HOG LAKE EDM Array
Number of Bench marks: 6
Number of Surveys to 1993: 4
Date of Initial Survey: 11 September 1988
Date of Latest Survey: 27 July 1992
Trespass Permission: None needed.
Directions: From Anza, proceed northwest 6 miles on Bautista Canyon Road to Hog Lake Road; thence northeast about 2 miles to a fork at the Ramona Indian reservation. Proceed on the left fork about one mile to another fork at the divide. Bench marks 1, 2, and 3 are o n the slope on the northeast side of the canyon; bench m arks 4, 5, and 6 are on the ridge southwest of the canyon. In the event that access is blocked along Hog Lake Road, proceed from Anza northwest along Bautista Canyon Road about 7 miles to the Cottonwood Firebreak Road, turn right and proceed about 3 miles along a curvy, rough dirt road to the divide at the San Jacinto fault.
Comments: This is a doubly-braced quadrilateral across the San Jacinto fault. Bench marks are Class B rod marks driven to refusal and capped with a stainless steel nipple. The firs t two surveys of the array were incomplete, owing to time and weather constraints. The second survey was performed to see if displacement had occurred following increased earthquake activity in the area. No significant changes were observed between those two surveys (Sylvester, et al., 1990). The third survey was plagued by unfavorable survey conditions of heat, wind, and shimmer. The fourth survey was complete, and no significant line length changes were noted relative to all the previous surveys.
Sylvester, A. G., J. Helm, C. Hitchcock, and N. Howe, 1990. Minor vertical, but no horizontal nearfield displacement across the San Jacinto fault at Anza and San Bernardino, California, from 1988 to 1990. Seismological Research Letters 61 (1), p.
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