What event brought thousands settlers to northern california via the california trail by 1848?

The California Gold Rush (1848-1855) began on January 24, 1848, when gold was found by James W. Marshall at Sutter's Mill in Coloma, California.

The sudden influx of immigration and gold into the money supply reinvigorated the American economy, and California became one of the few American states to go directly to statehood without first being a territory, in the Compromise of 1850. The Gold Rush had severe effects on Native Californians and resulted in a precipitous population decline from disease, genocide and starvation.