approximately 12 km length through the folds. SMQ (fig. 4). The system makes a left step of about 2.5 Despite the regional and local evidence for right- km in the north-central part of the SMQ. A complex lateral displacement on the Honey Lake fault system and syncline-anticline pair is developed in Dry Valley and depiction of several faults as strike-slip on the cross Seven Lakes Mountain along and south of the left step. sections, most faults in the SMQ show only vertical Modeling of gravity data indicates an abrupt change from displacement. For example, faults cutting the Pliocene to Mesozoic metavolcanic rocks (Mmv) southward across the late Miocene sedimentary deposits (Tf) and Quaternary fault system to granitic rock, probably granodiorite of the alluvial fans north of Dry Valley in the northwestern part Sand Hills (Kgs) (Widmer, this report). These data of the SMQ have scarps down either to the southwest or suggest that the discontinuously exposed fault at the north northeast. Similarly, faults cutting Quaternary fans edge of alluvium along Dry Valley Creek at cross section northeast of the Sand Hills in the southeast corner of the A and the concealed fault in the middle of the creek along SMQ also show vertical displacement, mostly down to the section B have the greatest lateral displacement. northeast.

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Several northeast-striking faults are observed or All parts of the Seven Lakes Mountain anticline inferred in the northeastern part of the SMQ (fig. 4). appear to have panels of relatively constant dip, commonly Observed faults cut alluvial fans and show down-to-the- separated by west- to west-northwest-striking, inward- southeast displacement. The two largest faults are inferred dipping normal faults. The faults may have acted as hinges beneath active alluvium (Qa) along the long northeast- to allow folding of shallow, brittle rocks (see the southern trending stretches of Dry Valley Creek and North Fork Dry end of cross section A for an illustration). Despite the Valley Creek. The one along Dry Valley Creek is based on obvious evidence of contraction, mapped faults appear the mismatch between ash-flow tuffs on the north and dominantly to have normal displacement (cross sections A south sides of the creek. The tuffs are younger on the north and B). However, faults are rarely exposed, and their side, which indicates it is down relative to the south side. attitudes are mostly based on their expression on The fault along the North Fork is based on the distinctly topography. Rocks adjacent to these faults are intensely lower surface elevation and lower elevation of older fan fractured to the point that coherent outcrops are lacking deposits (Qfvo) and Pliocene to late Miocene sedimentary within many tens of meters of mapped fault traces. A large deposits (Tf) north of the creek than south of the creek area north of Red Rock Canyon was mapped as breccia (easternmost fault of cross section B). This relationship because it was impossible to follow mappable rock units suggests this fault is down on the northwest. Left-lateral through the area. slip is possible along northeast-striking faults in a Two faults show possible thrust movement. A well- northwest-striking right-lateral zone, e.g., as with the exposed fault that cuts ash-flow tuff north of Red Rock Olinghouse fault, which approximately parallels the Canyon dips less than 10° northward and places older tuff Truckee River east of Reno (Briggs and Wesnousky, over younger tuff. Rocks adjacent to the fault are intensely 2005). However, no evidence of left-lateral slip was fractured. If this fault formed in its current orientation, it is observed on the northeast-striking faults in the SMQ. a thrust. However, the fault could have undergone purely Faults cut units as young as late to middle Holocene normal displacement if it formed before measurable alluvial fan deposits (Qfvy1) in the southeastern part of folding had occurred. Another possible thrust lies along the SMQ and as young as early Holocene to late Pleistocene south edge of the main anticline at the north end of Red alluvial fan deposits (Qfy2) in the northeastern part. Wills Rock Valley. At this location, Nine Hill Tuff (Tnh) and and Borchardt (1993) and Turner et al. (2008) found basaltic andesite (Tpp’) of the Pyramid sequence form a evidence for four surface-cutting earthquakes along the tight syncline. Alternatively, this fold could be a large Honey Lake fault system west of the Fort Sage Mountains gravity slide off the flank of the growing anticline. less than 10 km northwest of the SMQ during the late The Dry Valley syncline is largely covered by Holocene or the last 7000 years, respectively. Quaternary fans and alluvium along Dry Valley Creek.

The syncline also closely coincides with the Honey Lake Seven Lakes Mountain Anticline–Dry Valley fault system, and the northern limb may be significantly Syncline displaced relative to the southern limb. Both factors severely limit understanding of the structure of the A complex west-northwest-trending anticline– syncline, but detailed gravity data (Widmer, this report) syncline pair lies in the left step of the Honey Lake fault greatly help interpretation. The presence of the syncline is system in the middle of the SMQ (figs. 2 and 4; pl.). demonstrated by northward dips along the north flank of Although the left step is only about 2 to 3 km, the fold belt the Seven Lakes Mountain anticline and southward dips is about 9 km long. Seven Lakes Mountain is a large, north of Dry Valley Creek. Most southward dips are in doubly plunging anticline; the accompanying large Pliocene to late Miocene sedimentary deposits (Tf) or ash- syncline underlies Dry Valley. flow tuff along the south edge of the Fort Sage Mountains The eastern part of the Seven Lakes Mountain and are relatively gentle, no more than about 20°. The anticline is a single, asymmetric fold with an amplitude of sedimentary deposits between the mountain front and Dry at least 500 m (cross section B). Rocks in the south limb Valley Creek are mostly too poorly exposed to measure dip as steeply as 87°; dips greater than 70° are common. attitudes but appear to steepen southward. The hingeline of Rocks in the north limb mostly dip about 30 to 40° but as a tight syncline, with inward dips as much as 80°, is much as 77° at one location just south of Dry Valley exposed in Pliocene to late Miocene sedimentary deposits Creek. To the west, west of the northern continuation of (Tf) south of Dry Valley Creek at the western edge of the the Petersen Mountain fault, the fold divides into a steep map. Despite the steep dips, which might suggest that the southern anticline, a central syncline, and a northern, lower sedimentary deposits extend to considerable depth beneath amplitude anticline (cross section A). The amplitude of the Dry Valley, gravity data indicate that granitic rocks (Kgs) southern anticline is at least 700 m, and both limbs are and metavolcanic rocks (Mmv) probably lie at a depth of steep with dips up to 70°. The amplitude of the northern no more than about 600 m in the vicinity of cross section anticline is probably about 200 m. A. Also, whether this is the main syncline or a parallel,

12 minor fold as around the Seven Lakes Mountain anticline Qf Alluvial fan deposits (undifferentiated) (Holocene is uncertain. A small anticline just north of Dry Valley to Pleistocene) Small- to medium-size fans that typically Creek along cross section B appears to divide the eastern have small catchment areas. Bouldery, cobbly, pebbly sand end of the syncline in two, with an open fold on the north. deposits are typically clast supported and dominated by subangular to angular clasts. Surfaces range from smooth to rough. Soils with well-developed argillic horizons are DESCRIPTION OF MAP UNITS common, especially near the toe of the fans. Deposit thickness may locally exceed 20 m. Quaternary Deposits Qfy1, Qfvy1, Qfgy1 Younger alluvial fan deposits Alluvial Deposits (late and middle Holocene) Cobbly, pebbly, coarse sands with isolated boulders near canyon mouths; generally Qa Active alluvium Alluvium in recently to annually nonindurated, poorly to moderately stratified, moderately active washes generally consisting of cobble-pebble sorted, matrix-supported deposits with angular to gravels and sands. Surfaces have rough bar-and-swale subangular clasts. Surfaces commonly have rough bar-and- morphology where gravel dominated, and muted bar-and- swale morphology. Soil development ranges from absent swale morphology where sand dominated. Clasts are to A/Bw/C profiles, where cambic horizons are weakly generally subrounded to rounded, but subangular clasts are developed and as much as 20 cm thick. Deposits are as locally common. Deposits typically 0.5 to more than 3 m much as 3 m thick. Unit designation reflects dominant thick. clast lithology: Qfy1 – undifferentiated or mixed; Qfvy1 – volcanic; Qfgy1 – granitic. Qaf Fine-grained alluvium (Holocene and late Pleistocene) Unconsolidated silt and very fine sand Qfy2, Qfvy2, Qfgy2 Young alluvial fan deposits (early deposited in basin floors. Surfaces are generally flat, or Holocene and latest Pleistocene) Cobbly, pebbly, silty, locally hummocky due to undifferentiated eolian deposits. coarse sands with isolated boulders; generally non- to weakly indurated, poorly to moderately stratified, Qt1 Alluvial terrace deposits (late and middle moderately sorted, matrix-supported deposits with angular to subangular clasts. Surfaces are commonly smooth with Holocene) Cobbly and pebbly coarse to medium sands, poorly to moderately developed pavements and sparse mostly poorly sorted and matrix supported, but locally cobble or boulder gravel bars. Soil profiles typically have a clast supported; intercalated with well-sorted, medium- thin eolian silt cap (A or Av), cambic (Bw) or weak grained sand deposits up to 10 cm thick. Surfaces are argillic horizons (Bt) that are 20 to 50 cm thick, and calcic generally smooth, but commonly have muted bar-and- horizons (Bk) are absent to weakly developed (up to stage swale morphology. Soils are typically absent or show a II CaCO3 development). Deposits are as much as 4 m weak cambic horizon. Deposits are typically 1 m thick or thick. Unit designation reflects dominant clast lithology: less. Qfy2 – undifferentiated or mixed; Qfvy2 – volcanic;

Qfgy2 – granitic. Qs Spring deposits Organic-rich fine silt and clay around and down slope from active springs. The fine- grained materials are probably dominated by eolian Qfi, Qfvi, Qfgi Intermediate-age alluvial fan deposits material trapped by vegetation associated with spring (late and middle Pleistocene) Cobbly, pebbly, silty, coarse discharge, but may include material transported by surface sands with isolated boulders; generally weakly to water. The deposits are variably calcareous and locally moderately indurated, poorly to moderately stratified, weakly stratified. moderately sorted, matrix-supported deposits with angular to subangular clasts. Surfaces are generally smooth, Qp Ponded deposits Light-colored, silty, clayey, erosionally rounded near surface edges, and moderately to well dissected. Surficial granitic clasts are generally absent finely stratified sand deposited in small closed, fault- due to weathering. Soil profiles typically have eolian silt controlled basins, generally in the higher areas of Seven caps (A or Av) with varying thicknesses, well-developed, Lakes Mountain. Thickness of deposits is unknown but structured argillic horizons (Bt) up to 50 cm thick, probably ranges up to several meters. In most basins, the discontinuous calcic horizons (Bk) with up to stage III finer deposits surround exposed boulders of volcanic CaCO3 development, and oxidized, iron-stained horizons rocks, which suggests that the fine deposits are locally no (Bw) up to 2 m thick. Deposits are up to 4 m thick. Unit more than a few tens of centimeters thick. designation reflects dominant clast lithology: Qfi –

Alluvial Fan Deposits undifferentiated or mixed; Qfvi – volcanic; Qfgi – granitic.

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Qfo, Qfvo, Qfgo Older alluvial fan deposits (middle diatomite is commonly massive and in beds up to 1 m and early Pleistocene) Cobbly, pebbly, silty, coarse sands thick. Both weather to a lag of white chips. The deposits with local boulders; generally weakly to moderately are mostly poorly cemented but are highly calcite- indurated, poorly to moderately stratified, moderately cemented and indurated along the northwest flank of sorted, matrix-supported deposits with angular to Seven Lakes Mountain. subangular clasts. Surfaces are generally smoothed, Most extensive in the western part of the map broadly rounded, and moderately to well dissected. Soil area, especially in Long Valley where the deposits form a profiles typically have well-developed, structured argillic west-dipping homoclinal sequence at least 1 km thick. (Bt) horizons up to 50 cm thick, discontinuous calcic Also on the northwest and southwest flanks of Seven horizons (Bk) with up to stage III carbonate development, Lakes Mountain, the south flank of the Fort Sage and oxidized, iron-stained horizons (Bw) up to 1- to 2-m Mountains, and poorly exposed beneath Quaternary fan thick. Deposits are as much as 4 m thick. Unit designation deposits in the northeastern part of the map area. This reflects dominant clast lithology: Qfo – undifferentiated distribution suggests sedimentary deposits and basin they or mixed; Qfvo – volcanic; Qfgo – granitic. accumulated in were once continuous throughout the area and extended over Seven Lakes and Petersen Mountains. Slope Deposits In all areas, deposits are best exposed in the sides of gullies cut through Quaternary fans. Best outcrops are Qc Colluvial deposits (undifferentiated) (Holocene where the beds are indurated along the northwest flank of to Pleistocene) Colluvial and talus deposits generally Seven Lakes Mountain. Boulder beds and other coarse occurring at the base of steep slopes. Deposits typically conglomerates were mapped separately wherever possible consist of poorly sorted, angular to subangular, clast- but are included in this unit where not. The oldest deposits supported cobbles and boulders. Deposits are generally are at least as old as 11.66±0.25 Ma, the age of a basaltic less than 3 m thick. andesite lava near the base of the sequence in Long Valley south of the Seven Lakes Mountain quadrangle. The Qls Landslide deposits (Holocene to Pleistocene) youngest deposits are late Pliocene (Blancan) based on Coarse, unconsolidated debris composed of local bedrock, vertebrate remains in the upper part of the deposits on the particularly basaltic andesite lava of the Pyramid sequence. west side of Long Valley (Koehler, 1989; Grose and Clasts range from silt sized to large blocks. Deposits are up Mergner, 2000). to several meters thick. Original headwall scarp is commonly unrecognizable. Tfc Conglomerate Conglomerate marked by a lag of well-rounded clasts of Pyramid sequence rocks, Oligocene Eolian Deposits ash-flow tuff, and minor granitic rocks was mapped separately from the general sedimentary deposits (Tf) Qe Eolian deposits Light-colored, well-sorted sands where outcrops were sufficiently large and continuous. Clasts are mostly up to 30 cm in diameter but locally up to typically occurring as vegetated dunes or sand sheets. 70 cm. Generally forms layers at or near the base of the Deposits up to a few meters thick. unit, especially along the south flank of the Fort Sage

Mountains. Pliocene to late Miocene Sedimentary Deposits Tfm Conglomerate of metavolcanic rocks Trains of mostly metavolcanic (Mmv) boulders up to 2.5 m in Tf Pliocene to late Miocene sedimentary deposits diameter in two areas may mark late Miocene Heterogeneous, complexly interbedded sequence of conglomerate. These boulders, along with lesser Oligocene generally poorly indurated, non-resistant, and therefore ash-flow tuff and granitic rock, stick up through the mostly poorly exposed sandstone, conglomerate, extensive Quaternary fan deposits in the northeastern part diatomite, and diatomaceous siltstone. Sandstones are of the quadrangle. The northwest alignment of the boulder composed mostly of mineral fragments derived from trains, parallel to the strike of other Tertiary rocks, Cretaceous granodiorite or Tertiary ash-flow tuff, thin- to suggests they are also Tertiary and not part of the thick-bedded, and planar to cross-bedded. Coarser beds Quaternary deposits. Similar conglomerate also crops out range from pebbly sandstone to conglomerates with along the south flank of the Fort Sage Mountains where it generally well-rounded clasts commonly up to 1 m in overlies a thin sequence of Oligocene ash-flow tuff that diameter and as large as 12 m in boulder beds (Tfk, Tft). overlies metavolcanic rocks. This deposit is also Coarse clasts are mostly granodiorite with lesser tuff and surrounded by and difficult to distinguish from Quaternary rocks of the Pyramid sequence but vary across the map fan deposits. area, presumably reflecting local source areas. Diatomaceous siltstone is finely laminated, whereas purer

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Tfk Boulder beds of Cretaceous granodiorite Coarse Pyramid Sequence debris-flow deposits and conglomerate composed almost entirely of moderately to well-rounded clasts of Cretaceous Tppi Finely porphyritic basaltic andesite intrusion granodiorite of Petersen Mountain (Kgp) up to 12 m in An elongate (~200 m east-west by as much as 75 m north- diameter and commonly as large as 4 m, along with aplite south) body of finely porphyritic basaltic andesite sits and pegmatite. Rounding may have resulted in part from within granodiorite of Petersen Mountain west of weathering of corestones in granodiorite outcrop. Unit Porcupine Mountain. It is petrographically similar to the typically forms a lag of boulders with no exposed matrix. finely porphyritic lavas (Tpp’) but is probably a shallow Extensive in Long Valley along the west edge of the intrusion. The rock is massive, is surrounded by mapped area, where beds are found throughout the granodiorite, and has no breccia that would suggest a lava sequence of Pliocene to late Miocene sedimentary sitting on granodiorite. deposits. Although best exposed in sides of gullies, trails of residual boulders can be traced across Quaternary fan Tpp’ Finely porphyritic basaltic andesite lava The surfaces. most abundant Pyramid lava type in the Seven Lakes Mountain quadrangle is characterized by abundant, tabular Tft Boulder beds of Tertiary ash-flow tuff Coarse to more equant, plagioclase phenocrysts 1 to 3 mm long debris-flow deposits and conglomerate composed and pyroxene phenocrysts up to 5 mm in diameter. Occurs predominantly of moderately rounded clasts of Tertiary as a single flow about 20 m thick in the south-central part ash-flow tuff up to 2.5 m in diameter, and lesser rocks of of Seven Lakes Mountain and as several flows totaling the Pyramid sequence and Cretaceous granodiorite. Unit about 75 m thick in the northern and eastern parts. Basal typically forms a lag of boulders; matrix is generally not and upper breccias, marked by a residuum of massive to exposed. Beds occur low in the sedimentary sequence scoriaceous, finely porphyritic boulders, are common and along the northwest flank of Petersen Mountain and on can be difficult to distinguish from weathered southwest and northwest flanks of Seven Lakes Mountain. conglomerate (Tpc).

Late Miocene(?) Dacite or Andesite Tpp Porphyritic basaltic andesite lava Coarsely porphyritic lava distinguished by prominent, tabular Td Plagioclase-hornblende dacite or andesite lava plagioclase phenocrysts 5 to 20 mm long and also Light-gray weathering, finely porphyritic lava containing containing ~5% clinopyroxene phenocrysts crops out in abundant, aligned plagioclase laths up to ~1 mm long and two areas in the quadrangle. One flow ~20 m thick crops a few percent equant hornblende grains up to 0.5 mm in out in the northwestern part of Seven Lakes Mountain diameter crops out in one area in the northwestern part of between finely porphyritic flows. Another flow crops out the map area. Locally columnar jointed and with a basal in a small area overlying other Pyramid lavas in the breccia containing matrix- to clast-supported clasts of lava northeastern part of the quadrangle. Matrix consists of up to 30 cm in diameter in a rubbly matrix. Groundmass plagioclase, olivine, clinopyroxene, opaques, and variably consists of finer plagioclase, equant opaque grains altered, interstitial glass. (probably magnetite), and interstitial glass. Rests upon a thin layer of conglomerate that overlies granodiorite of the Tpc Conglomerate, sandstone, and breccia Massive Fort Sage Mountains (Kgf). The conglomerate is to moderately well stratified, matrix- to clast-supported, composed mostly of granitic and aplitic clasts but also poorly to moderately sorted, pale brown to light gray contains a few clasts of probable Pyramid sequence rocks. pebble to boulder conglomerate, breccia, and sandstone. Therefore, the lava is probably younger than the Pyramid Mostly marked by a residuum of clasts of Pyramid sequence and may correlate with dacite and andesite dated sequence, which can be difficult to distinguish from flow at between 9 and 11 Ma in the Diamond Mountains to the breccia. Clasts are subangular to subrounded and mostly west (Hinz, 2004). Pyramid lavas with rare ash-flow tuff or Cretaceous granitic rocks. Where exposed, conglomerate commonly Tdi Plagioclase-hornblende dacite or andesite dike includes lenses of fine- to coarse-grained, pebbly A 400 m long, ~20 m thick, northeast-striking dike of sandstone; sand grains are subangular to subrounded and plagioclase-hornblende dacite or andesite cuts granodiorite consist mainly of volcanic rock fragments and feldspar. of the Fort Sage Mountains (Kgf) about 700 m northwest The deposit is weakly to highly indurated and of the plagioclase-hornblende lava. The dike is noncalcareous. petrographically similar to the lava, containing abundant small plagioclase phenocrysts and ~5% hornblende needles Tpb Basalt lava Aphyric basalt crops out in three up to 5 mm long, and may be a feeder to the lava. areas. The largest area is in the northeastern part of the quadrangle, where one or more flows overlie Oligocene ash-flow tuffs. Another flow is marked by a lag of

15 boulders to 1 m in diameter and underlies part of hill 1506 brought up by excavation along a natural gas pipeline in north of the Sand Hills. Additional flows cap a ridge just Quaternary deposits just to the west. Additional boulders north of the northwest edge of the quadrangle and occur in tuff breccia (Tbt) still farther west. These comprise several large landslide (Qls) masses in the characteristics suggest hornblende andesite was once more quadrangle. Matrix consists of pilotaxitic, subophitic to extensive, including as lava flows in the upper part of the intergranular plagioclase, pyroxene, olivine, and opaque ash-flow sequence. minerals. Tphl Tuff of Painted Hills White to light gray, Tcp Pre-Pyramid sequence conglomerate nonwelded to poorly welded, nonresistant, pumiceous, Conglomerate consisting of moderately to well rounded moderately porphyritic ash-flow tuff. The tuff contains up clasts of various ash-flow tuffs, especially rhyolite-dacite to 20% white pumice up to 10 cm long and 3% fragments ash-flow tuff (Trt) up to 1 m in diameter and, rarely, of porphyritic andesite up to 8 cm in diameter. The tuff is Cretaceous felsite to 20 cm that underlies the Pyramid petrographically similar to the upper poorly welded part of sequence. Generally poorly exposed and probably poorly the tuff of Chimney Spring but has fewer phenocrysts, indurated and marked by a lag of boulders. Absence of more abundant biotite, less abundant quartz, and relatively Pyramid clasts indicates it is older than that sequence. sparse smoky quartz. Also, common presence of a red soil Could have been deposited immediately following ash- zone on top of the tuff of Chimney Spring and a white, flow eruptions or any time from then until just before platy, fine tuffaceous sandstone between the two tuffs emplacement of Pyramid sequence rocks. Preserved indicates they are separate ash flows with some erosion thickness is about 10 m. Lithologically similar and and weathering between them. Probably equivalent to the approximately equivalent to rhyolite-clast conglomerate lower tuff of Painted Hills in the Dogskin Mountain (Trds) of Dogskin Mountain quadrangle. quadrangle (Henry et al., 2004) and correlates with the tuff of Eleven Mile Canyon of the Stillwater Range (John, Oligocene-Miocene Ash-Flow Tuffs 1995), which is petrographically similar and has an indistinguishable age. Named for exposures in the Painted Trt Rhyolite-dacite ash-flow tuff Densely to Hills in the Tule Peak quadrangle (Faulds et al., 2003b). moderately welded but relatively non-resistant, light to medium gray, abundantly and coarsely porphyritic ash- Tcs/Tcsl Tuff of Chimney Spring Red-brown flow tuff crops out discontinuously above the Oligocene weathering, pinkish gray, densely to poorly welded, ash-flow tuffs and below rocks of the Pyramid sequence. abundantly porphyritic ash-flow tuff characterized by Contains common flattened pumice to 10 cm long and smoky quartz and adularescent sanidine. Most of the tuff sparse lithic fragments of biotite-hornblende dacite. The is densely welded and devitrified and has undergone vapor tuff is as much as 20 m thick. The tuff is petrographically phase crystallization. A basal, white, poorly welded part similar to and probably the same age (~23.7 Ma) as the (Tcsl) capped by a black vitrophyre is locally present in porphyritic rhyolite domes (Tri) in the Tule Peak, deeper parts of paleovalleys. An upper white, poorly Sutcliffe, and Fraser Flat quadrangles (Table 3; Faulds et welded tuff is rarely preserved. Greater abundance of al., 2003a, b; Garside et al., 2003). biotite and plagioclase in the lower and upper, poorly welded parts than in the densely welded part suggests Tbt Tuff breccia Reddish-brown breccia composed compositional zoning; however, intense devitrification and primarily of blocks of tuff of Chimney Spring (Tcs) in a vapor phase crystallization in the welded part has moderately silica(?)-cemented matrix. Many of the blocks destroyed most mafic minerals. The massive, densely also appear to be slightly silicified. Matrix, which is rarely welded part mostly contains little pumice, so eutaxitic exposed, consists of still finer and variably silicified texture is poorly developed, whereas upper and lower parts breccia. Most outcrops consist of a lag of boulders. contain as much as 20% white pumice to 15 cm long. Similar tuff breccia in the Dogskin Mountain and Tule Lithic fragments, most abundant in the lower part, consist Peak quadrangles (Faulds et al., 2003b; Henry et al., 2004) of porphyritic, silicic to intermediate volcanic rocks, and probably originated as rock avalanches induced by lesser quartzite and indurated shale. The tuff of Chimney slumping and catastrophic failure of steeply dipping strata Spring is as much as 30 m thick in a band from the western around the flanks of rhyolite domes. However, no domes part of Dogskin Mountain westward through the central have been recognized near the Seven Lakes Mountain part of Seven Lakes Mountain. However, it is commonly quadrangle. Thickness is as much as 20 m. absent because it was eroded before deposition of Pyramid sequence rocks or because it was not deposited over thick Tha Hornblende andesite dike and lavas(?) A deposits of Nine Hill Tuff. Based on its age and coarsely porphyritic, plagioclase-hornblende andesite dike distinctive phenocrysts, the tuff of Chimney Spring cuts ash-flow tuff on the west flank of Dogskin Mountain. correlates with the tuff of Poco Canyon in the Stillwater Boulders of flow breccia of similar rock occur as lag Range and with the New Pass Tuff east of Austin, Nevada (Deino, 1989; John, 1995; Hudson et al., 2000). The Poco

16

Canyon caldera in the Stillwater Range was the source the rhyolite of Campbell Creek (McKee and Conrad, 1987; (John, 1995; Hudson et al., 2000). Henry et al., 2004), which is an intracaldera tuff in the Desatoya Mountains approximately 200 km to the east- Tnh/Tnhu/Tnhl Nine Hill Tuff Sparsely to southeast. Equivalent to the Dry Valley tuff of Deino moderately porphyritic, commonly highly pumiceous, (1985). densely to poorly welded ash-flow tuff. A light-brown, poorly to densely welded, lower unit (Tnhl) contains ~5% Tcy Conglomerate below tuff of Campbell Creek A phenocrysts. The upper unit (Tnhu) is generally dark red- coarse to pebbly conglomerate marked by a lag of well- brown and densely welded and has 12–15% phenocrysts. rounded boulders commonly underlies the tuff of Where exposed, the contact between the two parts is sharp, Campbell Creek. Boulders are mostly tuff of Dogskin but more porphyritic pumice occurs in the top of the less Mountain (Tdm) up to 1.5 m in diameter. Where exposed porphyritic part. Prominent pumice fragments make in several uranium exploration pits, the poorly indurated flattened lenses up to 40 cm long in welded tuff and matrix consists of smaller clasts of ash-flow tuff. Most ellipsoids up to 20 cm long in poorly welded tuff. The tuff outcrops consist of a lag of coarse, rounded boulders. contains sparse lithic fragments of porphyritic to aphyric silicic volcanic rocks up to a few centimeters in diameter. Te Tuff E A light-colored, moderately porphyritic, Thickness, degree of welding, and presence of either or poorly to moderately welded ash-flow tuff characterized both parts are highly variable because the tuff filled by common, bipyramidal, smoky quartz phenocrysts. channels cut into older tuffs in the paleovalley through Recognized only north of Porcupine Mountain, where it is Seven Lakes Mountain. Maximum thickness is about 100 about 50 m thick. However, although distinguished by the m along the southern flank of Seven Lakes Mountain. The bipyramidal and non-vermicular quartz, it is similar to tuff Nine Hill Tuff is widely distributed through western of Campbell Creek (Tcc) and may have been mistakenly Nevada and the Sierra Nevada (Bingler, 1978; Deino, mapped as such along the southern flank of Seven Lakes 1985). Deino (1985, 1989) demonstrated that it correlates Mountain. Geochemical and petrographic data indicate it is with the ―D‖ unit of the Bates Mountain Tuff in central probably related to the tuff of Campbell Creek, Tcc and eastern Nevada and suggested a source beneath the (Brooks et al., 2003, 2008). Carson Sink. Tdm Tuff of Dogskin Mountain A thick, complex Tcn Conglomerate below Nine Hill Tuff Coarse, sequence of at least three cooling units of similar, poorly indurated conglomerate and conglomeratic plagioclase- and biotite-rich ash-flow tuff interbedded with sandstone consisting of subangular to rounded boulders of platy, compacted, probably mostly reworked tuff and ash-flow tuff (mostly tuff of Dogskin Mountain; Tdm) and tuffaceous sedimentary rocks. The ash-flow tuffs are dark quartz monzodiorite (Kqmd) up to 1 m in diameter. The red-brown to medium gray, moderately pumiceous, and mapped unit is mostly overlain by the tuff of Chimney densely to poorly welded. Poorly welded parts form Spring or the Nine Hill Tuff. It is possible but not certain slopes, whereas dense parts locally form resistant ledges. that some conglomerate is younger than Nine Hill Tuff. White pumice that weathers to form ellipsoidal cavities up The conglomerate is as much as 30 m thick. to 25 cm long is common in dense parts of the tuffs. The ash-flow tuffs are laterally discontinuous, probably Tcc Tuff of Campbell Creek A dark to light gray to reflecting both non-deposition and erosion. Individual cream-colored, sparsely porphyritic, pumiceous, densely to cooling units are 8 to 30 m thick. The composite unit, mostly moderately or poorly welded ash-flow tuff including reworked tuff, is as much as 120 m thick. The characterized by common, smoky, vermicular quartz tuff of Dogskin Mountain correlates with the tuff of phenocrysts and minor plagioclase. The tuff grades upward Coyote Spring of Garside and Bonham (1992) and is from a relatively sparsely and finely porphyritic, poorly widely distributed throughout the region. Equivalent to the welded and glassy base, which is commonly silicified, to Porcupine Mountain tuff of Deino (1985). more abundantly and coarsely porphyritic, densely welded, devitrified, nubbly weathering main part, to moderately or Thick-bedded to platy, dense but nonresistant and poorly welded top. Quartz and total phenocryst abundance generally poorly exposed, greenish gray to gray to white, decreases abruptly upward from the densely to moderately plagioclase- and biotite-rich tuff is common throughout the welded parts; biotite and plagioclase abundance increases. unit. This platy tuff shows no evidence of welding Pumice fragments up to about 25 cm long are common and zonation. Lithic fragments up to ~10 cm in diameter are locally include plagioclase-biotite-rich pumice unlike the scattered randomly through the unit. Based on these host tuff. Shards are easily visible with a hand lens. characteristics and local presence of pebble to cobble Widely but discontinuously distributed across Seven Lakes conglomerate and conglomeratic sandstone, most and Mountain, the tuff is as much as about 100 m thick. The possibly all of the platy tuff is reworked. The dense age and petrographic character indicate correlation with

17 character may result from sedimentary compaction rather less biotite and more sanidine. However, this difference than welding. can be difficult to recognize in altered or weathered samples. Both are similar in appearance to the plagioclase- Twc Tuff of Cove Spring A sparsely to moderately biotite-rich welded tuffs in the tuff of Dogskin Mountain porphyritic ash-flow tuff with a thick, red-brown to tan, (Tdm) but distinguished by the presence of common, large densely welded lower part that passes upward into a light sanidine. Pumice content is highly variable from ~1% in gray, poorly welded upper part, which is rarely preserved. most of the tuff to 10–15% in lithophysal zones in upper The tuff is characterized by large, abundant sanidine, fine, parts where pumice is up to 40 cm long. Small fragments mostly altered plagioclase, and sparse biotite: much less of shale and porphyritic andesite are common. Named for than 1% in the densely welded tuff to ~1% in the upper, exposures near Sutcliffe in the Sutcliffe quadrangle poorly welded part. Ellipsoidal cavities marking eroded (Faulds et al., 2003a). The upper unit is equivalent to the pumice fragments are common in the densely welded part. Harrys Spring tuff and the lower unit to the Constantia The tuff of Cove Spring is present along the south-central Station and Zamboni Spring tuffs of Deino (1985). flank of Seven Lakes Mountain. The tuff may be as much as 50 m thick there, but thickness is difficult to determine Tcu Sedimentary rocks below or within tuff of because of complex faulting. Named for exposures near Sutcliffe Poorly exposed sequence of tuff and tuffaceous Cove Spring in the Tule Peak quadrangle (Faulds et al., sedimentary rocks consisting mostly of platy tuffaceous 2003b). sandstone interbedded with thin pebble to cobble conglomerate. Twm Tuff of Western Mine A light-colored, moderately porphyritic, poorly to moderately welded ash- Trc Tuff of Rattlesnake Canyon Light red, densely flow tuff crops out only in a small area near some uranium welded grading upward to poorly welded ash-flow tuff prospects on the northwest flank of Seven Lakes characterized by large and abundant sanidine. Dense part is Mountain. The tuff is about 30 m thick and has a light commonly columnar jointed and shows nubbly weathering. gray, perlitic vitrophyre about 5 m thick. The finely and Upper, poorly welded part is more finely porphyritic and sparsely porphyritic rock has phenocrysts of sanidine, contains ~10% pumice up to 15 cm long. Fragments of plagioclase, and minor biotite and a few pumice fragments porphyritic andesite and quartzite up to 1 cm across are up to 1 cm long, The vitrophyre contains a few wood common near the base. Recognized only in scattered fragments up to about 1.5 cm long. Deino (1985) locations in the western part of Seven Lakes Mountain. introduced the informal name for the uranium prospect. Named for exposures in Rattlesnake Canyon in the Fraser Possibly related to the tuff of Sutcliffe (Tsu). Flat quadrangle (Garside et al., 2003).

Tts Conglomerate and tuffaceous sedimentary rock Tcr Sedimentary rocks below tuff of Rattlesnake Conglomerate and tuffaceous sandstone and siltstone Canyon Poorly exposed sequence of platy, poorly overlie the upper unit of the tuff of Sutcliffe (Tsu) and bedded tuffaceous rocks interbedded with thin lenses of underlie tuff of Cove Spring (Twc) in Red Rock Canyon. coarse sandstone and pebble to cobble conglomerate Clasts of tuff of Sutcliffe up to 1 m in diameter indicate the similar to those in unit Tts and Tcs. Mostly covered by rocks are mostly reworked from that tuff. Stratigraphic colluvium. May also include some tuff of Hardscrabble relationship to tuff of Western Mine (Twm) is unknown. Canyon (Thc).

Ts Tuff of Sutcliffe Light gray- to brick red- to Thc Tuff of Hardscrabble Canyon Poorly exposed, yellow-weathering, densely to moderately welded, mostly moderately to poorly welded, sparsely and finely abundantly porphyritic ash-flow tuff. The tuff is one of the porphyritic, white to light gray ash-flow tuff distinguished most widely distributed in the quadrangle and throughout by the presence of about 5%, small, angular, smoky quartz the region and may be as much as 150 m thick in the phenocrysts. The tuff contains a few small (<1 cm long) central part of Seven Lakes Mountain. As many as three pumice and sparse fragments of Cretaceous(?) granite. cooling units separated by poorly welded tuff or The tuff is exposed only in one location in the western part sedimentary rocks are recognized. Where separated by of Seven Lakes Mountain where it forms rubble on the sedimentary rocks in the western part of the quadrangle, slope below the communications towers. Named for we have divided the tuff into upper (Tsu) and lower (Tsl) exposures in Hardscrabble Canyon in the Tule Peak units. The upper unit commonly has a basal, light gray quadrangle (Faulds et al., 2003b). vitrophyre and is zoned upward from moderately porphyritic, plagioclase-sanidine tuff with ~2% biotite to Tac Tuff of Axehandle Canyon Moderately welded, abundantly porphyritic, plagioclase-biotite rich tuff with moderately pumice-rich, pink to light brown, dark red- lesser sanidine. The lower unit lacks a basal vitrophyre but brown weathering ash-flow tuff, the oldest exposed tuff in is petrographically similar except that it contains slightly the region. Grades upward from sparsely porphyritic base

18 with sanidine more abundant than plagioclase and 1% additional orientations on Petersen Mountain are north- biotite to upper part with plagioclase much more abundant northeast or east and northwest in the Sand Hills. than sanidine and 2–3% biotite. This upper part is similar in appearance to the tuff of Sutcliffe (Ts). Both parts Kgs Granodiorite of the Sand Hills Massive, contain common white pumice up to 10 cm long. Exposed medium- grained, speckled light gray to white, commonly only in the western part of Seven Lakes Mountain. Named deeply weathered granodiorite characterized by large, for exposures in Axehandle Canyon in the Griffith Canyon euhedral biotite and hornblende grains. Makes up all of quadrangle (Garside and Nials, 1999). the granitic rock of Seven Lakes Mountain and extends southeastward into the Sand Hills. Commonly forms Tck Basal Tertiary conglomerate Conglomerate prominent knobs surrounded by areas of deep sand. A pink composed exclusively of pre-Cenozoic clasts. Crops out to brick red, paleoweathered zone (Kgw) is developed in above granitic rocks in Seven Lakes and Porcupine granodiorite close to the overlying Oligocene ash-flow Mountains and in the Sand Hills. Exposed as a lag of tuffs. Biotite and hornblende decrease in abundance, with generally rounded boulders of granitic rock mostly up to hornblende becoming nearly absent, southward across a 50 cm but locally as much as 1.5 m in diameter. Clasts are transition zone in the Sand Hills near the southeastern most commonly locally reworked granitic rocks and aplite corner of the quadrangle. Mineralogy: orthoclase (15 to or pegmatite but include quartz monzodiorite (Kqmd) in 20%, to 1 cm, commonly enclosing plagioclase, biotite, the Sand Hills, which demonstrate transport from east to and hornblende), plagioclase (50 to 60%, subhedral to 7 west in the paleovalley. This unit includes a lens of coarse, mm), quartz (20 to 30%, to 4 mm), biotite (3 to 5%, to 5 matrix-supported conglomerate consisting of subangular to mm), and hornblende (0 to 3%, to 1 cm long rods). moderately rounded blocks of granodiorite and aplite and Sphene is a common accessory visible with a hand lens, underlying, poorly exposed, fine, white tuffaceous and zircon and titanomagnetite are apparent in thin section. sandstone and siltstone that in turn rest upon granodiorite of the Sand Hills (Kgs?) at the eastern end of Red Rock Kgpp Quartz-pegmatite of Petersen Mountain Canyon. North-elongate area about 250 by 150 m of abundant, irregularly shaped, quartz- and pegmatite-filled cavities Tt Oligocene ash-flow tuffs undivided Shown on developed in granodiorite of Petersen Mountain (Kgp) near cross sections only. the southwestern corner of the quadrangle. Observed quartz crystals are as much as 10 cm long. Pegmatite Mesozoic Rocks consists of quartz, orthoclase, and, locally, black tourmaline and muscovite. Cavities are developed both in unfractured, massive parts of the granodiorite and along Cretaceous granitic rocks (relative ages of the fractures, especially at intersections of multiple fractures, major intrusions are unknown) which appear to have no preferred orientation. A wide area of talus and colluvium on the west flank of Petersen Kqw Weathered Cretaceous granitic rocks Distinct, Mountain contains pieces of this rock and is hunted for nearly continuous paleoweathered zone as much as 15 m quartz crystals by rockhounds. thick developed in granodiorite of the Sand Hills (Kgs) and quartz monzodiorite of Dogskin Mountain (Kqmd) along Kgp Granodiorite of Petersen Mountain Massive, the unconformity with Cenozoic rocks. Distinguished by medium-grained, white to slightly speckled granodiorite its pink to brick-red color on the ground and air photos. characterized by prominent phenocrysts of orthoclase up to Locally, weathered and disaggregated granodiorite was 2 cm across and by a relatively low abundance of mafic recemented by silica? to form a hard, dark red zone up to 3 minerals crops out in the northern part of Petersen m thick at the unconformity. Mountain and on Porcupine Mountain. Variably weathered to rounded boulders up to 3 m in diameter Kf Aplitic to pegmatitic dikes and irregular surrounded by grus. Cut by numerous aplitic to pegmatitic intrusions Dikes and irregular shaped intrusions of dikes. Mineralogy: orthoclase (15 to 20%, both irregular, aplite and pegmatite in granodiorites of the Sand Hills interstitial grains and phenocrysts up to 2 cm), plagioclase (Kgs) and of Petersen Mountain (Kgp). Dikes are a few (60%, subhedral, 1 to 5 mm), quartz (20%, to 3 mm), centimeters to as much as 10 m wide. All rocks consist of biotite (4 to 5%, to 2 mm), and hornblende (0 to 1%, orthoclase, quartz, lesser plagioclase, and minor biotite. scattered rods, mostly to 5 mm long). Sphene is a common Grains in aplites are generally equant and less than 2 mm accessory visible with a hand lens, and zircon and in diameter. Pegmatites can contain orthoclase up to 6 cm titanomagnetite are apparent in thin section. in diameter and quartz up to 10 cm long. Many dikes have parallel, gradational bands of aplite and pegmatite. Aplite Ka Aplite dikes of the Fort Sage Mountains dikes with irregular pods of pegmatite. Most dikes on Numerous thick dikes of very light-colored, equigranular Petersen Mountain and in the Sand Hills strike northeast; to finely porphyritic aplite and rarely pegmatite cut

19 metavolcanic rocks (Mmv) and granodiorite of the Fort of quartz±epidote±tourmaline veinlets. Approximately Sage Mountains (Kgf) along the south flank of those equivalent to hornblende diorite of Grose (1984). mountains. Dikes generally intruded parallel to layering and foliation in the metamorphic rocks, are commonly Kqmd Quartz monzodiorite of Dogskin Mountain complexly branching, and are up to 2 km long and 50 m Coarse-grained, light to medium gray quartz monzodiorite thick. Dikes consist mostly of small (≤2 mm) orthoclase and granodiorite consisting of, in decreasing order of grains in a finer matrix of orthoclase, quartz, plagioclase, abundance, plagioclase, microcline, quartz, hornblende, and minor biotite. Cores of dikes are mineralogically biotite, and accessory titanomagnetite, anhedral sphene, similar but more equigranular. Local pegmatite lenses and zircon, make up most of the southern part of Dogskin contain orthoclase and quartz up to 5 cm in diameter and Mountain. A weak foliation defined by the preferred sphene up to 2 cm in diameter. Thin veinlets of quartz, orientation of hornblende is common. Enclaves of diorite epidote, and albite(?) cut the dikes, generally perpendicular range up to 20 cm long. Local veinlets of black to intrusive contacts. Many fractures parallel to intrusive tourmaline. Generally weathers to large angular blocks or contacts are bleached and coated with sprays of black rounded boulders surrounded by grus. Much greater tourmaline. abundance of plagioclase relative to potassium feldspar and quartz, weak foliation, and occurrence of potassium Kgf Granodiorite of the Fort Sage Mountains feldspar as microcline distinguish this from the Medium-grained, speckled, mafic granodiorite makes up granodiorites of Sand Hills (Kgs) and of Petersen most of the southwestern part of the Fort Sage Mountains, Mountain (Kgp). This unit is the same as unit Kqmd in the where it intruded metavolcanic rocks (Mmv) along a sharp, Dogskin Mountain quadrangle (Henry et al., 2004). northeast-striking contact that parallels layering and foliation in the metamorphic rocks. Along and near the Mmv Mesozoic (Jurassic?) metavolcanic and contact, the granodiorite is slightly foliated and contains metasedimentary rocks A heterogeneous assemblage of lenses of angular to rounded pods of diorite up to 1 m long, metamorphosed volcanic, volcaniclastic, and sedimentary possibly the mafic granodiorite of the Fort Sage Mountains rocks makes up most of the southeast flank of the Fort (Kgm). Two diorite pods consisting of plagioclase, Sage Mountains. Detailed gravity data (M. Widmer, hornblende, and minor biotite were large enough to map written communication, 2009) indicate that the separately. Elsewhere, the granodiorite is massive and metavolcanic rocks underlie much of Dry Valley Creek generally forms rounded boulders surrounded by grus. north of the Honey Lake fault system and the alluvial fan Black tourmaline coats many fractures. Mineralogy: area in the northeastern part of the map area. The plagioclase (70%, anhedral, 1 to 4 mm, slightly altered to metamorphic rocks commonly form dark, resistant crags sericite and epidote), quartz (10%, interstitial to 2 mm, separated by large areas with no outcrop. The rocks strike strained), orthoclase (5%, interstitial grains), biotite (9%, 1 northeast to north and dip steeply to moderately to the east. to 2 mm), and hornblende (6%, to 3 mm). Accessory Metavolcanic rocks are massive to rarely flow-banded, minerals are equant opaques (probably magnetite) mostly locally vesicular, and finely to coarsely porphyritic, with as inclusions in biotite or hornblende, apatite, anhedral phenocrysts of plagioclase 1 to 12 mm long, altered to sphene, and minor zircon. Equivalent to biotite granite of albite, epidote, and sericite and mafic phenocrysts Grose (1984) and hornblende-biotite granodiorite of Grose (pyroxene?) altered to opaque minerals and biotite. et al. (1989). Metamorphic hornblende and biotite are scattered through the matrix. The rocks were probably originally andesite Kgm Mafic granodiorite of the Fort Sage Mountains and basaltic andesite. Volcaniclastic rocks are massive to Heterogeneous, light to dark gray, fine- to medium- thickly bedded, contain matrix- to clast-supported angular grained, variably altered, mafic granodiorite and diorite fragments of the volcanic rocks up to 50 cm in diameter in crop out in the southeastern Fort Sage Mountains where a fine matrix, and probably include flow breccias, debris- both the main body and several dikes intrude Mesozoic flow deposits, and other sedimentary deposits. Finer metavolcanic rocks (Mmv). Forms large, massive, dark sedimentary rocks are well bedded, are as fine as siltstone, outcrops. Inclusions of the metavolcanic rocks are and increase in abundance westward. The finest deposits common near the contact. Mineralogy: plagioclase (45– were probably slightly clayey siltstones that are now 70%, subhedral, 1–2 mm), orthoclase (25%, as interstitial, metamorphosed to quartz, orthoclase, biotite, and poikilitic grains up to 5 mm in diameter enclosing muscovite, with different layers containing different plagioclase and mafic minerals), quartz (10%, interstitial, proportions of the minerals probably indicating different moderately strained), hornblende (10%, subhedral to detrital components. Numerous veins and irregular pods of anhedral, 1–3 mm), biotite (7%, anhedral <1–2 mm), epidote and quartz cut all rocks. Black tourmaline clinopyroxene (≤1%, <1 mm), and titanomagnetite (1%, commonly coats fracture surfaces. Equivalent to 0.5 mm). Mafic minerals are locally altered to chlorite. metavolcanic rocks of Grose (1984). Sphene and apatite are common accessories. Locally moderately sheared and with fracture coatings or veinlets

20

ACKNOWLEDGMENTS

We thank George Saucedo, John Bell, Craig dePolo, and Larry Garside for thorough, constructive reviews, and Mike Widmer and Dwight Smith for discussions of subsurface geology in the area. The help of Mike Widmer, who generously shared his detailed gravity data of the region that greatly helped us interpret the structure as shown along cross sections A, B, and C, is particularly appreciated. 40Ar/39Ar ages were determined at the New Mexico Geochronology Research Laboratory under the guidance of Bill McIntosh and Matt Heizler. All ages reported here are calculated relative to a monitor age of 28.02 Ma on sanidine from Fish Canyon Tuff (Renne et al., 1998).

21

Gravity-Based Geologic Cross Sections

by

Michael C. Widmer Washoe County Department of Water Resources 4930 Energy Way Reno, Nevada 89502

To better constrain geologic cross sections, gravity Unit symbol density profiles were used to define subsurface lithologic (g/cc) boundaries through the modeling of density contrasts. In Quaternary sediments Q 2.1 these models, calculated gravity was compared to observed Tertiary sediments Tf 2.3 gravity whereby the calculation is the product of densities Tertiary undivided tuffs Tuffs 2.4 and thicknesses of distinct lithologic layers. Models were Tertiary basalt Tpp 2.5 generated by duplicating the surface geologic contacts, Cretaceous granodiorite Kgr 2.67 adhering to lithologic borehole logs, and incorporating Mesozoic metavolcanic rocks Mmz 3.0 known geologic structural information. Because these models are usually non-unique, the estimation of lithologic In the two gravity models presented (fig. 5), several density is critical as is the simplification of the geologic hundred gravity observations were taken over 700 square model itself. In the models presented, density values are: kilometers within the study area and gridded at 200 m (Widmer et al., 2009). Profiles were then calculated precisely along the geologic cross sections. Within the modeling software, the geologic sections were then duplicated, simplified, and compared to the observed gravity profiles. Changes were then made to the thicknesses and subsurface areal extent of the generalized rock types in order to match the calculated gravity to the observed gravity.

22 Gravity-based geologiccrosssections A–A' (upper)andB–B'(lower),Dry Valley, Washoe County, Nevada symbols represent locationsoflithologic borings.SS0-4symbols represent locationsofstrike slipfaultsidentifiedbyHenry etal.,thisreport). Mesozoic metamorphicvolcanics (Mmz,3.0),Cretaceousgranodiorite(Kgr, 2.67),undifferentiated Tertiary tuffs (Tuffs, 2.4), Tertiary volcanicbasalt (Tpp,2.5), Tertiary sediments (Tf,2.3),andQuaternarysediments(Q,2.1). Derrick Figure 5.Geologicmodelswereinitially baseduponHenryetal.(2006)andrefined uponmatchingobservedgravityprofiles(Widme r, 2009)byadjusting geologicboundaries.Geologicunits(symbols and modeldensitying/cc)are

ElevationElevation (meters) (meters) Elevation (meters) Gravity (mGals) 1600 GravityGravity (mGals) (mGals) 1000 1200 1400 1800 1600 1000 1200 1400 1400 1800 1200 1000 1600 1800 1400 800 1200 1000 1600 1800 600 -180 -160 800 -140 600 -160 -180 -160 Elevation (meters) Gravity (mGals) -140 800 -180 -140 -160 600 -140 -180 800 600 16000 16000 Scale=24000 V.E.=1 symbols represent locationsoflithologic borings.SS0-4symbolsrepresent locationsofstrike slipfaultsidentifiedbyHenry et.al.,thisreport). Mesozoic metamorphic volcanics(Mmz, 3.0),Cretaceousgranodiorite, (Kgr, 2.67), undifferentiated Tertiary tuffs (Tuffs, 2.4), Tertiary volcanicbasalt (Tpp,2.5), Tertiary sediments (Tf,2.3),andQuaternary sediments(Q,2.1). Derrick Figure 5.Geologicmodels wereinitiallybaseduponHenry(et.al.,2006)andrefined baseduponmatchingobservedgravityprofiles(Widmer A B Scale=24000 V.E.=1 Vertical exaggeration=1,Scale=1:24,000 Vertical exaggeration=1,Scale=1:24,000 Gravity basedgeologiccrosssections AA' (upper)andBB’(lower),DryValley, Washoe County, Nevada A B Calculated Calculated Calculated Q Calculated Q Tf 15000 15000 Tf 17000 17000

Observed Observed 16000 16000 18000 18000 Observed Observed Error Error Error Error 17000 17000 19000 19000 Tuffs Kgr Tuffs 18000 18000 20000 20000 Distance (meters) Distance (meters) Tpp Tpp 23 Kgr SS4 Distance (meters) SS4 Distance (meters) 19000 19000 21000 21000

, 2009)byadjustinggeologic boundaries.Geologicunits(symbolsandmodeldensity ing/cc)are SS3 Tf SS3 Kgr Kgr Tf Well 14 Well 14 td 20000 Tf 20000 td Tf SS2 SS2 22000 22000 SS2 Tf Tf SS2 Qal Q Qal Q DVTW4 DVTW4 Tuff Tuff 21000 21000 Tuffs SS1 23000 23000 SS1 Mmv Mmv Tuffs

Mmv SS1 SS1 Mmv 22000 22000 24000 24000 Tf Tf SS0 SS0 DVTW2 DVTW2 Ts Ts Q Q V V 23000 B‘ 23000

25000 25000 B′ A‘ A′

REFERENCES California Geological Survey Map Sheet 55A, scale 1:12,000, 41 p. text. Bateman, P.C., and Wahrhaftig, C., 1966, Geology of the Brooks, E.R., Wood, M.M., Boehme, D.R., Potter, K.L., Sierra Nevada, in Bailey, E.H., ed., Geology of and Marcus, B.I., 2003, Geologic map of the Haskell northern California: California Division of Mines Peak area, Sierra County, California: California and Geology Bulletin 190, p. 107–172. Geological Survey Map Sheet 55, scale 1:12,000, 31 Bennett, R.A., Davis, J.L., and Wernicke, B.P., 1999, p text. Present-day pattern of Cordilleran deformation in Colgan, J.P., Shuster, D.L., and Reiners, P.W., 2008, the western United States: Geology, v. 27, p. 371– Two-phase Neogene extension in the northwestern 374. Basin and Range recorded in a single Bennett, R.A., Wernicke, B.P., Niemi, N.A., Friedrich, thermochronology sample: Geology, v. 36, p. 631– A.M., and Davis, J.L., 2003, Contemporary strain 634. rates in the northern Basin and Range province from Cousens, B., Prytulak, J., Henry, C.D., Alcazar, A., and GPS data: Tectonics, v. 22, no. 2, 1008, Brownrigg, T., 2008, The geology and geochemistry doi:10.1029/2001TC001355. of the Mio-Pliocene ancestral Cascades arc, northern Berger, D.L., Maurer, D.K., Lopes, T.J., and Halford, Sierra Nevada, California/Nevada—the roles of the K.J., 2004, Estimates of natural ground-water upper mantle, subducting slab, and the Sierra discharge and characterization of water quality in Nevada lithosphere: Geosphere, v. 4, p. 829–853. Dry Valley, Washoe County, west-central Nevada, Deino, A.L., 1985, Stratigraphy, chemistry, K-Ar dating, 2002–2003: U.S. Geological Survey Scientific and paleomagnetism of the Nine Hill Tuff, Investigations Report 2004-51, 39 p. California-Nevada [Ph.D. dissertation]: University Berggren, W.A., Kent, D.V., Swisher, C.C., and Aubry, of California, Berkeley, 457 p. M., 1995, A revised Cenozoic geochronology and Deino, A.L., 1989, Single crystal 40Ar/39Ar dating as an chronostratigraphy, in Berggren, W.A., Kent, D.V., aid in correlation of ash flows: Examples from the Swisher, C.C., Aubry, M., and Hardenbol, J., eds., Chimney Spring/New Pass Tuffs and the Nine Geochronology, time scales and global stratigraphic Hill/Bates Mountain Tuffs of California and correlation: SEPM Special Publication No. 54, p. Nevada: New Mexico Bureau of Mines and Mineral 1297–212. Resources, Continental Magmatism Abstracts Best, M.G., Christiansen, E.H., Deino, A.L., Gromme, Bulletin 131, p. 70. C.S., McKee, E.H., and Noble, D.C., 1989, Eocene dePolo, C.M., Rigby, J.G., Johnson, G.L., Jacobson, through Miocene volcanism in the Great Basin of S.L., Anderson, J.G., and Wythes, T.J., 1996, the western United States, in Chapin, C.E., and Planning scenario for a major earthquake in western Zidek, J., Field excursions to volcanic terranes in the Nevada: Nevada Bureau of Mines and Geology western United States, Volume II—Cascades and Special Publication 20, 128 p. Intermountain West: New Mexico Bureau of Mines Dixon, T.H., Miller, M., Farina, F., Wang, H., and and Mineral Resources Memoir 47, p. 91–133. Johnson, D., 2000, Present-day motion of the Sierra Bingler, E.C., 1978, Abandonment of the name Hartford Nevada block and some tectonic implications for the Hill Rhyolite Tuff and adoption of new formation Basin and Range Province, North American names for middle Tertiary ash-flow tuffs in the Cordillera: Tectonics, v. 19, p. 1– 24. Carson City-Silver City area, Nevada: U.S. Faulds, J.E., dePolo, C.M., and Henry, C.D., 2003a, Geological Survey Bulletin 1457-D, 19 p. Preliminary geologic map of the Sutcliffe Bonham, H.F., and Papke, K.G., 1969, Geology and quadrangle, Washoe County, Nevada: Nevada mineral deposits of Washoe and Storey Counties, Bureau of Mines and Geology Open-File Report 03- Nevada: Nevada Bureau of Mines and Geology 17, scale 1:24,000. Bulletin 70, 139 p. Faulds, J.E., Henry, C.D., and dePolo, C.M., 2003b, Briggs, R.W., and Wesnousky, S.G., 2005, Late Preliminary geologic map of the Tule Peak Pleistocene and Holocene paleoearthquake activity quadrangle, Washoe County, Nevada: Nevada of the Olinghouse fault zone, Nevada: Bulletin of Bureau of Mines and Geology Open-File Report 03- the Seismological Society of America, v. 95, p. 10, scale 1:24,000. 1301–1313. Faulds, J.E., Henry, C.D., and Hinz, N.H., 2005a, Brooks, E.R., Henry, C.D., and Faulds, J.E., 2008, Age Kinematics of the northern Walker Lane—an and character of silicic ash-flow tuffs at Haskell incipient transform fault along the Pacific–North Peak, Sierra County, California: Part of a major American plate boundary: Geology, v. 33, p. 505– Eocene(?)-Oligocene paleovalley spanning the 508. Sierra Nevada–Basin and Range boundary:

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Faulds, J.E., Henry, C.D., Hinz, N.H., Drakos, P.S., and P., Sanfilippo, A., Schmitz, B., Shackleton, N.J., Delwiche, B., 2005b, Transect across the northern Shields, G.A., Strauss, H., Van Dam, J., van Walker Lane, northwest Nevada and northeast Kolfschoten, T., Veizer, J., and Wilson, D., 2004: A California—an incipient transform fault along the geologic time scale 2004: Cambridge University Pacific–North American plate boundary, in Press, 589 pages. Pederson, J., and Debie, C.M., eds., Interior western Greene, R.C., Stewart, J.H., John, D.A., Hardyman, R.F., United States: Geological Society of America Field Silberling, N.J., and Sorensen, M.L., 1991, Geologic Guide 6, p. 129–150, doi:10.1130/2005.fld006(06). map of the Reno 1° by 2° quadrangle, Nevada and Garside, L.J., 1987, Reconnaissance geologic map of the California: U.S. Geological Survey Miscellaneous Granite Peak quadrangle, Nevada: Nevada Bureau Field Studies Map MF-2154-A, scale 1:250,000. of Mines and Geology Open-File Report 87-8, scale Grose, T.L.T., 1984, Geologic map of the Stateline Peak 1:24,000. quadrangle, Nevada-California: Nevada Bureau of Garside, L.J., 1993, Geologic map of the Bedell Flat Mines and Geology Map 82, scale 1:24,000. quadrangle, Nevada: Nevada Bureau of Mines and Grose, T.L.T., and Mergner, M., 2000, Geologic map of Geology Field Studies Map FS-3, scale 1:24,000. the Chilcoot 15’ quadrangle, Lassen and Plumas Garside, L.J., 1998, Mesozoic metavolcanic and Counties, California: California Division of Mines metasedimentary rocks of the Reno-Carson City and Geology Open-File Report 2000-23, scale area, Nevada and adjacent California: Nevada 1:62,500. Bureau of Mines and Geology Report 49, 30 p. Grose, T.L.T., Saucedo, G.J., and Wagner, D.L., 1990, Garside, L.J., and Bonham, H.F., Jr., 1992, Olinghouse Geologic map of the Susanville quadrangle, Lassen mining district, Washoe County, Nevada, in Craig, and Plumas Counties, California: California S.D., ed., Structure, tectonics, and mineralization of Division of Mines and Geology Open-File Report the Walker Lane: Geological Society of Nevada, 91-1, scale 1:100,000. Walker Lane Symposium, Proceedings Volume, Grose, T.L.T., Wagner, D.L., Saucedo, G.J., and April 23, 1992, p. 227–238. Medrano, M.D., 1989, Geologic map of the Doyle Garside, L.J., and Bonham, H.F., Jr., 2003, Geologic 15-minute quadrangle, Lassen and Plumas Counties, map of the Olinghouse quadrangle, Nevada: Nevada California: California Division of Mines and Bureau of Mines and Geology Open-File Report 03- Geology Open-File Report 89-31, scale 1:62,500. 29, scale 1:24,000. Hammond, W.C., and Thatcher, W., 2007, Crustal Garside, L.J., Castor, S.B., dePolo, C.M., and Davis, deformation across the Sierra Nevada, northern D.A., 2003, Geologic Map of the Fraser Flat Walker Lane, Basin and Range transition, western quadrangle and western half of the Moses Rock United States measured with GPS, 2000–2004: quadrangle, Nevada: Nevada Bureau of Mines and Journal of Geophysical Research, v. 112, B05411, Geology Map 146, scale 1:24,000. doi:10.1029/2006JB004625. Garside, L.J., Henry, C.D., Faulds, J.E., and Hinz, N.H., Henry, C.D., and Perkins, M.E., 2001, Sierra Nevada– 2005, The upper reaches of the Sierra Nevada Basin and Range transition near Reno, Nevada—two auriferous gold channels, in Rhoden, H.N., et al., stage development at ~12 and 3 Ma: Geology, v. 29, eds., Window to the World: Geological Society of p. 719–722. Nevada, Symposium Proceedings, May 14–18, Henry, C.D., Faulds, J.E., and dePolo, C.M., 2007, 2005, p. 209–235. Geometry and timing of strike-slip and normal faults Garside, L.J., and Nials, F.L., 1999, Preliminary geologic in the northern Walker Lane, northwestern Nevada map of the Griffith Canyon quadrangle, Nevada: and northeastern California: Strain partitioning or Nevada Bureau of Mines and Geology Open-File sequential extensional and strike-slip deformation?, Report 99-4, scale 1:24,000. in Till, A.B., Roeske, S.M., Sample, J.C., and GeoWhenDatabase: Foster, D.A., eds., Exhumation associated with http://www.stratigraphy.org/geowhen/stages/Blanca continental strike-slip systems: Geological Society n.html of America Special Paper 434, p. 59–79, doi: Gradstein, F.M., Ogg, J.G., and Smith, A.G., Agterberg, 10.1130/2007.2343(04). F.P., Bleeker, W., Cooper, R.A., Davydov, V., Henry, C.D., Faulds, J.E., dePolo, C.M., and Davis, Gibbard, P., Hinnov, L.A., House, M.R., Lourens, D.A., 2004, Geologic map of the Dogskin Mountain L., Luterbacher, H.P., McArthur, J., Melchin, M.J., quadrangle, northern Walker Lane, Nevada: Nevada Robb, L.J., Shergold, J., Villeneuve, M., Wardlaw, Bureau of Mines and Geology Geologic Map 148, B.R., Ali, J., Brinkhuis, H., Hilgen, F.J., Hooker, J., 1:24,000, 13 p. Howarth, R.J., Knoll, A.H., Laskar, J., Monechi, S., Hinz, N.H., 2004, Tertiary volcanic stratigraphy of the Plumb, K.A., Powell, J., Raffi, I., Röhl, U., Sadler, Diamond and Fort Sage Mountains, northeastern

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California and western Nevada—implications for McKee, E.H., and Conrad, J.E., 1987, Geologic map of development of the northern Walker Lane [M.S. the Desatoya Mountains Wilderness Study Area, thesis]: University of Nevada, Reno, 110 p. Churchill and Lander Counties, Nevada: U.S. Hinz, N.H., Faulds, J.E., and Henry, C.D., 2009, Tertiary Geological Survey Miscellaneous Field Studies Map volcanic stratigraphy and paleotopography of the MF-1944, scale 1:62,500. Diamond and Fort Sage Mountains, northeastern Mulch, A., Graham, S.A., and Chamberlain, P.C., 2006, California and western Nevada—implications for Hydrogen isotopes in Eocene river gravels and development of the northern Walker Lane, Tertiary paleoelevation of the Sierra Nevada: Science, v. 313, volcanic stratigraphy and paleotopography of the p. 87–89. Diamond and Fort Sage Mountains—constraining Renne, P.R., Swisher, C.C., Deino, A.L., Karner, D.B., slip along the Honey Lake fault zone in the northern Owens, T.L., and DePaolo, D.J., 1998, Walker Lane, northeastern California and western Intercalibration of standards, absolute ages and Nevada, in Oldow, J.S., and Cashman, P.H., eds., uncertainties in 40Ar/39Ar dating: Chemical Geology, Late Cenozoic structure and evolution of the Great v. 145, p. 117–152. Basin–Sierra Nevada transition: Geological Society Ressel, M.W., 1996, A transitional basaltic center in of America Special Paper 447, p. 101–132, doi: west-central Nevada: Petrochemistry and constraints 10.1130/2009.2447(07). on regional middle Miocene magmatism and Hudson, M.R., John, D.A., Conrad, J.E., and McKee, tectonics [M.S. thesis]: University of Nevada, Reno, E.H., 2000, Style and age of late Oligocene-early 197 p. Miocene deformation in the southern Stillwater Riehle, J.R., McKee, E.H., and Speed, R.C., 1972, Range, west central Nevada: Paleomagnetism, Tertiary volcanic center, west-central Nevada: geochronology, and field relations: Journal of Geological Society of America Bulletin, v. 81, p. Geophysical Research, v. 105, p. 929–954. 1383–1396. Jewel, E.B., Ponce, D.A., and Morin, R.L., 2000, Samson, S.D., and Alexander, E.C., Jr., 1987, Principal facts for gravity stations in the Antelope Calibration of the interlaboratory 40Ar/39Ar dating Valley-Bedell Flat area, west-central Nevada. U.S. standard, MMhb-1: Chemical Geology, v. 66, p. 27– Geological Survey Open-File Report 00-506. 34. John, D.A., 1995, Tilted middle Tertiary ash-flow Sanger, E.A., and Ponce, D.A., 2003, Principal facts for calderas and subjacent granitic plutons, southern gravity stations in the Dry Valley area, west-central Stillwater Range, Nevada—cross sections of an Nevada and east-central California: U.S. Geological Oligocene igneous center: Geological Society of Survey Open-File Report 03-006, 23 p. America Bulletin, v. 107, p. 180–200. Saucedo, G.J., and Wagner, S.L., 1992, Geologic map of John, D.A., Stewart, J.H., Kilburn, J.E., Silberling, N.J., the Chico quadrangle: California Division of Mines and Rowan, L.C., 1993, Geology and mineral and Geology Regional Geologic Map Series Map resources of the Reno 1° by 2° quadrangle, Nevada No. 7A, scale 1:250,000. and California: U.S. Geological Survey Bulletin Steiger, R.H., and Jäger, E., 1977, Subcommission on 2019, 65 p. geochronology: Convention on the use of decay Kelly, D.C., Zachos, J.C., Bralower, T.J., Schellenberg, constants in geo- and cosmochronology: Earth and S.A., 2005, Enhanced terrestrial weathering/runoff Planetary Science Letters, v. 36, p. 359–362. and surface ocean carbonate production during the Stewart, J.H., 1992, Paleogeography and tectonic setting recovery stages of the Paleocene-Eocene thermal of Miocene continental strata in the northern part of maximum: Paleoceanography, v. 20, p. 1–11. the Walker Lane belt, in Craig, S.D., ed., Structure, Koehler, B.M., 1989, Stratigraphy and depositional tectonics, and mineralization of the Walker Lane— environments of the late Pliocene (Blancan) Walker Lane Symposium, proceedings volume: Hallelujah Formation, Long Valley, Lassen County, Geological Society of Nevada, Reno, p. 53–61. California and Washoe County, Nevada [M.S. Thatcher, W., Foulger, G.R., Julian, B.R., Svarc, J., thesis]: University of Nevada, Reno, 120 p. Quilty, E., and Bawden, G.W., 1999, Present-day MacGinitie, H.D., 1941, A middle Eocene flora from the deformation across the Basin and Range Province, central Sierra Nevada: Carnegie Institute of western United States: Science, v. 283, p. 1714– Washington Publication 534, 178 p. 1718. McIntosh, W.C., Heizler, M., Peters, L., and Esser, R., Trexler, J.H., Cashman, P.H., Henry, C.D., Muntean, T., 2003, 40Ar/39Ar geochronology at the New Mexico Schwartz, K., TenBrink, A., Faulds, J.E., Perkins, Bureau of Geology and Mineral Resources: New M., and Kelly, T., 2000, Neogene basins in western Mexico Bureau of Geology and Mineral Resources Nevada document the tectonic history of the Sierra Open-File Report OF-AR-1, 10 p. Nevada–Basin and Range transition zone for the last

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12 Ma, in Lageson, D.R., Peters, S.G., and Lahren, M.M., eds., Great Basin and Sierra Nevada: Boulder, Colorado, Geological Society of America Field Guide 2, p. 97–116. Turner, R., Koehler, R.D., Briggs, R.W., and Wesnousky, S.G., 2008, Paleoseismic and slip rate observations along the Honey Lake fault zone, northeastern California, USA: Bulletin of the Seismological Society of America, v. 98, p. 1730– 1736. Van Buer, N.J., 2008, The Cathedral Range intrusive event in western Nevada—new constraints: Geological Society of America Abstracts with Programs, v. 40, no. 1, p. 92. Wagner, D.L., Saucedo, G.J. and Grose, T.L.T., 1989, The Honey Lake fault zone, northeastern California, its nature, age and displacement: EOS, Transactions, American Geophysical Union, v. 70, no. 43, p. 1358. Widmer, M.C., Oppliger, G.L., and Carpenter,T., 2009, Regional gravity study, southern Washoe County, Nevada—unpublished gravity database: Washoe County Department of Water Resources, Reno, Nevada. Wills, C.J., and Borchardt, G., 1993, Holocene slip rate and earthquake recurrence on the Honey Lake fault zone, northeastern California: Geology, v. 21, p.

27 15

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11

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8

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Prepared as part of the STATEMAP component of the National Cooperative Geologic Mapping Program in cooperation with the U.S. Geological Survey

NEVADA BUREAU OF MINES AND GEOLOGY ³ MAP 164

29 28

25 37 60 GEOLOGIC MAP OF THE SEVEN LAKES MOUNTAIN QUADRANGLE, WASHOE COUNTY, NEVADA

¦ ³

¦ ³ ³

¦ ³ 45 AND THE EASTERN PART OF THE CONSTANTIA QUADRANGLE, LASSEN COUNTY, CALIFORNIA

¹ 81 62 ¦ 42

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e

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o

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Tf Qls Ka Qfvy Alluvial fan deposits (undifferentiated),

Qfo ¦ Qfo Qfi ? 44 Qf Trc Tuff of Rattlesnake Canyon

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Qfo Kgf ? Tcs 22 Miocene - Oligocene Ash-Flow Tuffs

? ? Tn³hu17 ³

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Qfi ? Qfgy Qfvy Thc Tuff of Hardscrabble Canyon Tdi Tpc ¦ Tcn

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Qfi ¦ ³

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Qfo Qfi Qfy2

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8 A o Tf I : Aplitic to pegmatitic dikes and irregular Tf Tfc Tf ? Tf ³ 26 Kf 10 Tdm ³ Qls Landslide deposits Kf T Qa intrusions Tcn Tnh Nine Hill Tuff R Tnh Qfo ? Tnhu Twc E Tdm

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Qfy2 ³ : Qfvi Ts ? ? Tcy Ts

Qfi : ? Ts

o ? Tf Tf

Tf Qfy2 Qfvo ? 2 Ts

Qfo Qfvy2 Qp Tcu Tcu

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o 28 Qt ³

? o Tts 26 Tcc Tuff of Campbell Creek Trc Qfi : Trc Thc

60 Qfy2 Qfi Qfvi Tnhl 25 ³ Thc

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31

: Tcc

Qfy2 $ 24 ³

Qf Qfvo ? M Qfo ³ 17

Qfo Tdm

o ³ e

Qt Tf Tcu ³ Tft Boulder beds of Tertiary ash-flow tuff Kgm Mafic granodiorite of the Fort Sage Mountains

Tdm 41 Tcc n

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32 15

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Tcc

o Tcc

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30 Qfy1 : ³ Tts Kqmd

Qfvy2 Tcc ³

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Qt ³ : 28 ³ Tcc 27 Td Dacite lava Mesozoic Rocks

: 46 $ Twc Tnh

o ³ Qt S Tdm 25 o 40

13 : 57' 30" U

Qt Tdm ² 50 Mesozoic (Jurassic?) metavolcanic and Kf Tcc ³ Twc ³ Tdm

Qfvy Tdm Tcc Tdm ³ Twc Tuff of Cove Spring Mmv O 57' 30" Qa ³ Tdi Dacite dikes E

Qfvy1 Qt 33 Tcc Tcc metasedimentary rocks

Tf Twc C Qfvy2 ³ 44 Tpb 32 Tnh A

27 27 Qfvi ³ Tdm Qls Kgpp Ka

T : ³ 25 ³ 10

Qt Qfvo & Tdm Qfo E Qfvo Tdm 17 ?

Qf R

32 ? Tpp' Kgm

Qfvy2 D ³ Kgs Kgp Kgf Qt ³ Twc C r ?

Qfvy1 y Qt 36

Tdm Qt Qp Tnh Ts y ³

Valle Tf 6 Twc Qf

Qfvo Tf 39 ?

Qfvy1 ³Tdm Kqmd ) Qa ³ ³ 8 ?

42 Tnh Qfvi Tcy ³ Tnh

& Tcc Tcs ? 31 o ³ ?

Tcn See accompanying text for full unit descriptions ( ³

Tnh ³³ 80 Tf ³ Qfvy1 M Tcs ³ ³ 2 Qfo 30 Tbt Qfvy Tcc Tnhu ³ ³ Tdm 40 C Tnhl46 Qt Twc I Tf F ³ and references for this map. 49 Tpp' ³ 35 Tcp Tdm ³ 46 Tcc 5

: S 5 Tnhu 80 Tnh

Qfvy2 Tcs Tcc 59 Tcc T³cs Tdm Tnh Qfvo Qfvy2 ³ 35 S

Qt 46 Tcs Tpp' Tfc 47 44

50 Tpb Tbt ³ A Mmv Qf ¦30 25 26 24

Tf R ¦ ³32 ³ Qfvo Tf Tf ³ Tpp'

28 18

M Tnhl Tpp' U Qfvy2 Qfvo : Tpb ¦ Tpp' Qf J

Tfc 30 25 F

Tf Tfc ¦ 30 Tcs ³ Tcs Tcc Qt Tf Qt Tfc Tf Tcc Qa Tpp' 25 Tnh ³ Tcy Tf Qfvo Tnh ³³ 5

& Qfvy1 Qfvy2 Tcc Qs ³ 3 ¦ ³ Tpc Tpc Tpc Qfvy Tf Tpb 13

44 Qfvo Qfvy1 o 5 32 Tcy : ³ Qt Qt 22 Tpp' 26 41 Qfvy2 35 Qt Tcc ³ ³ Qt

Tf 37 Tpb Tpp' Tpp' 13

Qfvy2 Qfvy2 Twc Qfvy1 : Tcc 30 34 Tcc Tnh Qc Tpp' o Tf ³ ¦ Tnh Tcsl

7 ¦ 10 Qt

³ Tdm A

Tpc Qfvy2 Qfvy2 : Qa Qt Tcp Tcsl

o meters A'

Tdm ? Qfvo 20

9 o & Tpc 18 Trt ³ Tfc feet

5 Qfvo Tcp Tnhl Tf Qls Qfvi 2000 ³

30 ? ³ Tfc ³³ Fort Sage Tphl³ 37 25 43 Tpb Tcc

70 o Seven Lakes Mountain anticline

28 20 Tfc Tf Tdm 22 Qfvi Qt ³ Qfvy2 Tnh

³

5 18 ³ Tnhu Mountains

³ 60 o ? Qfvy Qfvy Tcs

Qfvi 2 2 Tnhu ³ ?

Qfvo Tpc Qf 85 35 1800 se 6000

³ o ba M

¦ of 35 n

70 o ectio o : j F o

70 20 ³ Qfvi Qf pr Tac 29 Tpp'

?

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o a

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27 28 Tphl Tpp' Qfvy 44 of Tsu

Qfvo F 53 o 2

o Honey Lake fau Qfvy 40 20 29 ³30 Tphl Qfvi 25 Tsl Tdm lt system

¦ ³³³

o 46 Tpp' Tfc

34 1600 Twc o Tdm Tf ³

30 o Qls Trt Trc Qfvi

36 20 ? Qfvi Qfvo Qfo

Qfvo Tcs Qfvy Dry Valley Qfy2 5000

³ Trt Qfi o

o F o Tf Tpp' Qfvi Qls Qfvo

40 25 Tf o Tsl 23 Tnhl ?

o Qfvo o Qfvo Tcy Tcc

28 Tft Trt Qc Qls³¦Tphl 39 Qa 1400 Qfvy1 Qa Qfy1 Qa

e 34 Qls Tft Tcp o

o 60 o Tcp Tpp' 10 Qfvy ? Tf Tpp' Ka 44 ? Tf

35 o 23 65 43 55 Qfvo Tdm Tdm

o ¦ 25 28 Qfvo

Qt o >

¦ ³ A

70 6 Qfvo T A? T

e o 15 10 o Tf Tpp' Tpp' Tsu Ts Tcs Tdm Qfy2 Tf Qf : o 55 1200 A T

o 10 Qf Tcc > A? 4000 60 ? T Tf 29 o M Tcp Tnh Tnh

o Qs

: >

30 : Tnh e

³ Qf : Tts

25 35

o Qls 22 Tdm

> Tf : ¦Tpp' Trt 12 Qfvi 1000 Qfvi Qfvo : Tpp' Tphl Tcp Tpc ? Qfvy o 10 Tcs Qfvo Qf 20 Qfvo Kgs o Qfvi Qf Tpp' 3000 Tphl Mmv M Tpp' 800

Qfy1 Tf Tf ³70Tcs Tft ¦ Tcs Tpp' 30

Qfy2 ³

Tpp 15 40 Qf Tdm

Qfvo Tft 10 Qfvi Qfvi 44 ³ Qls Kgs? Tft Tft ¦ : 17 Tpp' Tpp' 24 600

Tf 35 33 50 Tdm ³ 2000 ³ Qfvi Tcc 15 35 Tcp ³ Tcc ³ ¦¦

Qt 18 : Qfvy1 Tdm : ¦ Qls

³35 8 Tcp Tcp Qfvy Qfvo 2 Tcc 56 ¦30 30 Tsu Twm ¦ F :

³ : ³ 15 Tdm Some thin surficial units omitted. ³ Tdm 44 Tsu Tnhu Tcs &

24 Tf Qfgo Tcy 23 10 ³Tcs Tnh Tsl Tcc ¦ Qp Tnh Tsu Tpp' Ts Trt Tnh Tpc ³ Kgs 82 : Qf Qf

60 Tdm Tcc Qf

³³ Tdm Qfvi Qfvo Tdm ³ ³ 10

Tpp' Tcs

70 74 ³74 40 ³ Qfo Tphl

Kgs 15 Trt 12 25 Tphl 12

³ 12 Tpp' ³ Tsl Tphl ³ ³

Qfgy Tsu Qp Qfvi

¦ ¦ ³¥ 16 Tcp

30 ¦ ³ 19

: Tpp' 45 Tdm ³

³ Tnh Tphl ³ ³ Tphl ³

29 ¥ Tcc ¦ ¦ Tpp' 13 : ? Tsl ¥ Tpp' Tdm

Thc Tac Tcy 45 38 Tcc Qfvy2 32 ? Tnh Twc Ts 15 Tcc Tcp Tphl Qfo : ¦ 9 43 Qfvy Kgs 29 ³ 18 Tcs

Thc Qfvy Tcc ³ Tcc Tcs ³ 19 Tdm ? ³ 10 Tpc Tnh ³ Tcsl Tdm o

Trc Tac Qc ³ 46 56 Tpp'

Tsu ³

Tac : 32 Tdm

Tf Tac Twc Qfvy Qp Tphl ³ ³ 5o 0 Tpp' Trc ? Tcs

Tsu Qp Tcs 48 Tphl 16 ? Seven Lakes Mountain anticline 45 o 8 ³ ³ B B' ³ Tnh

¦ Qfvi Tbt 44 ³ 53

18 ³ 1 Tpp' ³ Tcs 43 ³

15 ¥ Tnhl Tcs

³ ³ 11 17 Tpp' 38

³ Tcc ¦ Tbt 17 Tnh Qfo 23 meters

Tf Tac Qp Tnh ³ feet 45 ³ ³ 6 Tac Tpp' 2

: : ³ Tphl

³ : Tdm 24 Qp 8

42 Qfo 1 50 Tcsl ³ 11 Qfo ³ ³ 17 Tdm Tpp' ³

o Qls

30 Tnhu 8 13 19 : ³ 1800 Tpp' 6000 Tac Tpp' Qfvi : Qfvi Qp Tpc

42 ³ Ts ¦ Qfvy ³ ³ Qls Trt 28 Tdm Tpc ³ 20 ³ F Qp Tnh

39 : Tpp' Tpc 65 11 8 Tpp'

³ o Trc Tsl Qfvy Tnhl Tnhu Tnh Tcs

25³ Tcs ³ :

45 Qfvi 51 10 Qfvi Red Rock Tcc 34 Qfvy ³

Tac Tpp' Tnhl ³ 80 14 Tdm Tpp' Qc Tdm Tcc Tpp' Honey Lake fault system North Fork ³ Tpp' 2 Tcs Qc ¦ Tbt Qfvy Tphl 8 Tnh

44 Tac 20 2 1600 Valley Tnhl Qls

³ Tdm Qf Tdm Trt ¦ Tdm Qls 23 o

61 43 15 Tpp' Qa @ > Twc? Tdm Tdm Tpp' Tcp Dry Valley Creek Tdm ? Qf

³ Tcy Tnh

Qfo Tcu ³ 20 ³ @ o

³ 78 Tnh @ Dry Valley 5000

Qfgy ³ ³ ³ > > ³ Qfo Tnh

Tnhu Tcs ³55 21 Qfo Qfo Qfvy1 Qfvy ?

: Tcs 26 Qa Tcn

14 Qfvo

³ Qfo ³ Twc? Twc?

Trc ³ Ts? Ts? Qfvo 30 Qf ? Qfvy2 Qt

42 o Tpp 5 45 Qa Twc? Tpp'

Tdm ³ ³50 0 Qfvi Qt 30 140 ³ Qa

Kgs Tsl 5 52 Tcc ? Tpp' Tdm M 9 Ts? Tnh

17 ³ ³ Tdm Ts Tnh 15 Qfo

20 Tpp' Qfvi Tft Tcp Tf Tdm Tf 60 Qfvy ³ >

Tac Tdm Twc Tbt ³ ? T A

80 Tnhl 17 Tcu? Tfc? A Tnh A >

55 ³ Qc Tdm T T

³ Tpp' Tcsl Tcsl Tf > Tdm ³ Twc ³ ³ 50 ? ¥ Twc?

³ ³ Ts³ 23 Tcs Tfc ³ ³ Tphl ?

Tck Tsl ? 40 28 Trc? Trc? Tcc Tf ¦ o Tdm 26 ³

43 50 Tnhl ³ 5 18 15 20 ? Tpc ³ Tf Tfc Tcc

Qfgi ³ ³ Ts? Trc Tdm

Tac Qc ³ Qfo Tnh Tp³ hl Tcs 17 : Tcs 1200 Tdm Thc? Trt 4000 Qf Ts Twc? ³ ³

Tac ³1 33 21 ³15 Trc? Tpp' Tf Tt

Tck Tcy Tpp' 20 1 Twc 35 55' Tac? Tac? @

Tsu Tcu 14 Tnh ?

Kgw Tcs ? Tt

³ Tcsl Tcs

³ Ts ³

Tdm 1 Tnhu 28 : ?

55' Kgs Tpp' o 48 ³ Tcc

: o ¦

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³ Qf

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Twc 5 2 ³ 51 Tnh ¦ Tnhu 1000 ? ³ Tdm ³

³ Tck 21 ³ 65 24 Tck? o

³

³ ³ Tcsl

Kgs Tdm ³ Tbt 22

Tts ³ Qfvy 28 Tcy 45 42 42 Qfvo Ts? Tcu? Trc?

o Tcu : 34 ³ Kgw Qfy

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³ 50 ³ Tcsl 28 Tt 3000 o Qfvi Tnh ³

Tck Tcy ³ 52 58 22 Tcu?

70 ³ ³

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Tf 55 o 45 12 8 Tcs ? 20 ³ Tphl ³ o

o :

³ 800

Tts 45 47 27 Tdm 25 45 Tcu 35 ³

Tft 50 ¦ Ts Twc 56 ³ ³ Kgw Tdm 42 Qfvo Tphl C''

F Tac 3 ³ Qfvi Tsl 3 ³

Twc Tsu Tpp' ³ 0 ³ 30 15 Trc Kgw 45 3 Tcsl

³ 23 Kgs? Mmv

Twc 46 ? o 40 18 Tcc

70 41 ³ Twc 45 10 ?

Kgw ³ Qfvy2 ? ³

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³ 60 Qf

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Qfgy Qf Tnh 62 Ts I Kgw Tcs Tha Qf 2000

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Tf 57 ? ³ Kgw 25 Qfvi 15

o 30 ? 57 ? Kgw Tcs

72 MT³ pp' Qf

25 : Tdm Kgs ³ Tf 0 o 50 5 33 ? 40 ³ 15

A 3³ 1 Ts Kgs Qfvi ³ Tnh Tcsl Ts

³

Qfo 15 o Qfvo 60 Qfy2 15 ³

³ ³³ Qfvi

Tf Tf 25 Tha Tnh

o ³ ? Twc Twc ? Kgs Tcs

Tfk 55 20 25 Qfvy Tf 64 Tcsl

³ Ts 82 Twc : 14 ¦ Qfvy1 Tdm Kqmd Some thin surficial units omitted.

20 Qfy1 Tpp'23

Tcc ³ : Tphl

Tf Qls 36 Qfy2 ? Qfo Tcs Tdm ³

15 Tcc ³ ¦ Tbt

Kgw Qfi ³

45 : Ts 15 ³ ³ 28 ³ Qf Tfk Tft Qa ?

Qfo 43 : Tcc 15 Tcc 37 Kgs Tcn 55 ³

Qf ³ Ts Tpb 47

³ ³ 30 ³ Kgs Qfvy2

o55 Qfvy Qfy2 Tphl Qfvi

Tnhu 25 24 30

Tf 72 ³ Qfvy Kgw Qfy1 Kgs

50 ³ Qfvi Tcn

31 20 Qfvy2 ³

Qf Tfk Tcs ? 31 ³ 38

o ³ Qfvy2 45 ³

o 29 Tnhu ³ 87

³ s

25 Qf Kqmd C''

Tdm Qfvy ³

o 48 78 Twc Tcu o Tnh Qfvy2 44 C Tnhl Tcs 35 Dogskin

Tft Tnh ³ ³ feet

Qfvy2 Tnhu ³ 10 ³ 21 me

30 Tnhl ³ Tnhl ters

Tf Qfgo 32 Ts Tpb Qt 80³ ?

Qfvi 79 30 51 Tnhl & 85 o 49 Mountain ³ ³ ³ ³27 ³ o 8 Tf ³ 30 Qfvy1 1800

Tf 43 Qe C 6000

58 Tdm ³ Tnh ' Honey Lake fault system Tcs

Tfk Qfvy 35 Qfy1 Qt 88 85 Petersen Tcsl ³ Porcupine ³ 1

Tfk 36 ³ ³ Qfgy Tdm ³

20 Tck Qfvy1 Qfi ³ 35 Sand Hills > Qfvy 80 ³

Qt Qa Qfvy2 Qfvi Tdm Qfvy2 2 Mountain Tnh

44 C Qfy2 Tpc Mountain Tcs

Tfk Tf Kgs 28 Qfy1 Tcs 1600 Tcc Qfo ³ Tcc 21 ³ 30 ³ 33 Red Rock Valley Tnhl Tphl

Tfk Qls ³ Qa 40 Lees Flat Qfvy2 µ Long Valley fault Tdm Qfgy1 Qfgy1 Qfvy1 B Tcc Tphl Qfgo Tfk Qfgy1

Ts : Tcc Qa Qfgy2 Qfgy1 Qt Qaf Qfgi Tcn 5000

35 Qc Tnhu : 31³ Tdm Tfk Qa Ts Tdm

> ?

o Tf 23 Qfvy2 Qc Tfk Tcu Qa Tft ? Twc? Tfk ³ Tdm 36 Tcc 1400 Ts Ts >

Kgs Qfy2 Tcc Tcc Ts?

Qt Tnhl Tck

15 Qa Qfvy1 Tf Tnhu A T

Tfk ³ >

12 Qfvi ³ Qa >

R ³ Qfgy1 Qfvy1 > >

³ Tf

³ Qa 30 46 ³ Qfvy Tfk > Kf

Tf Qfgy1 Tcc 2 Tdm Tf 4000 e ³ 1200 Tnhl Ts 40 Ts Qfvy2 ³ Tnhu ³ A T

Tf ³ Qfy1 Kgs Tnhu

d Tdm 32 Tnhu ³ Tcc

Qt Qfgy2 ¥ Qf 5 Tdm

Tfk 63 Ts A T 14 ³ 38 Qfy2 Tfk Tpb Kgp Kqmd? ³ 13 ³ 26 Tcc Qfgo 32 : Qfo ³ ³ 52 Tck Ts 1000 Kgs?

12 Ts Qfvy2 Qfvi ³ F Qfvy Kgs 2 44

Ts R 45 25 Kgp 3000

Tft 27 10 ³ Qt 20 Kgs Tnhu Te ³ Tfk Tf ³ o 23 Qfvy2 Some thin surficial units omitted. ³

Tf Qa ³ Tfk Tfk c 1³5 ¥ 18 Qfgi : Qfvy2 Qfgo k 35 1 Tfk Tf Qa Qfvy Tck Qfgy1 Qt Qe 44 Kf 2000 20 23 o y 30 Tfk Tfk Qs Qt Kgs Qfgy 22 Tft V Qt Ts Qfgy1 Tcc e o Tf Tf o Kf Qfgy2 Qaf Qfvi l Qfgo 26 a 21 Tf Qt ³ Tfk l o Tf Tfk : l 7 l Ts Tdm ³ Kf Qfgy1 Qfvy2 a e Tft Qfgy1 : Qf 32 Tf Tcu Qfgi V o y Qfvi

38 30 Qa L Qa 35 I Tnhl Qfvo Tfk o o oTf 22 e Sand Hills Tfk Tf 17 Ts : Qc ³Tnh³ 80 Qfgy2 e Qfgy Tfk 26 Tf Tfk 80 I Qfgi ³ s

g 44 000m

I 14 Qaf 19 N I ³ : Qfgo ? n 55 Qls A A' Tfk Qfgo 85 Qfgo Qfgy1 15 Contact Solid where certain and location accurate, dashed o Qa 7

5 I ³ F Line of cross section I Qfi C' 30 Kgs where approximate, dotted where concealed; queried if identity L Tcp l I Kf Tf Kf 70 I Ts Tfk 65 rcupine a Kf or existence uncertain.

44 Qfgo Po I Tpp' Tpp' Qfgy

19 Tf Mountain : t Kgs Tfk I Tfk Qfgo Qf 90 : Kf Tck Tfk Qfgo Qc Intraformational contact 36 46 85 58 Qfgy2 Breccia Intensely brecciated area along hinge zone of Qfgo Tf I 9 o o I 55 Qfgy2 Qt 25 ³ Qfgy1 Seven Lakes Mountain anticline. Qf I 10 45 Qe I Qfgo Qfgy1 Qaf I Form line Showing dip of beds in cross section. Tfk 85 Tppi Qfgi Kf 20 42 o I : Field work done in 2004-2006 90 I Strike and dip of bedding I 44 Kf Scale 1:24,000 Supported by the U.S. Geological Survey STATEMAP Program 70 Qf I : A Map location 40 33 : I I $ Inclined Horizontal Tfk o Qfgo Kgpp 90 Qfgy ? (Agreement No. 04-HQ-AG-0032 and 05-HQ-AG-0014) o Kgp T 20 e

40 o 0 0.5 1 kilometer 44 Adjoining 7.5' Qfgy o I Fault Solid where certain and location accurate, dashed where Tfk 90 Qe 18 I I 90 Qfgy2 Kgp quadrangle names Tf Qfgo Qf approximate, dotted where concealed; queried if identity or existence PEER-REVIEWED MAP

Tfk Tf 85 Qf Strike and dip of flow bands in lava or intrusion I Petersen I uncertain. Arrows show relative motion; ball and bar marks downthrown Office and Field review by George Saucedo, California Geological

Qfgo 68 90 73 Kf 1 2 3 I Qf I Qfgo side. On cross sections only, A, away from observer; T, toward observer. Inclined Horizontal 0 0.5 1 mile Survey; John Bell, Craig dePolo, and Larry Garside Tf Mountain 90 I Tf I 20 70 90 o ¦ ¥ 39o52' 30'' N 39 52' 30" N o o 4 5 6

241 242 243 120 00' W 244 245 246 57' 30" 248 249 250 55' 251 252 253 119 52' 30" W Edited by Nicholas Hinz, Jordan Hastings, and Daphne LaPointe

M Strike and dip of compaction foliation in ash-flow tuff Compilation by Christopher D. Henry and Alan R. Ramelli 0 1000 2000 3000 4000 5000 feet Syncline Solid where certain, dotted where concealed. Inclined Horizontal Vertical 7 8 9 Cartography and map production in ESRI ArcGIS v9.3 (ArcGeology v1.3) 20 µ by Heather Armeno, Christine Arritt, and Jennifer Mauldin

³ ² 1 Doyle CONTOUR INTERVAL 10 METERS (west half of Dogskin First Edition, December, 2009 F Printed by Nevada Bureau of Mines and Geology GEOLOGIC MAP OF THE SEVEN LAKES MOUNTAIN QUADRANGLE, WASHOE COUNTY, NEVADA 2 State Line Peak Mountain, Nevada-California, 7.5'x15' quadrangle) or 40 Anticline Dashed where approximately located. Strike and dip of metamorphic foliation in ash-flow tuff FEET (Constantia 7.5' quadrangle) This map was printed on an electronic plotter directly from digital files. Dimensional calibration may 3 Spanish Flat vary between electronic plotters and X and Y directions on the same plotter, and paper may change 40 Inclined Vertical 4 Constantia size; therefore, scale and proportions may not be exact on copies of this map. ! % ! ! ! 20 5 Seven Lakes Mountain Projection: Universal Transverse Mercator, Zone 11, AND THE EASTERN PART OF THE CONSTANTIA QUADRANGLE, LASSEN COUNTY, CALIFORNIA ¹ ½ For sale by: 6 Dogskin Mountain North American Datum 1983 (m) Vein with dip Nevada Bureau of Mines and Geology 7 Beckwourth Pass 2175 Raggio Pkwy. Christopher D. Henry, Alan R. Ramelli, and James E. Faulds 8 Granite Peak Base map: west half of the U.S. Geological Survey Dogskin Reno, Nevada 89512 Lineament 9 Bedell Flat Mountain, Nevada-California, 7.5' x 15' 1:24,000 scale ph. (775) 784-6691, ext. 2 www.nbmg.unr.edu; [email protected] 2009 quadrangle (1979) and Constantia 7.5' quadrangle (1994) 1937