The 1906 San Francisco Earthquake and Fires
At 5:12 a.m. on 18 April, a magnitude 7.8 earthquake ruptured hundreds of kilometers of the San Andreas Fault. Severe shaking damaged communities across northern California. In San Francisco, broken water mains, damaged gas systems, and hundreds of fires turned the earthquake into a multi-day urban disaster.
What existed before
San Francisco had expanded rapidly after the Gold Rush. Dense development, varied construction quality, and infrastructure crossing active faults created interconnected risks that were poorly understood by the public and only partly addressed by engineering practice.
Trigger and cause
The Pacific and North American plates slipped along the San Andreas Fault. The rupture propagated for roughly 300 miles. Shaking collapsed buildings and damaged utilities; with much of the water system disabled, firefighting became exceptionally difficult.
Aftermath
Large parts of the city burned, thousands died, and approximately 225,000 people were left homeless. Residents formed camps, relief systems distributed food and water, and rebuilding began amid contested decisions about land, housing, and whose losses were recorded.
Why it matters
The disaster remains a powerful example of cascading risk: a geologic event became an urban fire and housing emergency because critical systems failed together. Data gathered immediately afterward still support earthquake research.
Uncertainty note
Contemporary official counts substantially understated deaths, particularly among marginalized and transient residents. Modern estimates commonly cite at least 3,000 deaths, but a final exact total is not recoverable.