The territory included all of the present-day U.S. states of California, Nevada, and Utah, and parts of Arizona, Wyoming, and Colorado.

The territory was re-combined with Baja California (as a single departamento) in Mexico's 1836 Siete Leyes (Seven Laws) constitutional reform, granting it more autonomy.

The El Camino Real trail established by the Spanish extended from Mexico City west to Santa Fe, and California, as well as east to Florida.

[8][9] Plans in 1715 by Juan Manuel de Oliván Rebolledo resulted in a 1716 decree for extension of the conquest (of Baja California) which came to nothing.

"[11][12] Alta California was not easily accessible from New Spain: land routes were cut off by deserts and Indigenous peoples who were hostile to invasion.

[13] In subsequent decades, news of Russian colonization and maritime fur trading in Alaska, and the 1768 naval expedition of Pyotr Krenitsyn and Mikhail Levashov alarmed the Spanish government and served to justify Gálvez's vision.

[3][15] The expedition first established the Presidio of San Diego at the site of the Kumeyaay village of Kosa'aay, which became the first European settlement in the present state of California.

[32] Spanish, and later Mexican, governments rewarded retired soldados de cuera with large land grants, known as ranchos, for the raising of cattle and sheep.

Similar to the missions, the construction, ranching and domestic work on these vast estates was primarily done by Indigenous peoples, who learned to speak Spanish and ride horses.

[33][34] As the number of Spanish settlers grew in Alta California, the boundaries and natural resources of the mission properties became disputed.

[37] In 1804, due to the growth of the Spanish population in new northern settlements, the province of Las Californias was divided just south of San Diego, following mission president Francisco Palóu's division between the Dominican and Franciscan jurisdictions.

[2] With the establishment of a republican government in 1824, Alta California, like many northern territories, was not recognized as one of the constituent States of Mexico because of its small population.

[citation needed] Laws were imposed by the central government without much consideration of local conditions, such as the Mexican secularization act of 1833,[15] causing friction between governors and the people.

The capital of Alta California remained Monterey, as it had been since the 1769 Portola expedition first established a military/civil government, and the local political structures were unchanged.

The friction came to a head in 1836, when Monterey-born Juan Bautista Alvarado led a revolt against the 1836 constitution, seizing control of Monterey from Nicolás Gutiérrez.

Alvarado's actions nearly led to a civil war with loyalist forces based in Los Angeles, but a ceasefire was arranged.

In the final decades of Mexican rule, American and European immigrants arrived and settled in the former Alta California.

In Northern California, they mainly formed new settlements further inland, especially in the Sacramento Valley, and these immigrants focused on fur-trapping and farming and kept apart from the Californios.

After twenty-seven years as part of independent Mexico, California was ceded to the United States in 1848 with the signing of the Treaty of Guadalupe Hidalgo.