48 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
reported to have been thrown down in Palm Canyon, which issues from San Ysidro Moun- 
tain. Ten miles southeast of San Jacinto, on the line of the fault, it is said that a con- 
siderable area of land sank with formation of open fissures. Upon the Coahuila Indian 
Reservation, adobe buildings were thrown down and much damage was done in the 
town of San Jacinto. 
The regular mountain wall facing southwest and extending northwest from San Jacinto 
appears to be older than that toward the southern end of the fault. Mineral springs 
occur near or on this line, and the marshy area at the point where the San Jacinto River 
ceases following this fault-scarp and turns toward the southwest suggests very strongly a 
subsidence. 
REVIEW OF SALIENT FEATURES. 
It will be of advantage briefly to review the salient features of the San Andreas Rift, 
in the light of the facts presented in the foregoing detailed description of its extent and 
character, and of other facts to which attention will be directed. 
The San Andreas Rift has been traced with three interruptions from a point in Hum- 
boldt County, between Point Delgada and Punta Gorda, to the north end of the Colorado 
Desert, a distance of over 600 miles. These three interruptions are: The stretch between 
Shelter Cove and the mouth of Alder Creek, where for a distance of about 72 statute miles 
it traverses the bottom of the Pacific Ocean; the stretch from the vicinity of Fort Ross 
to Bodega Head, where for 13 miles it is similarly on the ocean bottom; and the stretch 
from Bolinas Lagoon to Mussel Rock, where it lies beneath the Gulf of the Farallones for 
about 19 miles. Of these interruptions only the first involves any doubt as to the con- 
tinuity of the feature, and this doubt is in large measure removed by the evidence cited 
hereafter as to the position of the trace of the fault of April 18, 1906. 
Thruout its extent the Rift presents a variable relation to the major geomorphic fea- 
tures of the region traversed by it. In Humboldt County it lies within the mountainous 
tract inland from the coast but to the seaward side of the higher land. From Shelter 
Cove to Alder Creek it lies to the west of a steep, terraced, coastal slope. From Alder 
Creek to Fort Ross, it finds its expression in a series of rectilinear, sharply incised valleys, 
the alinement of which converges upon the coast line to the south at a very acute angle. 
But near Fort Ross the Rift, without deviation of its general trend, crosses the divide 
to the coastal side of the ridge which separates these valleys from the ocean, and traverses 
the terraced coastal slope. Beyond Fort Ross it again lies to the west of a steep coastal 
slope. From Bodega Head to Bolinas Lagoon the Rift is a remarkably pronounced 
depression, lying between the main coastal slope and the rather high and precipitous 
easterly side of the Point Reyes Peninsula. About 0.6 of this depression is below sea- 
level, forming Tomales and Bodega Bays. This defile is one of the most remarkable and 
interesting phases of the Rift. It has been a line of repeated faulting in past geological 
time, and evidently separates a well-marked and probably relatively mobile crustal 
block from the main continental land mass. 
South of Mussel Rock the Rift traverses for a few miles a rolling upland, marked by 
ponds and old scarps, but with no very marked contrast in relief, and then passes into 
the very marked and rectilinear San Andreas Valley, along the base of the northeast flank 
of the Santa Cruz Range. From here to the gap at Wright Station it lies along the base 
of the range at a distance nowhere greater than 2 miles from the crest. Passing thru the 
gap at Wright, it crosses from the northeast flank of the range to the southwest flank. 
Similarly passing thru the gap between the Santa Cruz and Gavilan Ranges at Chitten- 
den, it is again found on the northeast flank of the latter. In effecting this last-mentioned 
change of position relatively to the mountain crests, a distinct deviation in the trend of 
the Rift is observable (see map No. 5) as if the path of the Rift accommodated itself to 
