While the great mining bonanzas of the nineteenth-century West made eastern California and Nevada the subject of legend, much of the wealth from the mines flowed to San Francisco and made possible the growth of the city and some fabulous personal fortunes. Among the wealthiest and most powerful of the Bonanza Kings was William Bowers Bourn I and his son and successor, William Bowers Bourn II.

The elder Bourn, descendant of an early New England family, arrived in San Francisco shortly after the discovery of gold in the Sierra foothills. Although he eventually invested heavily in mines in Grass Valley and on the Comstock, his initial success was as a businessman in the booming port city.

The younger Bourn built upon his fathers success, expanding the Empire Mine in Grass Valley into one of the largest, most productive, and most technologically advanced hard-rock gold mines in the West, acquiring additional mining properties on the Comstock and on Treasure Hill in eastern Nevada, and developing a range of business ventures, including a vast water system that was to become the basis for San Francisco's present water supply.

Like many other wealthy men of his generation, William Bourn II was a generous donor to worthy causes and an enthusiastic patron of the arts, supporting such projects as the San Francisco Symphony, the Panama Pacific International Exposition of 1915, the construction of the present quarters of the Pacific Union Club, and the creation of his own final home, Filoli, a vast Italianate estate on the Peninsula south of San Francisco.