It is estimated that the Cahuilla aboriginal tribes inhabited an area including what is today the Anza Valley more than two thousand years ago and encountered Europeans only as late as 1774, when a Spanish expedition in search of an overland route from Sonora to Alta California made its way from Tubac, Sonora through the valley to Monterey, Alta California. Explorer Juan Bautista de Anza first passed through the valley on March 16, 1774, and again on December 27, 1775. De Anza originally named the valley "San Carlos"; it was renamed in his honor from Cahuilla Valley to Anza Valley on September 16, 1926.