The Pecos River rises in the Pecos Wilderness of the Sangre de Cristo Range in north-central New Mexico; its uppermost tributaries gather east of Truchas Peak (13,102 feet), the second highest point in the State. Flowing southward, the river passes through the Pecos National Historic Site east of Santa Fe and soon enters canyonlands south of the mountains; there it runs through Villanueva State Park before rumbling onto the High Plains of eastern New Mexico.
Angling SSE across the plains, the Pecos River has been dammed to form Santa Rosa Lake, Sumner Lake, Brantley Lake and Avalon Lake (north to south); constructed primarily for irrigation and water supply purposes, these reservoirs are also used for recreation and attract large flocks of migrant waterfowl, cranes and shorebirds that travel above the arid planes of eastern New Mexico. The river also passes through Bitter Lake National Wildlife Refuge, northeast of Roswell, a major wintering area for sandhill cranes, and flows west of Bottomless Lakes State Park, which harbors deep, sinkhole lakes that formed in the Cretaceous limestone bedrock. South of Carlsbad, the Pecos receives flow from the Black River (draining the east edge of the Permian Reef complex), its only significant tributary between the Sangre de Cristo Mountains and the Rio Grande.
As the Pecos River leaves southeastern New Mexico and enters western Texas, it flows through the Red Bluff Reservoir; the backwater of this lake, which was impounded in 1936 and has a surface elevation of approximately 2840 feet, marks the lowest elevation in New Mexico, almost 10,000 feet below the headwaters of the Pecos. Below the Red Bluff reservoir, the river snakes through the High Plains and canyon country of West Texas, finally entering the Rio Grande just upstream from the Amistad Reservoir and nearly 930 miles from the alpine snow fields of the Sangre de Cristos.
