BAT CAVES Level Line

Latitude:N 33°25'26"
Longitude: W 115°49'04"

Length: 3658.0m
Number of Bench marks: 95

Number of Surveys to 2000: 15
Date of Initial Survey: 9 September 1985
Date of Latest Survey: 30 July 1996

Trespass Permission: None Needed

Drive southeast from Mecca along Hwy 111 about 18 miles to a railroad bridge over a gulch 0.75 mile southeast of the Riverside/Imperial County line. The southwest end of the line is at the lake shore; it continues northeastward beneath the Union Pacific Railway tracks at the bridge, thence over the crest of Durmid Hill through Bat Caves Buttes. The bridge is numbered 643-16 in large white letters and is 2.2 miles southeast of Salt Creek, and 8.4 miles from State Park Headquarters.

This line crosses the San Andreas fault and the crest of Bat Caves Butte, one and one-half miles northeast of the Salton Sea. It was established to determine if the buttes, which surmount Durmid Hill, are rising due to shortening related to the transpression on the San Andreas fault.

From 9 September 1985 to 28 June 1992, Durmid Hill has arched upward about 9 mm but not symmetrically relative to the crest of the hill. Vertical displacement is not apparent across the San Andreas fault itself. The uplift rate is consistent with the geological rate of about 1 mm/yr of uplift determined from the inception and rate of downcutting of Durmid Hill by Salton Creek and from tilting of ancient lake shorelines (Sylvester et al., 1993).

The line was lengthened in March 1992 from 2268 m to 3658 m to define the inflection points of the uplift more completely. Since the Landers earthquake of 28 June 1992, Durmid Hill has ceased to rise, implying that the strain field for the earthquake extended far beyond the region of surface rupture.


Sylvester, A. G., 1989. Triggered vertical strain across active strike-slip faults in southern California. Abstracts Volume, 28th International Geological Congress, Washington, D. C., v. 3, 207-208.

Sylvester, A., S. Barrientos, R. Bilham, and M. Jackson, 1991. Shear, uplift and shortening across Durmid Hill: Interseismic transpression on the southern San Andreas fault, California. EOS Transactions, American Geophysical Union, v. 72 (44), 497.

Sylvester, A. G., R. Bilham, M. Jackson, and S. Barrientos, 1993. Aseismic growth of Durmid Hill, southeasternmost San Andreas fault, California. Journal of Geophysical Research 98, 14,233-12,243.

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