Alta California
- Map of Territorio de Alta California
Capital Monterey, California
Last GovernorPío de Jesus Pico IV
DissolvedJune 14, 1846

Alta California (Upper California) was formed when Spain separated the Dominican Missions from the Franciscan Missions in approximately 1769 with the founding of the first Alta California mission in San Diego. Separate administrations were created in 1804 when the Province of the Californias, then a part of the Commandancy General of the Provincias Internas in the Viceroyalty of New Spain, was divided in two, along a line separating the Franciscan missions in the north from the Dominican missions in the south. The southern part became the territory of Baja California ("Lower California"), also referred to at times as Vieja California ("Old California"). The northern part became Alta California, also alternatively called Nueva California ("New California").

The new territory included land that today forms the modern American states of California and parts of Nevada. Because the eastern boundaries of the province were not defined, many maps from the period show its borders including parts of today's Utah, northern Arizona, western Colorado, and southwestern Wyoming. The province would have bordered on the east with the Spanish, later Mexican, settlements in Arizona and the Province, later Territory, of Nuevo México.

Mexico gained independence from Spain in 1821 upon conclusion of a decade-long war of independence. The region was automatically included in the short-lived First Mexican Empire. With the establishment of a republican United Mexican States in 1823, California, like many northern territories, was not recognized as one of the constituent states because of its small population. (The 1824 Constitution refers to Alta California as a "territory"). After Juan Bautista Alvarado's revolt in 1836, the territory was transformed into a department, which granted it more autonomy.

Mexico lost the territory two decades later as a result of the Mexican-American War. The last Mexican Governor of California was Pío Pico, who served until 1846. The capital of Alta California was Monterey.

In the second half of the nineteenth century, there was a San Francisco-based newspaper called The Daily Alta California (or The Alta Californian). Mark Twain's first widely successful book, The Innocents Abroad, was an edited collection of letters written for this publication.