Extent of the New Mexico Territory in the Early 1800s

During the early 19th century, the Spanish (later Mexican) territory of Santa Fe de Nuevo México encompassed present-day New Mexico, most of Arizona, and portions of Colorado, Nevada, Utah, and Texas. Its boundaries were loosely defined by the Rio Grande, the Continental Divide, and the 42nd parallel north. After the Mexican–American War (1846–48) and the Gadsden Purchase (1854), the region was gradually reorganized into the U.S. territories and states we know today.