Preliminary geologic map of the Mount Rose NW quadrangle, Washoe County, Nevada

Nicholas H. Hinz, Alan R. Ramelli, and Christopher D. Henry
Open-File Report 2018-03
supersedes Open-File Report 2016-06
Format: plate: 35 x 29 inches, color; text: 4 pages, B/W

This quadrangle straddles the north end of the Carson Range directly west-southwest of Reno and abuts the Nevada-California border. The Truckee River and Interstate 80 transect the northwest quarter of the quadrangle. Parts of the City of Reno urban area and Steamboat irrigation ditch fall within the northern part of the quadrangle, and part of a rural community along Thomas Creek is in the southeast quarter.

The bedrock exposures in the quadrangle consist of Mesozoic granitic and metamorphic basement, and Tertiary volcanic and sedimentary rocks. The Tertiary section includes a complex section of lavas, intrusions, and volcanic sedimentary rocks. Tertiary volcanic and sedimentary rocks in the northern part of the quadrangle are part of an ~1112 Ma ancestral Cascades volcanic center. Generally north-dipping Miocene basalt (~10 Ma) and fluvial-lacustrine sediments rest on the ~11–12 Ma volcanic rocks. Many of the volcanic and sedimentary rocks in the southern part of the quadrangle were derived from a ~6–7 Ma volcanic center in the Mount Rose quadrangle, directly south of this quadrangle. Plio-Pleistocene basaltic andesite lavas locally rest on these late Miocene volcanic rocks in the middle part of the quadrangle. Principal surficial deposits include late Pliocene to modern alluvial fan and fluvial deposits, deposits of the Truckee River, Quaternary glacial deposits, and extensive late Quaternary mass wasting deposits. Notable deep-seated landslide complexes reside in all major drainages—including Thomas Creek, Hunter Creek, Bronco Creek, and the smaller catchments along the west edge of the quadrangle. Most of the Carson Range is west-tilted with west-dipping Cenozoic strata. However, within the Mount Rose NW quadrangle, the dip domain flips and most all the Cenozoic strata dips east with numerous west-dipping normal faults. These west-dipping normal faults are cut by younger east-dipping normal faults of the Mount Rose fault zone on the east side of the range. East-facing Quaternary fault scarps occur on the east side of the range, west-facing Quaternary fault scarps occur on the west side of the range, and the crest of the range is cut by a complex zone of mostly west-facing faults.

This geologic map was funded in part by the USGS National Cooperative Geologic Mapping Program under STATEMAP award numbers G15AC00240, 2016, and G17AC00212, 2018.

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