During the Gold Rush boom, in San Francisco's early years, the city suffered six major fires. Because these fires destroyed 25 to 50% of the town, they were called Great Fires. As San Francisco quickly rebuilt herself rising from the ashes of those fires, the Phoenix became the symbol of the city.
On April 18, 1906, because the Richter magnitude of the earthquake was over 8.0, it is classified as a Great earthquake. In 1906, when half the city was lost, the earthquake caused 20% of the damage and the fire caused the other 80%.