Anza spent his first twenty years of military service in Sonora. During this time, he defended the frontier of New Spain against Indian tribes. During this time he made many explorations to the Gila and Colorado Rivers. He also assisted missionaries with the setting up of new missions on Indian lands.

Anza wanted to find an overland connection between the Sonora frontier and the western frontier of New Spain in Baja California. He started an expedition in 1773 to discover a route to Alta California, leaving Tubac Presidio, Arizona

  Tubac Presidio, Arizona

 in January 1774 and arriving back there in May after having successfully found the route and traveling to the newly established Presidio of Monterey.

He organized a second expedition in Mexico City in January 1775 to colonize the San Francisco Bay. The expedition arrived in Monterey, California in March, 1776.

Maps of Anza's 1775-1776 Colonizing Route

Upon his return to Mexico City, Anza was made commander of all the troops in Sonora in the fall of 1776 and was made Governor of New Mexico in 1777.

He had founded the cities of Los Angeles, San Francisco, and San Jose.