(If it was in this time January 24, 1848 – 1855) it's Cause when there is more people looking for gold, there will be less gold to get.
But if not in 1848 – 1855, it cause immigration laws were passed restricting immigration from Asia, the reasons are the same as the fears of Mexican immigrants now-that they would take jobs and provide an inexpensive workforce that would keep wages low. There were also fears that they wanted to take over land on the west coast. It was called the "yellow peril" and evidence of how people give in to irrational fears.