At 5:12 am on April 18, 1906, San Francisco residents were awakened by a 40-second tremor that moved furniture, shattered glass, and toppled chimneys. After a 10-second interval, an even stronger tremor struck, lasting 25 seconds.

Movement along the San Andreas Fault was to blame. The North American and Pacific tectonic plates had moved past each other by more than 15 feet — compared to an annual average of two inches. The earthquake is estimated to have measured 8.3 on the Richter scale, which had not yet been invented. Survivors saw the ground move in waves as high as three feet. The earthquake ripped open streets, twisted streetcar rails, and split sidewalks.

Fires broke out soon after the earthquake, caused primarily by overturned stoves or damaged electrical wiring. Because the city's water mains had suffered more than 300 ruptures, no water was available to combat the fires, which rapidly burned beyond control. In some places, temperatures reached 2,500 degrees Fahrenheit, melting glass, buckling steel and iron beams, and fusing dishes together. In a desperate attempt to contain the fire, firefighters began to dynamite buildings in its path. Unfortunately, this strategy sometimes spread the flames.

Mayor Eugene A. Schmitz decreed that all looters would be shot. He also imposed a dawn-to-dusk curfew. Most San Franciscans obeyed the laws; only nine were shot for looting. Most waited until they were certain their homes would be burned. Then they would leave, carrying as many possessions as they could.

By the evening of April 18th, 1,700 soldiers had arrived in San Francisco to assist both residents and the firefighters. Brigadier General Frederick Funston took over command of the city and declared martial law.

After raging uncontrolled for three days, the fire finally burned itself out by the morning of April 21st. Destruction in its 4.7-square-mile path was complete. More than 28,000 buildings had been destroyed, resulting in an estimated $500 million in damage — an amount equal to the federal budget of 1906.

Although the official number of casualties was 311, it is now believed that approximately 3,000 people perished. About 250,000 people (two-thirds of the city's population) were left homeless. They were temporarily sheltered in tents placed in public parks. These were later replaced by one-room wooden structures.

Among the earthquake's survivors was operatic tenor Enrico Caruso. On the night of April 17th, he had performed the role of Jose in Georges Bizet's 1875 opera, "Carmen," and had been scheduled for another performance on April 18th. Caruso was so distraught by the earthquake and its aftermath that he vowed never to return to San Francisco again.

Ansel Adams, age 4, survived the earthquake along with his family, though their house and many possessions were damaged. An aftershock tossed young Adams face-first into a garden wall, giving him what his friend Cedric Wright would call an "earthquake nose." Describing his broken nose, which was never repaired, Adams would later joke, "My beauty was marred forever." But he felt the horror of the quake, which he called his "closest experience with profound human suffering."

One of the few buildings that survived with little damage was the Old Mint. It was able to withstand the tremors due its strong foundation, which was made of large blocks of solid granite. To save it from the flames, Mint employees used water from cisterns in the basement to keep the roof and outer walls wet. Although the fire's heat melted the building's windows, the Mint otherwise suffered little damage.

Relief poured in from many states and foreign countries. Japan gave nearly $250,000 — more than all other foreign countries combined. Reconstruction began in the summer. San Francisco filed $175 million in claims with insurance companies.

It was due in large part to these settlements that San Franciscans were able to begin rebuilding their city in the summer.