The azimuthal variations of P wave velocity measured in U.S. Geological Survey (USGS) seismic refraction experiments around Mount Hood, Oregon, are modeled by propagation through the effective anisotropy of parallel vertical cracks. The three refractors at 1, 3.7, and 8.5 km depth show different behavior. The shallow refractor at 1 km displays P wave velocity variations typical of the parallel water-filled vertical microcracks found throughout much of the upper continental crust. The arrivals from the refractor at 3.7 km display velocity variations consistent with either dry cracks or, more probably, with cracks filled with supercritical water, as one interpretation of the heat flow around Mount Hood suggests that temperatures at 3.7 km would be above the critical temperature for water at in situ pressures. The velocity variations at the deepest refractor at 8.5 km depth are poorly constrained but again suggest liquid-filled cracks. The possibility of high temperatures suggests that, at this depth, the cracks could be thin skins of melt along grain boundaries. The vertical cracks in all three refractors strike in the northwest to southeast quadrants, which is consistent with the compressional quadrants in the mechanisms of local earthquakes. Shear-wave splitting reported elsewhere indicates that there are stress-aligned water-filled microcracks (extensive-dilatancy anisotropy or EDA) throughout at least the brittle upper 10 or 20 km of the continental crust. The high heat flow in the High Cascades may confine the range of crack behavior, usually spread over the whole thickness of the crust, to the top 10 km beneath Mount Hood. Thus the P wave velocity variations beneath Mount Hood may indicate that EDA cracks occur throughout the whole of the continental crust. The large number of shot-to-recorder travel times measured by the USGS allows extensive-dilatancy anisotropy to be recognized from the analysis of P wave velocity variations for the first time.