Native Americans
Stewardship Center
Education Program
Community Involvement
Media and Links
Roger Williams



What had begun as a rebellion of peasants against their colonial Spanish masters in Mexico had evolved into a full-scale war. Mexico declared its independence from Spain on September 16, 1810, and as the Mexican War of Independence (1810-21) raged on, the U.S. ceded to Spain its claim to lands south and west of the Arkansas River (which originates in the Rocky Mountains) in 1819. At the same time, the U.S. purchased Florida from Spain.


When Mexico gained its independence from Spain in 1821 it assumed ownership of western and southern Colorado. In order to secure the frontier, the Mexican government awarded large amounts of land to Mexican citizens who were willing to establish colonies in the San Luis Valley and other border areas, but few settlers moved there. Mexico was forced to cede its territories in what later became the southern part of the United States, including Colorado, to the United States following the end of the Mexican War in 1848. The U.S. government recognized the original Mexican land grants, and colonists, mostly Spanish and Mexican, began to settle in the San Luis Valley during the 1850s.

Between the 1830s and 1850s, French and American traders, trappers and settlers established trading posts along the Arkansas River and on the South Platte River (which starts to the southwest of present-day Denver). The most famous of the trappers was Kit Carson (1809-68), who gained notoriety as a guide to American explorer John C. Frémont (1813-90) as he traversed the Wild West.
America's western frontier grew by more than 500,000 square miles when the U.S. won the Mexican-American War in 1848. As the victor, the U.S. was ceded territory extending west from the Rio Grande River (which originates in southwest Colorado) to the Pacific Ocean.