INTRODUCTION. 3 
This differential displacement of the earth’s crust along the plane of rupture constitutes 
a fault, and will be so referred to in the text of the report. It is named the San Andreas 
fault. ‘The intersection of the fault plane or narrow zone with the surface of the ground 
is manifested by cracks, heaved sod, scarps, etc., and these manifestations are desig- 
nated the fault-trace. As a result of this fault, all the fences, roads, railways, bridges, 
tunnels, dams, pipes, and other structures which crost its path were dislocated. All 
property lines and other survey lines which were intersected by it were offset.. Inasmuch 
as the movement of the earth which caused the fault was not confined to its immediate 
vicinity, but was distributed over a considerable belt of country on either side of the 
trace of the rupture, the latitudes and longitudes of a large portion of the Coast Ranges 
of California were changed, and the triangles established by the Coast and Geodetic 
Survey in its triangulation of the region were distorted. 
In addition to the horizontal displacement there was, particularly toward the northern 
end of the fault, a vertical displacement probably nowhere exceeding 2 to 3 feet, whereby 
the country to the southwest was raised relatively to that to the northeast. In many 
places, however, particularly toward the southern end of the fault, no vertical displace- 
ment can be detected; and there is some indication that, if there was vertical displace- 
ment in this region, it was the reverse of that observed in the northern portion of the 
fault. This rupture of the earth’s crust gave rise to certain manifestations at the surface 
which resemble those described above as a result of the vibratory commotion of the 
earth, due to the sudden displacement. The cracking and rending of the surface along 
the line of the fault is a direct expression of the rupture and displacement which origi- 
nated the earthquake, whereas the cracks, fissures, and lurching of the soft bottom lands 
and the landslide cracks on the hillsides, whether near the fault line or remote from it, 
are referable to the oscillation of the crust. The two classes of phenomena must, there- 
fore, be discriminated, particularly as there has been a tendency on the part of some 
observers to class the secondary phenomena with the primary and interpret the former 
as indicative of fault lines in the earth’s crust, when in reality they are merely superficial 
phenomena. 
While the shock was perceptible to the senses to the extent above indicated in California, 
Nevada, and Oregon, the distribution of the higher grades of intensity was remarkably 
linear and was definitely related to the fault line, and to the general trend of the coast of 
California. This may be brought out in a preliminary way by stating that a zone of 
destructive effects extends parallel to the Rift from Humboldt Bay, in Humboldt County, 
to the vicinity of King City in Monterey County, a distance of 350 miles. If we take the 
throw of brick chimneys and allied phenomena as indicating the limits of what may be 
called destructive effects, the width of this zone may be fairly approximated at about 
70 miles, or about 35 miles on either side of the fault, or its prolongation where no actual 
fault is observable at the surface. The length of this zone of destruction is thus five 
times greater than its width, and the total area within which the shock was sufficiently 
severe to throw brick chimneys may be placed at something over 25,000 square miles; 
it being assumed that the severity to the southwest of the fault, beneath the waters of 
the Pacific, was equal to that on the land. If the fault-near Point Delgada be regarded 
as distinct from that extending from Point Arena southeasterly, then the total area of 
these high intensities would be considerably larger in the direction of the Pacific. 
Within this outer limit of destructive effects the intensity increased toward the fault. 
But proximity to the fault was not the only factor determining the degree of intensity. 
The soft, more or less incoherent, and water-saturated alluvial formations of the valley- 
bottoms were much more severely shaken than the rocky slopes of the intervening 
ridges, and the structures upon them were consequently more commonly and more 
completely wrecked. It is not understood by this excessive damage on the valley- 
