Colorado River, Mexico (now in United States and Mexico)
Also known as Rio Colorado, or Red River, because of area’s red clay that lends river its hue. One of longest rivers in North America; drains about 245,000 square miles. Runs southwest about 1,500 miles from Rocky Mountains in present-day northern Colorado to Gulf of California. Lower branch of river separates Mojave Desert from Sonoran Desert. Partially explored by Spaniards, early 1500s. Council of Fifty considered creating settlements at both head and mouth of river, 1845.