The Mexican-American War (1846-1848) made New Mexico part of the United States. In 1849, the first Army expedition reached El Morro, and it was at this time Inscription Rock acquired its name. Emigrants to California also used the route through El Morro, as did Mormon settlers, Puebloan, and Navajo people. However, after 1881, when the first train crossed over the Continental Divide, the El Morro route ceased to be a common thoroughfare. Learn more on the NPS webpage The Americans.