The Pecos River ( PAY-kəs; Spanish: Río Pecos) originates in north-central New Mexico and flows into Texas, emptying into the Rio Grande. Its headwaters are on the eastern slope of the Sangre de Cristo mountain range in Mora County north of Pecos, New Mexico, at an elevation of over 12,000 feet (3,700 m). The river flows for 926 miles (1,490 km) before reaching the Rio Grande near Del Rio. Its drainage basin encompasses about 44,300 square miles (115,000 km2).
The name "Pecos" derives from the Keresan (Native American language) term for the Pecos Pueblo, [p'æyok'ona]. The river was also historically referred to as the Río Natagés for the Mescalero people.

Quelle: Wikipedia