Alta California was settled by Spanish missionaries beginning in 1776. Discovered earlier, to be sure, by both Spanish (Balboa, DeAnza, etc) and English (Drake) explorers in the 16th century, but not settled.
The missions were all built by the Spanish between 1776 and 1820 before Mexico declared independence from Spain.
Mexico ruled California only until 1848, some 27 years. And even then their possession of the area north of San Francisco Bay was disputed, the Russians had a settlement at Ft. Ross (which ultimately Gen. Mariano Vallejo bought from the Russians). Even during the period of Mexican rule, the people who really ran California looked to Spain for goods and education, not to Mexico!