2 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
The most disastrous of the effects of the earthquake were the breaking out of fires and, 
at the same time, the destruction of the pipe systems which supplied the water neces- 
sary to combat them. Such fires caused the destruction of a large portion of San Fran- 
cisce, as all the world knows; and they also intensified the calamity due to the earth- 
quake at Santa Rosa and Fort Bragg. The degree of intensity with which the earthquake 
made itself felt by these various manifestations diminished with the distance from the 
seat of disturbance, and at the more remote points near the limits of its sensibility it 
was perceived only by a feeble vibration of buildings during a brief period. 
The area over which the shock was perceptible to the senses extends from Coos Bay, 
Oregon, on the north, to Los Angeles on the south, a distance of about 730 miles; and 
easterly as far as Winnemucca, Nevada, a distance of about 300 miles from the coast. 
The territory thus affected has an extent, inland from the coast, of probably 175,000 
square miles. If we assume that the sea-bottom to the west of the coast was similarly 
affected, which is very probably true, the total area which was caused to vibrate to such 
an extent as to be perceptible to the senses was 372,700 square miles. Beyond the 
limits at which the vibrations were sufficiently sharp to appeal to the senses, earth waves 
were propagated entirely around the globe and were recorded instrumentally at all the 
more important seismological stations in civilized countries. 
The various manifestations of the earthquake above cited, including the cracking and 
deformation of the soil and incoherent surface formations, were the results of the earth 
jar, or commotion in the earth’s crust. The cause of the earthquake, as will be more . 
fully set forth in the body of this report, was the sudden rupture of the earth’s crust 
along a line or lines extending from the vicinity of Point Delgada to a point in San 
Benito County near San J uan; a distance, in a nearly straight course, of about 270 miles. 
For a distance of 190 miles from Point Arena to San Juan, the fissure formed by this 
rupture is known to be practically continuous. Beyond Point Arena it passes out to 
sea,.so that its continuity with the similar crack near Point Delgada is open to doubt; 
and the latter may possibly be an independent, tho associated, rupture parallel to the 
main one south of Point Arena. It is most probable, however, that there is but one 
continuous rupture. The course of this fissure for the 190 miles thru which it has been 
followed is nearly straight, with a bearing of from N. 30° to 40° W., but with a slight 
general curvature, the concavity being toward the northeast, and minor local curvatures. 
The fissure for the extent indicated follows an old line of seismic disturbance which 
extends thru California from Humboldt County to San Benito County, and thence 
southerly obliquely across the Coast Ranges thru the Tejon Pass and the Cajon Pass into 
the Colorado Desert. This line is marked by features due to former earth movements 
and will be referred to in a general way as a rift, the term being adopted from the 
usage for analogous features in Palestine and Africa.“ To distinguish it from other rifts 
of similar origin, it will be referred to more specifically as the San Andreas Rift, the 
name being taken from the San Andreas Valley on the peninsula of San Francisco, where 
it exhibits a strongly pronounced character and where its diastrophic origin was first 
recognized in literature: 
The plane or zone on” which the rupture took place is, so far as can be determined 
from a study of the surface phenomena, nearly vertical; and upon this vertical plane 
there occurred a horizontal displacement of the earth’s crust or at least of its upper 
part. The displacement was such as to cause the country to the southwest of the rift 
line to be moved northwesterly relatively to the country on the northeast side of that 
line. ‘The differential displacement in a horizontal direction was probably not less than 
10 feet for the greater part of the Rift; in many places it measured over 15 feet, and in 
one place as much as 21 feet. 

* Roy. Geograph. Soc. vol. rv, 4, 1894. The Great Rift Valley, by J. W. Gregory, London, 1896. 
