Ruins of City Hall, [1906 earthquake, San Francisco, Calif.]

Originally a Spanish (later Mexican) mission and pueblo, it was conquered by the United States in 1846 and by an invading army of prospectors following the 1848 discovery of gold in its hinterland. The Gold Rush made San Francisco a cosmopolitan metropolis with a frontier edge. In early 1900s the city tried to remake itself into a grand and modern Paris of the West.

The 1906 San Francisco earthquake struck the coast of Northern California at 5:12 a.m. on April 18 with an estimated "moment magnitude" of 7.8 and a maximum "Mercalli intensity" of "XI" ("Extreme"). Severe shaking was felt from Eureka on the North Coast to the Salinas Valley, an agricultural region to the south of the San Francisco Bay Area of the long vast Central Valley. Devastating fires fueled by broken and twisted underground natural gas supply pipes sparked by downed poles with tangles of overloaded new electric lines, soon broke out in the city that lasted for several days. As a result, about 3,000 people died and over 80% of the city of San Francisco was destroyed. The earthquake and resulting fire are remembered as one of the worst and deadliest natural disasters in the history of the United States. The death toll remains the greatest loss of life from a natural disaster in California's history and high in the lists of American urban disasters.