The correct answer to this open question is the following.
Significant international events, such as the Gold Rush, sometimes cause conflict because of the number of people that arrives in the region without certainly knowing what is going to happen. The California locations did not have any kind of infrastructure to attend the basic necessities of so many people that arrive expecting to become rich in finding gold.
When people knew about gold in California in 1848, large numbers of frenzy people rushed to this state believing that they were going to find gold "everywhere." Of course, sudden massive migration never results in good things for the region. So many people in such a few time affected and changed the landscape of this part of California.