1599, PILOT CREEK VALLEY FAULT ZONE

Structure number: 1599.

Comments: Referred to as fault number WE17 by dePolo (1998); part of Hecker's (1993) Pilot Range faults (number 6-11).

Structure name: Pilot Creek Valley fault zone.

Comments: Refers to faults mapped by Slemmons (1967), Miller and others (1982, 1990), Dohrenwend and others (1991), and Miller and Lush (1991), and named the Pilot Creek Valley fault zone by dePolo (1998). The fault zone extends from Crystal Cave in the northern Pilot Range along the western range front to the southern end of the range in the Elko quadrangle (Dohrenwend and others, 1991).

Synopsis: This poorly understood, discontinuous zone of normal faults bounds the western flank of the Pilot Range. Although not studied in detail, two sections are suggested by general movement history and geometry of the fault. The northern and southern sections are separated by a 10-kilometer gap, over which the fault makes a 5-kilometer-wide right step. The northern section bounds the western front of the northern Pilot Range along the Utah-Nevada border; it forms fault scarps on early to middle Pleistocene alluvium and has range-front faults that juxtapose Quaternary alluvium against bedrock (Dohrenwend and others, 1991). The southern section extends from west of Pilot Peak south to the southern end of the range and is entirely in Nevada; it is expressed as a range-front fault juxtaposing Quaternary alluvium against bedrock (Dohrenwend and others, 1991).

Date of compilation: 9/30/98 and 6/27/00 (Nevada); 10/99 (Utah).

Compiler and affiliation: John A. Oswald and Thomas L. Sawyer (Piedmont Geosciences, Reno, Nevada) and Peter D. Rowley (U.S. Geological Survey) (Nevada); Bill D. Black (Utah Geological Survey) and Suzanne Hecker (U.S. Geological Survey) (Utah).

State: Nevada; Utah.

County: Elko; Box Elder.

1° x 2° sheet: Wells, Elko.

Province: Basin and Range.

Geologic setting: Discontinuous, down-to-the-west, right-stepping normal fault bounding the western front of the Pilot Range. The Pilot Range bounds the western edge of the Great Salt Lake Desert in northwestern Utah. Northern and southern fault sections are separated by a 10-kilometer gap, over which the fault makes a 5-kilometer right step.

Number of sections: 2

Comments: Although not studied in detail, two sections are suggested by general movement history and geometry of the fault. The northern and southern sections are separated by a 10-kilometer gap, over which the fault makes a 5-kilometer-wide right step. The northern section bounds the western front of the northern Pilot Range and forms fault scarps on early to middle Pleistocene alluvium and has range-front faults that juxtapose Quaternary alluvium against bedrock (Dohrenwend and others, 1991). The southern section extends from west of Pilot Peak south to the southern end of the range, and is expressed as a range-front fault juxtaposing Quaternary alluvium against

bedrock (Dohrenwend and others, 1991). The northern section lies along the Utah-Nevada border; the southern section is entirely in Nevada.

Length: End to end (km): 18

Cumulative trace (km): 21

Average strike (azimuth): N0°W

1599a, NORTHERN PILOT CREEK VALLEY SECTION

Section number: 1599a.

Section name: Northern Pilot Creek Valley section.

Comments: Refers to the northern part of the Pilot Creek Valley fault zone of dePolo (1998). Section extends from Crystal Cave to Killian Springs along western front of the Pilot Range.

Reliability of location: Good.

Comments: Location based on 1:24,000-scale preliminary geologic mapping of Miller and others (1982, 1990) and Miller and Lush (1991), and 1:250,000-scale mapping of Dohrenwend and others (1991); small-scale mapping by photogeologic analysis of 1:58,000-nominal-scale color-infrared photography transferred directly to 1:100,000-scale topographic quadrangle maps enlarged to scale of the photographs.

Sense of movement: N.

Comments: See Miller and others (1982); dePolo (1998).

Dip: No data.

Comments:

Dip direction: W.

Geomorphic expression: The section is expressed by rounded and barely recognizable scarps on early to middle Pleistocene piedmont-slope deposits adjacent to the range front between Hogans Alley north to Regulator Canyon, and by Quaternary alluvium juxtaposed against bedrock along the range-front fault (Miller and others, 1982, 1990; Dohrenwend and others, 1991). North of the scarps, aligned springs and topographic lineaments suggest a probable buried Quaternary(?) fault that may form the western margin of elevated Tertiary and Quaternary deposits. Well-rounded scarps on Pleistocene older alluvium and abundant fault-aligned springs extend from west of Parson Springs to the southern end of the section (Miller and others, 1982).

Age of faulted deposits: Early to middle Pleistocene. Faults displace alluvium interpreted from photogeologic mapping to be early to middle Pleistocene in age (Dohrenwend and others, 1991). Faults adjacent to and south of Parson Springs displace Pleistocene alluvium and alluvial-fan deposits (Miller and others, 1982, 1990; Miller and Lush, 1991).

Paleoseismology studies: None.

Timing of most recent paleoevent: (4) Middle and late Quaternary (<750 ka).

Comments: Timing of the most recent event is not well constrained; Dohrenwend and others (1991, 1996) suggested a Quaternary age based on reconnaissance photogeologic studies. A southern fault trace displaces alluvium of “probable Holocene age,” forming 2- to 3-meter-high scarps (Miller and Lush, 1991).

Recurrence interval: No data.

Comments:

Slip-rate category: Unknown, probably <0.2 mm/yr.

Comments: dePolo (1998) estimated a late Pleistocene vertical slip rate of 0.01 millimeters/year (0.003 to 0.07 millimeters/year) for the Pilot Creek Valley fault zone based on a comparative geomorphic analysis.

Length: End to end (km): 18

Cumulative trace (km): 21

Average strike (azimuth): N0°W

REFERENCES

dePolo, C.M., 1998, A reconnaissance technique for estimating the slip rate of normal-slip faults in the Great Basin, and application to faults in Nevada, U.S.A.: Reno, University of Nevada, unpublished Ph.D. dissertation, 199 p.

Dohrenwend, J.C., McKittrick, M.A., and Moring, B.C., 1991, Reconnaissance photogeologic map of young faults in the Wells 1° x 2° quadrangle, Nevada, Utah, and Idaho: U.S. Geological Survey Miscellaneous Field Studies Map MF-2184, 1 sheet, scale 1:250,000.

Dohrenwend, J.C., Schell, B.A., Menges, C.M., Moring, B.C., and McKittrick, M.A., 1996, Reconnaissance photogeologic map of young (Quaternary and late Tertiary) faults in Nevada, in Singer, D.A., editor, Analysis of Nevada's metal-bearing mineral resources: Nevada Bureau of Mines and Geology Open-File Report 96-2, 1 plate, scale 1:1,000,000.

Hecker, Suzanne, 1993, Quaternary tectonics of Utah with emphasis on earthquake-hazard characterization: Utah Geological Survey Bulletin 127, 2 plates, scale 1:500,000, 257 p.

Miller, D.M., and Lush, A.P., 1991, Geologic map of the Pilot Peak quadrangle, Box Elder County, Utah, and Elko County, Nevada: Utah Geological and Mineral Survey Open‑File Report 208, 49 p., scale 1:24,000.

Miller, D.M., Lush, A.P., and Schneyer, J.D., 1982, Preliminary geologic map of Patterson Pass and Crater Island NW quadrangles, Box Elder County, Utah, and Elko County, Nevada: U.S. Geological Survey Open-File Report 82-834.

----1990, Geologic map of the Patterson Pass quadrangle, Box Elder County, Utah, and Elko County, Nevada: Utah Geological and Mineral Survey Open‑File Report 172, 56 p., scale 1:24,000.

Slemmons, D.B., 1967, Pliocene and Quaternary crustal movements of the Basin-and-Range province, USA: Journal of Geosciences, Osaka City University, v. 10, p. 91-103.