The gold rush increased pressure on the Native Americans of California, because miners forced Native Americans off their gold-rich lands. Many were pressed into service in the mines; others had their villages raided by the army and volunteer militia. Some Native American tribes fought back, beginning with the Ahwahnechees and the Chowchilla in the Sierra Nevada and San Joaquin Valley leading a raid on the Fresno River post of James D. Savage, in December 1850. In retaliation Mariposa County Sheriff James Burney led local militia in an indecisive clash with the natives on January 11, 1851 on a mountainside near present-day Oakhurst, California.