Alta California: Spanish Colonial Territory to US State

Alta California ("Upper California") was the Spanish colonial province** (1769–1821) and **Mexican territory** (1821–1848) encompassing present-day **California, Nevada, Utah, Arizona, and parts of Wyoming, Colorado, New Mexico**.

Geographic Definition

• South Boundary: Separated from Baja California ("Lower California") by the line from the Pacific coast at **Rosario** (approx. 30°N) eastward to the **Colorado River** — roughly the **Sierra de San Pedro Mártir** / mission frontier.
• North Boundary: 42nd Parallel (Adams–Onís Treaty 1819 / Treaty of 1818 with US).
• East Boundary: Vague; generally the Continental Divide / Rocky Mountains / Colorado River.

Historical Timeline

• 1769: Portolá expedition; Serra founds Mission San Diego de Alcalá (first of 21).
• 1776: Anza establishes Presidio of San Francisco.
• 1821: Mexican Independence → Alta California becomes Mexican territory.
• 1846–1848: Mexican–American War. US conquest (Bear Flag Revolt, Stockton, Kearny, Frémont).
• 1848: Treaty of Guadalupe Hidalgo → Ceded to US.
• 1850: California admitted as 31st state (current boundaries). Rest became Utah, New Mexico Territories.

Legacy

Mission chain (El Camino Real), rancho land grants, Hispanic toponymy (Los Angeles, San Francisco, San Diego, Sacramento), water law (prior appropriation roots).