ISOSEISMALS: DISTRIBUTION OF APPARENT INTENSITY.  . 253 
Pilarcitos Canyon. — In Pilarcitos Canyon, the stone dam of the artificial lake was unin- 
jured and the flume down the canyon sprung only a few leaks. Mr. Ebright’s house, at 
the lower end of the lake, lost two out of three chimneys by the shock. The spring water 
at this place, which is used for house supply, is said to have been milky-white during the 
day of the earthquake. This canyon is made by one of the large faults mentioned in 
the first part of the paper. If there had been any movement along this fault, it would 
have been shown at the dam which crosses the canyon at a right angle to the fault-line. 
Cahill’s Ridge. — This range of hills forms the northeast side of Pilarcitos Canyon, 
and is the second ridge southwest of Crystal Springs Lake, with the same general north- 
west-southeast trend. On the top of this ridge, a small house lost one of two chimneys, 
and things inside were shaken around. A table is said to have tilted enough for dishes 
to slide off. 
Just southeast of the house is a depression in the ridge, across which furrows and cracks 
formed similar to those along the main fault-line, but not extending more than several 
hundred feet. These cracks do not seem to have been landslide cracks, for they are on 
top of the ridge and on a flat piece of ground. 
Another peculiar phenomenon was observed upon Cahill’s Ridge, less than 1 mile north- 
west of the cracks mentioned. In an area of limestone, a small patch some 30 feet in 
diameter was torn up as tho it had been plowed and harrowed, and no large pieces of sod 
were left intact. Around this in various places were cracks of a few inches in width, 
with one or two over a foot wide. There was a slight downthrow on the uphill side to 
be noticed in some of these cracks, which eliminated the possibility that they were cracks 
preparatory to landsliding. 
Sawyer’s Ridge. — On Sawyer’s Ridge, about 9 miles north of the region described on 
Cahill’s Ridge, there were cracks several hundred feet long almost at the top of the ridge. 
These were parallel to the line of the main fault, which is a mile to the east, and there was 
a marked downthrow of from 2 to 3 inches on the southwest side, which in this case was 
the uphill side. If the downthrow were on the downhill side, then it could be possible 
that these were landslide cracks. The exact cause or mode of the formation of these 
cracks, or the breaking of the ground on Cahill’s Ridge, is not clear. 
Tn the canyon between Sawyer’s Ridge and Sweeney’s Ridge, a 2-story wooden house 
did not suffer much, and out of 4 chimneys only 2 were cracked. One of those that 
remained standing was a tall top-heavy chimney of brick; the other was only a tin pipe. 
At Byrne’s store, on the Half Moon Bay road, half a mile west of Crystal Springs Lake, 
it was reported by the keeper that the water from their spring, on the day of the shock, 
was muddy and was not tasted. On the second day after the earthquake, it had a very 
salty taste, but on the third day was normal. A house on the northwest side of Half 
Moon Bay road, 2,000 feet southwest of the dam, was thrown from its foundations, 
while some 200 feet northwest of this house there was a slide in the canyon. 
CONCLUSIONS. 
There was no marked difference of intensity on the two sides of San Andreas fault-line. 
There was a decrease of intensity on both sides of the fault-line, as one goes away from it. 
The distribution of intensity bears no evident relation to the minor faults or structure 
of this area. 
It is evident that the intensity varies with the geology, or with the areal distribution 
of rocks and soils. 
The areas that suffered most severely were those upon filled ground. 
Areas upon marshy ground showed destructive effects similar to artificial filled land. 
Next in intensity to areas of filled land are those upon incoherent sands. The damage 
in sandy areas was due partly to the shaking of sand like jelly and partly to settling and 
sliding. 
