U.S. Department of the Interior

U.S. Geological Survey

Data Series 916

Geochronology of Cenozoic Rocks in the Bodie Hills, 

California and Nevada
Cover. Steeply flow-banded lava dome, trachyandesite of Willow Springs, east of Warm Spring in the Bodie Hills, California.
Geochronology of Cenozoic Rocks in the 

Bodie Hills, California and Nevada

By Robert J. Fleck, Edward A. du Bray, David A. John, Peter G. Vikre, Michael A. 

Cosca, Lawrence W. Snee, and Stephen E. Box

Data Series 916

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

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Suggested citation:

Fleck, R.J., du Bray, E.A., John, D.A., Vikre, P.G., Cosca, M.A., Snee, L.W., and Box, S.E., 2015, Geochronology of 

Cenozoic rocks in the Bodie Hills, California and Nevada: U.S. Geological Survey Data Series 916, 26 p.,

http://dx.doi.org/10.3133/ds916.

ISSN 2327-638X (online)
iii

Appendixes

[Available for download at http://pubs.usgs.gov/ds/916/]

1. Analytical results of CO2-laser-fusion and resistance-furnace incremental heating 40Ar/39Ar experiments (Menlo Park lab) for samples of the Bodie Hills volcanic field

2. Analytical results of furnace incremental heating 40Ar/39Ar experiments (Denver lab, 

Snee) for samples of the Bodie Hills volcanic field

3. Analytical results of CO2-laser incremental heating 40Ar/39Ar experiments (Denver lab, 

Cosca) for samples of the Bodie Hills volcanic field

Contents

Introduction.....................................................................................................................................................1

40Ar/39Ar Analytical Methods ........................................................................................................................8

K-Ar Analytical Methods ............................................................................................................................13

Data................................................................................................................................................................ 13

Acknowledgments.......................................................................................................................................13

References Cited..........................................................................................................................................25

Figures

1. Map showing location of and major physiographic features near the Bodie Hills 

volcanic field ..........................................................................................................................7

2. Locations of samples with 40Ar/39Ar age determinations shown on a simplified 

geologic map of the Bodie Hills volcanic field, California and Nevada .......................9

3. Locations of samples with K-Ar age determinations shown on a simplified geologic 

map of the Bodie Hills volcanic field, California and Nevada......................................11

Tables

1. Map location numbers for 40Ar/39Ar geochronology samples from the Bodie Hills 

volcanic field, California and Nevada ................................................................................2

2. Map location numbers for K-Ar geochronology samples from the Bodie Hills volcanic 

field, California and Nevada ................................................................................................5

3. Summary compilation of geochronologic data for samples of the Bodie Hills volcanic 

field, California and Nevada ..............................................................................................14

Introduction

The purpose of this report is to present geochronologic data 

for unaltered volcanic rocks, hydrothermally altered volcanic 

rocks, and mineral deposits of the Miocene Bodie Hills and 

Pliocene to Pleistocene Aurora volcanic fields of east-central 

California and west-central Nevada. Most of the data presented 

here were derived from samples collected between 2000–13, 

but some of the geochronologic data, compiled from a variety of 

sources, pertain to samples collected during prior investigations. 

New data presented here (tables 1 and 2; Appendixes 1–3) were 

acquired in three U.S. Geological Survey (USGS) 40Ar/39Ar labs 

by three different geochronologists: Robert J. Fleck (Menlo 

Park, CA), Lawrence W. Snee (Denver, CO), and Michael A. 

Cosca (Denver, CO). Analytical methods and data derived from 

each of these labs are presented separately.

The middle to late Miocene Bodie Hills volcanic field 

(BHVF) is a large (>700 km2), long-lived (~9 million years 

[m.y.]), episodic eruptive complex (John and others, 2012) in 

the southern segment of the ancestral Cascades arc (du Bray 

and others, written commun., 2015) north of Mono Lake and 

east of Bridgeport, California (fig. 1). The field is near the west 

edge of the Walker Lane and the northwest edge of the Mina 

deflection where structures related to these shear zones may 

have localized magmatism. The Walker Lane (fig. 1) is a broad, 

northwest-striking zone of right-lateral shear that accommodates 

right-lateral motion between the Pacific and North America 

plates; the Mina deflection constitutes a 60-km-long right step 

in the Walker Lane (Faulds and Henry, 2008; Oldow, 1992, 

2003; Stewart, 1988). The Bodie Hills volcanic field includes at 

least 31 volcanic rock units erupted from 21 significant volcanic 

eruptive centers.

Four trachyandesite stratovolcanoes developed along 

the margins of the volcanic field and numerous silicic 

trachyandesite to rhyolite flow dome complexes erupted 

more centrally. Volcanism in the Bodie Hills volcanic field 

peaked at two periods, ~15.0 to 12.6 million years before 

present (Ma) and ~9.9 to 8.0 Ma, which were dominated 

by emplacement of large stratovolcanoes and large silicic 

trachyandesite-dacite lava domes, respectively. A final period 

of small-volume silicic dome emplacement began in the 

western part of the volcanic field at ~6 Ma and culminated at 

~5.5 Ma (John and others, 2012).

Compositions of Bodie Hills volcanic rocks vary from 

~50 to 78 weight percent SiO2, although rocks with <55 

weight percent SiO2 are rare. Rock compositions form a 

high-potassium (K) calc-alkaline series with pronounced 

negative titanium-phosphorus-niobium-tantalum anomalies 

and high barium/niobium, barium/tantalum, and lanthanum/

niobium typical of subduction-related continental margin 

arcs (Gill, 1981). Most rocks are porphyritic and commonly 

contain 15–35 volume percent phenocrysts of plagioclase, 

pyroxene, and hornblende±biotite. Although the oldest 

eruptive centers have the most mafic compositions, erupted 

rock compositions oscillated between mafic and intermediate 

to felsic compositions through time. Following a brief hiatus 

in volcanism, post subduction rocks of the ~3.9- to 0.1-Ma, 

bimodal, high-K Aurora volcanic field were erupted onto 

the Bodie Hills volcanic field. Volcanism in the Bodie Hills 

volcanic field persisted until 8 Ma without apparent changes 

in rock composition or style of eruption despite the transition 

from subduction of the Farallon plate beneath the west coast 

of North America to establishment of a transform plate 

margin at ~10 Ma (John and others, 2012).

The eastern and southeastern parts of the Bodie Hills 

volcanic field and Miocene sedimentary rocks on the southern 

edge of Fletcher Valley are unconformably overlain by Pliocene 

to late Pleistocene (~3.9 to 0.1 Ma) rocks of the Aurora volcanic 

field (Gilbert and others, 1968; Al-Rawi, 1969; Chesterman and 

Gray, 1975; Kleinhampl and others, 1975; Lange and others, 

1993; Lange and Carmichael, 1996; Kingdon and others 2013). 

The field covers ~325 km2 and includes many well-preserved 

volcanic centers. These centers consist of monogenetic lava and 

cinder cones, valley-filling lava flows, shield volcanoes, and 

lava domes. Compositions of the Aurora volcanic field rocks are 

bimodally distributed and consist principally of trachyandesite 

and trachydacite to high-silica rhyolite.

Numerous hydrothermal systems were operative in the 

Bodie Hills during the Miocene (Vikre and others, in press). 

Structurally focused hydrothermal systems formed large 

epithermal gold-silver vein deposits in the Bodie and Aurora 

mining districts that are temporally and spatially related to 

intermediate- to silicic-composition dome complexes (John 

and others, 2012).

Geochronology of Cenozoic Rocks in the Bodie Hills, 

California and Nevada

By Robert J. Fleck, Edward A. du Bray, David A. John, Peter G. Vikre, Michael A. Cosca, Lawrence W. Snee, 

and Stephen E. Box
2 Geochronology of Cenozoic Rocks in the Bodie Hills, California and Nevada

Map 

location 

number

Sample number Latitude Longitude Unit; alteration zone; or mining district Appendix 

number

1 098-12B 38.38762 −119.18139 Trachyandesite of Masonic 1

2 098-12A 38.35923 −119.19917 Eureka Valley Tuff 1

3 MAS10-72 38.40189 −119.13718 Trachyandesite of Masonic Gulch 1

4 RW08-1 38.41123 −119.12414 Alteration: Red Wash-East Walker River alteration zone 1

5 MAS10-73 38.39643 −119.13470 Trachyandesite of Masonic Gulch 1

6 098-12D 38.39951 −119.11939 Trachyandesite of Masonic 1

7 MAS10-55 38.41419 −119.10259 Alteration: Red Wash-East Walker River alteration zone 1

8 098-12E 38.39143 −119.12397 Trachyandesite of Masonic Gulch 1

9 MAS10-75 38.39169 −119.11549 Trachyandesite of Masonic Gulch 1

10 07-BA-38 38.36049 −119.14502 Andesite of Lakeview Spring 1

11 MAS07-1A 38.34992 −119.14832 Alteration: Masonic mining district, Chemung mine 1

12 MAS12-10 #1 38.33716 −119.16013 Alteration: Masonic mining district, Success mine 1

13 MAS12-10 #2 38.33716 −119.16013 Alteration: Masonic mining district, Success mine 1

14 MAS10-76 38.38169 −119.11534 Trachyandesite of Masonic, plug 1

15 MAS09-1A 38.35847 −119.13824 Alteration: Masonic mining district, Red Rock mine 1

16 12-BA-20 38.33410 −119.15949 Trachyandesite of Masonic 1

17 MAS09-1 38.35783 −119.13268 Alteration: Masonic mining district, Red Rock mine 1

18 098-12F 38.37542 −119.11418 Trachyandesite of Masonic 1

19 MAS07-3 38.35968 −119.12682 Alteration: Masonic mining district, Sarita mine 1

20 07-BA-40 38.36544 −119.11607 Alteration: Masonic mining district, Pittsburg-Liberty mine 1

21 088-22A 38.36731 −119.10727 Alteration: Masonic mining district, Maybelle mine 1

22 10-BA-15 38.34130 −119.11570 Trachyandesite of Masonic 1

23 10-BA-13 38.35154 −119.10419 Trachyandesite of Masonic 1

24 088-22B 38.37937 −119.07802 Trachyandesite of Masonic 1

25 MAS11-2B 38.36064 −119.08681 Alteration: Masonic mining district, Perini mine 1

26 MAS11-1 38.36041 −119.08369 Alteration: Masonic mining district, Perini mine 1

27 11-BA-40 38.41155 −119.01907 Trachydacite of Rough Creek 1

28 09-BA-7 38.33786 −119.08727 Trachyandesite of Masonic 1

29 12-BA-9 38.33679 −119.07378 Trachydacite of East Canyon 1

30 08SB038 38.40828 −118.97383 Trachyandesite of Del Monte 1

31 10-BA-29 38.36466 −119.01452 Trachydacite of Rough Creek 1

32 10-BA-9 38.35278 −119.02068 Trachyandesite of Masonic, plug 1

33 6-289-2/45/DD72 38.3729 −118.9993 Eureka Valley Tuff 2

34 10-BA-62 38.36327 −119.00635 Tephra in sedimentary rocks of Fletcher Valley 1

35 10-BA-6 38.33375 −119.02470 Trachydacite of Rough Creek 1

36 10-BA-5 38.33945 −118.99699 Pyroxene rhyolite 1

37 11-BA-41 38.35057 −118.98085 Trachyandesite of Del Monte 1

38 11-BA-32 38.33637 −118.97804 Rhyolite of Bodie Creek 1

39 08SB032 38.34561 −118.95580 Unwelded tuff, Fletcher Basin 1

40 5-152-9/50/72 38.3548 −118.9261 Hornblende trachydacite 2

41 5-152-9/56/72 38.3548 −118.9261 Hornblende trachydacite 2

42 12-BA-3 38.34974 −118.84729 Trachyandesite of Mud Spring Canyon 3

43 10-BA-69 38.30537 −119.13652 Trachyandesite of Masonic 1

44 098-13D 38.27655 −119.16062 Trachyandesite of Clark Canyon 1

45 09-BA-43 38.26358 −119.16825 Trachyandesite of Clark Canyon 1

46 203195 38.2823 −119.1479 Basaltic andesite of Locomotive Point 3

47 09-BA-47 38.28409 −119.13821 Rhyolite of Bodie Hills 1

48 09-BA-42 38.27001 −119.14887 Rhyolite of Big Alkali 1

Table 1. Map location numbers for 40Ar/39Ar geochronology samples from the Bodie Hills volcanic field, California and Nevada.
Introduction 3

Map 

location 

number

Sample number Latitude Longitude Unit; alteration zone; or mining district Appendix 

number

49 088-21A 38.27363 −119.13962 Trachyandesite of Aurora Canyon 1

50 098-13B 38.26802 −119.13218 Rhyolite of Bodie Hills 1

51 MC-12-20 38.2701 −119.1261 Hornblende trachyandesite plug 3

52 088-23F 38.31068 −119.11700 Trachyandesite of Masonic 1

53 088-23D 38.28113 −119.10206 Trachyandesite of Aurora Canyon 1

54 088-23A 38.27852 −119.10021 Trachyandesite of Aurora Canyon 1

55 088-23B 38.27831 −119.09908 Trachyandesite of Aurora Canyon 1

56 08-BA-62 38.32006 −119.04943 Trachyandesite of Masonic 1

57 088-25A 38.27322 −119.09077 Trachyandesite of Aurora Canyon 1

58 09-BA-1 38.31968 −119.04411 Trachyandesite of Cow Camp Creek 3

59 077-8C 38.27145 −119.07783 Trachyandesite of Aurora Canyon 1

60 077-8B 38.28334 −119.05617 Trachydacite intrusion 1

61 088-21B 38.26418 −119.07504 Trachydacite of Potato Peak 1

62 09-BA-35 38.29048 −119.04642 Trachydacite intrusion 1

63 09-BA-49 38.26389 −119.04748 Eureka Valley Tuff 1

64 11-BA-60 38.32693 −118.97204 Rhyolite of Bodie Creek 1

65 08-BA-65 38.31071 −118.97808 Rhyolite of Bald Peak 1

66 10-BA-67 38.26200 −118.98300 Rhyolite of Bald Peak 1

67 AU-10/61/DD61 38.26 −118.981 Eureka Valley Tuff 2

68 108-11A 38.27826 −118.94807 Rhyolite of Bodie Creek 1

69 077-9B 38.26971 −118.95063 Rhyolite of Bodie Creek 1

70 077-9D 38.28562 −118.92803 Rhyolite of Del Monte Canyon 1

71 AU-6/60/DD61 38.285 −118.928 Rhyolite of Del Monte Canyon 2

72 077-9C 38.27661 −118.93036 Rhyolite of Del Monte Canyon 1

73 SAW11-9 38.29036 −118.91657 Alteration: Sawtooth Ridge alteration zone 1

74 077-9E 38.31905 −118.91003 Trachyandesite of Del Monte 1

75 10-BA-20 38.31679 −118.91129 Rhyolite of Aurora Creek 1

76 10-BA-21 38.30315 −118.89740 Rhyolite of Aurora Creek 1

77 108-10C 38.28052 −118.90623 Trachyandesite of West Brawley Peak 1

78 108-10A 38.27293 −118.91272 Trachyandesite of Aurora 1

79 FA1 38.2931 −118.8914 Alteration: Aurora mining district, adularia in Prospectus vein 2

80 10-BA-27 38.27500 −118.90498 Rhyolite of East Brawley Peak 1

81 AU-2/59/DD61 38.282 −118.896 Aurora mining district, adularia in Del Monte shaft dump 2

82 AU-1/58/DD61 38.266 −118.9 Alteration: Aurora mining district, adularia in Esmeralda vein dump 2

83 00-BA-16 38.2708 −118.8908 Trachyandesite of Aurora 2

84 MC-12-19 38.31952 −118.78154 Trachyandesite of Borealis 3

85 39509-10 38.21532 −119.22755 Dacite of Hot Springs Canyon 1

86 39509-3K 38.20793 −119.22751 Alteration: Cinnabar Canyon-US 395 alteration zone 1

87 088-24B 38.25504 −119.14115 Trachyandesite of Willow Springs 1

88 088-24A 38.25278 −119.13951 Rhyolite of Big Alkali 1

89 PP09-10A1 38.25309 −119.13844 Alteration: Aurora Canyon alteration zone 1

90 098-13A 38.25754 −119.12788 Rhyolite of Big Alkali 1

91 CC09-9D1 38.19869 −119.17050 Alteration: Cinnabar Canyon-US 395 alteration zone 1

92 CC09-9D2 38.19869 −119.17050 Alteration: Cinnabar Canyon-US 395 alteration zone 1

93 088-24C 38.24786 −119.11208 Trachydacite of Potato Peak 1

94 12-BA-1 38.18995 −119.16513 Trachydacite of Cinnabar Canyon 1

95 077-7C 38.19677 −119.15829 Rhyolite of Del Monte Canyon 1

96 08-BA-46 38.24430 −119.10385 Alteration: Potato Peak alteration zone, Alta Pina mine 1

Table 1.—Continued
4 Geochronology of Cenozoic Rocks in the Bodie Hills, California and Nevada

Map 

location 

number

Sample number Latitude Longitude Unit; alteration zone; or mining district Appendix 

number

97 08-BA-50 38.24816 −119.09663 Rhyolite of Bodie Hills 1

98 077-7B 38.19178 −119.15240 Trachyandesite of Willow Springs 1

99 098-13C 38.25072 −119.09223 Trachydacite of Potato Peak 1

100 098-10C 38.24919 −119.09203 Trachydacite of Potato Peak 1

101 088-21D 38.24330 −119.09209 Trachydacite of Potato Peak 1

102 098-10B 38.25135 −119.08382 Rhyolite of Bodie Hills 1

103 088-21C 38.25134 −119.08382 Rhyolite of Bodie Hills 1

104 088-24D 38.22678 −119.10376 Trachydacite of Potato Peak 1

105 088-21E 38.23457 −119.08582 Trachydacite of Potato Peak 1

106 088-24E 38.21809 −119.10188 Trachydacite of Potato Peak 1

107 08-BA-61 38.20769 −119.10175 Trachydacite of Potato Peak 1

108 088-24F 38.20176 −119.08978 Trachyandesite of Willow Springs 1

109 108-12A 38.24252 −119.04825 Trachydacite of Potato Peak 1

110 08-BA-68 38.19323 −119.06835 Trachydacite of Potato Peak 1

111 108-12B 38.23830 −119.00784 Trachydacite of Potato Peak 1

112 08-BA-66 38.18629 −119.05680 Dacite of Silver Hill, debris flow clast 1

113 12-BA-17 38.21961 −119.00019 Alteration: Bodie mining district, vein adularia, west of Bodie Bluff 1

114 077-7F 38.20252 −119.02630 Dacite of Silver Hill 1

115 BOD11-3A 38.21961 −119.00354 Alteration: Bodie mining district, vein adularia, Upper Hobart Tunnel dump 1

116 BOD11-3B 38.21961 −119.00354 Alteration: Bodie mining district, vein adularia, Bodie Bluff 1

117 077-6C 38.21870 −119.00050 Alteration: Bodie mining district, vein adularia, Bodie Bluff 1

118 AU-16/63/DD61 38.215 −119.004 Alteration: Bodie mining district, vein adularia, south of Bodie Bluff 2

119 077-6A 38.21490 −119.00370 Alteration: Bodie mining district, vein adularia, south of Bodie Bluff 1

120 11-BA-22 38.21257 −119.00402 Alteration: Bodie mining district, vein adularia, south of Bodie Bluff 1

121 BOD11-4E 38.21257 −119.00402 Alteration: Bodie mining district, vein adularia, Standard Hill Mine 1

122 11-BA-21 38.20370 −119.00919 Alteration: Bodie mining district, vein adularia, Red Cloud mine 1

123 AU-17/64/DD61 38.215 −118.997 Alteration: Bodie mining district, vein adularia, south of Bodie Bluff 2

124 BOD09-5 38.20424 −119.00755 Alteration: Bodie mining district, vein adularia, Oro mine dump 1

125 11-BA-7G 38.20420 −119.00649 Alteration: Bodie mining district, vein adularia, Silver Hill 1

126 BOD09-3 38.20138 −119.00575 Alteration: Bodie mining district, vein adularia, Red Cloud Mine 1

127 09-BA-28I 38.20151 −119.00360 Alteration or mineralization: Bodie, Red Cloud mine 1

128 AU-18/65/DD61 38.201 −119.004 Alteration or mineralization: Bodie, Red Cloud mine 2

129 09-BA-26 38.20360 −119.00021 Dacite of Silver Hill 1

130 077-7G 38.23439 −118.96671 Trachyandesite of West Brawley Peak 1

131 077-6F 38.18809 −119.00854 Dacite of Silver Hill-Sugarloaf plug 1

132 077-9A 38.22088 −118.97443 Eureka Valley Tuff 1

133 108-12C 38.18925 −118.98343 Dacite of Silver Hill 1

134 108-12E 38.20763 −118.96489 Dacite of Silver Hill 1

135 FA66 38.2375 −118.9008 Alteration: East Brawley Peak alteration zone, vein alunite 2

136 00-BA-26 38.2542 −118.8841 Trachyandesite of Aurora 2

137 AUR10-3 38.23752 −118.89919 Alteration: East Brawley Peak alteration zone, vein alunite 1

138 077-7A 38.17860 −119.19476 Trachyandesite of Willow Springs 1

139 08-BA-51 38.17449 −119.15441 Trachyandesite of Willow Springs 1

140 09-BA-22 38.14302 −119.17974 Trachyandesite of Mt. Biedeman 1

141 09-BA-23 38.12851 −119.17491 Tuff of Jacks Spring 1

142 098-11B 38.12451 −119.17126 Trachydacite of Bridgeport Canyon 1

143 098-11A 38.12239 −119.16954 Tuff of Jacks Spring 1

Table 1.—Continued
Introduction 5

Map 

location 

number

Sample number Latitude Longitude Unit; alteration zone; or mining district Appendix 

number

144 10-BA-46 38.17380 −119.11508 Trachyandesite of Mount Biedeman 1

145 10-BA-66 38.17250 −119.10125 Trachydacite of Potato Peak 1

146 09SB015A 38.12310 −119.14843 Trachyandesite of Mount Biedeman 1

147 098-11E 38.11099 −119.15841 Trachyandesite of Mount Biedeman 1

148 077-7D 38.16719 −119.09983 Rhyolite of Bodie Hills 1

149 09SB020A 38.13230 −119.13277 Trachydacite of Bridgeport Canyon 1

150 108-9A 38.16540 −119.09816 Trachyandesite of Mount Biedeman 1

151 108-12F 38.16336 −119.09918 Trachyandesite of Mount Biedeman 1

152 MC-12-18 38.15575 −119.07825 Trachyandesite of Mount Biedeman 3

153 12-BA-22 38.10151 −119.12400 Trachyandesite of Mount Biedeman 1

154 6-181-12/52/DD72 38.1193 −119.1039 Tuff of Jacks Spring 2

155 6-181-12/53/DD72 38.1193 −119.1039 Tuff of Jacks Spring 2

156 6-215-1/121/72 38.1344 −119.0825 Trachyandesite of Mount Biedeman 2

157 119-20B 38.13452 −119.07613 Trachyandesite of Mount Biedeman, plug 1

158 09-BA-20 38.15662 −119.04741 Rhyolite of Bodie Hills 1

159 10-BA-61 38.14005 −119.01551 Trachyandesite of Mount Biedeman 1

160 108-12D 38.17315 −118.97800 Dacite of Silver Hill 1

Map location 

letter Sample number Latitude Longitude Unit

A 1071 38.175 −118.832 Pyroxene trachyandesite of Cedar Hill

B 469 38.179 −118.826 Pyroxene trachyandesite of Cedar Hill

C 468 38.178 −118.819 Hornblende trachydacite of Cedar Hill

D 466 38.179 −118.821 Pyroxene trachyandesite of Cedar Hill

E 465 38.181 −118.823 Pyroxene trachyandesite of Cedar Hill

F 1069 38.188 −118.850 Hornblende trachydacite of Cedar Hill

G 139 38.209 −118.880 Hornblende trachydacite of Cedar Hill

H 199 38.153 −119.008 Hornblende trachydacite of Cedar Hill

I 144 38.184 −118.894 Trachyandesite of Cedar Hill

J 1092A 38.255 −118.810 Rhyolite of Spring Peak

K 25 38.261 −118.973 Basaltic trachyandesite of Beauty Peak

L 120 38.240 −118.829 Trachyandesite of Mount Hicks

M 15 38.194 −118.961 Dacite of Silver Hill

N 414 38.177 −119.193 Trachyandesite of Willow Springs

O 406 38.234 −119.085 Trachydacite of Potato Peak

P 507 38.154 −119.089 Rhyolite of Bodie Hills

Q 459 38.097 −119.064 Eureka Valley Tuff

R 31 38.247 −118.990 Eureka Valley Tuff

S 27 38.247 −118.990 Eureka Valley Tuff

T W24 38.102 −119.066 Eureka Valley Tuff

U W25 38.131 −119.181 Eureka Valley Tuff

V 547 38.255 −118.948 Trachyandesite of West Brawley Peak

W USGS(M)-711-67 38.2894 −118.9092 Trachyandesite of Aurora

Table 2. Map location numbers for K-Ar geochronology samples from the Bodie Hills volcanic field, California and Nevada.

Table 1.—Continued
6 Geochronology of Cenozoic Rocks in the Bodie Hills, California and Nevada

Map location 

letter Sample number Latitude Longitude Unit

X USGS(M)-668-G10 38.2403 −118.8917 Trachyandesite of Aurora

Y USGS(M)-711-8 38.2681 −118.8917 Trachyandesite of Aurora

Z USGS(M)-712-1 38.2522 −118.9175 Trachyandesite of West Brawley Peak

AA USGS(M)-710-7 38.2822 −118.9281 Rhyolite of Del Monte Canyon

BB USGS(M)-NTS10B 38.3021 −118.8967 Rhyolite of Aurora Creek

CC USGS(M)-Baghdad 38.2786 −118.9467 Rhyolite of Bodie Creek

DD USGS(M)-670G4 38.2811 −118.8842 Rhyolite of Martinez Hill

EE USGS(M)-610-1B 38.2778 −118.8586 Rhyodacite of Aurora Peak

FF USGS(M)-672-2 38.3128 −118.8825 Trachyandesite of Aurora Crater

GG USGS(M)-611-5 38.2578 −118.8558 Trachyandesite south of Aurora Peak

HH BH31 38.194 −119.008 Dacite of Silver Hill, plug

II 5 38.0978 −119.1475 Trachyandesite of Sinnamon Cut

JJ 6 38.1256 −119.1697 Basaltic trachyandesite of Rancheria

KK 37 38.287 −118.887 Alteration or mineralization: Trachyandesite of Aurora

LL CH8Z1 38.288 −118.882 Trachyandesite of Aurora

MM USGS(M)-7346-1 38.215 −119.004 Alteration or mineralization: Bodie

NN USGS(M)-RCD1B 38.201 −119.005 Alteration or mineralization: Bodie

OO USGS(M)-B270 38.216 −119.004 Alteration or mineralization: Bodie

PP USGS(M)-BH15 38.201 −119.003 Dacite of Silver Hill

QQ USGS(M)-S1 38.188 −119.008 Dacite of Silver Hill

RR USGS(M)-B271 38.215 −119.003 Dacite of Silver Hill

SS USGS(M)-856-8 38.214 −119.004 Dacite of Silver Hill

TT USGS(M)-BH17 38.193 −119.012 Dacite of Silver Hill

UU USGS(M)-7346-3 38.216 −118.981 Hornblende trachydacite of Cedar Hill

VV USGS(M)-BH32 38.200 −118.995 Dacite of Silver Hill

WW USGS(M)-856-32 38.209 −118.997 Dacite of Silver Hill

XX USGS(M)-856-10 38.205 −119.028 Trachydacite of Potato Peak

YY USGS(M)-BH26 38.194 −119.003 Dacite of Silver Hill

ZZ USGS(M)-BH16 38.200 −118.999 Dacite of Silver Hill

AAA USGS(M)-854-1 38.182 −119.003 Dacite of Silver Hill

BBB USGS(M)-BH29 38.196 −118.958 Dacite of Silver Hill

CCC USGS(M)-BM2 38.221 −119.057 Trachydacite of Potato Peak

DDD USGS(M)-BH9 38.157 −119.116 Trachyandesite of Mount Biedeman

EEE USGS(M)-MTB1 38.146 −119.073 Trachyandesite of Mount Biedeman

FFF USGS(M)-BH27 38.140 −119.056 Rhyolite of Bodie Hills

GGG USGS(M)-BH19A 38.222 −119.172 Trachyandesite of Willow Springs

HHH USGS(M)-BH6 38.1655 −119.1512 Rhyolite of Big Alkali

III USGS(M)-BH20 38.220 −119.149 Rhyolite of Big Alkali

JJJ 23 38.156 −118.860 Trachybasalt of Cedar Hill

KKK 158 38.368 −118.812 Trachyandesite of Mud Spring

LLL 160 38.357 −118.896 Trachyandesite of Aurora Crater

MMM KA2362 38.4408 −118.9725 Hornblende andesite

NNN KA2364 38.4408 −118.9725 Hornblende andesite

OOO KA2368 38.4408 −118.9725 Hornblende andesite

PPP KA2379R 38.4133 −118.9417 Aldrich Station Formation, tuff

QQQ 742-45 38.0869 −119.1431 Basaltic trachyandesite of Rancheria

RRR EL-KA-2 38.3047 −118.7799 Andesite

Table 2.—Continued
Introduction 

7

Reno

Hawthorne

Tonopah

Bridgeport

CALIFORNIA

NEVADA

Maparea

WALKER LANE

BASIN

AND

RANGE

BASIN

AND

RANGE

SIERRA

NEVADA

MINA

DEFLECTION

BH

NEVADA CALIFORNIA

Lake

Tahoe

Pyramid

Lake

Walker

Lake

Mono

Lake

Little

Walker

Caldera

Long

Valley

Caldera

figure 2

SIERRA NEVADA

40°38°

120° 118°

0 25 50 75 KILOMETERS0 25 50 MILES

Figure 1. Map showing location of and major physiographic features near the Bodie Hills volcanic field (BH). Mina deflection (vertical red line pattern) and outline of the Walker Lane (red shaded area) modified from Faulds and Henry (2008), Busby (2013), and Carlson and others (2013). Also see John and others, 2015.
8 Geochronology of Cenozoic Rocks in the Bodie Hills, California and Nevada

40Ar/39Ar Analytical Methods

New 40Ar/39Ar age determinations provide temporal 

constraints on volcanic and hydrothermal activity in the 

Bodie Hills (figs. 2 and 3). Volcanic rocks were dated 

using either separates of one or more phenocryst mineral 

(plagioclase, sanidine, biotite, hornblende) or whole-rock 

aggregates. Ages of hydrothermal alteration were determined 

using separates of alunite, K-feldspar, or adularia. Where 

practical, multiple minerals from individual samples were 

dated to provide abundant confirmation of the results, but 

also to evaluate and document argon systematics of the 

different mineral phases nucleated under various magmatic 

and hydrothermal conditions.

Samples collected for 40Ar/39Ar analysis were crushed 

and sieved to sizes appropriate for preparation of high-purity

separates. Standard magnetic and heavy-liquid separation 

techniques were used to make mineral separations. Wholerock samples were prepared by crushing and isolating 

~1 mm3 rock fragments from fresh rock that was free of 

obvious alteration and xenocrysts. Analyzed samples were 

washed in deionized water. In many cases, final separates 

were prepared by hand picking individual crystals.

Samples whose ages were determined at the U.S. 

Geological Survey 40Ar/39Ar lab in Menlo Park, CA 

(Appendix 1) were irradiated in the U.S. Geological 

Survey TRIGA Reactor Facility in Denver, Colorado; 

irradiation times were between 10 and 16 hours, although 

biotite, plagioclase, and sanidine from the rhyolite of 

Bodie Hills (map location number 102) were also analyzed 

in both 2-hour and 24-hour irradiations. Plagioclase, 

biotite, hornblende, and alunite ages were obtained using 

incremental-heating analysis, that is, incremental extraction 

of argon at progressively higher temperatures until all 

gas is released. Incremental heating analyses utilized a 

low-blank, tantalum and molybdenum, resistance-heated 

furnace. During heating, all argon gas was released in 8–15 

temperature-controlled increments or steps; a few hornblende 

and potassium feldspar experiments required as many 

as 18 steps. Ages from incremental-heating experiments 

were determined by evaluating 40Ar/39Ar age spectra and 

isochron diagrams. Data for many of the individual sample 

ages constitute 40Ar/39Ar plateaus, defined as the weighted 

mean age of contiguous gas fractions representing >50% of 

the 39Ar released for which no difference can be detected 

between the ages of any two fractions at the 95% level of 

confidence (Fleck and others, 1977). Where no plateau was 

defined, either the 40Ar/39Ar isochron age or the integrated 

age of all increments was defined as the age of the sample.

Most sanidine and biotite ages determined at the U.S. 

Geological Survey 40Ar/39Ar lab in Menlo Park, CA were 

obtained by laser-fusion analysis, whereby grains were fused 

with a CO2 laser in a single heating step (Appendix 1). One or 

several grains were used in each analysis, depending on grain 

size. In all cases, a minimum number of grains were used to 

permit recognition and elimination of most xenocrystic or 

detrital contamination through identification of outliers. The 

reported age for laser-fusion analyses represents the weighted 

mean of the replicate analyses, with the inverse variance of 

propagated, within-run (internal) errors of each used as its 

weighting factor (Taylor, 1982). Sanidine from the Taylor 

Creek Rhyolite (TCR-2) was used for calculation of neutron 

flux in all irradiations up to IRR290 (Appendix 1). Subsequent 

irradiations (higher IRR numbers in Appendix 1) used Bodie 

Hills sanidine (098-10B), calibrated to TCR-2, as the flux 

monitor. Regardless of the monitor mineral used, all ages in 

Appendix 1 are reported relative to an age of 28.02 Ma for the 

Fish Canyon Tuff sanidine standard (Renne and others, 1998) 

with uncertainties estimated at the one-sigma level, unless 

stated. Decay and abundance constants are those recommended 

by Steiger and Jäger (1977). Ages were calculated assuming a 

40Ar/36Ar ratio of trapped argon equal to the atmospheric value 

of 295.5.

The 40Ar/39Ar ages reported in Appendix 2, determined in 

the U.S. Geological Survey 40Ar/39Ar lab in Denver, Colorado 

by L.W. Snee, are based on analyses of biotite, hornblende, 

plagioclase, or sanidine phenocrysts; hydrothermal K-feldspar, 

adularia, or alunite; and one whole rock analysis (Appendix 

2). Analyzed materials were packaged in aluminum foil and 

stacked in quartz glass vials with monitor minerals placed 

between every second sample and at the top and bottom of 

each vial. Samples were irradiated in the U.S. Geological 

Survey’s TRIGA reactor in Denver, Colorado, in irradiation 

packages DD61, DD72, and DD78. Irradiated samples were 

heated in temperature steps in a double-vacuum furnace, and 

the released gasses were cleaned according to procedures 

described by Snee (2002). Argon isotopic total abundances 

(

40ArT

, 39ArT, 38ArT, 37ArT, and 36ArT) were measured on a 

MAP 215 mass spectrometer on a Faraday collector in volts 

to five decimal places. Corrected abundances for 40ArR

(radiogenic 40Ar), 40ArK (irradiation-produced K-derived 

40Ar), 40ArI (initial 40Ar), 39ArK (irradiation-produced 

K-derived 39Ar), 38ArCl (irradiation-produced Cl-derived 

38Ar), 37ArCa (irradiation produced Ca-derived 37Ar, and 

36ArI (initial 36Ar) are in volts. All estimated uncertainties in 

measured voltages are reported in Appendix 2 at one sigma. 

Voltages may be converted to moles using 1.160×10−12

moles argon per volt signal. The “F” value (40ArR/

39ArK) 

for each temperature step was directly calculated from 

40ArR divided by 39ArK. K/Ca was calculated from the 

expression K/Ca=0.5(39ArK/

37ArCa). All isotopic abundances 

in Appendix 2 have been corrected for mass discrimination.

Mass discrimination was determined by calculating the 

40Ar/36Ar ratio of aliquots of atmospheric argon pipetted 

from a fixed pipette on the extraction line; the ratio during 

these experiments was 298.9, which was corrected to 

295.5 to account for mass discrimination. Final isotopic 

abundances were corrected for all interfering isotopes of 

argon including atmospheric argon. 37Ar and 39Ar, which 

are produced during irradiation, are radioactive and their 
Acknowledgments 9

abundances were corrected for radioactive decay. Abundances 

of interfering isotopes from K and Ca were calculated from 

reactor production ratios determined by irradiating and 

analyzing pure CaF2 and K2SO4; the K2SO4 was degassed in 

a vacuum furnace prior to irradiation to release extraneous 

argon. Corrections for Cl-derived 36Ar were determined using 

the method of Roddick (1983). Production ratios for these 

experiments are documented by Snee (2002). Apparent ages of 

each fraction include the error in J value (0.1 percent), which 

was calculated from the reproducibility of splits of the argon 

from several standards. The standards for this experiment were 

hornblende MMhb-1, using an age of 523.1±2.6 Ma (Samson 

and Alexander, 1987; Renne and others, 1998), and sanidine 

FCT1, using an age of 27.84 Ma, as measured in the Denver 

Argon Laboratory against MMhb-1 (Snee, 2002). Apparent 

ages were calculated using decay constants of Steiger and 

Jäger (1977). All apparent age errors are cited at one sigma. 

Uncertainties associated with apparent ages of individual 

fractions were calculated using equations of Dalrymple and 

others (1981). Isochron diagrams were produced for all 

samples and may be derived by using 40ArI (initial 40Ar) and 

36ArI (initial 36Ar). Plateaus were determined according to the 

method of Fleck and others (1977).

The 40Ar/39Ar ages reported in Appendix 3, determined 

in the U.S. Geological Survey 40Ar/39Ar lab in Denver, CO by 

M.A. Cosca, are based on analyses of amphibole (hornblende), 

plagioclase, and whole rock samples. Samples, together with 

standards, were irradiated for 20 MW (megawatt) hours in 

the central thimble position of the USGS TRIGA reactor. 

Laser fusion of >10 individual Fish Canyon Tuff sanidine 

crystals (28.201±0.09 Ma; Kuiper and others, 2008) at each 

closely monitored position within the irradiation package 

resulted in neutron flux ratios reproducible to ±0.25% (two 

sigma). Isotopic production ratios and interfering nucleogenic 

reactions were determined from irradiated CaF2 and KCl salts 

and zero age K-silicate glass, and for this study the following 

values were measured: (36Ar/37Ar)Ca=(2.77 ± 0.03)×10−4; 

(

39Ar/37Ar)Ca=(6.54 ± 0.33)×10−4; and (38Ar/39Ar)K=(1.29 ± 

0.03)×10−2. Cadmium shielding during irradiation prevented 

any measurable nucleogenic (40Ar/39Ar)K. The irradiated 

samples and standards were loaded into numbered positions of 

a stainless steel planchette, placed into a laser sample chamber 

with an externally pumped ZnSe window, and evacuated to 

ultrahigh vacuum conditions in a fully automated stainless 

steel extraction line designed and built at the USGS in Denver. 

The samples were incrementally heated using a 25W CO2 laser 

equipped with a beam homogenizing lens and the liberated 

gas was expanded and purified by exposure to a cryogenic 

trap maintained at −140 °C and two hot SAES GP50 getters. 

Following purification the gas was expanded online into a 

Thermo Scientific ARGUS VI mass spectrometer (except 

sample 203195, which was analyzed using a Mass Analyzer 

Products 215–50 mass spectrometer) in static mode and Ar 

isotopes were measured by peak jumping using an electron 

multiplier in analog mode. Data were acquired during 10 

measurement cycles and time zero intercepts were determined 

by best-fit linear and (or) polynomial regressions to the data. 

Ages were calculated assuming a 40Ar/36Ar ratio of trapped 

argon equal to the atmospheric value of 298.56 (Lee and 

others, 2006) and using decay constants of Steiger and Jäger 

(1977). Data were corrected for mass discrimination, blanks, 

radioactive decay, and interfering nucleogenic reactions.

K-Ar Analytical Methods

Conventional K-Ar analyses were not carried out as part 

of the this study, but previous workers produced considerable 

K-Ar age data that constitute an important source of stratigraphic 

information on the Bodie Hills volcanic field and on the timing 

of mineralization in the Bodie and Aurora mining districts. Many 

earlier K-Ar analyses were performed in K-Ar laboratories at 

USGS facilities in Menlo Park and Denver or at University of 

California laboratories in Berkeley. An appropriate reference 

for K-Ar techniques used in all three laboratories is found in 

Dalrymple and Lanphere (1969).

Data

All available geochronology data for Bodie Hills volcanic 

field are summarized in table 3. These data are synthesized and 

interpreted in other publications, including John and others 

(2012, 2015), Vikre and others (2015) and du Bray and others 

(written commun., 2015). As described previously, ages reported 

in Appendixes 1–3 utilized several slightly different ages for the 

Fish Canyon Tuff sanidine standard as a consequence of these 

age determinations having been conducted in several different 

labs, over a period of almost fifteen years, during which the 

accepted age for the sanidine standard was refined. In order to 

render ages calculated using different values for the sanidine 

standard comparable, ages calculated using a sanidine standard 

age different from 28.02 Ma were recalculated using that value 

and are summarized in the column titled “Age recalculated for 

FCT= 28.02” (table 3).

Acknowledgments

Geologic mapping and sample collection for this study 

were conducted as part of the Mineral Systems of the Ancestral 

and Modern Cenozoic Cascades Arcs Project funded by the 

U.S. Geological Survey Mineral Resources Program. Technical 

assistance was provided in Menlo Park laboratories by Dean 

Miller, Donald Shamp, and James Saburomaru. In Denver, Ross 

Yeoman and John Lee offered similar assistance. Byron R. Berger 

(deceased) introduced L.W. Snee to the geology of the Bodie 

Hills and was instrumental in geochronology sample collection. 

Constructive reviews by R.D. Taylor and J.N. Aleinikoff are much 

appreciated and helped clarify data presentation.
10 Geochronology of Cenozoic Rocks in the Bodie Hills, California and Nevada

Figure 2. (A) Locations of samples (solid black circles) with 40Ar/39Ar age determinations (table 1) shown on a simplified geologic map of the Bodie Hills volcanic field, California and Nevada. Colored polygons portray extent of eruptive products associated with particular volcanic centers within the Bodie Hills volcanic field (modified from John and others, 2012; 2015). Uncolored areas are underlain by either older basement rocks, rocks of the Aurora volcanic field, or surficial deposits. (

B) Inset map 

showing locations of samples (solid circles) with 40Ar/39Ar age determinations (table 1) in densely sampled Bodie mining district.

CALIFORNIA

NEVADA Mt. Biedeman

PotatoPeak Bodie

Mountain

MasonicMountain

BrawleyPeaks

BeautyPeak

AuroraCrater Bald

 Peak

Mono Lake

Mono Valley

Fletcher

Valley

Bridgeport

Bridgeport Valley Bodie

Aurora

Rough

Creek

East

Walker

River

395

Aurora 

Canyon

Big Alkali

Bodie

Creek

167

182

Masonic

The 

Elbow

395

WASSUK RANGE

SWEETWATER

MOUNTAINS

Bridgeport

Reservoir

A

118°45' 118°50' 118°55' 119°00' 119°05' 119°10' 119°15'

38°25'38°20'38°15'38°10'38°05'

9

8

7

6

5

4

3

2

1

99

98

97

96

95

94

93

91,92

90

89

88

87

85

86

84

83

82

81

80

79

78

77

76

75

74

73

72

71 70

69

68

67

66

65

64

63

62

61

60

59

58

57

56

55

53

54

52

51 50

49

48

47 46

45

44

43

42

40,41

39

37

38 36 35

34

33

31

32

30

29

28

27

25

26

24

23

22

21 20

19

18

17

16

15

14

12,13

11

10

160

159

158

157

156

154,155

153

152 151

150

149

147

146

145

148 144

143

142

141

140

139

138

137

136

135

134

133

132

131

130

114

113

112

111

110

109

108

107

106

105

104

102,103

101

100

Inset map

0

2.5 7.5 5 10 KILOMETERS 0

4 2 6 MILES

Rhyolite of Big Alkali Trachyandesite of Willow Springs Trachydacite of Potato Peak Dacite of Silver Hill Trachyandesite of Mount Biedeman Rhyolite of the Bodie Hills Rhyolite of Bald Peak Rhyolite of Bodie Creek 

Trachyandesite of Aurora Canyon 

Rhyolite of Rock Springs Canyon Trachyandesite of Del Monte Trachydacite of Bridgeport Canyon Rhyolite of Del Monte Canyon Rhyolite of Aurora Creek Trachyandesite of West Brawley Peak 

Basaltic trachyandesite of Rancheria 

Trachydacite of Rough Creek Trachyandesite of Aurora Trachyandesite of East CanyonTrachyandesite of Mud Spring Canyon Trachyandesite of Masonic

EXPLANATION

40Ar/39Ar sample locality
!

! !

122 125 129

120,121

119

117

115,116

127

124

126

B

128

123

118

Ç

Tailings 

Pond

Ç

#

#

!

!

!

!

!

!

!

!

!

!

!

119°01' 119°00'

38°13'

38°12'

0 1 KILOMETER

Main road

40Ar/39Ar sample locality

Mine

Bodie

 Bluff

 RED CLOUD

 MINE

Bodie

Silver

 Hill

EXPLANATION

Figure 2.—Continued

Figure II 11
12 Geochronology of Cenozoic Rocks in the Bodie Hills, California and Nevada

Figure 3. (A) Locations of samples (solid black circles) with K-Ar age determinations (table 2) shown on a simplified geologic map of the Bodie Hills volcanic field, California and Nevada. Colored polygons portray extent of eruptive products associated with particular volcanic centers within the Bodie Hills volcanic field (modified from John and others, 2012; 2015). (

B) Inset map showing locations of samples (solid circles) with K-Ar age determinations (table 2) in densely sampled Bodie mining district.

Inset map

M

118°45' 118°50' 118°55' 119°00' 119°05' 119°10' 119°15'

38°25'38°20'38°15'38°10'38°05'

CALIFORNIA

NEVADA Mt. Biedeman

Potato

Peak

Bodie

Mountain

Masonic

Mountain

Brawley

Peaks

Beauty

Peak

Aurora

Crater

Bald

 Peak

Bodie

Mono Lake

Rough

Creek

East

Walker

River

395

Aurora 

Canyon

Big Alkali

Bodie

Creek

167

182

Masonic

The 

Elbow

395

Aurora

WASSUK RANGE

Fletcher

Valley

Bridgeport

Reservoir

SWEETWATER

MOUNTAINS

A

Mono Valley

Bridgeport Valley

II

QQQ

JJ

U

MMM,NNN,OOO 

PPP

LLL

KKK

RRR FF

EE

KK

LLDD

Y

BB

W

AA CC

K

N

HHH

GGG

III

DDD P

O

CCC

XX

AAA

H

EEE FFF

BBB

L

J GG

X

V Z

I F

A

G

JJJ

B

E D

C

Q

T

R,S

QQ

UU

0

2.5 7.5 5 10 KILOMETERS 0

4 2 6 MILES

Bridgeport

Rhyolite of Big Alkali Trachyandesite of Willow Springs Trachydacite of Potato Peak Dacite of Silver Hill Trachyandesite of Mount Biedeman Rhyolite of the Bodie Hills Rhyolite of Bald Peak Rhyolite of Bodie Creek 

Trachyandesite of Aurora Canyon 

Rhyolite of Rock Springs Canyon Trachyandesite of Del Monte Trachydacite of Bridgeport Canyon Rhyolite of Del Monte Canyon Rhyolite of Aurora Creek Trachyandesite of West Brawley Peak 

Basaltic trachyandesite of Rancheria 

Trachydacite of Rough Creek Trachyandesite of Aurora Trachyandesite of East CanyonTrachyandesite of Mud Spring Canyon Trachyandesite of Masonic

EXPLANATION

40Ar/39Ar sample locality
#

#

Ç

 RED CLOUD

 MINE

Tailings 

Pond

119°01'

38°13'

38°12'

119°

0 1 KILOMETER

B

HH

TT

YY

VV ZZ

NN PP

WW

RR

OO

MM

SS

Bodie

 Bluff

Bodie

Silver

 Hill

!

Main road

K-Ar sample locality

Mine

EXPLANATION

Ç

Figure 3.—Continued

Figure III 13
14 Geochronology of Cenozoic Rocks in the Bodie Hills, California and Nevada Table 3. Summary compilation of geochronologic data for samples of the Bodie Hills volcanic field, California and Nevada. Sample number Lab_no. Latitude Longitude Unit Age, Ma Error, Ma Method Source1 Mineral Decay constant2 Recalculated age, using new decay constants Age recalculated for FCT=28.02 Ma Summary age 158

— 38.368 −118.812 Trachyandesite of Mud Spring 0.11 0.08 K-Ar 8 Groundmass new

—

— 0.11

EL-KA-6

— 38.3635 −118.8169 Trachyandesite of Mud Spring 0.04 0.04 Ar-Ar3 13 Groundmass

—

— 0.04 0.04

USGS(M)-672-2

— 38.3128 −118.8825 Trachyandesite of Aurora 

Crater

0.25 0.05 K-Ar 2 Whole rock old* 0.26

— 0.26

160

— 38.357 −118.896 Trachyandesite of Aurora 

Crater

0.47 0.19 K-Ar 8 Groundmass new

—

— 0.47

EL-KA-9

— 38.3630 −118.8461 Trachyandesite 2 1.32 0.08 Ar-Ar3 13 Groundmass

—

— 1.33 1.33

EL-KA-2

— 38.3047 −118.7799 Andesite 1.44 0.06 K-Ar 13 Whole rock new

—

— 1.44

EL-KA-7

— 38.3306 −118.7901 Andesite 1.6 0.02 Ar-Ar3 13 Groundmass

—

— 1.6 1.6

120 KA-2089 38.240 −118.829 Trachyandesite of Mount 

Hicks

1.6 0.1 K-Ar 1 Whole rock old* 1.6

— 1.6

09-BA-1

— 38.31968 −119.04411 Trachyandesite of Cow Camp 

Creek

2.00 0.04 Ar-Ar4 14 Whole rock

—

— 1.99 1.99

USGS(M)-611-5

— 38.2578 −118.8558 Trachyandesite south of 

Aurora Peak

2.2 0.1 K-Ar 2 Whole rock old* 2.3

— 2.3

USGS(M)-611-5

— 38.2578 −118.8558 Trachyandesite south of 

Aurora Peak

2.5 0.2 K-Ar 2 Hornblende old* 2.6

— 2.6

USGS(M)-670G4

— 38.2811 −118.8842 Rhyolite of Martinez Hill 2.5 0.1 K-Ar 2 Biotite old* 2.6

— 2.6

23

— 38.156 −118.860 Trachybasalt of Cedar Hill 2.60 0.06 K-Ar 8 Groundmass new

—

— 2.60

USGS(M)-610-1B

— 38.2778 −118.8586 Trachydacite of Aurora Peak 2.5 0.2 K-Ar 2 Biotite old* 2.6

— 2.6

USGS(M)-610-1B

— 38.2778 −118.8586 Trachydacite of Aurora Peak 2.7 0.2 K-Ar 2 Hornblende old* 2.8

— 2.8

1071 KA-1999 38.175 −118.832 Pyroxene trachyandesite of 

Cedar Hill

61.0 0.1 K-Ar 1 Plagioclase old* 61.0

— 61.0

469 KA-2003 38.179 −118.826 Pyroxene trachyandesite of 

Cedar Hill

2.7 0.8 K-Ar 1 Plagioclase old* 2.8

— 2.8

466 KA-1912 38.179 −118.821 Pyroxene trachyandesite of 

Cedar Hill

2.7 0.2 K-Ar 1 Biotite old* 2.8

— 2.8

465 KA-1857 38.181 −118.823 Pyroxene trachyandesite of 

Cedar Hill

66.2 2.5 K-Ar 1 Plagioclase old* 66.4

— 66.4

25 KA-2086 38.261 −118.973 Basaltic trachyandesite of 

Beauty Peak

2.8 0.1 K-Ar 1 Whole rock old* 2.9

— 2.9

468 KA-1859 38.178 −118.819 Hornblende trachydacite of 

Cedar Hill

2.8 0.4 K-Ar 1 Plagioclase old* 2.9

— 2.9

1069 KA-2002 38.188 −118.850 Hornblende trachydacite of 

Cedar Hill

2.5 0.3 K-Ar 1 Plagioclase old* 2.6

— 2.6

1069 KA-2004 38.188 −118.850 Hornblende trachydacite of 

Cedar Hill

2.5 0.1 K-Ar 1 Biotite old* 2.6

— 2.6

[Entries in the “Summary age” column represent a recapitulation of K-Ar ages, recalculated using the decay constants of Steiger and and Jäger (1977), and 40Ar/39Ar ages, calculated assuming a Fish Canyon Tuff age of 28.02 Ma]
Sample number Lab_no. Latitude Longitude Unit Age, Ma Error, Ma Method Source1 Mineral Decay constant2

Recalculated 

age, 

using new 

decay 

constants

Age 

recalculated 

for FCT=28.02 

Ma

Summary 

age

139 KA-1984 38.209 −118.880 Hornblende trachydacite of 

Cedar Hill

3.4 0.3 K-Ar 1 Biotite old* 3.5 — 3.5

139 KA-1984R 38.209 −118.880 Hornblende trachydacite of 

Cedar Hill

3.1 0.3 K-Ar 1 Biotite old* 3.2 — 3.2

139 KA-1993 38.209 −118.880 Hornblende trachydacite of 

Cedar Hill

2.3 1.6 K-Ar 1 Plagioclase old* 2.4 — 2.4

199 KA-1980 38.153 −119.008 Hornblende trachydacite of 

Cedar Hill

3.2 0.7 K-Ar 1 Plagioclase old* 3.3 — 3.3

USGS(M)-7346-3 — 38.216 −118.981 Hornblende trachydacite of 

Cedar Hill

2.7 0.1 K-Ar 6 Whole rock old* 2.8 — 2.8

5-152-9/50/72 — 38.3548 −118.9261 Hornblende trachydacite 3.04 0.03 Ar-Ar3 9 Whole rock — — 3.06 3.065-152-9/56/72 — 38.3548 −118.9261 Hornblende trachydacite 3.53 0.18 Ar-Ar3 9 Plagioclase — — 3.55 3.55144 KA-2076 38.184 −118.894 Trachyandesite of Cedar Hill 3.6 0.4 K-Ar 1 Plagioclase old* 3.7 — 3.71092A KA-2066 38.255 −118.810 Rhyolite of Spring Peak 3.6 0.1 K-Ar 1 Sanidine old* 3.7 — 3.7203195 — 38.2823 −119.1479 Basaltic andesite of 

Locomotive Point

3.9 0.06 Ar-Ar4 14 Groundmass — — 3.87 3.87

USGS(M)-BH6 — 38.1655 −119.1512 Rhyolite of Big Alkali 5.7 0.2 K-Ar 6 Biotite old* 5.9 — 5.9USGS(M)-BH20 — 38.220 −119.149 Rhyolite of Big Alkali 5.2 0.3 K-Ar 6 Biotite old* 5.3 — 5.3USGS(M)-BH20 — 38.220 −119.149 Rhyolite of Big Alkali 5.4 0.6 K-Ar 6 Hornblende old* 5.5 — 5.5077-7C — 38.19677 −119.15829 Rhyolite of Big Alkali 5.478 0.024 Ar-Ar 7 Plagioclase FCT=28.02 — — 5.478088-24A — 38.25278 −119.13951 Rhyolite of Big Alkali 6.201 0.026 Ar-Ar 7 Plagioclase FCT=28.02 — — 6.201098-13A — 38.25754 −119.12788 Rhyolite of Big Alkali 6.173 0.028 Ar-Ar 7 Plagioclase FCT=28.02 — — 6.17309-BA-42 — 38.27001 −119.14887 Rhyolite of Big Alkali 5.455 0.025 Ar-Ar 7 Biotite FCT=28.02 — — 5.45539509-10 — 38.2153 −119.22755 Dacite of Hot Springs Canyon 8.070 0.017 Ar-Ar 7 Plagioclase FCT=28.02 — — 8.070414 KA-1973 38.177 −119.193 Trachyandesite of Willow 

Springs

7.8 0.2 K-Ar 1 Plagioclase old* 8.0 — 8.0

USGS(M)-BH19A — 38.222 −119.172 Trachyandesite of Willow 

Springs

8.0 0.2 K-Ar 6 Biotite old* 8.2 — 8.2

077-7A — 38.17860 −119.19476 Trachyandesite of Willow 

Springs

8.004 0.037 Ar-Ar 7 Biotite FCT=28.02 — — 8.004

077-7A — 38.17860 −119.19476 Trachyandesite of Willow 

Springs

8.051 0.019 Ar-Ar 7 Plagioclase FCT=28.02 — — 8.051

077-7B — 38.19178 −119.15240 Trachyandesite of Willow 

Springs

8.122 0.029 Ar-Ar 7 Biotite FCT=28.02 — — 8.122

077-7B — 38.19178 −119.15240 Trachyandesite of Willow 

Springs

8.070 0.021 Ar-Ar 7 Hornblende FCT=28.02 — — 8.070

077-7B — 38.19178 −119.15240 Trachyandesite of Willow 

Springs

8.139 0.024 Ar-Ar 7 Plagioclase FCT=28.02 — — 8.139

088-24B — 38.25504 −119.14115 Trachyandesite of Willow 

Springs

8.575 0.022 Ar-Ar 7 Plagioclase FCT=28.02 — — 8.575

Table 3.—Continued

Table III 15
16 Geochronology of Cenozoic Rocks in the Bodie Hills, California and Nevada Sample number Lab_no. Latitude Longitude Unit Age, Ma Error, Ma Method Source1 Mineral Decay constant2 Recalculated age, using new decay constants Age recalculated for FCT=28.02 Ma Summary age 088-24F

— 38.20176 −119.08978 Trachyandesite of Willow 

Springs

8.155 0.019 Ar-Ar 7 Plagioclase FCT=28.02

—

— 8.155

08-BA-51

— 38.17449 −119.15441 Trachyandesite of Willow 

Springs

8.305 0.017 Ar-Ar 7 Sanidine FCT=28.02

—

— 8.305

12-BA-1

— 38.18995 −119.16512 Trachydacite of Cinnabar 

Canyon

8.548 0.028 Ar-Ar 7 Plagioclase FCT=28.02

—

— 8.548

406 KA-1990 38.234 −119.085 Trachydacite of Potato Peak 8.4 0.2 K-Ar 1 Plagioclase old* 8.6

— 8.6

USGS(M)-856-10

— 38.205 −119.028 Trachydacite of Potato Peak 8.9 0.2 K-Ar 6 Biotite old* 9.1

— 9.1

USGS(M)-856-10

— 38.205 −119.028 Trachydacite of Potato Peak 9.0 0.2 K-Ar 6 Hornblende old* 9.2

— 9.2

USGS(M)-BM2

— 38.221 −119.057 Trachydacite of Potato Peak 9.1 0.1 K-Ar 6 Biotite old* 9.3

— 9.3

088-21B Run 2

— 38.26418 −119.07504 Trachydacite of Potato Peak 8.927 0.010 Ar-Ar 7 Plagioclase FCT=28.02

—

— 8.927

088-21D

— 38.24330 −119.09209 Trachydacite of Potato Peak 8.964 0.027 Ar-Ar 7 Plagioclase FCT=28.02

—

— 8.964

088-21E

— 38.23457 −119.08582 Trachydacite of Potato Peak 8.863 0.050 Ar-Ar 7 Plagioclase FCT=28.02

—

— 8.863

088-24C

— 38.24786 −119.11208 Trachydacite of Potato Peak 8.996 0.025 Ar-Ar 7 Plagioclase FCT=28.02

—

— 8.996

088-24D

— 38.22678 −119.10376 Trachydacite of Potato Peak 9.056 0.045 Ar-Ar 7 Plagioclase FCT=28.02

—

— 9.056

088-24E

— 38.21809 −119.10188 Trachydacite of Potato Peak 8.926 0.025 Ar-Ar 7 Plagioclase FCT=28.02

—

— 8.926

08-BA-68

— 38.19323 −119.06835 Trachydacite of Potato Peak 8.99 0.02 Ar-Ar 7 Plagioclase FCT=28.02

—

— 8.99

098-10C

— 38.24919 −119.09203 Trachydacite of Potato Peak 8.982 0.023 Ar-Ar 7 Plagioclase FCT=28.02

—

— 8.982

098-13C

— 38.25072 −119.09223 Trachydacite of Potato Peak 8.998 0.021 Ar-Ar 7 Plagioclase FCT=28.02

—

— 8.998

108-12A

— 38.24252 −119.04825 Trachydacite of Potato Peak 8.963 0.016 Ar-Ar 7 Plagioclase FCT=28.02

—

— 8.963

108-12B

— 38.23830 −119.00784 Trachydacite of Potato Peak 9.032 0.022 Ar-Ar 7 Biotite FCT=28.02

—

— 9.032

10-BA-66

— 38.17250 −119.10125 Trachydacite of Potato Peak 8.749 0.019 Ar-Ar 7 Plagioclase FCT=28.02

—

— 8.749

10-BA-66

— 38.17250 −119.10125 Trachydacite of Potato Peak 8.735 0.015 Ar-Ar 7 Sanidine FCT=28.02

—

— 8.735

15 KA-1972 38.194 −118.961 Dacite of Silver Hill 8.9 0.2 K-Ar 1 Plagioclase old* 9.1

— 9.1

USGS(M)-BH15

— 38.201 −119.003 Dacite of Silver Hill 8.6 0.4 K-Ar 6 Hornblende old* 8.8

— 8.8

USGS(M)-BH15

— 38.201 −119.003 Dacite of Silver Hill 8.7 0.2 K-Ar 6 Biotite old* 8.9

— 8.9

USGS(M)-S1

— 38.188 −119.008 Dacite of Silver Hill 8.5 0.4 K-Ar 6 Whole rock old* 8.7

— 8.7

USGS(M)-S1

— 38.188 −119.008 Dacite of Silver Hill 8.3 0.4 K-Ar 6 Plagioclase old* 8.5

— 8.5

USGS(M)-S1

— 38.188 −119.008 Dacite of Silver Hill 8.9 0.4 K-Ar 6 Plagioclase old* 9.1

— 9.1

USGS(M)-B271

— 38.215 −119.003 Dacite of Silver Hill 8.4 0.2 K-Ar 6 Hornblende old* 8.6

— 8.6

USGS(M)-B271

— 38.215 −119.003 Dacite of Silver Hill 8.5 0.3 K-Ar 6 Plagioclase old* 8.7

— 8.7

USGS(M)-856-8

— 38.214 −119.004 Dacite of Silver Hill 8.2 0.2 K-Ar 6 Whole rock old* 8.4

— 8.4

USGS(M)-856-8

— 38.214 −119.004 Dacite of Silver Hill 9.2 0.5 K-Ar 6 Hornblende old* 9.4

— 9.4

USGS(M)-BH17

— 38.193 −119.012 Dacite of Silver Hill 9.2 0.5 K-Ar 6 Hornblende old* 9.4

— 9.4

USGS(M)-BH32

— 38.200 −118.995 Dacite of Silver Hill 8.8 0.2 K-Ar 6 Biotite old* 9.0

— 9.0

USGS(M)-856-32

— 38.209 −118.997 Dacite of Silver Hill 8.9 0.3 K-Ar 6 Biotite old* 9.1

— 9.1

USGS(M)-BH26

— 38.194 −119.003 Dacite of Silver Hill 9.1 0.5 K-Ar 6 Hornblende old* 9.3

— 9.3

USGS(M)-BH16

— 38.200 −118.999 Dacite of Silver Hill 9.4 0.2 K-Ar 6 Biotite old* 9.7

— 9.7

USGS(M)-854-1

— 38.182 −119.003 Dacite of Silver Hill 8.7 0.2 K-Ar 6 Biotite old* 8.9

— 8.9

Table 3.—Continued
Sample number Lab_no. Latitude Longitude Unit Age, Ma Error, Ma Method Source1 Mineral Decay constant2

Recalculated 

age, 

using new 

decay 

constants

Age 

recalculated 

for FCT=28.02 

Ma

Summary 

age

USGS(M)-BH29 — 38.196 −118.958 Dacite of Silver Hill 8.7 0.2 K-Ar 6 Biotite old* 8.9 — 8.9077-7F — 38.20252 −119.02630 Dacite of Silver Hill 8.928 0.024 Ar-Ar 7 Plagioclase FCT=28.02 — — 8.92809-BA-26 — 38.20360 −119.00021 Dacite of Silver Hill 9.132 0.020 Ar-Ar 7 Biotite FCT=28.02 — — 9.132108-12C — 38.18925 −118.98343 Dacite of Silver Hill 9.089 0.014 Ar-Ar 7 Plagioclase FCT=28.02 — — 9.089108-12D — 38.17315 −118.97800 Dacite of Silver Hill 9.018 0.014 Ar-Ar 7 Plagioclase FCT=28.02 — — 9.018108-12E — 38.20763 −118.96489 Dacite of Silver Hill 9.140 0.020 Ar-Ar 7 Plagioclase or 

Biotite

FCT=28.02 — — 9.140

08-BA-66 — 38.18629 −119.05680 Dacite of Silver Hill debris 

flow clast

9.064 0.024 Ar-Ar 7 Plagioclase FCT=28.02 — — 9.064

BH31 — 38.194 −119.008 Dacite of Silver Hill, plug 8.6 0.4 K-Ar 3 Sericite-chlorite old* 8.8 — 8.8077-6F — 38.18809 −119.00854 Dacite of Silver HillSugarloaf plug 9.086 0.028 Ar-Ar 7 Plagioclase FCT=28.02 — — 9.086459 KA-1907 38.097 −119.064 Eureka Valley Tuff 9.8 0.2 K-Ar 1 Biotite old* 10.1 — 10.131 KA-1909 38.247 −118.990 Eureka Valley Tuff 9.5 0.3 K-Ar 1 Biotite old* 9.8 — 9.827 KA-1908 38.247 −118.990 Eureka Valley Tuff 9.6 0.3 K-Ar 1 Biotite old* 9.9 — 9.9W24 — 38.102 −119.066 Eureka Valley Tuff 9.19 0.28 K-Ar 1 Biotite old* 9.4 — 9.4W25 — 38.131 −119.181 Eureka Valley Tuff 9.35 0.37 K-Ar 1 Biotite old* 9.6 — 9.6W25 — 38.131 −119.181 Eureka Valley Tuff 9.01 0.27 K-Ar 1 Biotite old* 9.2 — 9.2077-9A — 38.22088 −118.97443 Eureka Valley Tuff 9.401 0.023 Ar-Ar 7 Biotite FCT=28.02 — — 9.401077-9A — 38.22088 −118.97443 Eureka Valley Tuff 9.383 0.026 Ar-Ar 7 Plagioclase FCT=28.02 — — 9.383098-12A — 38.35923 −119.19917 Eureka Valley Tuff 9.45 0.04 Ar-Ar 7 Plagioclase FCT=28.02 — — 9.4509-BA-49 — 38.26389 −119.04748 Eureka Valley Tuff 9.267 0.019 Ar-Ar 7 Biotite FCT=28.02 — — 9.267AU-10/61/DD61 — 38.260 −118.981 Eureka Valley Tuff 9.20 0.04 Ar-Ar3 9 Biotite — — 9.26 9.266-289-2 — 38.3729 −118.9993 Eureka Valley Tuff 9.30 0.29 Ar-Ar3 9 Biotite — — 9.36 9.36USGS(M)-BH9 — 38.157 −119.116 Trachyandesite of Mount 

Biedeman

9.3 0.3 K-Ar 6 Whole rock old* 9.5 — 9.5

USGS(M)-MTB1 — 38.146 −119.073 Trachyandesite of Mount 

Biedeman

9.5 0.2 K-Ar 6 Hornblende old* 9.8 — 9.8

098-11E — 38.11099 −119.15841 Trachyandesite of Mount 

Biedeman

9.019 0.028 Ar-Ar 7 Plagioclase FCT=28.02 — — 9.019

09-BA-22 — 38.14302 −119.17974 Trachyandesite of Mount 

Biedeman

9.022 0.024 Ar-Ar 7 Plagioclase FCT=28.02 — — 9.022

09SB015A — 38.12310 −119.14843 Trachyandesite of Mount 

Biedeman

8.890 0.064 Ar-Ar 7 Plagioclase FCT=28.02 — — 8.890

108-12F — 38.16336 −119.09918 Trachyandesite of Mount 

Biedeman

9.987 0.015 Ar-Ar 7 Plagioclase FCT=28.02 — — 9.987

108-9A — 38.16540 −119.09816 Trachyandesite of Mount 

Biedeman

9.947 0.019 Ar-Ar 7 Plagioclase FCT=28.02 — — 9.947

10-BA-46 — 38.17380 −119.11508 Trachyandesite of Mount 

Biedeman

8.779 0.013 Ar-Ar 7 Plagioclase FCT=28.02 — — 8.779

Table 3.—Continued

Table III 17
18 Geochronology of Cenozoic Rocks in the Bodie Hills, California and Nevada Sample number Lab_no. Latitude Longitude Unit Age, Ma Error, Ma Method Source1 Mineral Decay constant2 Recalculated age, using new decay constants Age recalculated for FCT=28.02 Ma Summary age 10-BA-61

— 38.14005 −119.01551 Trachyandesite of Mount 

Biedeman

10.018 0.164 Ar-Ar 7 Plagioclase FCT=28.02

—

— 10.018

12-BA-22

— 38.10155 −119.12395 Trachyandesite of Mount 

Biedeman

8.933 0.042 Ar-Ar 7 Plagioclase FCT=28.02

—

— 8.933

6-215-1/121/72

— 38.1344 −119.0825 Trachyandesite of Mount 

Biedeman

9.18 0.08 Ar-Ar3 9 Hornblende

—

— 9.24 9.24

MC-12-18

— 38.15575 −119.07825 Trachyandesite of Mount 

Biedeman

9.24 0.09 Ar-Ar4 14 Hornblende

—

— 9.18 9.18

119-20B

— 38.13452 −119.07613 Trachyandesite of Mount 

Biedeman, plug

9.073 0.033 Ar-Ar 7 Plagioclase FCT=28.02

—

— 9.073

08-BA-65

— 38.31071 −118.97808 Rhyolite of Bald Peak 9.682 0.013 Ar-Ar 7 Sanidine FCT=28.02

—

— 9.682

10-BA-67

— 38.26203 −118.98303 Rhyolite of Bald Peak 9.652 0.016 Ar-Ar 7 Sanidine FCT=28.02

—

— 9.652

507 KA-1998 38.154 −119.089 Rhyolite of Bodie Hills 9.5 0.3 K-Ar 1 Plagioclase old* 9.8

— 9.8

507 KA-2049 38.154 −119.089 Rhyolite of Bodie Hills 9.3 0.3 K-Ar 1 Biotite old* 9.5

— 9.5

USGS(M)-BH27

— 38.140 −119.056 Rhyolite of Bodie Hills 9.1 0.2 K-Ar 6 Biotite old* 9.3

— 9.3

077-7D

— 38.16719 −119.09983 Rhyolite of Bodie Hills 9.858 0.027 Ar-Ar 7 Plagioclase FCT=28.02

—

— 9.858

077-7D

— 38.16719 −119.09983 Rhyolite of Bodie Hills 9.860 0.013 Ar-Ar 7 Sanidine FCT=28.02

—

— 9.860

088-21C

— 38.25134 −119.08382 Rhyolite of Bodie Hills 9.776 0.017 Ar-Ar 7 Biotite FCT=28.02

—

— 9.776

088-21C

— 38.25134 −119.08382 Rhyolite of Bodie Hills 9.893 0.025 Ar-Ar 7 Biotite FCT=28.02

—

— 9.893

088-21C

— 38.25134 −119.08382 Rhyolite of Bodie Hills 9.800 0.020 Ar-Ar 7 Plagioclase FCT=28.02

—

— 9.800

088-21C

— 38.25134 −119.08382 Rhyolite of Bodie Hills 9.806 0.018 Ar-Ar 7 Plagioclase FCT=28.02

—

— 9.806

088-21C

— 38.25134 −119.08382 Rhyolite of Bodie Hills 9.740 0.023 Ar-Ar 7 Plagioclase FCT=28.02

—

— 9.740

088-21C

— 38.25134 −119.08382 Rhyolite of Bodie Hills 9.766 0.020 Ar-Ar 7 Sanidine FCT=28.02

—

— 9.766

088-21C

— 38.25134 −119.08382 Rhyolite of Bodie Hills 9.770 0.009 Ar-Ar 7 Sanidine FCT=28.02

—

— 9.770

088-21C

— 38.25134 −119.08382 Rhyolite of Bodie Hills 9.774 0.008 Ar-Ar 7 Sanidine FCT=28.02

—

— 9.774

08-BA-50

— 38.24816 −119.09663 Rhyolite of Bodie Hills 9.757 0.013 Ar-Ar 7 Sanidine FCT=28.02

—

— 9.757

098-10B

— 38.25135 −119.08382 Rhyolite of Bodie Hills 9.819 0.013 Ar-Ar 7 Biotite FCT=28.02

—

— 9.819

098-10B

— 38.25135 −119.08382 Rhyolite of Bodie Hills 9.786 0.022 Ar-Ar 7 Biotite FCT=28.02

—

— 9.786

098-10B (BHb)

— 38.25135 −119.08382 Rhyolite of Bodie Hills 9.819 0.017 Ar-Ar 7 Biotite FCT=28.02

—

— 9.819

098-10B

— 38.25135 −119.08382 Rhyolite of Bodie Hills 9.778 0.031 Ar-Ar 7 Plagioclase FCT=28.02

—

— 9.778

098-10B

— 38.25135 −119.08382 Rhyolite of Bodie Hills 9.748 0.021 Ar-Ar 7 Sanidine FCT=28.02

—

— 9.748

098-10B

— 38.25135 −119.08382 Rhyolite of Bodie Hills 9.779 0.005 Ar-Ar 7 Sanidine FCT=28.02

—

— 9.779

098-10B

— 38.25135 −119.08382 Rhyolite of Bodie Hills 9.756 0.002 Ar-Ar 7 Sanidine FCT=28.02

—

— 9.756

098-13B

— 38.26802 −119.13218 Rhyolite of Bodie Hills 9.813 0.027 Ar-Ar 7 Sanidine FCT=28.02

—

— 9.813

09-BA-20

— 38.15662 −119.04741 Rhyolite of Bodie Hills 9.609 0.013 Ar-Ar 7 Sanidine FCT=28.02

—

— 9.609

09-BA-47

— 38.28409 −119.13821 Rhyolite of Bodie Hills 9.877 0.012 Ar-Ar 7 Sanidine FCT=28.02

—

— 9.877

USGS(M)-Baghdad

— 38.2786 −118.9467 Rhyolite of Bodie Creek 9.9 0.3 K-Ar 2 Sanidine old* 10.2

— 10.2

USGS(M)-Baghdad

— 38.2786 −118.9467 Rhyolite of Bodie Creek 10.2 0.4 K-Ar 2 Plagioclase old* 10.5

— 10.5

077-9B

— 38.26971 −118.95063 Rhyolite of Bodie Creek 10.163 0.029 Ar-Ar 7 Sanidine FCT=28.02

—

— 10.163

Table 3.—Continued
Sample number Lab_no. Latitude Longitude Unit Age, Ma Error, Ma Method Source1 Mineral Decay constant2

Recalculated 

age, 

using new 

decay 

constants

Age 

recalculated 

for FCT=28.02 

Ma

Summary 

age

108-11A — 38.27826 −118.94807 Rhyolite of Bodie Creek 9.890 0.008 Ar-Ar 7 Sanidine FCT=28.02 — — 9.89011-BA-32 — 38.3364 −118.97804 Rhyolite of Bodie Creek 10.127 0.013 Ar-Ar 7 Sanidine FCT=28.02 — — 10.12711-BA-60 — 38.32693 −118.97204 Rhyolite of Bodie Creek 11.335 0.138 Ar-Ar 7 Feldspar FCT=28.02 — — 11.335077-8C — 38.27145 −119.07783 Trachyandesite of Aurora 

Canyon

10.460 0.020 Ar-Ar 7 Biotite FCT=28.02 — — 10.460

077-8C#2 — 38.27145 −119.07783 Trachyandesite of Aurora 

Canyon

10.481 0.025 Ar-Ar 7 Biotite FCT=28.02 — — 10.481

077-8C Run 1 — 38.27145 −119.07783 Trachyandesite of Aurora 

Canyon

10.427 0.028 Ar-Ar 7 Plagioclase FCT=28.02 — — 10.427

077-8C Run 2 — 38.27145 −119.07783 Trachyandesite of Aurora 

Canyon

10.426 0.030 Ar-Ar 7 Plagioclase FCT=28.02 — — 10.426

077-8C — 38.27145 −119.07783 Trachyandesite of Aurora 

Canyon

10.444 0.014 Ar-Ar 7 Sanidine FCT=28.02 — — 10.444

077-8C Run 2 — 38.27145 −119.07783 Trachyandesite of Aurora 

Canyon

10.464 0.015 Ar-Ar 7 Sanidine FCT=28.02 — — 10.464

077-8C Run 3 — 38.27145 −119.07783 Trachyandesite of Aurora 

Canyon

10.458 0.016 Ar-Ar 7 Sanidine FCT=28.02 — — 10.458

088-21A — 38.27363 −119.13962 Trachyandesite of Aurora 

Canyon

10.358 0.025 Ar-Ar 7 Plagioclase FCT=28.02 — — 10.358

088-23A — 38.27852 −119.10021 Trachyandesite of Aurora 

Canyon

10.583 0.032 Ar-Ar 7 Biotite FCT=28.02 — — 10.583

088-23A — 38.27852 −119.10021 Trachyandesite of Aurora 

Canyon

10.275 0.109 Ar-Ar 7 Plagioclase FCT=28.02 — — 10.275

088-23B — 38.27831 −119.09908 Trachyandesite of Aurora 

Canyon

10.534 0.052 Ar-Ar 7 Biotite FCT=28.02 — — 10.534

088-23B — 38.27831 −119.09908 Trachyandesite of Aurora 

Canyon

10.318 0.023 Ar-Ar 7 Plagioclase FCT=28.02 — — 10.318

088-23D — 38.28113 −119.10206 Trachyandesite of Aurora 

Canyon

10.463 0.047 Ar-Ar 7 Biotite FCT=28.02 — — 10.463

088-23D — 38.28113 −119.10206 Trachyandesite of Aurora 

Canyon

10.265 0.052 Ar-Ar 7 Plagioclase FCT=28.02 — — 10.265

088-25A — 38.27322 −119.09077 Trachyandesite of Aurora 

Canyon

10.425 0.026 Ar-Ar 7 Plagioclase FCT=28.02 — — 10.425

10-BA-62 — 38.36327 −119.00635 Tephra in sedimentary rocks 

of Fletcher Valley

10.464 0.041 Ar-Ar 7 Biotite FCT=28.02 — — 10.464

10-BA-62 — 38.36327 −119.00635 Fletcher Valley sediments 10.582 0.023 Ar-Ar 7 Plagioclase FCT=28.02 — — 10.582077-9E — 38.31905 −118.91003 Trachyandesite of Del Monte 10.949 0.025 Ar-Ar 7 Plagioclase FCT=28.02 — — 10.94908SB038 — 38.40828 −118.97383 Trachyandesite of Del Monte 10.982 0.050 Ar-Ar 7 Biotite FCT=28.02 — — 10.98211-BA-41 — 38.35057 −118.98085 Trachyandesite of Del Monte 10.942 0.024 Ar-Ar 7 Plagioclase FCT=28.02 — — 10.942098-11B — 38.12451 −119.17126 Trachydacite of Bridgeport 

Canyon

11.067 0.022 Ar-Ar 7 Plagioclase FCT=28.02 — — 11.067

Table 3.—Continued

Table III 19
20 Geochronology of Cenozoic Rocks in the Bodie Hills, California and Nevada Sample number Lab_no. Latitude Longitude Unit Age, Ma Error, Ma Method Source1 Mineral Decay constant2 Recalculated age, using new decay constants Age recalculated for FCT=28.02 Ma Summary age 09SB020A

— 38.13230 −119.13277 Trachydacite of Bridgeport 

Canyon

11.080 0.019 Ar-Ar 7 Plagioclase FCT=28.02

—

— 11.080

08SB032

— 38.34561 −118.95580 Unwelded tuff in sedimentary 

rocks of Fletcher Valley 

10.918 0.043 Ar-Ar 7 Plagioclase FCT=28.02

—

— 10.918

10-BA-5

— 38.33945 −118.99699 Pyroxene rhyolite 11.153 0.011 Ar-Ar 7 Plagioclase FCT=28.02

—

— 11.153

10-BA-27

— 38.27500 −118.90498 Rhyolite of East Brawley 

Peak

11.179 0.016 Ar-Ar 7 Sanidine FCT=28.02

—

— 11.179

USGS(M)-NTS10B

— 38.3021 −118.8967 Rhyolite of Aurora Creek 10.9 0.2 K-Ar 2 Biotite old* 11.2

—

—

USGS(M)-NTS10B

— 38.3021 −118.8967 Rhyolite of Aurora Creek 11.0 0.2 K-Ar 2 Sanidine old* 11.3

—

—

10-BA-20

— 38.31679 −118.91129 Rhyolite of Aurora Creek 11.177 0.013 Ar-Ar 7 Plagioclase FCT=28.02

—

— 11.177

10-BA-21

— 38.30315 −118.89740 Rhyolite of Aurora Creek 11.181 0.022 Ar-Ar 7 Sanidine FCT=28.02

—

— 11.181

077-9D

— 38.28562 −118.92803 Rhyolite of Del Monte 

Canyon

11.200 0.032 Ar-Ar 7 Plagioclase FCT=28.02

—

— 11.200

077-9D

— 38.28562 −118.92803 Rhyolite of Del Monte 

Canyon

11.139 0.020 Ar-Ar 7 Sanidine FCT=28.02

—

— 11.139

AU-6/60/DD61

— 38.285 −118.928 Rhyolite of Del Monte 

Canyon

11.21 0.03 Ar-Ar3 9 Biotite

—

— 11.28 11.28

USGS(M)-710-7

— 38.2822 −118.9281 Rhyolite of Del Monte 

Canyon?

11.2 0.2 K-Ar 2 Biotite old* 11.5

— 11.5

077-9C

— 38.27661 −118.93036 Rhyolite of Del Monte 

Canyon

11.258 0.142 Ar-Ar 7 Plagioclase FCT=28.02

—

— 11.258

077-9C

— 38.27661 −118.93036 Rhyolite of Del Monte 

Canyon

11.220 0.017 Ar-Ar 7 Sanidine FCT=28.02

—

— 11.220

077-8B

— 38.28334 −119.05617 Trachydacite intrusion 11.153 0.028 Ar-Ar 7 Plagioclase FCT=28.02

—

— 11.153

09-BA-35

— 38.29048 −119.04642 Trachydacite intrusion 11.269 0.034 Ar-Ar 7 Biotite FCT=28.02

—

— 11.269

098-13D

— 38.27655 −119.16062 Trachyandesite of Clark 

Canyon

11.341 0.017 Ar-Ar 7 Plagioclase FCT=28.02

—

— 11.341

09-BA-43

— 38.26358 −119.16825 Trachyandesite of Clark 

Canyon

11.268 0.112 Ar-Ar 7 Plagioclase FCT=28.02

—

— 11.268

KA2379R

— 38.4133 −118.9417 Tuff in Aldrich Station Formation 11.40 0.54 K-Ar 11 Biotite old* 11.70

— 11.70

547 KA-2048 38.255 −118.948 Trachyandesite of West Brawley Peak 12.5 0.2 K-Ar 1 Plagioclase old* 12.8

— 12.8

USGS(M)-712-1

— 38.2522 −118.9175 Trachyandesite of West Brawley Peak 11.2 0.2 K-Ar 2 Biotite old* 11.5

— 11.5

USGS(M)-712-1

— 38.2522 −118.9175 Trachyandesite of West Brawley Peak 10.9 0.3 K-Ar 2 Plagioclase old* 11.2

— 11.2

USGS(M)-712-1

— 38.2522 −118.9175 Trachyandesite of West Brawley Peak 11.6 0.3 K-Ar 2 Hornblende old* 11.9

— 11.9

077-7G

— 38.23439 −118.96671 Trachyandesite of West Brawley Peak 11.323 0.032 Ar-Ar 7 Plagioclase FCT=28.02

—

— 11.323

Table 3.—Continued
Sample number Lab_no. Latitude Longitude Unit Age, Ma Error, Ma Method Source1 Mineral Decay constant2

Recalculated 

age, 

using new 

decay 

constants

Age 

recalculated 

for FCT=28.02 

Ma

Summary 

age

108-10C — 38.28052 −118.90623 Trachyandesite of West Brawley Peak 11.514 0.019 Ar-Ar 7 Plagioclase FCT=28.02 — — 11.5146 — 38.1256 −119.1697 Basaltic trachyandesite of 

Rancheria

11.3 0.9 K-Ar 4 Whole rock old* 11.6 — 11.6

742-45 — 38.0869 −119.1431 Basaltic trachyandesite of 

Rancheria

11.7 0.5 K-Ar 12 Whole rock new — — 11.7

MC-12-20 — 38.27010 −119.12610 Hornblende trachyandesite 

intrusion

11.9 0.20 Ar-Ar4 14 Hornblende — — 11.82 11.82

098-11A — 38.12239 −119.16954 Tuff of Jacks Spring 12.069 0.015 Ar-Ar 7 Sanidine FCT=28.02 — — 12.06909-BA-23 — 38.12851 −119.17491 Tuff of Jacks Spring 12.044 0.015 Ar-Ar 7 Sanidine FCT=28.02 — — 12.0446-181-12/52/DD72 — 38.1193 −119.1039 Tuff of Jacks Spring 11.87 0.16 Ar-Ar3 9 Sanidine — — 11.95 11.956-181-12/53/DD72 — 38.1193 −119.1039 Tuff of Jacks Spring 11.90 0.14 Ar-Ar3 9 Sanidine — — 11.98 11.98KA2362 — 38.4408 −118.9725 Hornblende andesite 12.11 0.39 K-Ar 11 Plagioclase old 12.43 — 12.43KA2364 — 38.4408 −118.9725 Hornblende andesite 12.07 0.50 K-Ar 11 Hornblende old 12.39 — 12.39KA2368 — 38.4408 −118.9725 Hornblende andesite 12.33 0.31 K-Ar 11 Biotite old 12.66 — 12.6610-BA-29 — 38.36466 −119.01452 Trachydacite of Rough Creek 11.675 0.016 Ar-Ar 7 Plagioclase FCT=28.02 — — 11.67510-BA-6 — 38.33375 −119.02470 Trachydacite of Rough Creek 12.945 0.020 Ar-Ar 7 Plagioclase FCT=28.02 — — 12.94511-BA-40 — 38.41155 −119.01907 Trachydacite of Rough Creek 12.804 0.023 Ar-Ar 7 Plagioclase FCT=28.02 — — 12.80407-BA-38 — 38.36049 −119.14502 Andesite of Lakeview Spring 12.930 0.033 Ar-Ar 7 Plagioclase FCT=28.02 — — 12.930USGS(M)-711-67 — 38.2894 −118.9092 Trachyandesite of Aurora 13.5 0.3 K-Ar 2 Hornblende old* 13.9 — 13.9USGS(M)-668-G10 — 38.2403 −118.8917 Trachyandesite of Aurora 14.4 0.3 K-Ar 2 Hornblende old* 14.8 —USGS(M)-711-8 — 38.2681 −118.8917 Trachyandesite of Aurora 15.4 0.3 K-Ar 2 Plagioclase old* 15.8 — 15.8CH8Z1 — 38.288 −118.882 Trachyandesite of Aurora 10.9 0.3 K-Ar 5 Whole rock new — — 10.9108-10A — 38.27293 −118.91272 Trachyandesite of Aurora 12.580 0.024 Ar-Ar 7 Plagioclase FCT=28.02 — — 12.58000-BA-16 — 38.2708 −118.8908 Trachyandesite of Aurora 13.05 0.44 Ar-Ar3 9 Hornblende — — 13.13 13.1300-BA-26 — 38.2542 −118.8841 Trachyandesite of Aurora 13.05 0.08 Ar-Ar3 9 Hornblende — — 13.13 13.13098-12E — 38.39143 −119.12397 Trachyandesite of Masonic 

Gulch

13.441 0.026 Ar-Ar 7 Plagioclase FCT=28.02 — — 13.441

MAS10-72 — 38.40189 −119.13718 Trachyandesite of Masonic 

Gulch

13.485 0.017 Ar-Ar 7 Plagioclase FCT=28.02 — — 13.485

MAS10-73 — 38.39643 −119.13470 Trachyandesite of Masonic 

Gulch

13.467 0.016 Ar-Ar 7 Plagioclase FCT=28.02 — — 13.467

MAS10-75 — 38.39169 −119.11549 Trachyandesite of Masonic 

Gulch

<13.497 0.024 Ar-Ar 7 Plagioclase FCT=28.02 — — <13.497

12-BA-9 — 38.33681 −119.07377 Trachydacite of East Canyon 13.782 0.025 Ar-Ar 7 Plagioclase FCT=28.02 — — 13.7825 — 38.0978 −119.1475 Trachyandesite of Sinnamon 

Cut

13.3 0.4 K-Ar 4 Hornblende old* 13.7 — 13.7

12-BA-3 — 38.34974 −118.84729 Trachyandesite of Mud Spring 

Canyon

13.96 0.11 Ar-Ar4 14 Plagioclase — — 13.87 13.87

10-BA-9 — 38.35278 −119.02068 Trachyandesite of Masonic, 

plug

14.998 0.019 Ar-Ar 7 Plagioclase FCT=28.02 — — 14.998

Table 3.—Continued

Table III 21
22 Geochronology of Cenozoic Rocks in the Bodie Hills, California and Nevada Sample number Lab_no. Latitude Longitude Unit Age, Ma Error, Ma Method Source1 Mineral Decay constant2 Recalculated age, using new decay constants Age recalculated for FCT=28.02 Ma Summary age MAS10-76

— 38.38169 −119.11534 Trachyandesite of Masonic, 

plug

14.190 0.021 Ar-Ar 7 Hornblende FCT=28.02

—

— 14.190

088-22B

— 38.37937 −119.07802 Trachyandesite of Masonic 14.067 0.081 Ar-Ar 7 Plagioclase FCT=28.02

—

— 14.067

088-23F

— 38.31068 −119.11700 Trachyandesite of Masonic 14.193 0.039 Ar-Ar 7 Plagioclase FCT=28.02

—

— 14.193

08-BA-62

— 38.32006 −119.04943 Trachyandesite of Masonic 14.131 0.030 Ar-Ar 7 Plagioclase FCT=28.02

—

— 14.131

098-12B

— 38.38762 −119.18139 Trachyandesite of Masonic 14.715 0.025 Ar-Ar 7 Plagioclase FCT=28.02

—

— 14.715

098-12D

— 38.39951 −119.11939 Trachyandesite of Masonic <14.80 0.02 Ar-Ar 7 Plagioclase FCT=28.02

—

— <14.80

098-12F

— 38.37542 −119.11418 Trachyandesite of Masonic 14.094 0.017 Ar-Ar 7 Hornblende FCT=28.02

—

— 14.094

09-BA-7

— 38.33786 −119.08727 Trachyandesite of Masonic 14.674 0.025 Ar-Ar 7 Plagioclase FCT=28.02

—

— 14.674

10-BA-13

— 38.35154 −119.10419 Trachyandesite of Masonic 14.410 0.016 Ar-Ar 7 Plagioclase FCT=28.02

—

— 14.410

10-BA-15

— 38.34130 −119.11570 Trachyandesite of Masonic 14.141 0.017 Ar-Ar 7 Plagioclase FCT=28.02

—

— 14.141

10-BA-69

— 38.30537 −119.13652 Trachyandesite of Masonic 14.107 0.014 Ar-Ar 7 Plagioclase FCT=28.02

—

— 14.107

12-BA-20

— 38.33410 −119.15949 Trachyandesite of Masonic 14.136 0.020 Ar-Ar 7 Plagioclase FCT=28.02

—

— 14.136

MC-12-19

— 38.31952 −118.78154 Trachyandesite of Borealis 16.06 0.10 Ar-Ar4 14 Hornblende

—

— 15.96 15.96

FA1

— 38.2931 −118.8914 Alteration: Aurora 10.04 0.03 Ar-Ar3 10 Adularia

—

— 10.10 10.10

FA66

— 38.2375 −118.9008 Alteration: East Brawley Peak 

alteration zone 

12.34 0.04 Ar-Ar3 10 Alunite

—

— 12.42 12.42

PP09-10A1

— 38.25309 −119.13844 Alteration: Aurora Canyon 

alteration zone

10.865 0.065 Ar-Ar 7 Alunite FCT=28.02

—

— 10.865

USGS(M)-7346-1

— 38.215 −119.004 Alteration: Bodie, Standard 

Hill

7.2 0.1 K-Ar 6 Adularia old* 7.4

— 7.4

USGS(M)-7346-1

— 38.215 −119.004 Alteration: Bodie, Standard 

Hill

7.0 0.1 K-Ar 6 Adularia old* 7.2

— 7.2

USGS(M)-RCD1B

— 38.201 −119.005 Alteration: Bodie, Red Cloud 

mine

7.7 0.1 K-Ar 6 Adularia old* 7.9

— 7.9

USGS(M)-B270

— 38.216 −119.004 Alteration: Bodie, Standard 

Hill

8.0 0.2 K-Ar 6 Adularia old* 8.2

— 8.2

077-6A

— 38.2149 −119.0037 Alteration: Bodie, south of 

Bodie Bluff

8.286 0.024 Ar-Ar 7 Adularia FCT=28.02

—

— 8.286

077-6C

— 38.2187 −119.0005 Alteration: Bodie, Bodie Bluff 7.179 0.417 Ar-Ar 7 Adularia FCT=28.02

—

— 7.179

11-BA-7G

— 38.20420 −119.00649 Alteration: Bodie, Silver Hill 8.217 0.012 Ar-Ar 7 Adularia FCT=28.02

—

— 8.217

11-BA-21

— 38.20370 −119.00919 Alteration: Bodie, Red Cloud 

mine

8.124 0.006 Ar-Ar 7 Adularia FCT=28.02

—

— 8.124

BOD09-5

— 38.20430 −119.00660 Alteration: Bodie, Oro mine 

dump

8.473 0.007 Ar-Ar 7 Adularia FCT=28.02

—

— 8.473

BOD09-3

— 38.20146 −119.0048 Alteration: Bodie, Red Cloud 

mine

8.628 0.014 Ar-Ar 7 Adularia FCT=28.02

—

— 8.628

09-BA-28I

— 38.2015 −119.0036 Alteration: Bodie, Red Cloud 

mine

8.852 0.013 Ar-Ar 7 Adularia FCT=28.02

—

— 8.852

11-BA-22

— 38.21257 −119.00402 Alteration: Bodie, south of 

Bodie Bluff

8.498 0.005 Ar-Ar 7 Adularia FCT=28.02

—

— 8.498

Table 3.—Continued
Sample number Lab_no. Latitude Longitude Unit Age, Ma Error, Ma Method Source1 Mineral Decay constant2

Recalculated 

age, 

using new 

decay 

constants

Age 

recalculated 

for FCT=28.02 

Ma

Summary 

age

AU-18/65/DD61 — 38.201 −119.004 Alteration: Bodie, Red Cloud 

mine

8.41 0.02 Ar-Ar3 9 Adularia — — 8.46 8.46

AU-17/64/DD61 — 38.215 −118.997 Alteration: Bodie, south of 

Bodie Bluff

8.23 0.04 Ar-Ar3 9 Adularia — — 8.28 8.28

AU-16/63/DD61 — 38.215 −119.004 Alteration: Bodie, south of 

Bodie Bluff

8.33 0.02 Ar-Ar3 9 Adularia — — 8.38 8.38

SAW11-9 — 39.29036 −118.91657 Alteration: Sawtooth alteration zone 11.105 0.011 Ar-Ar 7 Alunite FCT=28.02 — — 11.10539509-3K — 38.20793 −119.22751 Alteration: Hwy 395 alteration 

zone

8.169 0.013 Ar-Ar 7 Alunite FCT=28.02 — — 8.169

08-BA-46 — 38.24430 −119.10385 Alteration: Potato Peak alteration zone, Alta Pina mine 10.769 0.034 Ar-Ar 7 Alunite FCT=28.02 — — 10.769MAS09-1 — 38.35783 −119.13268 Alteration: Masonic, Red 

Rock mine 

13.269 0.144 Ar-Ar 7 Alunite FCT=28.02 — — 13.269

MAS09-1A — 38.35847 −119.13824 Alteration: Masonic, Red 

Rock mine

13.471 0.038 Ar-Ar 7 Alunite FCT=28.02 — — 13.471

MAS07-1A — 38.34992 −119.14832 Alteration: Masonic, 

Chemung mine

13.386 0.068 Ar-Ar 7 Alunite FCT=28.02 — — 13.386

088-22A — 38.36731 −119.10727 Alteration: Masonic, 

Maybelle mine

13.018 0.061 Ar-Ar 7 Alunite FCT=28.02 — — 13.018

07-BA-40 — 38.36544 −119.11607 Alteration: Masonic, 

Pittsburg-Liberty mine

13.027 0.049 Ar-Ar 7 Alunite FCT=28.02 — — 13.027

MAS10-55 — 38.41419 −119.10259 Alteration: Masonic, Redwash 

alteration zone

13.27 0.02 Ar-Ar 7 Alunite FCT=28.02 — — 13.27

RW08-1 — 38.41123 −119.12414 Alteration: Masonic, Redwash 

alteration zone

13.338 0.035 Ar-Ar 7 Alunite FCT=28.02 — — 13.338

MAS07-3 — 38.35968 −119.12682 Alteration: Masonic, Sarita 

mine

13.253 0.051 Ar-Ar 7 Alunite FCT=28.02 — — 13.253

CC09-9D1 — 38.19869 −119.17050 Alteration: Cinnabar Canyon 

alteration zone

8.824 0.294 Ar-Ar 7 Alunite FCT=28.02 — — 8.824

CC09-9D2 — 38.19869 −119.17050 Alteration: Cinnabar Canyon 

alteration zone

8.682 0.020 Ar-Ar 7 Alunite FCT=28.02 — — 8.682

MAS11-1A — 38.36041 −119.08369 Alteration: Masonic, Perini 

mine

12.956 0.020 Ar-Ar 7 Alunite FCT=28.02 — — 12.956

MAS11-2B — 38.36064 −119.08681 Alteration: Masonic, Perini 

mine

12.960 0.014 Ar-Ar 7 Alunite FCT=28.02 — — 12.960

AUR10-3 — 38.23752 −118.89919 Alteration: East Brawley Peak 

alteration zone 

11.954 0.016 Ar-Ar 7 Alunite FCT=28.02 — — 11.954

BOD11-4E — 38.21257 −119.00402 Alteration: Bodie, Standard 

Hill mine

8.425 0.003 Ar-Ar 7 Adularia FCT=28.02 — — 8.425

Table 3.—Continued

Table III 23
24 Geochronology of Cenozoic Rocks in the Bodie Hills, California and Nevada Sample number Lab_no. Latitude Longitude Unit Age, Ma Error, Ma Method Source1 Mineral Decay constant2 Recalculated age, using new decay constants Age recalculated for FCT=28.02 Ma Summary age MAS12-10 (#1)

— 38.33716 −119.16013 Alteration: Masonic, Success 

mine

13.398 0.081 Ar-Ar 7 Alunite FCT=28.02

—

— 13.398

MAS12-10 (#2)

— 38.33716 −119.16013 Alteration: Masonic, Success 

mine

13.638 0.077 Ar-Ar 7 Alunite FCT=28.02

—

— 13.638

37

— 38.287 −118.887 Altered trachyandesite of 

Aurora

10.3 0.2 K-Ar 4 Adularia old* 10.6

— 10.6

AU-1/58/DD61

— 38.266 −118.900 Alteration: Aurora, Esmeralda 

vein

10.63 0.05 Ar-Ar5 9 K-feldspar

—

— 10.70 10.70

AU-2/59/DD61

— 38.282 −118.896 Alteration: Aurora, Del Monte 

shaft

10.28 0.05 Ar-Ar5 9 K-feldspar

—

— 10.35 10.35

BOD11-3A

— 38.21961 −119.00354 Alteration: Bodie, Upper 

Hobart Tunnel 

8.194 0.005 Ar-Ar 7 Adularia FCT=28.02

—

— 8.194

BOD11-3B

— 38.21961 −119.00354 Alteration: Bodie Bluff, 

Incline vein

8.542 0.025 Ar-Ar 7 Adularia FCT=28.02

—

— 8.542

12-BA-17

— 38.21961 −119.00019 Alteration: Bodie Bluff, west 

side

8.357 0.028 Ar-Ar 7 Adularia FCT=28.02

—

— 8.357

1Sources: 1, Gilbert and others (1968); 2, Silberman and McKee (1972); 3, Silberman and others (1972); 4, Kleinhampl and others (1975); 5, Morton and others (1977); 6, Silberman and Chesterman (1972); 7, 

R.J Fleck, this report; 8, Lange and others (1993); 9, L.W. Snee, this report; 10, Breit, (2000); 11, Gilbert and Reynolds (1973); 12, Marvin and Dobson (1979); 13, Reheis and others (2002); 14, M.A. Cosca, this report.

2Old*: All ages with this notation adjusted in “Recalculated age” column to account for new decay constants of Steiger and Jäger (1977).3Age initially calculated for Fish Canyon tuff=27.84 Ma.4Age initially calculated for Fish Canyon Tuff=28.201 Ma.5Age initially calculated for Fish Canyon tuff=27.84 Ma; isochron age.6Likely an inaccurate age.

Table 3.—Continued
References Cited 25

References Cited

Al-Rawi, Y.T., 1969, Cenozoic history of the northern part of 

Mono Basin, California and Nevada: Berkeley, University 

of California, Ph.D. dissertation, 163 p.

Breit, F.J., Jr., 2000, Structural and temporal relationships and 

geochemical characteristics of the East Brawley Peak acidsulfate prospect and the adjacent Aurora adularia-sericite 

system: Reno, University of Nevada, M.S. thesis, 215 p.

Busby, C.J., 2013, Birth of a plate boundary at ca. 12 Ma in 

the Ancestral Cascades arc, Walker Lane belt of California 

and Nevada: Geosphere, v. 9, p. 1147–1160.

Carlson, C.W., Pluhar, C.J., Glen, J.M.G., and Farner, M.J., 

2013, Kinematics of the west-central Walker Lane—

Spatially and temporally variable rotations evident in the 

late Miocene Stanislaus Group: Geosphere, v. 9, 

p. 1530–1551.

Chesterman, C.W., and Gray, C.H., Jr., 1975, Geology of the 

Bodie 15-minute quadrangle, Mono County, California: 

California Division of Mines and Geology, Map Sheet 21, 

scale 1:48,000.

Dalrymple, G.B., Alexander, B.C., Lanphere, M.A., and 

Kraker, G.P, 1981, Irradiation of samples for 40Ar/39Ar 

dating using the Geological Survey TRIGA reactor: U.S. 

Geological Survey Professional Paper 1176, 55 p.

Dalrymple, G.B., and Lanphere, M.A., 1969, Potassiumargon dating—principles, techniques and applications to 

geochronology: San Francisco, Freeman, 258 p.

du Bray, E.A., John, D.A., and Cousens, B.L., 2014, 

Petrologic, tectonic, and metallogenic evolution of the 

southern segment of the ancestral Cascades magmatic arc, 

California and Nevada: Geosphere, v. 10, p. 1–39.

Faulds, J.E., and Henry, C.D., 2008, Tectonic influences on 

the spatial and temporal evolution of the Walker Lane—An 

incipient transform fault along the evolving Pacific – North 

American plate boundary, in Spencer, J.E., and Titley, 

S.R., eds., Ores and orogenesis: Circum-Pacific tectonics, 

geologic evolution, and ore deposits: Arizona Geological 

Society Digest 22, p. 437–470.

Fleck, R.J., Hagstrum, J.T., Calvert, A.T., and Evarts, R.C., 

2014, 40Ar/39Ar geochronology, paleomagnetism, and evolution of the Boring volcanic field, Oregon and Washington, 

USA: Geosphere, v. 10, no. 6, p. 1283–1314, doi:10.1130/

GES00985.1

Fleck, R.J., Sutter, J.H., and Elliot, D.H., 1977, Interpretation 

of discordant 40Ar/39Ar age-spectra of Mesozoic tholeiites 

from Antarctica: Geochimica et Cosmochimica Acta, v. 41, 

p. 15–32.

Gilbert, C.M., Christiansen, M.N., Al-Rawi, Yehya, and 

Lajoie, K.R., 1968, Structural and volcanic history of Mono 

Basin, California-Nevada, in Coats, R.R., Hay, R.L., and 

Anderson, C.A., eds., Studies in Volcanology: Geological 

Society of America Memoir 116, p. 275–329.

Gilbert, C.M., and Reynolds, M.W., 1973, Character and 

chronology of basin development, western margin of the 

Basin and Range Province: Geological Society of America 

Bulletin, v. 84, p. 2489–2510.

Gill, J., 1981, Orogenic andesites and plate tectonics: New 

York, Springer-Verlag, 390 p.

John, D.A., du Bray, E.A., Box, S.E., Vikre, P.G., Rytuba, J.J., 

Fleck, R.J., and Moring, B.C., 2015, Geologic map of the 

Bodie Hills, California and Nevada: U.S. Geological Survey 

Scientific Investigations Map 3318, 64 p., 2 sheets, scale 

1:50,000, http://dx.doi.org/10.3133/sim3318.

John, D.A., du Bray, E.A., Fleck, R.J., Vikre, P.G., Box, S.E., 

and Moring, B.C., 2012, Miocene magmatism in the Bodie 

Hills volcanic field, California and Nevada—A long-lived 

eruptive center in the southern segment of the ancestral 

Cascades arc: Geosphere, v. 8, p. 44–97.

Kingdon, S., Cousens, B., John, D.A., and du Bray, E.A., 

2013, Pliocene to late Pleistocene magmatism in the Aurora 

Volcanic Field, Nevada and California, USA [abs.]: Eos 

Transactions AGU V13G-2700.

Kleinhampl, F.J., Davis, W.E., Silberman, M.L., Chesterman, 

C.W., Chapman, R.H., and Gray, C.H., Jr., 1975, 

Aeromagnetic and limited gravity studies and generalized 

geology of the Bodie Hills region, Nevada and California: 

U.S. Geological Survey Bulletin 1384, 38 p.

Kuiper, K.F., Deino, A., Hilgen, F.J., Krijgsman, W., Renne, 

P.R., and Wijbrans, J.R., 2008, Synchronizing rock clocks 

of Earth history: Science, v. 320, p. 500–504.

Lange, R.A., and Carmichael, I.S.E., 1996, The Aurora 

volcanic field, California-Nevada—Oxygen fugacity 

constraints on the development of andesitic magma: 

Contributions to Mineralogy and Petrology, v. 125, 

p. 167–185.

Lange, R.A., Carmichael, I.S.E., and Renne, Paul, 1993, 

Potassic volcanism near Mono Basin, California—Evidence 

for high water and oxygen fugacities inherited from 

subduction: Geology, v. 21, p. 949–952.

Lee, J.-Y., Marti, K., Severinghaus, J.P., Kawamura, K., Yoo, 

H.-S., Lee, J.B., and Kim, J.S., 2006, A redetermination of 

the isotopic abundances of atmospheric Ar: Geochimica et 

Cosmochimica Acta, v. 70, p. 4507–4512.

Marvin, R.F., and Dobson, S.W., 1979, Radiometric ages; 

compilation B, U.S. Geological Survey: Isochron/West, no. 

26, p. 3–30.
26 Geochronology of Cenozoic Rocks in the Bodie Hills, California and Nevada

McIntyre, G.A., Brooks, C., Compston, W., Turek, A., 1966, 

The statistical assessment of Rb-Sr isochrons: Journal of 

Geophysical Research, v. 71, p. 5459–5468.

Morton, J.L., Silberman, M.L., Bonham, H.F., Jr., Garside, 

L.J., and Noble, D.C., 1977, K-Ar ages of volcanic rocks, 

plutonic rocks, and ore deposits in Nevada and eastern 

California; determinations run under the USGS-NBMG 

Cooperative Program: Isochron/West, no. 20, p. 19–29.

Oldow, J.S., 1992, Late Cenozoic displacement partitioning in 

the northwestern Great Basin, in Craig, S.D., ed., Structure, 

tectonics, and mineralization of the Walker Lane; Walker 

Lane Symposium, proceedings volume: Reno, Nevada, 

Geological Society of Nevada, p. 17–52.

Oldow, J.S., 2003, Active transtensional boundary zone 

between the western Great Basin and Sierra Nevada block, 

western U.S. Cordillera: Geology, v. 31, p. 1033–1036.

Reheis, M.C, Stine, Scott, and Sarna-Wojcicki, A.M., 2002, 

Drainage reversals in Mono Basin during the late Pliocene 

and Pleistocene: Geological Society of America Bulletin, 

v. 114, p. 991–1006.

Renne, P.R., Swisher, C.C., Deino, A.L., Karner, D.B., Owens, 

T.L., and DePaolo, D.J., 1998, Intercalibration of standards, 

absolute ages and uncertainties in 40Ar/39Ar dating: 

Chemical Geology, v. 145, p. 117–152.

Roddick, J.C., 1983, High precision intercalibration of 40Ar/39Ar standards: Geochimica et Cosmochimica Acta, 

v. 47, p. 887–898.

Samson, S.D., and Alexander, E.G., 1987, Calibration of 

interlaboratory 40Ar/39Ar dating standard MMhb-1: Isotope 

Geoscience, v. 66, p. 27–34.

Silberman, M.L., and Chesterman, C.W., 1972, K-Ar age 

of volcanism and mineralization, Bodie mining district 

and Bodie Hills volcanic field, Mono County, California: 

Isochron/West, no. 3, p. 13–22.

Silberman, M.L., Chesterman, C.W., Kleinhampl, F.J., and 

Gray, C.H., Jr., 1972, K-Ar ages of volcanic rocks and goldbearing quartz-adularia veins in the Bodie mining district, 

Mono County; California: Economic Geology, v. 67, 

p. 597–604.

Silberman, M.L., and McKee, E.H., 1972, A summary of 

radiometric age determinations on Tertiary volcanic rocks 

from Nevada and eastern California—part II, western 

Nevada: Isochron/West, no. 4, p. 7–28.

Snee, L.W., 2002, Argon thermochronology of mineral 

deposits—A review of analytical methods, formulations, 

and selected applications: U.S. Geological Survey Bulletin 

2194, 39 p.

Steiger, R.H., and Jäger, E., 1977, Subcommission on 

geochronology—Convention on the use of decay constants 

in geo- and cosmochronology: Earth and Planetary Science 

Letters, v. 36, p. 359–362.

Stewart, J.H., 1988, Tectonics of the Walker Lane belt, 

western Great Basin—Mesozoic and Cenozoic deformation 

in a zone of shear, in Ernst, W.G., ed., Metamorphism and 

crustal evolution of the western United States: Englewood 

Cliffs, N. J., Prentice Hall, p. 681–713.

Taylor, J.R., 1982, An introduction to error analysis—The 

study of uncertainties in physical measurements: Mill 

Valley, California, University Science Books, 270 p.

Vikre, P.G., John, D.A., du Bray, E.A., and Fleck, R.J., in 

press, Gold-silver mining districts and alteration zones 

in the Miocene Bodie Hills volcanic field, California and 

Nevada: U.S. Geological Survey Scientific Investigations 

Report SIR–2015–5012, available at 

http://dx.doi.org/10.3133/sir20155012.
Menlo Park Publishing Service Centers, California 

Manuscript approved for publication January 23, 2015

Edited by Sarah Nagorsen

Design and Layout by Cory Hurd
Fleck and others—Geochronology of Cenozoic Rocks in the Bodie Hills, California and Nevada—Data Series 916

ISSN 2327-638X (online)

http://dx.doi.org/10.3133/ds916