It is not possible to discuss the Rio Grande or any of its tributaries without recognizing the complex interconnectivity of the entire hydrologic system that is the Rio Grande Basin. This includes the mountain streams and underground aquifers discussed above, as well as the underlying alluvial deposits of sand and clay that lie under the valley floor. Yet the Rio Grande itself is the most well-known water feature within the heritage area, for it is the longest, widest, most visible, and continuous water body within the San Luis Valley.

The Colorado portion of the Rio Grande Basin (or watershed) encompasses approximately 7,500 square miles. Originating in the San Juan Mountains just to the northwest of the heritage area, the Rio Grande flows through the center of the San Luis Valley on its way to New Mexico before passing along the southern border of Texas to separate the United States from Mexico. In total, the river flows approximately 1,200 miles before reaching the Gulf of Mexico. Within the heritage area, the Rio Grande flows through the City of Alamosa. South of Alamosa County, it forms the boundary between Conejos and Costilla Counties.

Mountain Streams Most of the water entering the Sangre de Cristo Heritage Area originates from rainfall that channels into mountain streams high above the valley floor. In the southern portion of the San Luis Valley these streams merge into rivers and creeks that serve as tributaries to the Rio Grande. Among these are Rock Creek, Alamosa River, La Jara Creek, Conejos River, and San Antonio River from the west; and Trinchera Creek, Culebra Creek, and Costilla Creek from the east. North of Alamosa, no mountain streams reach the Rio Grande because surface waters disappear into the gravel and sands contained within the valley floor. Among others, these include Saguache Creek, Medano Creek, Zapata Creek, and San Luis Creek, the latter of which often disappears and reappears before reaching its destination at the San Luis Lakes.