ZTEM (Z-Tipper Axis Electromagnetic) airborne AFMAG surveys have been conducted over geothermal test areas such as Reese River, in central Nevada, since 2009. The Reese River prospect is a "blind" geothermal resource that lacks surface characteristics such as hot springs. A number of geophysical surveys have been conducted at the prospect, including seismic, gravity, magnetotelluric (MT) and radiometric surveys. Resistivity methods, such as MT, are typically used to map structure, lithology and alteration, particularly the smectite-zeolite zones which form a low resistivity cap over the outer margins of the higher resistive reservoir at depth. The ZTEM survey at Reese River overflew lines previously surveyed using MT for comparison purposes. The ZTEM results appear to correlate very well with previous magnetotelluric results and the known geology, in particular the presence of both major and secondary fault structures and geologic contacts. 2D inversions of the airborne ZTEM appear to agree very well with the inversions obtained from ground MT. 3D joint MT-ZTEM inversion results improve the quality of the subsurface resistivity structure. Other test cases in Nevada and South America will be presented.