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University of Nevada Reno Geology of the Wild Horse Canyon Area, Fox Range, Washoe County, Nevada a Thesis Submitted in Partial

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University of Nevada Reno Geology of the Wild Horse Canyon Area, Fox Range, Washoe County, Nevada a Thesis Submitted in Partial University of Nevada Reno Geology of the Wild Horse canyon area, Fox Range, Washoe County, Nevada A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Geology oy 1 y v The thesis or Barnes 3. Dixon is approved: University of Nevada Reno 1.1 acknowledgements I wish to express thanks to Dr. E.R. Larson who suggest ed the problem, and whose assistance and contributions prior to and during this project have been enormous. Special app­ reciation is also extended to my family for their patience and understanding. Thanks also goes to Rod Campbell who ably typed the manuscript. James B. Dixon iii GEOLOGY OF THE WILD HORSE CANYON AREA, FOX RANGE, WASHOE COUNTY, NEVADA By James B. Dixon ABSTRACT The Wild Horse canyon area includes about 41 square kilometers on the western side of the Fox Range of southern Washoe County, Nevada. The area lies about 100 airkilomet- ers north of Reno, Nevada. Wild Horse canyon provides the major drainage channel of that protion of the Fox Range and empties into the eastern side of the Smoke Creek desert playa. Rocks in the canyon area range in age from Early .Meso­ zoic to Recent. The oldest rocks exposed in the area are the Triassic-Jurassic Nightingale sequence composed of met­ amorphosed, quartz-rich, argillaceous, sandy, fine-grained elastics and intercalated limestones. The Nightingale rocks were regionally metamorphosed, folded, and faulted by late- stage Sierran batholithic intrusions in the late-Middle Cretaceous period, and locally further dynamothermally met­ amorphosed by post-batholithic granodiorite intrusions in the Late Cretaceous. The Nightingale rocks were also intrud­ ed by several possible differentiates of the granodiorite magmas during Late Cretaceous time. The Mesozoic rocks of the canyon area have undergone two episodes of deformation, with each episode resulting in the development of two distinct structural grains. The earliest episode originated and ended in the Late Mesozoic period and developed an east-west and a north-south struc­ tural grain. Late Tertiary Basin and Range faulting initia­ ted the latest deformation episode developing a northwest and a northeast structural grain and forming the Fox Range horst. Continued horsting of the Fox Range fault block along Basin and Range structures has resulted in the folding of local Late Tertiary volcanics into a broad anticline. The axis of the anticline generally parallels the north-north­ east trend of the Fox Range fault block. The Late Cretaceous to Middle Tertiary period of erosion and peneplanation is represented locally by a few outcrops of stream channel deposits developed in the peneplaned Nightin­ gale sequence. Tertiary volcanism in the area began in the lower Oligo- cene with the eruption and flows of the South Willow formation. IV The area was volcanically quiescent from the middle of the Oligocene until the lower to middle Miocene when dacite "in­ truded Basin and Range fault planes and related structures. The volcanic flows and sediments of the Pyramid seauence were deposited from the middle Miocene to Mio-Piiocene time. Erosion has oeen continuous in the elevated canyon areas since the beginning of the Pliocene epoch. In the ad­ jacent Smoke Creek desert, pluvial lakes formed lacustrine and subaarial deposits in Quaternary time. Mineralization in the Wild Horse canyon area is limited to gold-quartz veins developed in the post-batholithic Wild Horse mine granodiorite stock. V CONTENTS Page Acknowledgements .... ...................... ..... ii A b s t r a c t ....................................................iii List of Illustrations .....................................vii Introduction .............................................. 1 Location and Accessibility ........................ 1 Physiography ............... 4 Climate and Vegetation ............................ 5 Wildlife ........................................... 6 Land U s e ........................................... 6 Scope of Investigation ............................ 6 Method of Investigation ............................ 7 Previous Investigations ............................ 8 Mining History ........................................... 9 Lithologic Sequence ..................................... 10 G e n e r a l ................................................ 10 Rock Descriptions..................................... 14 Nightingale Sequence .......................... 14 G a b b r o ................. 17 Granodiorite ................................... 18 M o n z o n i t e ........................................19 North-South Mafic Dikes ...................... 21 East-West Mafic D i k e .............................23 Stream Gravels ................................. 24 South Willow Formation ........................ 25 Dacite Dikes ................................... 26 Pyramid Sequence .............................. 28 Lake Sediments ................................... 32 Quaternary Alluvium .......................... 33 Structural Geology ....................................... 34 Regional Framework ................................. 34 Fox R a n g e ...............................................35 Wild Horse Canyon A r e a ............................... 38 F a u l t i n g .......................................... 38 F o l d i n g .......................................... 46 Economic Geology .......................................... 47 Wild Horse Mine Geology ............................... 47 A l t e r a t i o n ............................................ 50 Ground Preparation ................................. 51 vi CONTENTS Page Geologic History ......................................... 52 Correlations . ................... 55 Nightingale Sequence ............................ 55 Granodiorite ....................................... 57 South Willow Formation ............................ 57 Pyramid Sequence .................................. 57 Lake Sediments ........................................ 58 Summary ........... ........................ ............ 59 Appendix .................... ......... ........ 61 References Cited ...... ................... .... 62 V1X LIST OF ILLUSTRATIONS Page Plate 1. Geologic map of the Wild Horse Canyon area ............................ In Pocket 2. Cross-sections ..... ............. in Pocket 3. View of the front of the Fox Range at the mouth of Wild Horse c a n y o n .............13 4. Blue-gray mica schists along fault plane at the mouth of Wii d Horse canyon . 16 5 „ Bed of recrystallized limestone inter­ calated in slates and phyilites of the Nightingale sequence ..... ............. 17 6. Sills of monzonite containing xenoliths of Nightingale rocks in lower Wild Horse 7. North-south mafic dike along old fault in lower Wild Horse canyon ................. .. 22 8. East-west mafic dike along older fault in lower Wild. Horse canyon ...................... 2 3 9. Folded dacite dike in Basin and Range Fault plane at the front of the Fox R a n g e .........27 10. View of the Wild Horse granodiorite stock and the workings of the Wild Horse mine as they appear today ............................ 4 8 Figure 1A. Location of the Fox Range quadrangle in Washoe County ........................ .... 2 IB. Route map to study area ...................... 2 2. Map of the Fox Range showing location of the Fox Range anticline ............. .. 37 3. Block diagram, showing scissor effect of ro­ tation of faults during anticlinal folding. 41 4. Diagramatic sequential formation of Fox Range anticline ........... ................... 43 1 INTRODUCTION Location and Accessibility Wild Horse canyon, in the Cottonwood mining district is located on the western slope of the Fox Range of southern Washoe' County, Nevada (Figure 1A). The canyon empties into the eastern side of the playa lake of the Smoke Creek desert. The canyon is labeled and appears near the north-central portion of the Fox Range Quadrangle of the U.S. Geological Survey's 15 minute topographic series. The mouth of the canyon lies approximately 100 airkilo- meters north of the city of Reno, Nevada along a bearing of N. 6°E. By road, the mouth of the canyon is some 130 kilo­ meters from Reno. Access to Wild Horse canyon from Reno is gained by traveling north on State Route 33 to Pyramid Lake and turn­ ing northwest along the western shore of the lake and con­ tinuing through Sutcliffe, Nevada (Figure IB). The paved Route 33 changes to improved dirt 13 kilometers northwest of Sutcliffe. Travel is continued along the improved dirt route for 44 kilometers to Sand Pass at the southern-most end of the Smoke Creek desert. Useful land marks at this location are the Western Pacific Railroad's gravel pit and construc­ tion crew house to the right or east of-the road. Also a rather large gravel pile is visible almost straight ahead of the driver when positioned in the road at the crest of Sand Pass. Travel is continued on the main improved dirt 2 IC O ' 118* MS* (14* Figure IA. Location of Fox Range Quadrangle in Washoe County. c JO 20 30 40 30 60 70 80 b m m m a m i m m — ■ — ■> ■ ftiii'iii« — ..n lV KILO M E S S P S Figure IB. Route mop to study area. ® State Route improved dirt route Jeep frail Wesren Pacific Railroad Reno 1 120- road around the western side of the gravel pile for about 1.2 kilometers to the junction of an unimproved jeep trail branching eastward off the main dirt road. This unimproved jeep trail crosses the southeastern tip of the Smoke Creek desert and continues northward paralleling the Smoke Creek desert and
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