THE GEOLOGICAL HISTORY OF A SAN FRANCISCO MANSION

The James C. Flood mansion at 1000 California Street, San Francisco, California was built in 1885-86 of blocks of Jurassic red sandstone from the Connecticut Valley rift basin. The sandstone was quarried at Portland, Connecticut, cut and dressed in New Jersey, and shipped around Cape Horn to San Francisco. The 42-room mansion withstood the 1906 earthquake because of its massive stone walls and its location on the solid bedrock of Nob Hill. It was gutted by the fire that followed the earthquake, but was restored; it now houses the Pacific Union Club. The money to build the mansion—around $26 million in modern dollars— was a silver fortune dug out of a Miocene hydrothermal metal deposit in a fault at the base of Mount Davidson in Washoe County, Nevada. This deposit was the Comstock Lode that prompted the Nevada silver rush of the 1850’s. The Flood mansion’s building material and history make it a worthy subject of study for students in introductory geology or urban geology classes, since it embodies the close relationship between geological, architectural, and social history.