The river reach considered the Upper Rio Grande in New Mexico runs from the Colorado-New Mexico state line to the Otowi gage located near State Highway 4 and San Ildefonso Pueblo. Upper Rio Grande tributaries include the Red River, Rio Hondo, Pueblo de Taos, Embudo Creek and the largest tributary, the Rio Chama. While the annual flow of the Rio Grande is quite variable, of the approximate long-term average 1.1 million acre-feet of native Rio Grande surface water that leaves the Upper Rio Grande and is measured at the Otowi stream flow gage, about one-third comes from Colorado, one-third comes from the Sangre de Cristo Mountains, and another third comes from the Rio Chama watershed.
Water storage on the Upper Rio Grande includes waters stored on the Rio Chama as part of San Juan Chama Project, and they include Heron, El Vado, and Abiquiu Reservoirs. The San Juan Chama Project was authorized by Congress in 1962 and completed in 1971. The Project was developed to bring a portion of New Mexico's allocation of Upper Colorado River basin water to the Rio Grande basin via the Rio Chama watershed for beneficial use in New Mexico. It is not subject to the provisions of the Rio Grande Compact.
The Upper Rio Grande contains all or parts of Taos, Rio Arriba and Santa Fe counties. Española is the largest city in the basin, and other towns include Taos, Chama, and Tierra Amarilla. The Upper Rio Grande includes the Rio Arriba, Jemez y Sangre, and Taos Water Planning regions.