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New!  Geologic Map of Spanish Springs Peak Quadrangle, Washoe County, Nevada
Geologic Map of Spanish Springs Peak Quadrangle, Washoe County, Nevada
 
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Product Code: OF2025-06

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Title: Geologic Map of Spanish Springs Peak Quadrangle, Washoe County, Nevada

Author: William Junkin and Seth Dee
Year: 2025
Series: Open-file reports
Version: OF2025-06
Format: 42" x 33" color map; text, 21 pages
Scale: 1:24,000

Mapping within the Spanish Springs Peak quadrangle provides insight into Oligocene–Miocene depositional processes, the geometry of the southern end of the Quaternary-active Warm Springs Valley fault system, and the distribution of Oligocene ash-flow tuffs that serve as key structural markers for Walker Lane tectonic deformation. Rock units in the map area include Mesozoic granitic plutonic, metasedimentary, and metavolcanic rocks; multiple Oligocene ash-flow tuff units; intercalated Miocene basalt/basaltic-andesite flows, clastic deposits including coarse tuffaceous breccia and megabreccia, and a dacitic tuff; Miocene mafic and felsic intrusions; and unconsolidated Quaternary sediments. A prominent deposit of the Oligocene tuff of Painted Hills several hundred meters thick with no exposed base crops out in the map area. This and other newly mapped Oligocene ash-flow tuffs support the previously proposed approximate location of an east-west trending Oligocene paleovalley several hundred meters deep that extends through the north half of the quadrangle. Basalt to basaltic-andesite lava flows intercalated with laterally discontinuous, coarse breccia and megabreccia deposits overlie the ash-flow tuffs. The megabreccia deposits, which attain a maximum thickness of approximately 200 m, contain predominantly tuff clasts, including clasts as large as 10s of meters in diameter, and share similarities to other megabreccia deposits in northwest Nevada interpreted as originating from landslides or “dam-burst” type floods. New geochronologic data from Miocene lavas and intercalated tuffs provide age controls and constraints on the timing of volcanism and tectonic extension in the map area. A newly dated dacitic tuff near the base of the sedimentary basin deposits in southern Warm Springs Valley indicates that extension and basin opening began prior to ~10.8 Ma, synchronous with widespread volcanism in the area. Several previously unmapped fault strands observed in newly available LiDAR data displace late Pleistocene alluvial fan surfaces and trend parallel to strands of the Warm Springs Valley fault system previously mapped to the north.

Suggested Citation: Junkin, W., and Dee, S., 2025, Geologic map of the Spanish Springs Peak quadrangle, Washoe County, Nevada: Nevada Bureau of Mines and Geology Open-File Report 2025-06, scale 1:24,000, 21 p.

© Copyright 2025 The University of Nevada, Reno. All Rights Reserved.

Original Product Code: OF2025-06