Author: Seth Dee
Series: Open-File Report 2019-05
Version: supersedes Open-File Report 1987-08
Format: plate: 28 x 32.5 inches, color; text: 5 pages, color
The Granite Peak 7.5-minute quadrangle is located immediately north of Reno, and abuts the Nevada-California state line in an area known as the ‘North Valleys’. The quadrangle includes the summits of Petersen Mountain and Granite Peak, and portions of Red Rock Valley and Cold Springs valley. The bedrock exposures in the quadrangle consist primarily of Cretaceous granitic rocks related to the Sierra Nevadan batholith. The granitic rocks include three distinct lithologies with relative ages constrained by clear crosscutting relationships. Miocene to Pliocene clastic and fluvio-lacustrine sediments are deposited in a shallow basin west of Freds Mountain in the easternmost part of the quadrangle. On the western flank of Petersen Mountain, west-dipping Oligocene ash-flow tuff deposits nonconformably overlie Cretaceous granite. Quaternary sediments largely consist of alluvial fans and several large landslide deposits (up to 2.7 sq. km.).
The quadrangle is bisected by the Petersen Mountain fault zone. The fault zone consists of two subparallel traces (western and eastern) that extend from Cold Springs valley in the south to Seven Lakes Mountain in the north. The western trace of the fault strikes generally north-south along the eastern range front of Petersen Mountain, dips steeply east, and locally displaces surficial deposits as young as Holocene. The eastern trace consists of several north-south striking strands that displace surficial deposits as young as late Pleistocene and locally forms a narrow graben infilled by faulted fanglomerate material. Fault surfaces on the eastern trace have subhorizontal slickenlines demonstrating a history of dextral-oblique motion. Long-term late Cenozoic normal displacement across the western trace is demonstrated by the high relief of the Petersen Mountain range front (>500 m) as well as the accumulation of Miocene-Pliocene sediments to the east that were likely deposited into a basin controlled by early displacement along the fault. This is in contrast to the eastern strand, which has been active since at least the middle Pleistocene but for much of its length does not bound basins with significant accumulations of late Cenozoic deposits. These map relationships suggest the Petersen Mountain fault zone initially developed as a Basin and Range extensional structure with displacement primarily along the western fault trace, and has evolved into a Walker Lane structure with dextral-oblique motion focused on the eastern trace.
This geologic map was funded by the USGS National Cooperative Geologic Mapping Program under STATEMAP award number G18AC00198, 2019.