132 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
Tho the inferred displacements of these four points for 1906 are all very doubtful, the 
observed combined displacements of 1868 and 1906 for these four points, as shown in table 
3, are all certain, being clearly beyond the possible range of errors of observation. So also 
are the combined displacements of 1868 and 1906 for Loma Prieta and Black Mountain. 
It appears then that the combined effects of the earthquakes of 1868 and 1906 were to 
move the whole region from Black Mountain to Point Pinos to the southeastward by 
from 2.11 to 5.89 meters (6.9 to 19.3 feet). The mean azimuth of these six displacements 
is 321° (89° E. of S.).. The most startling evidence of the combined effects of the two 
earthquakes is the increase of 3 meters (10 feet) in the width of Monterey Bay from Santa 
Cruz Azimuth Station to Point Pinos Light-house, both of these points having moved in a 
southerly direction, but the latter much more than the former. The length of the line 
Santa Cruz Azimuth Station to Point Pinos Light-house is only 39.8 kilometers (24.7 
miles). The increase is therefore one part in 13,000. 
Not much significance should be attached to the fact that Point Pinos Latitude Station 
has apparently moved one meter less than Point Pinos Light-house. This one meter is the 
difference of the combined displacements of two earthquakes. It is subject to the errors 
of observation in two determinations of each point by triangulation in somewhat different 
ways. Moreover, the determination of the position of the Latitude Station after the 
earthquake of 1906 was made without a check. It is for this reason that the displacement 
at Point Pinos Light-house is considered to be the more reliable determination of the two. 
DISTRIBUTION OF EARTH MOVEMENT; SUMMARY. 
In reaching the conclusions stated below, the evidence has been studied much more in 
detail than it has been given in the preceding pages. The conclusions are based on both 
the positive and negative evidence. The positive evidence is given by the displacements 
marked “certain” or “reasonably certain” in tables 1, 2, and 3. The negative evidence 
is given by displacements marked “doubtful,” of which Rocky Mound is an example. 
“At this point the observed apparent displacement of 1906 was only 0.34 meter (1.1 feet). 
The accuracy of the triangulation is such that it is practically certain that any displace- 
ment of this station as great as one meter would be detected. Hence the evidence given 
by this station is that the displacement, if any, was less than one meter and probably 
was less than 0.3 meter. 
Maps 24 and 25 should be consulted while reading the following conclusions. 
During an earthquake in 1868 or about that time, about 1,000 square miles of the 
earth’s crust, comprized between the four stations Mount Tamalpais, Farallon Light-house, 
Ross Mountain, and Chaparral, were permanently displaced to the northward about 1.6 
meters (5.2 feet), in azimuth 169° (11° W. of N.). The indications are that this whole 
area moved as a block without distortion or rotation; at least the triangulation furnishes 
no evidence competent to prove either distortion or rotation of the block (about a vertical 
axis), or to locate accurately any boundary of the block. It is probable that the block 
included Sonoma Mountain. It is reasonably certain that Rocky Mound and the group 
of points near the southern end of San Francisco Bay, Red Hill, Pulgas Base stations, and 
Guano Island, were not on this block, tho they were probably displaced somewhat irregu- 
larly during the earthquake of 1868. 
During the earthquake of 1868, or about that time, Loma Prieta was permanently 
displaced about 3.03 meters (9.9 feet), in azimuth 807° (53° E. of S.). This displacement 
is in a direction at an angle of 138° with that of displacements of same date, referred 
to in the preceding paragraph. Loma Prieta moved to the southeastward, whereas Mount 
Diablo, Farallon Light-house, Ross Mountain, and Chaparral moved to the northward. 
It is reasonably certain that Santa Cruz Azimuth Station, Point Pinos Light-house, Point 
Pinos Latitude Station, and Gavilan were similarly displaced. It is probable that the last 
