Control of the area was contested by nomadic Navajo and Ute for centuries. Spanish friars and military passed through the area as part of the Old Spanish Trail connecting New Mexico and California in the 18th century. The name Mancos comes from the Domínguez-Escalante expedition of 1776, though the reason for the name remains unclear (see below). By some unverified accounts, the name Mancos refers to the crippled nature of the Spanish explorers' horses after they crossed the San Juan Mountains. According to unverified lore, the horses were rejuvenated by the lush green grass in the Mancos Valley. Somewhere in the town is the point at which the expedition crossed the Rio Mancos on its way to California from Old Mexico.