In 1769 Gaspar de Portolà led an expedition to the canyons of the Santa Ana Mountains. They camped on a bluff east of Arroyo Trabuco on the night of July 24-25, and the next day, one of the soldiers found his trabuco, or blunderbuss (the type of gun), missing. The expedition never found the gun, and they named the creek Arroyo Trabuco as a memorial. Mission San Juan Capistrano was established in 1776 at the confluence of San Juan Creek and Arroyo Trabuco.