This arroyo, honoring San Joseph, patron saint of flight and students, was first discovered and traversed by Spanish explorers in 1769. On March 25-26, 1776, Colonel Juan Bautista de Anza made it his encampment No. 99 as mapped by his cartographer Padre Pedro, before continuing on to the San Francisco Bay Area where he initiated steps to found a colony, a mission and a presidio.