At 5:12 AM on April 18, 1906, Edwardian-era San Francisco was rocked by an estimated 7.9 earthquake - one of the worst natural disasters in United States history.
More than half of the city's 410,000 population were left homeless (the current population is about 800,000) and the dead weren't fully counted for fear of (further) damaging the real estate market.
Other than the Golden Fire Hydrant which miraculously saved the area west and south of Dolores Park in the Mission, the Fire Department Museum and Coit Tower (built to honor SF firefighters), few remnants of San Francisco's fire-y past remain.
Earthquakes however remain a topic close-at-mind with Bay Area homeowners hoping to avoid the "Big One" (few have earthquake insurance because it's so expensive) and renters hoping for it - and the chance to buy a house more affordably. Compared to these options, throwing it all in for a technology startup doesn't sound too risky :)
Website: http://en.wikipedia.org/wiki/1906_San_Francisco_earthquake