Petersburg (also, Petersburgh and Greenhorn) is a former settlement in Kern County, California. It was located on Greenhorn Creek west-northwest of Miracle Hot Springs, at an elevation of 4731 feet (1442 m). Petersburg still appeared on maps as of 1956.
A post office operated at Petersburgh from 1858 to 1863. The place was named for Peter Gardett, early merchant there.