YMCA Level Line

Latitude: N 37°37'34"
Longitude: W 118°55'37"

Length: 1019m
Number of Bench marks: 10

Number of Surveys to 2000: 11
Date of Initial Survey: 11 July 1984
Date of Latest Survey: 26 August 1995

Trespass Permission: None needed.

From Highway 395, proceed south at the Sheriff's substation on an unsigned gravel road that is, in fact, Sherwin Creek Road. Proceed southwest and west about 2.5 miles to the turnoff to the YMCA camp. The southwest leg of the array is on the southwest side of the road.

This L-shaped tilt-array was established by John Estrem of the U.S. Geological Survey along Sherwin Road 3 miles southeast of Mammoth Lakes to monitor tilt in Long Valley caldera. All bench marks are set in 20 cm diameter, white PVC pipe.

From 1984 to 1986 the relative heights of bench marks changed but little. Between 1986 and 1992, however, the array tilted southwestward about 15 microradians. This is the direction one would expec t tilt to occur if uplift in the caldera is centered northeast of the array.

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