THE EARTH MOVEMENT ON THE FAULT OF APRIL 18, 1906, 95 
Nowhere along this portion of the fault-trace between the slide at Mussel Rock and 
San Andreas Lake was there observed any definite evidence of vertical displacement. 
There was a hint of slight upthrow on the western side, but it could not be tested by 
measurement. ‘There were, in general, furrows on either side of the main fault, at various 
distances up to 200 feet. Some of these were persistent for considerable distances. 
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San Bruno 
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Fig. 30.— Index map showing positions of three fences, A, B, and C, the 
offsets of which are shown in figs. 31, 37, and 38. 
About 2 miles from the upper end of San Andreas Lake the fault encounters the 30-inch, 
laminated, wrought-iron pipe of the Spring Valley Water Company, which prior to the 
earthquake conveyed the water from Pilarcitos Lake to San Francisco. The metal of 
the pipe is about 0.1875 inch thick and coated with asphaltum. ‘The pipe is buried in the 
soil at a depth of 3 to 4 feet. The point of intersection is near Small Frawley Canyon. 
Here the course of the pipe swings from a northwesterly to a more northerly course, 
and the fault consequently intersects it at an acute angle. At the point of intersection, 
the pipe was obliquely sheared apart and telescoped upon itself, effecting a shortening 
of about 6 feet. The amount of the transverse offset involved in the shear was about 
half the diameter of the pipe. The portion north of the break was moved east and tele- 
scoped southerly. For 0.875 mile southeast of this point, the path of the fault lay on the 
northeast side of the pipe and nearly parallel to it, but a short distance away. About 
220 yards southeast of the intersection, where the pipe, buried a few feet below the sur- 
face, ascends a rising slope, the pipe had completely collapsed for a distance of several 
