GEOLOGICAL DATING OF INDIGENOUS RESERVOIRS AND ADJUDICATION OF WATER RIGHTS, LAGUNA, NEW MEXICO

Recent geomorphological and stratigraphic investigations were conducted at two reservoirs located along the Rio San José in western New Mexico in support of efforts by the Pueblo of Laguna to adjudicate their water rights. Objectives of our study included confirmation of human construction and determination of reservoir ages. Remnants of dams constructed of earth and stone masonry by the Laguna people were identified at both reservoirs. Chronometry was provided by single grain optically stimulated luminescence (OSL) of reservoir and adjacent alluvial deposits. One reservoir near the community of Casa Blanca had a storage capacity of ~1300 ac-ft and dates to the late A.D. 1700s to early A.D. 1800s. The other reservoir, located adjacent to Old Laguna Pueblo, represents an expansion of a natural marsh upstream from a bedrock constriction on the Rio San José. This reservoir had a storage capacity of ~5300 ac-ft and was constructed between A.D. 1370 and A.D. 1750. This research confirms indigenous construction of significant water-storage reservoirs on the Rio San José prior to the late nineteenth century and demonstrates the value of geological methods in evaluating the antiquity of water use by modern tribal communities in water rights cases.