The pressure-volume relationship, strength, differential stress-strain, and acoustic velocities were studied as a function of pressure for several samples of graywacke sandstone from the emplacement hole at the site of the Rio Blanco gas stimulation experiment. The results of these measurements are intended for use as input parameters in calculation codes which seek to predict the amount and extent of fracturing produced as a result of the detonation of an underground nuclear explosion. At laboratory strain rates (--10- 5 sec -1) the sandstones from the emplacement well are found to be rather compressible at overburden pressures) but have the relatively high shear modulus characteristic of other similar graywacke sandstones. As with these other sandstones, the simulated plane shock-loading path shows pronounced departure away from the failure envelope. Some of this departure may be the result of strain-rate dependent processes. Failure in uniaxial compression is characterized by brittle fracture at mean pressures below 5 kbar and by macroscopic ductile flow above this pressure. Strength properties and the brittle to ductile transition are midway between those found for similar rock-types from the Gasbuggy and Wagon Wheel gas stimulation experiments.