This is the first of two significant assessments of the geological energy potential of the U.S. The second one is U.S.G.S. Circular 790. Systems analyzed include: Hydrothermal convection systems (with estimates of potential for many specific sites in the West), Igneous related systems (related to current or recent volcanism), Estimates of the conductive transport of heat in most areas of CONUS, Recovery of heat from molten igneous systems (magma), and Geopressured geothermal energy in the Gulf Coast area. The significance of this report is that it began to give policy makers a first handle on the quantities and qualities of geothermal energy in the ground in much of the U.S. Economics (costs and revenues) are not considered. (DJE - 2005)