92 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
MUSSEL ROCK TO CRYSTAL SPRINGS LAKE. 
Course of the fault-trace. — The point at which the fault-trace intersects the shore, on 
emerging from the ocean on the south side of the Golden Gate, is only approximately 
known. About 0.875 mile to the southeast of Mussel Rock, it has been located with 
precision at its intersection with the wagon road on the west side of the coastal ridge a little 
below its crest,-and thence followed continuously for many miles. Projecting its course, 
there determined, in a northwesterly direction, it would pass out to sea in the midst of 
the large landslide which scars the coast immediately to the north of Mussel Rock, where 
the basal beds of the Merced series rest upon the older rocks. At the time of the earth- 
quake there was an extensive movement of the landslide, and a tongue of landslide mate- 
rial, about 50 feet high and about 200 feet wide, was projected into the ocean across the 
narrow strip of beach.‘ This movement naturally obscured all evidence of the position 
of the fault-trace, which was doubtless overridden by the slide. All about the crest to 
the east of the landslide, and on its south side, the ground was greatly disturbed by fresh 
landslide cracks, scarps, and fissures, extending well back from the edge of its encircling 
cliffs. It appears to be probable that not only did the movement of the landslide obscure 
the evidence of the fault-trace, but also that the latter was here diffuse and scattered, and 
that the displacement was superficially taken up by the plasticity of the landslide material. 
From the point southeast of the Mussel Rock slide where the fault-trace resumes its 
definite and easily recognizable character, to Crystal Springs Lake, our information re- 
garding the course of the fault-trace and the earth movement on the fault is in part from 
observations made by Mr. Robert Anderson, and in part from observations recorded in a 
paper by Herman Schussler,’ supplemented by the observations of Mr. H. O. Wood, 
Andrew C. Lawson, and others. 
South of the road, at a point 0.875 mile southeast of Mussel Rock, begins the furrow 
which marks the surface path of the fault. The furrow as such does not cross the road 
to the north of this point. The side-hill slope, however, is very much fissured by land- 
slide movements both above and below the road, and scarps are seen. From this point, 
the furrow runs uninterruptedly southeastward to the east side of the north end of San 
Andreas Lake, where, with a course of about 8. 33° E., it passes beneath the waters of 
that reservoir. As it approaches the lake, the trace of the fault does not lie in the axis 
of the valley, but runs along its eastern side. It thence passes thru the lake on the north- 
east side, crossing a number of small promontories, to the east end of San Andreas dam; 
thence, with a course of 8. 37° E., it traverses the east side of the valley between this 
dam and Lower Crystal Springs Lake, passes thru the latter and intersects the old dam 
between Upper and Lower Crystal Springs Lakes. Beyond this it skirts the southwest 
side of the upper lake, partly in the water and partly on the projecting points, and finally 
leaves the lake about a 0.25 mile from its end, for the stage of the water of April, 1906, 
having here a course of 8. 40° E. 
The mean course of the fault, as thus closely followed from the vicinity of Mussel Rock 
to the end of Upper Crystal Springs Lake, a distance of about 15 miles, is S. 36° 30’ EK. 
But the trace is not a perfectly straight line. Between Mussel Rock and San Andreas 

On February 27, 1907, according to the observations of Mr. H. O. Wood, this projecting tongue of 
landslide had been entirely removed by the action of the waves, and alinement of the beach and sea-cliff 
had been reéstablished. 
The Water Supply of San Francisco before, during, and after the Earthquake of April 18, 1906, and 
the Subsequent Conflagration. New York, 1906. 
