Rising at 11,750 feet in the Sangre de Cristo range and snaking 926 miles through New Mexico and Texas to the Rio Grande, the Pecos River is one of the most storied waterways in the American West. It is also one of the most troubled. In 1942, the National Resources Planning Board observed that the Pecos River basin "probably presents a greater aggregation of problems associated with land and water use than any other irrigated basin in the Western...