who led a small force to overthrow mexican rule in northern california
California Republic In June 1846, thirty-three American immigrants in Alta California rebelled against the Mexican department's[notes 1][2] government. The immigrants had not been allowed to buy or rent land and had been threatened with expulsion from California because they had entered illegally without official permission.[3][4] Mexican officials were concerned about a coming war with the United States coupled with the growing influx of Americans into California. The rebellion was soon overtaken by the beginning of the Mexican–American War.
Californio The only other United States military force in California at the time was a small exploratory expedition led by Lieutenant Colonel John C. Frémont, made up of 30 topographical, surveying, etc. army troops and about 25 men hired as guides and hunters. The Frémont expedition had been dispatched to California, in 1845, from the United States Army Corps of Topographical Engineers.