This paper reports the geotechnical characterization of pyroclastic sand and a tuff formation, both finding at the Valley of Pichin Leufú River, Río Negro province, Argentina. The geological origin of these materials is the precipitation of volcanic ash. The materials studied present singular mechanical characteristics. Tests results show that both materials present a low unit weight and low plasticity, but high liquid limit, high compressibility and high strength parameters. The aim of the geotechnical characterization is to determine an exhaustive set of both stiffness and strength parameters. A series of conventional laboratory techniques, such as one-dimensional compression, triaxial compression and direct shear tests were performed in order to determine both deformational and strength parameters of the pyroclastic sand. On the other hand, unconfined compression tests were performed on specimens of the tuff rock in order to characterize this material. Also, a series of direct shear tests in concrete-tuff interfaces were performed in order to evaluate the skin friction for different of normal stress levels and concrete roughness. A comparison with other tests results finding at the literature also are presented.