The terrifying rumble of an earthquake shattered the early morning silence of April 18 at 5:15 AM. The quake lasted only a minute but caused the worst natural disaster in the nation's history. Modern analysis estimates it registered 8.25 on the Richter scale (By comparison, the quake that hit San Francisco on October 17, 1989 registered 6.7). The earthquake was felt from southern Oregon to south of Los Angeles and inland as far as central Nevada.
However, the greatest destruction came from the fires the quake ignited. These ravaged the city for three days before burning themselves out. The maelstrom destroyed 490 city blocks, a total of 25,000 buildings, made over 250,000 homeless and killed between 450 and 700 people. Damage estimates topped $350,000,000.
Two Whitley County men, Ancil Brown and Joe Archer, were in the San Francisco area at the time of the earthquake. Their letters published in the Columbia City Post can be found at Whitley County Kinexxions.
The Virtual Museum of the City of San Francisco has a timeline, scans of some newspaper clippings and transcriptions of others, eyewitness accounts which are incredible - including one from Jack London. They have a list of "names compiled from newspapers of those persons who died as a direct result of injuries received either at the time of the earthquake and fire, or during the latter half of April 1906" and of course, lots of photographs.
These are some of the other sites that I found interesting (a Google search turned up 956,000 hits for “San Francisco Earthquake”).
Eyewitness to History
The Library of Congress American Memory
Berkeley Seismological Laboratory