Airborne synthetic aperture radar (SAR)-derived soil moisture (mv) estimates were evaluated using field measured and distributed hydrologic model simulated mv values in the Reynolds Creek Experimental Watershed (RCEW), located in a semi-arid mountainous watershed in Southwest Idaho. A soil moisture inversion algorithm was developed by comparing L-HH SAR sigma0 (dB), corrected for surface roughness and topographic effects, with field measurements. The algorithm was found to be consistent with an algorithm developed in a previous study done on other rangelands. The corrected SAR-based soil moisture maps show relatively dry conditions at lower elevations and vice-versa, which is consistent with field observations. Change detection was found to give results similar to those from the corrected SAR, but it tends to give lower soil moisture values than the field measured or corrected SAR-based approaches. Out of the two SAR-based approaches used for the determination of mv, change detection is simpler and adequate for the measurement of soil moisture changes. The corrected SAR approach is relatively difficult but it is better for the areas where absolute mv measurements are required and SAR data under dry conditions are not available. The hydrologic model tended to overestimate surface mv, which is what SAR senses. This was due to the failure of the model in accurately accounting for surface evaporation processes unless subsoil was relatively dry. In general, the overall trends in mv, especially for 1989 and 1991, were reasonably represented but probably a little over the actual values. The soil moisture simulation model, corrected SAR, and ground measurements provided a unique mounds to study the moisture changes and distribution patterns in rangelands with an imaging SAR.