River, southwestern U.S. It rises in the San Juan Mountains of southern Colorado, on the western side of the Continental Divide .
It flows southwest into New Mexico, northeast into Utah, and west to the Colorado River . It is 360 mi (580 km) long and not navigable. The section of the river where the boundaries of New Mexico, Utah, Arizona, and Colorado meet, into which the San Juan has carved numerous S-shaped canyons more than 1,000 ft (300 m) deep, is known as the Goosenecks.