Under Mexican authority many land grants were made to private citizens and Monterey received its Pueblo grant of 30,000 acres. The once proud missions were secularized in the mid-1830s, and their lands were dispersed as part of the grants. In California those early settlers and native born citizens inherited the name of Californios. They became the romanticized vision of Mexican California that was reflected in such novels as Helen Hunt Jackson's Ramona.

In July 1846, during the Mexican-American War, Commodore John Drake Sloat's Pacific squadron arrived in Monterey Bay. On July 7, his troops landed, raised the American flag, claiming California for the United States. This began a period of American occupation that lasted until 1848 when the Treaty of Guadalupe Hidalgo was signed making all of Alta California part of the United States. This acquisition included the land now known as California, Utah, Nevada, parts of Arizona, Colorado, New Mexico, and Wyoming.