Latitude: N 33°56'47"
Longitude: W 116°38'01"
Length: 1381.4m
Number of Bench marks: 47
Number of Surveys to 2000: 6
Date of Initial Survey: 29 August 1986
Date of Latest Survey: 18 December 1994
Trespass Permission: None needed.
Directions:
From San Bernardino, drive east on Interstate 10 Freeway toward Palm Springs
and take the Whitewater exit . Proceed east 0.2 mile, thence left onto Whitewater
Canyon Road. Proceed 1.15 mile to the first bench mark (P410), which is 7
m east of the east si de of the road.
Comments:
This is one of several fault-crossing leveling arrays established by the
U.S. Coast and Geodetic Survey (NGS) in 1935. The line crosses the Banning
fault in Whitewater Canyon, one and one-half miles north of Whitewater. The
UCS B surveys have observed only a subset of the bench marks in the NGS line
since the North Palm Springs earthquake of July 1986.
Results:
A UCSB leveling in August 1986, a few weeks after the earthquake, is compared
with NGS levelings in 1949 and 1986 in an accompanying figure. Relative to
an NGS bench mark at the south end of the line, the height of the bench marks
decreases systematically northward, as if the entire line tilted northward
about 6 microradians. This is opposite to the topographic rise, sug gesting
that the tilt is tectonic and not due to refraction error. The tilt is also
opposite to the relative sense of vertical displacement across the fault,
suggesting that the active structure may be south of the fault itself. A
resurvey in 1988 found no signifcant change. Then in August 1992, following
the 28 June 1992 Landers earthquake sequence, the bench marks returned nearly
to the height they enjoyed in 1986. This may be evidence of nearfield, surficial
perturbation of the Mission Creek strand of the San Andreas fault by the
Landers earthquake sequence.
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