THE EARTH MOVEMENT ON THE FAULT OF APRIL 18, 1906. 1038 
a disjointing, resulting in a narrowing and bending of the channel at one point. The 
banks on the northeast and southwest sides of the fault were thrust past each other south- 
east and northwest, respectively. Usually the movement resulted in the crushing of the 
loose earth at the surface, while the roots of plants tended to hold it in place, so that the 
displacement was not evident in its full effect. An example where this is well shown 
occurs in the channel of a small stream running at right angles to the fault valley just 
north of the north end of Crystal Springs Lake. The banks of the gully were about 20 
feet high. Where the fault crosses the southeast bank, the parts on either side of the 
crack faulted past each other horizontally, the result being a relative displacement of 
the northeast side of the fracture at least 8 feet toward the southeast. There is no 
vertical movement apparent. An escarpment is left exposed on the southwest side of 
the fault from top to bottom of the embankment. The material of the bank, plastic, 
argillaceous earth derived from weathered shale, was slightly moist at the time. The 
fault planes are closely apprest 
and the clay was left slicken-sided 
and lined with distinct. horizontal 
striations. (Plate 62a.) The op- 
\ 
N \ 
\\A 
\ 
posite bank of the stream gives | cower cars. 
\ 
SPRINGS RESERVOIR \\\\\ 
\ ) 
evidence of a similar movement, 
but the loose earth was held by 
large roots and the displacement 
of the underlying earth was ob- 
secured. The two projecting faces 
of the opposite banks almost met, 
making the channel very narrow 
and curved.* 
A steep embankment of weath- 
ered serpentine and soil occurs at 
the southern end of San Andreas ‘ 
Lake, where it is crost by the 68S A\W/i7" dween cavstar 
fault. The zone of rupture is (gQtZ/////, SPRINGS RESERVOIR 
several feet in width and the YY 
broken material on the northeast 
side is shown projecting several Scale in feet 
feet beyond its previous position 
in continuity with the serpentine 7 oe oa Maca Sonosgae 
slope. A displacement of the 
shore line is observable at several places where the fault fissure enters the lake. 
Wherever cracks were opened, search was made for the disjointing of squirrel holes and 
other discrepancies due to shifting, but with rather unsatisfactory results. Roots, 
however, were found broken and displaced in accordance with the general movement 
as shown by other things. In general, the search for evidence in the separation of 
different zones of vegetation or of color in the earth, etc., failed to add anything of value 
to evidences of other kinds. 
Vertical movement (R. Anderson). — No proof was found of a vertical movement along 
the fault line. Here and there occur small escarpments along the fissures, varying from 
a few inches to several feet in height. They were only local, however; they exhibited 
no constancy in the side of the fault upon which they appeared, and were invariably 
explainable either as fault exposures such as are discust in the previous paragraphs, or as 



1 The writer is indebted to Mr. C. E Durrell and Mr. F. D. Posey, of St. Matthews School, San Mateo, 
for the discovery of this interesting example of faulting. 
