52 CRANDALL— SAN FRANCISCO PENINSULA. [January 4, 



to the loosening of the soil by the circulation of waters made nec- 

 essary by the filling of the old stream channel. The area on Howard 

 street shows merely what happens when houses are on a landslide, 

 as this is nothing more or less than a small, low angle landslide. 

 These low angle slides are common in the soft Merced beds and 

 at one place, near Mt. Olivet Cemetery, the soft wet seolian sand 

 flowed several hundred yards down hill at a low angle, damaging 

 the power house and carrying a lumber pile along with it. It is 

 evident that the places that suffered most were those that stood 

 upon loose sands or soils. 



Other districts on the Franciscan rocks did not suffer so much 

 and two areas especially, the Potrero and the Presidio, though offer- 

 ing no large buildings for comparison, seem to have suffered least. 

 It is supposed that the reason for this is that the serpentine, with its 

 many slickensided faces, has taken up a large part of the movement. 



Along the San Andreas-Portola fault line the fissure formed by 

 the movement may be seen plainly until it reaches the serpentine of 

 Las Pulgas sill, where it almost disappears, but reappears plainly 

 upon the southeast side of the serpentine. This fault line along 

 which the movement took place in causing the earthquake may be 

 plainly traced from Mussel Rock to Spring Valley lakes at Crystal 

 Springs and on toward the southeast. It has the appearance of an 

 irregular plowed furrow with occasional side furrows. The general 

 downthrow cannot be observed continuously and persistently, but 

 occasionally local variations of even as much as four or five feet 

 occur, crevices being opened from a few inches to a few feet in 

 one spot. The lateral thrust is not always apparent on the ground, 

 but it may be clearly seen in the broken and offset fences across 

 the fault. Various measurements of the slippage gave an average 

 of three feet, but as much as eight and a half feet has been found 

 near Woodside, San Mateo Comity. 



Movements Along the San Bruno and Lone Monntaln Faults. — 

 The other two fault' zones of the San Francisco peninsula, the Lone 

 Mountain and San Brimo faults, show no discernible movement, 

 and the intensity in the city of San Francisco shows no relation to 

 these or any other structural features. In the area mapped the 

 part that seems to have suft'ered most is in the soft Merced beds 



