Latitude: N 34°55'30"
Longitude: W 118°55'30"
Number of Bench marks: 25
Number of Surveys to 2000: 16
Date of Initial Survey: 27 July 1979
Date of Latest Survey: 28 June 1995
Trespass Permission: Contact Four Corners Pipe Line Co.
The line is located in the field west of the old highway 99 at the townsite of Grapevine, 13 miles north of Gorman. The southernmost bench mark is NGS bench mark G540 in a bridge abutment that carries traffic from old highway 99 west to a pipeline maintenance facility and a house, both south of the fault.
This line crosses the most recent scarp of the Pleito fault. It ties three bench marks of a regional NGS line, P1098, Q1098, and G540. Because the diameter of the PVC pipes installed around the benchmarks is to o small to accommodate NA3000 bar code rods, the PVC pipes were broken to allow leveling with the NA3000.
As of 12 May 2004 all of the bench marks on and north of the fault scarp have
been obliterated by a bulldozer to establish a vineyard.
Three recent surveys are compared with a 1980 survey in an accompanying figure. Over a period of eight years the changes among the bench marks have been insignificant. No permanent vertical strain was observed following the North Garlock earthquake (M 5. 3) of 10 June 1988; however, six days after a M 4.8 earthquake on 4 November 1981, 10 km northwest of the array, all bench marks on the sout h, or hanging wall of the fault rose an average of 2 mm relative to those on the footwall. Six months later, the array returned to its pre-earthquake datum (Sylvester, 1989).
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.
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