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Open-File Report 99-35

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# Geologic Map of the East of Grotto Hills Quadrangle, California: A Digital Database

#### By Jane E. Nielson

#### Digital database by David R. Bedford

| Introduction
The East of Grotto Hills 1:24,000-scale quadrangle of California lies west of the ColoradoRiver about 30 km southwest of Searchlight, Nevada, near the boundary between thenorthern and southern parts of the Basin and Range Province. The quadrangle includes theeastern margin of Lanfair Valley, the southernmost part of the Castle Mountains, and part of thenorthwest Piute Range. The generally north-trending Piute Range aligns with the Piute and DeadMountains of California and the Newberry and Eldorado Mountains and McCullough Range ofNevada. The southern part of the Piute Range adjoins Homer Mountain (Spencer andTurner, 1985) near Civil War-era Fort Piute. Adjacent 1:24,000-scale quadranglesinclude Castle Peaks, Homer Mountain, and Signal Hill, Calif.; also Hart Peak, Tenmile Well,and West of Juniper Mine, Calif. and Nev.

The mapped area contains Tertiary (Miocene) volcanic and sedimentary rocks, interbedded          with and overlain by Tertiary and Quaternary surficial deposits. Miocene intrusions mark          conduits that served as feeders for the Miocene volcanic rocks, which also contain late magma          pulses that cut the volcanic section. Upper Miocene conglomerate deposits interfinger with the          uppermost volcanic flows. Canyons and intermontane valleys contain dissected Quaternary          alluvial-fan deposits, mantled by active alluvial-fan deposits and detritus of active drainages.          The alluvial materials were derived largely from Early Proterozoic granite and gneiss complexes,          intruded by Mesozoic granite, dominate the heads of Lanfair Valley drainages in the New York          Mountains and Mid Hills (fig. 1; Jennings, 1961). Similar rocks also underlie Tertiary deposits          in the Castle Peaks, Castle Mountains, and eastern Piute Range | First posted January 28, 1999
-  **Map** PDF (2.5 MB)
- **Pamphlet** PDF (182 kB) 

**Data files**
- **Geology** E00.GZ (146 kB)
- **Structure** E00.GZ (3 kB)   
- **Sample localities** E00.GZ (1 kB)   
- **Scanned topo base** E00.GZ (6.7 MB)   
- **All coverages** E00.GZ (6.9 MB) 
- **Import**AML (1 kB)
-  **Database explanation** TXT (28 kB)  View the database explanation pamphlet as an unformatted, text-only file 

**For additional information, contact:**          Geology, Minerals, Energy, and Geophysics Science CenterU.S. Geological Survey345 Middlefield Road, MS 901Menlo Park, CA 94025-3591http://geomaps.wr.usgs.gov/gmeg/

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### Suggested citation:

Nielson, J. E., Bedford, D. R., 1999, Geologic Map of the East of Grotto Hills Quadrangle, California: A Digital Database: U. S. Geological Survey Open-File Report 99-35, 9 pp., *https://pubs.usgs.gov/of/1999/0035/*.

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U.S. Department of the Interior |            U.S. Geological Survey           	URL: *http://pubsdata.usgs.gov/pubs/of/1999/0035/index.html*            Page Contact Information: GS Pubs Web Contact           	Page Last Modified: Wednesday, 07-Dec-2016 17:50:20 EST