EFFECTS ON STRUCTURES OUTSIDE OF SAN FRANCISCO. 17 
passing under the ocean bed just west of the Golden Gate, reappear- 
ing on the land at Mussel Rock, and following the Pilarcitos and San 
Andreas pipe lines of the Spring Valley Water Company in a direct 
line to Hollister. The zone included San Francisco Bay, Russian 
River, and the Sonora, Santa Clara, and Salinas valleys. The first 
movement was. along this zone in a southeasterly direction, and the 
vibrations set up on all sides produced a continuous twisting, rocking, 
wrenching movement that brought down chimneys, walls, towers, etc. 
In the opinion of the California earthquake investigation commission 
the slip commenced at the northwest end of the zone, and the force 
which occasioned the rupturing or shearing movement was a progress- 
ively decreasing one to the southeast end. As in the earthquake of 
18G8, the destruction was greatest in proportion to the nearness to 
the fault trace, and in parts built on soft or alluvial soil, or on " made 
ground." The earthquake as recorded by the seismographs showed a 
horizontal movement of about 3 inches and a vertical movement of 
about 1 inch, the velocity of propagation being about 2.1 miles per 
second. The wave movement was long and slow in hard soil and 
rock and comparatively short and incoherent in soft ground. 
EFFECTS ON STRUCTURES OUTSIDE OF SAN FRANCISCO. 
In considering in detail the damage wrought by the earthquake 
one must look for evidence in the country surrounding San Francisco, 
since the fire in that city obliterated most of the signs of the damage. 
The greatest loss in the city of San Francisco was principally the 
result of the fire, which was rendered uncontrollable owing to the 
wrecking of the water-supply system by the earthquake. (See the 
maps of the city and vicinity, Pis. LVI and LVII.) An examination 
of the damage to the system at once suggests itself, especially as some 
of the main conduits are located on or near the fault line. 
The city is supplied principally by gravity from three main dis- 
tributing reservoirs, viz, University Mound, College Hill, and Lake 
Honda ; there are also two supplementary sources — Alameda Creek, 
on the east side of the bay, and Lake Merced. The University Mound 
reservoir, having a capacity of 83,000,000 gallons, is supplied from 
Crystal Springs Lake through 17 miles of 41-inch wrought-iron pipe, 
carried for a considerable distance on trestles over the marshes. The 
College Hill reservoir lias a capacity of 15,000,000 gallons and is sup- 
plied from San Andreas Lake through 14 miles of 44-inch, 37-inch, 
and 30-inch wrought-iron pipe. The Lake Honda reservoir, with a 
capacity of 31,000,000 gallons, is fed from Pilarcitos Lake through 
16 miles of conduit, 1-J- miles of which is wooden flume and the re- 
mainder cast-iron and Avrought-iron pipe and brick tunnel. Of the 
two supplementary supplies, the water from Alameda Creek is car- 
