Latitude: N 34°10'38"
Longitude: W 118°01'03"
Number of Bench marks: 27
Number of Surveys to 2000: 9
Date of Initial Survey: 14 August 1984
Date of Latest Survey: 14 July 1995
Trespass Permission: Permission to trespass is required from the Los Angeles Flood Control District.
From Santa Barbara, drive to Pasadena and continue east on the 210 freeway to Santa Anita Boulevard. Drive north on Santa Anita Boulevard 1.5 miles to Elkins Avenue and turn right. Then drive 0.4 mile and turn left onto Highland Oaks, where after 0.6 mil e there is an entrance to Arcadia Wilderness Park. The entrance is across the street from #2235 Highland Oaks.
*Before 8 AM or after 5 PM: Continue straight on Elkins to a locked gate, use the key, and proceed to the right and cross a bridge over a concre te channel. Bear left up the canyon. The level line begins about 100 m down the canyon from the first unlocked gate south of the park.
This line crosses the Sierra Madre fault in Arcadia Wilderness Park at the southern front of the San Gabriel Mountains, 7 miles northeast of Santa Anita (Proctor and Crook, 1987). The line was established to detect vertical creep or displacement. Much of the line is behind fences and locked gates belonging to the Los Angeles County Flood Control District.
Four levelings, from August 1984 to June 1992, are compared in an accompanying figure and show that height changes among the bench marks are negligible in eight years. We did not detect apparent vertical displacement across the fault in response to the 1 October 1987 Whittier Narrows earthquake (M 5.9), 13 km south-southwest of the array (Sylvester, 1989), or to the 28 June 1991 Sierra Madre earthquake (M 5.4), 3 km km east of the array. This is not especially surprising, because the latter earthqua ke occurred on the northeast-striking Sawpit Canyon fault
Proctor, R. J., and R. Crook, Jr., 1987. Sierra Madre thrust fault, Arcadia, California. Geological Society of America Centennial Field Guide - Cordilleran Section - Volume 1, pp. 217-218.
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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