From the plaque:
This redwood structure was
completed in 1868 by William Chapman Ralston, San Francisco
financier. Incorporating Count Cipriani's earlier villa,
this enlarged mansion with its mirrored ballroom became
the symbol of the extravagance of California's Silver
Age. It anticipated features later incorporated into Ralston's
Palace Hotel in San Francisco.
Plaque placed by the State Department of Parks and Recreation in cooperation with the California Historical Society, November 5, 1972.