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Brief Report for Garlock fault zone, Western Garlock section (Class A) No. 69a

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citation for this record: Bryant, W.A., compiler, 2000, Fault number 69a, Garlock fault zone, Western Garlock section, in Quaternary fault and fold database of the United States: U.S. Geological Survey website,, accessed 09/17/2014 05:34 PM.

Synopsis General: Major Holocene active, east to northeast-striking sinistral strike-slip fault that forms the boundary between the Tehachapi Mountains, Sierra Nevada, and Basin and Range province on the north and the Mojave Desert province to the south. Garlock fault zone is divided into 3 sections in this compilation, based on McGill (1992 #6053). The western Garlock fault section extends from the complex intersection with the San Andreas fault [1g] near Frazier Park east-northeast to a 3-km-wide left-releasing step-over in the vicinity of Koehn Lake. The central Garlock section extends from the left-releasing step-over near Koehn Lake eastward to the Quail Mountains where the Owl Lake fault [70] intersects the Garlock fault zone. The eastern Garlock fault section extends from the Owl Lake fault [70] eastward to the complex intersection with the southern extent of the Southern Death Valley fault zone [143b]. Aseismic fault creep has been reported along the westernmost 60 km of the Garlock fault zone (Rodgers, 1979 #6071; Snay and Cline, 1980 #6070; Louie and others, 1985 #5731). However, U.S. Geological Survey quadrilateral sites spaced at 15 km intervals along this part of the fault zone have not detected evidence of fault creep (M. Clark, personal communication in McGill, 1992). There are 7 paleoseismic study sites involving trenching along the western and central Garlock fault sections described in this compilation, with additional slip rate sites involving geomorphic analysis (Burke, 1979 #2985; Carter, 1980 #6043; LaViolette, 1981 #6051; Roquemore and others, 1982 #2993; McGill and Sieh, 1991 #6062; McGill, 1992 #6053; McGill and Sieh, 1993 #6063; McGill, 1994 #6056; McGill and Rockwell, 1998 #6064; McGill, 1999 #6060; McGill, in preparation #6061). A Holocene slip rate for the western Garlock fault section of 1.6-3.3 mm/yr was reported by LaViolette (1981 #6051) for the Oak Creek Canyon site [69a-3]. McGill and others (in preparation #6061) reported a preferred minimum Holocene slip rate of at least 6.8?1.5 mm/yr at the Lone Tree Canyon site [69a-4]. Clark and others (1984 #2876), based on data reported by Carter (1980 #6043), calculated a preferred long-term sinistral slip rate of 11 mm/yr near Mesquite Canyon. Near Koehn Lake a sinistrally offset 11- to 15-ka lake bar indicates a slip rate of 5-8 mm/yr (radiocarbon years) (Clark and others, 1984 #2876). McGill and Sieh (1991 #6062), using the calibration of Bard and others (1990 #6042), re-calculated the slip rate reported by Clark and others (1984 #2876) at Koehn Lake to be 4-7 mm/yr. McGill and Sieh (1993 #6063) reported a slip rate of 5-11 mm/14Cyr or 4-9 mm/yr after calibration of the radiocarbon dates. Their preferred slip rate was 6-8 mm/14Cyr (or 5-7 mm/yr in calibrated years) calculated from the southern Searles Valley site [69b-3]. McGill and Sieh (1991 #6062) and McGill (1992 #6053) concluded that some sinistral slip is transferred to the Owl Lake fault [70]. The slip rate of the Garlock fault east of its intersection with the Owl Lake fault [70] is not known with any certainty. Recurrence intervals for the Garlock fault zone are 800-2,700 yr for the western Garlock fault section (McGill, 1994 #6056); 190-3,405 yr for the central Garlock fault section (McGill and Rockwell, 1998 #6064); and 200-3,000 yr for the eastern Garlock fault section (McGill and Sieh, 1991 #6062). McGill and Rockwell (1998 #6064) noted that recurrence intervals are irregular at the El Paso Peaks site [69b-2] and reported preferred average recurrence intervals of 1,230 yr assuming 5 events or 700 yr assuming 8 events. In a deeper re-excavation at the El Paso Peaks site, Dawson (2000 #6047) confirmed the irregular nature of recurrence, but eliminated one of McGill and Rockwell's events, and added an older event that was not exposed in the original trench.

Sections: This fault has 3 sections.
Physiographic province(s) BASIN AND RANGE
Length (km) This section is 110 km of a total fault length of 257 km.
Average strike N55°E (for section) versus N68°E (for whole fault)
Sense of movement Sinistral
Dip Direction V
Historic earthquake
Most recent prehistoric deformation Latest Quaternary (<15 ka)
Slip-rate category Greater than 5.0 mm/yr
Date and Compiler(s) 2000
William A. Bryant, California Geological Survey