Geologic Map and Cross-Sections of The

117º 00’ 00” 116º 52’ 30” 116º 45’ 00” 116º 37’ 30” CAETANO CALDERA AND RELATED ROCKS Ts? �� Tbm? �s 35 Pzrm CORRELATION OF MAP UNITS �� Pzrm ��

45 s Tcic Carico Lake pluton (Eocene)—Carico Lake pluton consists of 50–60%, 1–5 mm

�

Pzrm �

� 35

L phenocrysts of smoky quartz, sanidine, plagioclase and 2–3% biotite and �

� Pzrm Pzrm �� U s�

� A Pzrm Qp Qal Qaf QUATERNARY hornblende in a microcrystalline quartz-feldspar groundmass. Scattered sanidine

Tcs �� Qaf Y

� F

� �

�

Tad �

45 s

Tbm? Ts E

� phenocrysts are as much as 2 cm long. Small miarolitic cavities are common.

�

� � � L

Tad Pzlc � 40 39

Tad � PLIOCENE

40 �

� L Locally flow banded. Intrudes and deforms Caetano Tuff. Sanidine Ar/ Ar

�

� s �

�

� � � Figure 14 � s � � cross-sections only � Greystone QTs �� Horse A

30 x mine age is 33.78 ± 0.05 Ma (John et al., 2008).

Tad 06DJ13

Mountain

N l

l Tcir

Redrock Canyon pluton (Eocene)—Strongly altered fine- to medium-grained l

Tct?

Tad l Pzlc

Tbm? Qaf

Pipeline pits

l S granite porphyry containing about 30% phenocrysts of rounded smoky quartz

Wilson

l and dumps 21 l 50

Pass NEOGENE Tcb E (2006) and altered sanidine and plagioclase in a felsite groundmass now altered to R Ts R Tob 44 Tmr MIOCENE Qaf Qaf G Gold kaolinite and quartz. Undated but presumed to be late Eocene. Intrudes and 70

Acres 35 T Tcm 40º 15’ 00” hydrothermally alters Caetano Tuff. D Tcl 33 Tcs CJV2 40º 15’ 00” Tcs 13 Barite N Pzrm Tb Tci R Caetano intrusive rocks, undivided (Eocene)—Small ring-fracture intrusion in Tad Tbm pit E Tcl T O northwestern Carico Lake Valley is a fine- to medium-grained porphyry with Tcs L Tad Qaf C U

C T Qaf Unconformity A sparse white K-feldspar phenocrysts as much as 1 cm long. It consists of about

A Tad L Qaf S

F U K E

A 45% phenocrysts of plagioclase, K-feldspar, and dark-gray quartz and 3% biotite

Tad Tcs d

Qaf W

K 24 Ts and sparse hornblende in a microcrystalline groundmass. Small intrusion 2 km

Ts l C

Tcs

s l

o l

Tbm

c OLIGOCENE northwest of Carico Lake is fine-grained granite porphyry containing about l

Qal

A Tcu 25–30%, 0.1–3 mm phenocrysts of rounded smoky quartz, sanidine, and

42 66

Tcs N

plagioclase, and 1-2% biotite and hornblende in an aphanitic groundmass

Tcu

40 l

S l

CENOZOIC

CT120 Y

containing abundant miarolitic cavities. Both intrusions are undated but

O Tcs l

67 l

Tbm O Tcs CT107O Y Tcb M N 40 presumed to be late Eocene.

50 30 Tci A N 46 CT116

C Y 05DJ27 Pzrm Tct Caetano Tuff, outflow sheet (Eocene)—Densely welded, crystal-rich rhyolite

CT121

68 Tcu

Qaf 46

C E 30 an Tad CAETANO CALDERA ash-flow tuff identical in composition and age to intracaldera Caetano Tuff (unit

Tad y Ts? o Qal n � � Tcl 55 65 � A’

36 � L

Qaf � Tcc). Forms densely welded, reddish weathering ledges with up to 250 m

Tcl s

Tad H03-94 18 62 Cortez Tog Tog

� Tcu 40 39 V A L L E Y �

L �

Ts? 50 PALEOGENE composite thickness. Black vitrophyric zones locally present. Sanidine Ar/ Ar �

� l l l 60 47 �� Tcu �� Tcs 40 Tcu 30 �

A s ages are 33.83 ± 0.05 and 33.75 ± 0.06 Ma (John et al., 2008).

CT108 K Tcl �

Tcs C Tbm 40 V 43 O Tcb Caetano Tuff, breccia (Eocene)—Mesobreccia and megabreccia dominated by

28 Tcl Pzlc

R 53 Tcir 77 Tcb 41 Tcs D Tcir Tct coarse clasts of quartzite and chert. Mesobreccia is massive to thick bedded,

E Tcu 15 Cortez

R 70

Tcs? T EOCENE

B Qal L quartzite-dominated breccia containing clasts up to 2 m in diameter, mostly 37 AU 31 Tcl Qp F MILL CANYON STOCK 62 61 75 25 Tcl matrix supported. Matrix varies from tuffaceous to finely ground quartzite. Also

45 Tcu Rocky 15

44 ?

Figure 15 77 51 Pass � Tcic includes matrix-supported, quartzite-argillite pebble layers and sparse interbeds

�

T � Tci �

Tbm

L Ts Tcic �

25 Jgr �

64 Tog? Qaf T Tor �

Tcu U Qaf � of volcanic sandstone and tuff. Probably deposited by rock falls and debris

N 6 Tad? Tbm? H05-62 Ts �

E � A s

C 20

F 24 Pzlc Tcic �

21 Tcic S � flows, and possibly by fluvial processes. Megabreccia is composed of individual

�

Tcm

49 20 �

Tcic �

E �

Tcu

�

R Tor � Tb

05DJ27 blocks up to 50 m in diameter, mostly of chert or quartzite, but also Eocene

R Cortez � Tcc

�

45 55 10 C s

Tbm Tcir Tci 41 39 Hills 30 � H03-96 H03-84 20

� (35 Ma) rhyolite in the northeastern part of the caldera (probably equivalent to

Pzrm �

�

40 l

Tbm

�

37 Tor

Tob l

�

L l

�

� Tor), and composite areas of blocks up to ~1 km across, locally with a

E V

Tcir U �

Tbm Mount

�

Pediment

�

Horse l

Tcl l �

�

Tenabo �

O tuffaceous matrix.

Tcu �

Canyon �

�

T 87

Tcu 73 �

�

R s

Tcu l DC99-15

Unconformity

47 Tcb l Tcu

Tcl

Caetano Tuff, upper intracaldera unit (Eocene)—Multiple, thin, cooling units of

Qaf �

Y 15 �

H03-82

�

S 334m

�

Tcic E

37 �

S 40 �

30 � Tmr

� Tcu Tcic poorly welded to moderately or (rarely) densely welded ash-flow tuffs locally

s MESOZOIC

A l

Tcic l

00DJ34

37 P � G

Tbm Tcir

�

JURASSIC

�

Ts 45 � Jgr

interbedded with coarse conglomerate, sandstone, and fine, platy tuffaceous

40 �

� 6

Tbm �

�

? Ts

Tcl �

Qaf

Tbm �

l s B’

Tbm

25 siltstone. Generally forms pale or banded slopes punctuated by thin ledges of

Y 40

�

30 �

Tcir K �

�

� more resistant welded tuff. Tuffs commonly contain angular fragments of

Tor

C �

35 Tcs? �

Pzh Tcl �

O �

Tcu l

45 l

20 R Ts densely welded lower Caetano Tuff up to 1.4 m in diameter and locally contain

�

Pzlc

Qaf �

Tbm 80 45

T T �

31 30

�

64 ��s��s�

L � L

� hornblende-pyroxene andesite and Paleozoic fragments to 15 cm. Poorly to

l GOLCONDA THRUST

�

25 l

U �

�

Tcc �

A s

Qaf

20 A

80 99DJ80

moderately welded tuffs are characterized by distinctive orange pumice

�

Tcc 25 �

23 Tcl

38 50 45 l

Tcl �

l Pzo �

Carico 30 15 �

Qaf Tcl � 33 fragments. Up to 1000 m thick; base of unit defined as a prominent welding �

62 45 Ts � T Tbm

C Lake � L 40 s CT101 Pzrm

H 37 U Tcc Tcu 20 10 l

l 25 � PALEOZOIC break at the top of the lower unit (Tcc), which generally forms a conspicuous � C A Tcl CT102 35 � Unconformity

F 38 Figure 19 50 25 � 40º 07’ 30” 37 �

Tcu Qaf N 26 25 l � 40º 07’ 30” 72 60 Tad l 25 �

� slope break marked by a vitrophyre or several meters of conglomerate or A

� 44 Z

T 75 35 � s

L Tcc 41 15 30 R

39 E Tcs

5 43 43 30 �

U Elephant l sandstone.

�

45 9 45 T Pzrm x � Tcc

A Tct 29 �

E Tbm

F 32 H03-88B �

Head

�

Tcl

�

l 40 30

52 42 Compound cooling unit of

l � Caetano Tuff, lower intracaldera unit (Eocene)— 37

50 O �

25 32 s D

35 l 30

S Tct Qal N

25 Qp

A 40 40 ��s��s�

C �

50 l A ROBERTS MOUNTAIN THRUST

l l l Tbm? �

densely welded, crystal-rich, rhyolite ash-flow tuff, containing about 35–50 k l 30 Qal

50 l n �

i T 40 �

30 50

E E H s Tub Spring �

25 E �

Tog

a 50 25 �

T �

l B A l volume % phenocrysts as much as 5 mm in maximum dimension. Quartz,

� 34 L 40 25 l R �

Tcu s Pzlc E 55 C Tcu U 30 Tcl C

� A 60 � sanidine, and plagioclase form >90% total phenocrysts. Distinctive quartz Tcu Ts Caetano n Tbm � i F � 37 Tcl 45

40 � R 16 T b �

x 70

Ranch � 46

a l

Ts 50 �

Qaf 35

� phenocrysts are dark gray to black (smoky) and partly resorbed. Total mafic

N 48 s

S I 10 35 50 A Qaf T

35 l

l �

S 50 A 40

�

H l L A K E L Mount

l Pzo x �

T l l T

mineral content generally <4 volume %, consisting mainly of biotite with minor

�

40 G O �

P L

60 �

Tbm N l

�

l Tad Caetano

Tcl �

Pzrm

E A

M �

U U � C’

29 e 35

L s F opaque minerals and locally trace hornblende. Euhedral allanite crystals as much

n Pzrm A O 28

H03-89 E 23

o 70 F 11

35 Tcu

45 35

48 l

S as 1 mm long, apatite, and zircon are common accessory phenocryst phases.

Qaf

80 l

27 R D 21 9 A 60

Tcu? 45

Tct 48

20 l

Tad Strongly flattened pumice fragments generally are crystal rich and contain

Pzrm N

28 30 60 I S

l l 30 Tcl

40 l B Tad l l 37 l l phenocryst assemblages similar to the matrix. Exposed thickness ranges from l

Pzo A 43 Tcb W S 40 Qaf E 23 C l l 40 39 40 N l l

l l l l Tcs 1800 to >3400 m. Weighted mean of nine sanidine Ar/ Ar ages from both B 40 A

N 20

42 l Tcb F T E AUL l l l

E DESCRIPTION OF MAP UNITS

T Figure 12 45 Wenban upper and lower units is 33.80 ± 0.05 Ma (John et al., 2008). N

L N 12 I l l Qaf

l l U Spring Tad O Ts M Tcc Pzrm l

Qaf Figure 18 l Caetano Tuff, upper and lower units (Tcu and Tcl) undivided.

l l A Tad T 40 l

l F S l l l 8 l l l 52

30 l l Tog l l Pzrm

Alluvium (Holocene)—Unconsolidated alluvial sand and gravel and lacustrine Red Qal x Tct 40 Tct Qaf

Mountain 7 V Hydrothermal alteration—Hydrothermally altered Caetano Tuff and intrusive D Tct deposits in modern stream beds and valleys. S A rocks. White, dark-gray, and dark yellow-gray, commonly red weathering R Pzrm ? 50 Qaf Alluvial-fan deposits (Quaternary)—Unconsolidated to poorly consolidated 26 A 25

45 Tct? D L hydrothermally altered rocks. Variable intermediate and advanced argillic

deposits of boulders, gravel, and sand that form the modern alluvial fans and E

Pzh 30

Pzo

C 35

25 L

alteration assemblages in which plagioclase phenocrysts replaced by kaolinite, Qal

Pzrm Pzrm pediment surfaces mostly developed on Miocene sedimentary rocks.

E 33 34

37 �� E

B � 40 T Tbm �� sanidine is unaltered, perthitic, or replaced by kaolinite, biotite replaced by

��s

Pzrm A �� Bald Qp Playa deposits (Quaternary)—Clay, silt, and sand forming surface deposits in

� � s D’

U �� Y x

�s �

A � 22 � Y I �

E �

Ts F

� �� Mountain kaolinite, white mica, and/or opaque oxides, and groundmass replaced by

� �

�

H O � ephemeral lake basins in Carico Lake Valley �

Tct �

W � � �

T Qaf T � s

�

34 � � � �

� s � fine-grained silica and/or kaolinite and fine-grained pyrite. Locally, plagioclase o �

Tad 52 s � QTs � Sediments filling Crescent Valley,

o � � Basin fill (Quaternary to late Miocene)—

�

Y � ��

d Ts �

�� s �

�� N

�

� and sanidine are completely leached leaving prominent voids in a siliceous

�

� �

A Pzlc shown in cross section only. Inferred to have been deposited during late

Qaf

�

� Qal

�

Tct 46 C

� � �

�

� matrix. Most pyrite is oxidized. Locally contains abundant hematite.

Tbm Qal Qaf Miocene to Holocene slip on the Crescent Fault.

Pzrm C A R I C O Spring Ca Pzo Y n 12 yon

R Tmr Rhyolite dome (Miocene)—Flow-banded rhyolite dome intruding Paleozoic

Pzh 40 Tct D Toiyabe 50 72 sedimentary rocks and Tertiary gravel (Tog) along crest of Cortez Range. CENOZOIC ROCKS PREDATING THE CAETANO CALDERA 117º 00’ 00” 116º 52’ 30” 116º 45’ 00” 116º 37’ 30” Sanidine K-Ar age is 15.6 ± 0.4 Ma (Wells et al., 1971, recalculated). Tcm Tb Basaltic andesite (Miocene)—Basaltic andesite lava flows up to 100 m thick Tuff of Cove Mine (Eocene)—Crystal-rich, rhyolite ash-flow tuff with 30–50% on the southeastern crest of the Cortez Range. Whole-rock 40Ar/39Ar ages are phenocrysts of quartz, sanidine, plagioclase, biotite, and hornblende. 16.36 ± 0.05 and 16.67 ± 0.14 Ma (Colgan et al., 2008). Distinguished from the petrographically similar Caetano Tuff by greater total Shaded-relief topography from USGS National 15° SCALE 1:100,000 Sources of map data mafic mineral (6–10 volume %) and plagioclase content. Typically contains 5–8 2 1,2,9 7 Elevation Dataset (30m grid; http://ned.usgs.gov). MIDDLE MIOCENE SEDIMENTARY ROCKS volume % biotite and 1–2% hornblende. Weighted mean of four sanidine MAP LOCATION 40 39 TH 1 0 1 2 3 4 5 6 7 8 9 10 KILOMETERS 1. New mapping by the authors. Ar/ Ar ages is 34.22 ± 0.01 Ma (John et al., 2008). R Base map from USGS Crescent Valley and Fish TH R 2. Gilluly and Gates (1965) Tor Rhyolite domes and dikes (Eocene)—Flow-banded, finely, sparsely porphyritic Creek Mountains quadrangles (1:100,000 scale). Ts Sedimentary rocks (Miocene)—Poorly exposed sandstone and conglomerate 1 0 1 2 3 4 5 MILES 3. Gilluly and Masursky (1965) sanidine-quartz-biotite rhyolite lava dome in the southern Cortez Range and NEVADA 1,4,9 with lesser finer-grained tuffaceous deposits. Mostly light gray-brown, fine- to UTM Projection, Zone 11 TRUE NO 4. McKee and Stewart (1969) numerous dikes in the northern Toiyabe Range. U-Pb zircon age of lava dome MAGNETIC NO medium-grained sandstone in beds 10–20 cm thick, containing variable 1,8,9 1,3,9 1,3,7 5. Stewart and McKee (1969) is 35.2 ± 0.2 Ma (Mortensen et al., 2000). K-Ar ages from lava dome are 35.2 NATIONAL GEODETIC VERTICAL DATUM OF 1983 amounts of pyroclastic material including glass shards and crystal and lithic 6. Moore et al. (2007) ± 1.1 Ma (sanidine) and 35.3 ± 1.2 Ma (biotite); K-Ar ages from dikes are 34.7 APPROXIMATE MEAN fragments. Sandstones locally contain thin (~10 cm) lenticular beds of DECLINATION, 2000 7. Roberts et al. (1967) conglomerate with 1–5 cm clasts of quartzite, chert, and/or volcanic rocks. ± 1.1 to 35.8 ± 1.2 Ma (Wells et al., 1971, recalculated). Tad 1,6 8. Stewart and McKee (1969) More extensive conglomerate deposits consist of poorly consolidated, Andesite and dacite lava (Eocene and Oligocene)—Finely to coarsely porphyritic 9. Stewart and McKee (1977) light-brown, massively bedded, medium- to fine-grained sandstone containing andesite and dacite lava flows with phenocrysts comprised mostly of plagioclase matrix-supported (locally channelized), angular to subrounded cobbles as and pyroxene with local hornblende. Composite unit includes lavas that predate much as 50 cm across (generally 1–5 cm). Clasts most commonly consist of formation of the Caetano caldera together with flows interbedded in post-caldera gray Paleozoic quartzite and chert and locally of Caetano Tuff. Sandstone and sedimentary rocks (unit Tcs). Includes dacite of Wood Canyon mapped by conglomerate interbedded with thinly laminated (<1 cm), white tuffaceous Moore et al. (2007) in the southwestern part of the map area. shale and 2–5 m thick beds of light gray to white volcanic ash. Age Tob Basaltic lava flows (Eocene)—Dark gray, weakly propylitized, fine-grained Reese River Valley Redrock Canyon Wilson Canyon Cooks Creek Carico Lake Valley Crescent Valley Cortez Range A A’ approximately 16–12 Ma, based on sanidine 40Ar/39Ar dates and tephra sparsely porphyritic plagioclase-pyroxene basalt lava flows on the floor of the Caetano caldera west of Wilson Pass. Undated but stratigraphically beneath the T L T 3 correlations (Colgan et al., 2008). 3 LT? L F F ROCKY PASS FAULT? F tuff of Cove Mine. RS Tcu Tog K A T T ED Tbm FL N E C Qaf Tcl Qaf NE fault oblique E Tog Boulder to pebble conglomerate and sandstone (Miocene to Eocene)—Poorly E HE Tbm O C Tad Tad Qaf T T Qaf kilometers CENOZOIC ROCKS POSTDATING THE CAETANO CALDERA Tcs R Tcl S Ts S EY to section E 2 C GR Tcu 2 sorted and poorly lithified unit deposited unconformably on Paleozoic basement. R C More than 400 m thick in the southern Cortez Range, where it contains blocks Ts Tcs Pzrm Tbm Bates Mountain Tuff (Oligocene)—Composite map unit composed of rhyolite Tcs Tcl Pzrm Tcs Tcu Ts Tcl Pzrm Pzrm Tcc Pzrm? QTs up to 10 m across of Paleozoic rocks, granitic rocks, porphyritic andesites, S T Ts? ash-flow tuffs and locally interbedded sedimentary rocks (Tcs). This unit kilometers FL Pzlc? 1 1 S YN Pzrm? flow-banded rhyolites, Caetano Tuff, and several units of Bates Mountain Tuff. O K C encompasses three genetically unrelated ash-flow tuffs corresponding to units M OC Caldera margin 40 39 DR Sanidine Ar/ Ar age from a reworked ash layer in this deposit is 33.97 ± 0.20 RE Tob? Tcm? faulted out TOIYBALE MINE FLT? Pzlc/Pzrm? B, C, and D of the Bates Mountain Tuff as defined for exposures at Bates Tcc? ROBERTS THRUST? CAETANO RANCH FLT? 0 CORTEZ FLT? 0 Mountain about 60 km south of the map area (Stewart and McKee, 1968; Ma (John et al., 2008). Forms part of the caldera floor near Wenban Spring in McKee, 1968; Sargent and McKee, 1969; Gromme et al., 1972). Not all units Toiyabe Range, where it is dark red, moderately well bedded and calcite caldera floor exposed structures projected north from B–B’ are present in all sections. 40Ar/39Ar ages from John et al. (2007). cemented with angular to subrounded clasts of Paleozoic limestone, chert, and 2 km north of A–A’ Tbm D unit of Bates Mountain Tuff—Mostly densely welded, pumice-rich, and minor quartzite to 90 cm. Also inferred to form part of caldera floor on sparsely porphyritic ash-flow tuff containing ~5% phenocrysts of sanidine, northwest edge of Toiyabe Range, where lithified conglomerate contains anorthoclase, plagioclase, and sparse quartz and biotite. Sanidine 40Ar/39Ar subrounded clasts of quartzite, chert, argillite, granite, diorite, and flow-banded age is 25.27 ± 0.07 Ma. Equivalent to Nine Hill Tuff (Bingler, 1978; Deino, porphyritic rhyolite as much as 1.5 m in diameter in a sandy non-calcareous 1989). matrix. Reese River Valley Redrock Canyon Carico Lake Valley Rocky Pass Toiyabe Range Grass Valley Cortez Range B T? LT B’ Tbm FL F T C unit of Bates Mountain Tuff—Poorly to densely welded, pumiceous, T L L S N T R Y F L MESOZOIC ROCKS F DA F 3 sparsely porphyritic ash-flow tuff containing phenocrysts of plagioclase, 3 E C T C K Z Tb K HE C N TE 40 39 E T Qaf O LT LT E Qaf R sanidine, prominent embayed quartz, and biotite. Sanidine Ar/ Ar age is E R Tbm Tcu F F O D LT? S NE C Ts C Jgr R Tbm E Tbm F S I S � Mill Canyon Stock (Jurassic)—Biotite quartz monzonite, locally with plagioclase Qaf Qaf E A M Qaf �� kilometers C Tcs R N Qaf P Qaf E �� 28.64 ± 0.06 Ma. Equivalent to tuff of Campbell Creek in central and Qaf TO Y BE Tog Tcl �s S K A R 2 2 Tcu Y Tcc C IY �� Tog phenocrysts. Zircon U-Pb age is 158.4 ± 0.6 Ma (Mortensen et al., 2000). RE O O C ��Pzrm western Nevada (McKee and Conrad, 1987; Henry et al., 2004; Faulds et al., G R T �� Tmr Ts Tcir �s Pzlc �� Tcc Tcu Tcb �� 2005). Tcl �� Tcs Tcir? Tbm? ? Ts Tcl Tcl �� Tcu PALEOZOIC ROCKS Tbm kilometers B unit of Bates Mountain Tuff—Moderately to densely welded, sparsely 1 Ts 1 S Tcir? Tcic Tcl faulted Tcs/Tad? S Tcic? Tcl ROBERTS MTN THRUST pumiceous, moderately porphyritic ash-flow tuff containing phenocrysts of O Tcc? 40 39 Pzh H a v a l l a h S e q u e n c e ( G o l c o n d a A l l o c h t h o n ) ( P e r m i a n t o M Tcir? Pzrm? Tog? Pzrm? Pzlc? plagioclase, sanidine, and biotite. Sanidine Ar/ Ar age is 30.48 ± 0.07 Ma. 0 Tcic? 0 Equivalent to tuff of Sutcliffe in western Nevada (Henry et al., 2004; Faulds Mississippian)—Argillite, chert, sand, and siltstone mapped by Moore et al. et al., 2005). (2005) in the southwestern part of the map area. Tcs Post-caldera sedimentary rocks (Oligocene)—Platy to poorly bedded, pale Pzo Antler Overlap Assemblage (Permian to Pennsylvanian)—Rocks deposited in Redrock Canyon pluton Carico Lake pluton caldera floor inferred inferred caldera floor gray to greenish weathering, tuffaceous sandstone and siltstone, white finely angular unconformity on the Roberts Mountains Allochthon. Includes from Tog exposure laminated shale, and boulder to pebble conglomerate containing clasts of predominantly clastic rocks of the Permian Horseshoe Basin Sequence porphyritic andesite to 60 cm in diameter and some Paleozoic rocks. Present (Raucheboeuf et al., 2004) and the Pennsylvanian and Permian Cedars Sequence within the Caetano caldera where they overlie Caetano Tuff. Probably (Moore et al., 2005). deposited in lacustrine, fluvial and (locally) alluvial fan settings. Pzrm Roberts Mountains Allochthon (Devonian to Ordovician)—Argillite, chert, Reese River Valley T Elephant Head Carico Lake Valley Tub Spring Caetano Ranch Mt. Caetano Grass Valley Cortez Range C L C’ quartzite, sandstone, greenstone, and minor limestone. Includes rocks assigned to F

K S T? T the Valmy Formation, Vinini Formation, Elder Sandstone, and Slaven Chert 3 E Tcs T FL FL LT 3 E ? O Tbm Qaf S H F T? S NC Z (Gilluly and Gates, 1965; Gilluly and Masursky, 1965). R LT N L PA Qaf FLT RA E C F E F Y E O Qaf T E K IN Tad N Qal R Pzlc S N C M TA O L o w e r p l a t e o f R o b e r t s M o u n t a i n s A l l o c h t h o n ( D e v o n i a n t o Qaf Qal/Qp O O Tcu E AE Pzrm C kilometers Qaf S T R AB C �� S S Y Tcu �� EXPLANATION O Ts? I s 2 2 R T Tcc Y Tbm TO �� Cambrian)—Limestone, dolomite, quartzite, and shale. Includes rocks assigned A L E �� M D R Tcl �� E Tcc F G ��s Tog D �� C Pzlc �� to the Wenban Limestone, Roberts Mountains Formation, Hanson Creek E EA C Tcl Tcl Ts? ��s Pzrm H H A Tcl Pzo faulted Tcs/Tad? T T B Tcl Tcu Ts Tcl Formation, Eureka Quartzite, and Hamburg Dolomite (Gilluly and Gates, 1965;

kilometers Tcc N I ? 1 A N Tcl Pzrm? 1 H Contact—Solid where observed in the field by the authors. P Gilluly and Masursky, 1965). E F L L Dashed where interpreted from air photos or other E T Pzlc? ROBERTS MTN THRUST Pzo? Tad? published maps. 0 0 Tcu? 27 REFERENCES Upper Caetano considered too thick Normal Fault—Ball and bar on downthrown side. Arrow and probably repreated by unmapped fault(s) caldera floor exposed indicates dip and dip direction. Solid where observed ?1 km south of D–D’ Bingler, E.C., 1978, Abandonment of the name Hartford Hill Rhyolite Tuff and adoption of new formation names for middle (see Colgan et al., 2008) in the field by the authors. Dashed where interpreted Tertiary ash-flow tuffs in the Carson City-Silver City area, Nevada: Nevada Bureau of Mines and Geology Bulletin from air photos or other published maps. Dotted 1457-D, 19 p. where concealed by alluvium. Colgan, J.P., John, D.A., and Henry, C.D., 2008, Large-magnitude Miocene extension of the Eocene Caetano caldera, Shoshone and Toiyabe Ranges, Nevada: Geosphere, doi: 10.1130/GES00115.1. T L S Deino, A.L., 1989, Single crystal 40Ar/39Ar dating as an aid in correlation of ash flows: Examples from the Chimney F T l l l l l l l l The Cedars T O Stone Cabiin Basin Carico Lake Valley Red Mountain Wood Spring Canyon Bald Mountain Grass Valley Cortez Range K L Caldera Margin—Tick marks toward caldera interior. Solid Springs/New Pass Tuffs and the Nine Hill/Bates Mountain Tuffs of California and Nevada: New Mexico Bureau of Mines D F N D’ E S E R E where observed in the field by the authors. Dashed and Mineral Resources, Continental Magmatism Abstracts Bulletin 131, p. 70. A T R D C L LT T 3 3 C A F F L Faulds, J.E., Henry, C.D., and dePolo, C.M., 2003, Preliminary geologic map of the Tule Peak Quadrangle, Washoe County, E N E F where interpreted from air photos or other published S C B O IN E I Qaf Y M Z Nevada: Nevada Bureau of Mines and Geology Open-File Report 03-10, 1:24,000. S H N Qaf AN Tbm BE Qaf Qaf E O Qaf A Qal T maps. Dotted where concealed by alluvium. T F Qal C IY R Gilluly, J., and Gates, O., 1965, Tectonic and igneous geology of the northern Shoshone Range, Nevada: U.S. Geological Pzh Y Tct Tog kilometers M L R TO O 2 T D C 2 Survey Professional Paper 465, 153 p., scale 1:31,680. Tad �� s��s��s��s Gilluly, J., and Masursky, H., 1965, Geology of the Cortez quadrangle, Nevada: U.S. Geological Survey Bulletin 1175, scale Ts Ts s�� Pzrm; structure unknown Thrust Fault—Teeth on upper plate. Solid where observed in the Pzrm Pzrm �� Pzo Pzrm Tct s� Pzrm 1:62,500. Tad Pzrm Tct �� Pzo? Pzlc? �� Buried Ts? field by the authors. Dashed where interpreted from Gromme, C.S., McKee, E.H., and Blake, M.C., Jr., 1972, Paleomagnetic correlations and potassium-argon dating of middle kilometers 1 Tad?/Tct? 1 Ts? air photos or other published maps. Dotted where Tertiary ash-flow sheets in the eastern Great Basin, Nevada and Utah: Geological Society of America Bulletin, v. 83, p. concealed by alluvium. 1619–1638. Henry, C.D., Faulds, J.E., dePolo, C.M., and Davis, D.A., 2004, Geology of the Dogskin Mountain Quadrangle, northern 0 0 7 Walker Lane, Nevada: Nevada Bureau of Mines and Geology Map 148, scale 1:24,000, 13 p. text. Strike and dip of inclined bedding John, D.A., Henry, C.D., and Colgan, J.P., 2008, Magmatic and tectonic evolution of the Caetano caldera, north-central Nevada: A tilted mid-Tertiary eruptive center and source of the Caetano Tuff: Geosphere, doi: 10.1130/GES00116.1. Inferred structure beneath Carico Lake Valley McKee, E.H., 1968, Geologic map of the Spencer Hot Springs Quadrangle, Lander and Eureka Counties, Nevada: U.S. Geological Survey Geologic Quadrangle Map GQ-770. (see Colgan et al., 2008) 33 Strike and dip of compaction foliation in ash-flow tuff McKee, E.H., and Conrad, J.E., 1987, Geologic map of the Desatoya Mountains Wilderness Study Area, Churchill and Lander counties, Nevada: U.S. Geological Survey Miscellaneous Field Studies Map MF-1944, scale 1:62,500. McKee, E.H., and Stewart, J.H., 1969, Geologic map of The Cedars [15'] quadrangle, Lander County, Nevada: U.S. 00DJ34 40Ar/39Ar sample locality Geological Survey Open-File Report 69-268, scale 1:62,500. Moore, T.E., O'Sullivan, P.B., Murchey, B.L., Moring, B.C., Harris, A.G., Blodgett, R.B., and Fleck, R.J., 2005, Geologic map of The Cedars quadrangle, southern Shoshone Range, Nevada: Window to the world: Reno, Nevada, Geological Society of Nevada Symposium Proceedings, May 14-18, p. 67. DC99 40 39 334m Ar/ Ar sample locality from drill hole—Depth in meters. Mortensen, J.K., Thompson, J.F.H., and Tosdal, R.M., 2000, U-Pb age constraints on magmatism and mineralization in the northern Great Basin, Nevada, in Cluer, J.K., Price, J.G., Struhsacker, E.M., Hardyman, R.F., and Morris, C.L., eds., GEOLOGIC MAP AND CROSS-SECTIONS OF THE CAETANO CALDERA, LANDER COUNTY, NEVADA Geology and ore deposits 2000: The Great Basin and beyond: Reno, Nevada, Geological Society of Nevada Symposium CT101 Proceedings, May 15-18, p. 419-438. Tephrachronology sample locality Racheboeuf, P.R., Moore, T.E., and Boldgett, R.B., 2004, A new species of Dyoros (brachiopoda, chonetoidea) from Nevada (United States) and stratigraphic implication for the Pennsylvanian and Permian Antler overlap assemblage: Geobios, v. 37, p. 382-394. CT107 40 39 Roberts, R.J., Montgomery, K.M., and Lehner, R.E., 1967, Geology and mineral resources of Eureka County, Nevada: Nevada By Ar/ Ar and tephrachronology sample locality Bureau of Mines and Geology Bulletin 64, 164 p., scale 1:250,000. Sargent, K.A., and McKee, E.H., 1969, The Bates Mountan Tuff in northern Nye County, Nevada: U.S. Geological Survey Joseph P. Colgan, Christopher D. Henry, and David A. John Bulletin, v. 1294-E, 12 p. Stewart, J.H., and McKee, E.H., 1968, Geologic map of the Mount Callaghan Quadrangle, Lander County, Nevada: U.S. Mineral deposit Geological Survey Geologic Quadrangle Map GQ-730, 1:62,500. Stewart, J.H., and McKee, E.H., 1969, Geology of the Carico Lake quadrangle, Lander County, Nevada: U.S. Geological Survey Open-File Report 69-268, scale 1:62,500. 2008 Extent of detailed geologic map—Figure numbers correspond to Stewart, J.H., and McKee, E.H., 1977, Geology and mineral deposits of Lander County, Nevada: Nevada Bureau of Mines and Geology Bulletin 88, 114 p., scale 1:250,000. Geologic Map and Cross Sections of the Caetano Caldera, Lander County, Nevada Figure 12 1:24,000-scale geologic maps in John et al. (2008). Colgan et al. Wells, J.D., Elliott, J.E., and Obradovich, J.D., 1971, Age of the igneous rocks associated with ore deposits, Cortez-Buckhorn Plate 1 area, Nevada: U.S. Geological Survey Professional Paper 750-C, p. C127-C135. Supplement to Geosphere, v. 4, no. 1 (February 2008)