The Colorado River's headwaters are located high in Rocky Mountain National Park, just west of the Continental Divide. After leaving Rocky Mountain National Park the river follows the Kewuneeche Valley and is then dammed to create Grand Lake and Shadow Mountain Reservoir.
The lower course of the river, which forms the border between Baja California and Sonora, is essentially a trickle or a dry stream today due to use of the river as Imperial Valley's irrigation source. Prior to the mid 20th century, the Colorado River Delta provided a rich estuarine marshland that is now essentially desiccated, but nonetheless is an important ecological resource.
Prior to the construction of major dams along its route, the Colorado River fed one of the largest desert estuaries in the world. Spread across the northernmost end of the Gulf of California, the Colorado River delta’s vast riparian, freshwater, brackish, and tidal wetlands once covered 1,930,000 acres
Current Delta Conditions
Today, conditions in the delta have changed. Like other desert river deltas, such as the Nile Delta and the Indus River, the Colorado River delta has been greatly altered by human activity. Decades of dam construction and water diversions in the United States has reduced the delta to a remnant system of small wetlands and brackish mudflats. As reservoirs filled behind dams and captured floodwaters, freshwater flows no longer reached the delta.