Valles caldera was home to the first experiments into development of an Enhanced geothermal system (EGS) or Hot-dry-rock (HDR) geothermal system, beginning in 1974 by the Los Alamos National Laboratory at the Fenton Hill reservoir, approximately 3 km west of Valles caldera. Originally, the Fenton Hill site was chosen as an EGS laboratory in hopes that the proximity to Valles caldera would increase the temperature of the bedrock, thus requiring shallower drill depths. However, the abundance of hydrothermal fluids discharged from the nearby caldera resulted in hydrothermal alteration of the rocks at depth, weakening the sealed nature of the reservoir. The Fenton Hill HDR experiment was finally abandoned in 1998. The Fenton Hill experiments demonstrated that a potential EGS reservoir must be characterized by low permeability, crystalline basement rock with no active faults or joints.