SAN FRANCISCO -- Most San Franciscans were still in bed at 5:12 a.m. when the earthquake hit on April 18, 1906 -- first as a foreshock that sent people scrambling.
The main temblor, its epicenter offshore, arrived with such fury that it flattened crowded rooming houses, was felt as far away as Oregon and Nevada, and in 28 seconds brought down the City Hall it had taken 27 years to build.
From cracked chimneys, broken gas lines, and toppled chemical tanks, fires broke out almost immediately and swept across the city, burning for days. Ruptured water pipes left firefighters helpless, while families carrying what they could fled the advancing flames to parks that had become makeshift morgues.
The 7.8-magnitude quake caused a 296-mile rupture along the San Andreas Fault.
Taking in the devastation afterward, Jack London wrote: ''An enumeration of the buildings destroyed would be a directory of San Francisco. An enumeration of the buildings undestroyed would be a line and several addresses. An enumeration of the deeds of heroism would stock a library. . . . An enumeration of the dead will never be made."
Researchers are still trying to set a death toll for the disaster, which ranks as one of the costliest in US history, a benchmark with which later calamities are compared. Reliable estimates put the loss at 3,000 lives and possibly as high as 6,000.
Meanwhile, scientists and historians are still working to separate the facts from the folklore that envelops the 1906 quake like so much San Francisco fog.
Here are some of the generally accepted facts:
The worst shaking lasted 45 to 60 seconds. Areas of Sonoma County felt it the most intensely.
Fires stoked by unseasonably warm weather raged for three days, lasting through April 20. Firefighting efforts were hampered by ruptured water lines and the loss of Chief Dennis Sullivan, who died in the quake.
About 28,000 of San Francisco's 53,000 buildings were destroyed.
Nearly 250,000 of San Francisco's nearly 400,000 residents were left homeless.
The quake left property damage estimated at $400 million (equivalent to $8.2 billion in today's dollars).
Many historians say human acts played a big role in fueling the conflagration.
The Army, lacking water to fight the flames, resorted to blowing up buildings to create a firebreak, but this spread the firestorm. And some homeowners purposely set fire to their quake-damaged houses, which were insured against fires but not earthquakes, according to Gladys Hansen, a retired city archivist.
Even before the earthquake, San Francisco had chosen the symbol of the phoenix for its municipal flag. And though downtown was destroyed, the city labored to live up to that rising-from-ashes image by rebuilding as quickly as possible.
What stands out to California State Library curator Gary Kurutz is ''the strength and indefatigability of San Francisco. . . . Yes, it was a disaster, but people did see it with a sense of adventure, too."
At times, San Francisco was a harsh place as it struggled to rebuild. Mayor Eugene Schmitz issued an order authorizing soldiers and hastily-deputized ''special police" to shoot anyone suspected of looting. Xenophobic policies directed at segregating Asian immigrants got so bad that President Theodore Roosevelt intervened to prevent a diplomatic crisis.
But decorum reigned, too -- as glimpsed in photographs from the period showing survivors smiling as they cooked meals on the street and children playing at pristine camps.
''It's not that there weren't heroic things happening, but at the same time there were a lot of terrible things happening," said Charles Wollenberg, a history professor at Vista College in Berkeley. ''You can find the same thing in New Orleans today. When a disaster of this magnitude occurs, you are going to find both the best and worst in people."
Many landmarks visitors recognize in San Francisco today grew out of the quake and fire -- from the Portals of the Past columns in Golden Gate Park, which were the salvaged entranceway from a collapsed mansion, to Coit Tower, erected to honor the firefighters its benefactress admired.
Chinatown did not have its Far East-inspired appearance until after the earthquake. When the city tried to use the disaster as an excuse for driving out immigrants, a savvy Chinese businessman came up with the idea of using the ersatz architectural theme to turn Chinatown into a tourist draw.
The rebuilt City Hall, with a shock-absorbing foundation, has the world's fifth-largest dome and stands taller than the US Capitol.