The *Colorado River is one of the most important water systems in the United States. Draining watersheds from seven western states, it is divided into two major districts, the Upper Basin comprised of Wyoming, Colorado, Utah, and New Mexico, and the Lower Basin formed by Nevada, Arizona, and California. With its headwaters in Wyoming and Colorado and its mouth (until recently) flowing into the Gulf of California, this river serves as a focal point for both prehistoric and historic events in the West.
The Colorado courses through Utah in a southwesterly direction and has two major tributaries, the Green and San Juan rivers, with smaller, additional sources flowing in from east and west. During prehistoric times it constituted a permeable boundary between the Anasazi populations to the south and east, and the Fremont and western Anasazi populations to the northwest and west, respectively. The Anasazi farmed tributary canyons and alluvial bottom lands where soil was rich and water adequate. These early Indians also created a system of trails that crossed both the San Juan and Colorado rivers. Spanish and Anglo-Americans later used some of these paths in their exploration and settlement of the West.