Alta California was a province and territory in the Viceroyalty of New Spain, encompassing the lands along the Pacific coast of North America, from roughly present-day Oregon to Baja California. It was administered by Spain from the late 18th century until Mexico's independence in 1821, when it became part of the new nation.
The exploration of the region began with Juan Rodríguez Cabrillo in 1542, who sailed along the coast and claimed it for Spain. However, significant Spanish settlement did not occur until the late 18th century when Spain felt threatened by the expansion of other European powers, notably the Russian Empire and Great Britain. In response, the Spanish Crown authorized the establishment of missions, presidios (military forts), and pueblos (towns) to secure their claims.
Following Mexico's independence from Spain in 1821, Alta California came under Mexican rule. This era saw a shift in policy where the secularization of the missions began in 1833, leading to the redistribution of mission lands to private individuals, often through land grants known as ranchos. This period also saw an increase in American and European immigration, which would later play a role in the Mexican-American War.
The territory of Alta California effectively ceased to exist in its original form after the Treaty of Guadalupe Hidalgo in 1848, which ended the Mexican-American War. Under this treaty, Mexico ceded most of its northern territories to the United States, including what is now California, Nevada, Utah, and parts of Arizona, Wyoming, Colorado, and New Mexico.
The legacy of Alta California includes its influence on the cultural, architectural, and agricultural practices in modern California. The mission system, ranchos, and the introduction of European livestock and crops significantly shaped the state's early development. Furthermore, the Treaty of Guadalupe Hidalgo and subsequent land grants have had lasting legal and cultural implications for land ownership and Hispanic heritage in the region.