52 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
crust has continued to manifest itself, and several slight movements have been observed 
by residents of the country. In 1857 there was a movement extending from San Benito 
County probably as far as San Bernardino Valley. The earthquake caused by this 
movement was not less severe than that of 1906, but we have unfortunately no measure 
of the extent or direction of the displacement. In this southern region described by 
Fairbanks, the displacements, even from the first, do not appear to have been of such a 
nature as to give rise to a continuous cliff or scarp upon either side of the fault; and this 
observation is generally true thruout the Rift. In one place the scarp faces southwest, 
in another northeast. In other places the vertical displacement has been very small 
and the scarps correspondingly insignificant. In several places, as, for example, at Fort 
Ross and between Mussel Rock and San Andreas Lake, displacements have occurred on 
subparallel lines, giving rise to opposing scarps, as if a wedge of ground, perhaps several 
hundred feet across, had dropt in. In such depressions lie the sinks; but the latter are 
more commonly formed by a low scarp facing up a slope, or by a ridge of surface com- 
pression formed across the path of the drainage from a slope. They have also been formed 
by landslides, which have shown little tendency to move save under seismic impulse. 
It remains to call attention, in a word, to the alinement of the Rift with certain of the 
larger continental features. The Rift is known from Humboldt County to the north 
end of the Colorado Desert. As a line of small displacements it has not been traced 
farther; and in the usage of the term it has been understood as terminating at the point 
where it eluded field observation. But it is by no means certain that, as a larger feature, 
it does not extend far to the south. The Colorado Desert and its continuation in the 
Gulf of California are certainly diastrophic depressions, and may with much plausibility 
be regarded as a great Rift valley of even greater magnitude than the now famous African 
prototype first recognized by Suess. This great depression lies between the Peninsula 
of Lower California and the Mexican Plateau. All three of these features find their 
counterpart in southern Mexico. The Sierra Madre del Sur is the analogue of the penin- 
sular ridge; it lies on the line of its prolongation, and is similarly constituted geologically. 
Inside of this range, and between it and the edge of the Mexican Plateau, is a pronounced 
valley system which is the analogue of the Gulf of California. 
On this valley-line lies the deprest region about Salina Cruz, well known to be subject 
to repeated seismic disturbances. On the same general line lies Chilpancingo, the seat 
of the recent disastrous Mexican earthquake. Following these great structural lines 
southward, they take on a more and more latitudinal trend; and beyond Salina Cruz 
the geological structure indicates that this seismic belt crosses the state of Chiapas and 
Guatemala, to the Atlantic side of Central America with an east and west trend, and 
falls into alinement with Jamaica. It thus seems not improbable that the three great 
earthquakes of California, Chilpancingo, and Jamaica may be on the same seismic line 
which is known in Califor nia as the San Andreas Rift. 
