Pilot Knob, an isolated volcanic plug in southeastern Imperial County, California, has long served as a prominent landmark near the lower Colorado River. Seen by Juan Bautista de Anza in 1774 and later used as a guide on the Southern Emigrant Trail during the California Gold Rush, it marked the area of Emigrant Crossing near present-day Yuma. In 1858, the Butterfield Overland Mail placed a station nearby, and the peak also helped Colorado River pilots navigate in the 19th and early 20th centuries. Its solid rock supported the Alamo Canal intake, and the site later carried a Yuma television transmitter. Today it is managed as an Area of Critical Environmental Concern.