The Great Chicago Fire
Push factor is a reason to leave the place you are currently residing in.
Pull factors are reasons you want to go to the place you are going to.
This caused California's population to boom, causing it to become a state before even being a territory. It boosted U.S economy(helping the Union win the Civil War). Many immigrants came to California as well, different people groups didn't get along, causing racial tension.
It was an affordable opportunity for everyone of any race. Most settlers would farm or raise livestock.