LEWIS CREEK Level Line

Latitude: N 36°17'42"
Longitude: W 120°52'30"

Length: 1715.0m
Number of Bench marks: 49

Number of Surveys to 2000: 5
Date of Initial Survey: 31 July 1985
Date of Latest Survey: 1 July 1993

Trespass Permission: Level line is on a private ranch. Permission to trespass is reqired

Directions:
From King City, proceed east-southeast 14 miles on Lonoak Road to its intersection with Hwy 25; tu rn left and proceed east-northeast about 3 miles to the Lewis Creek Road; turn right and proceed 2.8 miles to the Rist Ranch. Lewis Creek forms the county line in this vicinity between Monterey and San Benito counties.

Comments:
This line follows the floor of Lewis Creek across the San Andreas fault 3.5 miles east of Lonoak, on the San Benito-Monterey County line. Several of the bench marks are considered as little more than temporary, because they are in rather small boulders th at may be dislodged during a flood.  Many bench marks in this line were obliterated in the flood of 1993 and have not been replaced.

Four levelings are graphed in an accompanying figure; four bench marks on the east side of the fault have risen about 10 mm relative to those on the west side of the fault, for a rate of 2 mm/yr. Except for bench mark LC32, one may infer that the east block is tilting slightly to the east as well. I conclude that a tectonic wedge perhaps 200m wide is rising relative to the remainer of the land. The horizontal creep in this segment of the fault is nearly 30 mm/yr. (Burford and Harsh, 1980).

References:
Burford, R.O. and P.W. Harsh, 1980. Slip on the San Andreas fault from alignment array surveys. Seismological Society of America Bulletin 70, 1233-1262.
Sylvester, A. G.,  1995. Nearfield vertical displacement in the creeping segment of the San Andreas fault, central California, 1975 to 1994. Tectonophysics 247, 25-47.

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