In 1848, after the Mexican War, Americans assumed control of the territory of Utah and inherited many of the same knotty problems of Indian control. The Navajos living in New Mexico, Arizona, and southeastern Utah fell into the same pattern with their new white neighbors, who again turned to the Utes for help. Although there were some peaceful periods shared between the two groups, the Utes looked upon this opportunity for war with the Navajos as a chance to improve their economic standing, especially since their eastern territories in Colorado had been invaded by gold miners in 1859.

The Weeminuche, with other bands, joined in extensive forays which caused the major portion of Navajos in Utah to flee to isolated, peripheral areas, though some remained. Paiutes sometimes assisted the Navajos in avoiding detection through early warning. Between 1858 and 1864, a period known to the Navajos as "the Fearing Time," the Utes wreaked havoc on Navajo settlements, though there is strong indication that perhaps because of marriage and trade ties, some families were not bothered. By 1868, when the majority of Navajos returned from their forced exile at Fort Sumner, New Mexico, there was little love lost between them and the Utes.

Ironically, the same year-1868-that the Navajos received their reservation, the Utes received theirs. The original Ute reservation of 56 million acres comprised approximately the western third of present-day Colorado. Subsequent treaties in 1873, 1880, and 1934 saw a land base of 56 million acres shrink to 553,600 acres. For the Weeminuche in southwestern Colorado and southeastern Utah, the days of hunting and gathering came rapidly to a close. The Southern Ute Reservation in Colorado, eventually consisted of a strip of land 15 miles wide and 110 miles long.