In the early morning hours of April 18, 1906, a devastating earthquake shook the town. On that date earth science was a very young science. The idea that San Francisco sat astride two massive and drifting plates, one of which was moving toward Alaska, would have been laughable. Fifty years later, such thinking was widely accepted in the theory of plate tectonics.
....Though the quake lasted less than a minute, its immediate impact was disastrous. The earthquake also ignited several fires around the city that burned for three days and destroyed nearly 500 city blocks.
Despite a quick response from San Francisco's large military population, the city was devastated. The earthquake and fires killed an estimated 3,000 people and left half of the city's 400,000 residents homeless. Aid poured in from around the country and the world, but those who survived faced weeks of difficulty and hardship.
The survivors slept in tents in city parks and the Presidio, stood in long lines for food, and were required to do their cooking in the street to minimize the threat of additional fires. The San Francisco earthquake is considered one of the worst natural disasters in U.S. history.
You can read the rest of the article and view scores of historic photographs and documents related to the event here. The National Park Service has a fine resource newsletter on the quake. Below are several stereoscope cards from the family archives showing the scene following the earthquake and fire.
In Alaska in 2000 I experienced one serious earthquake - 5.5+ on the Richter Scale - that scared me. It lasted lasted less than a minute and was strong enough to keep me and several visitors at Chugach National Forest's Begich, Boggs Visitor Center swaying in our seats in a dark theater. When it was safe to stand and walk we emerged from the building to the sound of thunder and several small rock slides tumbling down the mountain across the Portage River next to the center. Our guides told us not to worry because earthquakes happened all the time at the site. Later in the day they acknowledged that we experienced "a good one." Easy for them to say!