Gusev Crater, the Mars Exploration Rover Spirit landing site (160 km diameter; 14.5°S, 184.5°W), has been identified in previous studies as a prime site of geological and exobiological interest on the basis of its potential for having hosted a fluviolacustrine environment; such environment may have been favorable for the development of biological activity. The origin and nature of the materials present at the surface of Gusev Crater are still being debated. In previous studies based on geomorphological and thermophysical data, surface materials in the crater have been interpreted as originating from fluviolacustrine, volcanic, or aeolian processes, or combinations thereof. We present results from the analysis of newly compiled thermophysical (Thermal Emission Spectrometer (TES) and Thermal Emission Imaging System (THEMIS)), spectroscopic (TES), and visible (THEMIS and Mars Observer Camera) data for the Gusev region. These data were analyzed using a new mosaicking technique developed to match the values of contiguous scenes and to produce seamless mosaics apt for geological interpretation. Thermophysical, spectroscopic, and morphological evidence point to the presence of local outcrops of lava flows of basaltic composition, materials consistent with a regolith developed from basaltic materials, fine-grained deposits of basaltic composition strongly modified by wind erosion, and wind deposits. According to these findings, we conclude that most of the materials occupying the present surface of Gusev have characteristics consistent with those of volcanic and aeolian deposits. Fluviolacustrine deposits proposed by other authors may exist under the volcanic materials and may be exposed in impact craters.