Three anomalous areas containing shallow-depth warm water have been located in the San Pedro study area: (1) the San Manuel-Mammoth area; (2) the A.C. Gruwell Ranch; (3) Hookers Hot Springs at the Muleshoe Ranch. The probable explanation for these warm water resources is as follows. The Galiuro Mountains, the remains of a volcanic pile deposited along the axis of a large synform (Rehrig and Heidrick, 1976), are in all probability an area of recharge for the ground water system in the area. The meteoric water falling down upon the Galiuro Mountains percolates downward to great depths through fractures in the volcanic rocks, becomes heated, rises by convection along faults, encounters late Tertiary sedimentary units overlying these faults and migrates laterally through these sediments out into the basin. These warm waters are now near the surface because of erosion of the late Tertiary and Quaternary sedimentary units by the San Pedro River. This type of phenomenon will readily explain the unreasonably high gradients encountered in some of the more shallow wells. This low- to moderate-temperature geothermal resource may be utilized using current heat-pump technology for space heating and cooling, green house operations or in health spas. However, the size and production capabilities of the reservoir has yet to be established.