Paradox Valley is a basin located in western Montrose County in the U.S. state of Colorado. The dry, sparsely populated valley is named after the apparently paradoxical course of the Dolores River—instead of flowing down the length of the valley, the river cuts across the middle and through the sheer walls of large mesas on either side. The valley is the site of a Bureau of Reclamation salinity-control project which has caused thousands of earthquakes, and is the proposed location of a new uranium mill which would be the first built in the United States in over 25 years.

The Dolores River is a tributary of the Colorado River, approximately 241 miles (388 km) long, in the U.S. states of Colorado and Utah. The river drains a rugged and arid region of the Colorado Plateau west of the San Juan Mountains. Its name derives from the Spanish El Rio de Nuestra Señora de Dolores, River of Our Lady of Sorrows. The river was explored and possibly named by Juan Maria Antonio Rivera during a 1765 expedition from Santa Fe.