Presidio San Ignacio de Tubac, founded in 1752 in the Santa Cruz River valley after the Pima Rebellion, became an important Spanish frontier fort protecting nearby settlements and missions. A civilian community grew around its garrison, and Tubac gained lasting significance when Captain Juan Bautista de Anza organized and led expeditions from there that opened an overland route from Sonora to California and reached Monterey and present-day San Francisco. Though its military role shifted, the post was repeatedly reoccupied, later passed from Spanish to Mexican and then United States control, and saw conflict, decline, and reuse before its remains were preserved as a historic and archaeological site.