We have integrated and analyzed a 3D ground-penetrating radar (GPR) volume with a trenching exposure data set to evaluate the potential of these methods individually and combined for study of a fault zone. We chose a test site across a branch of the active Castrovillari fault in the Northern Calabria (Southern Italy). This tectonic structure is one of the most active in the area, and it has generated strong earthquakes in the past. Based on analysis of previously collected data, a 3D GPR survey was carried out 1.2 m from a fault outcrop. The goal was to use the GPR volume to guide and optimize the excavation of a trench and then to use the trenching data to validate the GPR volume interpretation. We used seismic interpretation software to display vertical and horizontal sections and for horizon tracking and attribute analyses. We obtained quantitative information on the geometry of structural and geologic features, such as fault strike and dip angle, defining the boundaries of different stratigraphic units. We validated our GPR data interpretation with the outcrop section and trench wall demonstrating the benefits of GPR in extensional tectonics environments and the great potential of the combined geologic and geophysical approach.