The suggestion is tested that variations in P travel-times to a station near a large dam might signal an impending local earthquake, perhaps induced by the reservoir. P travel-times to the Oroville station (relative to Jamestown) from precisely located underground nuclear explosions at the Nevada Test Site from December 1970 to March 1976 provide a suitable stochastic time series of uniform precision. Fluctuations before, during and after the 1975 Oroville earthquake sequence (main shock ML = 5.7) are analyzed for significance. Although the ray paths pass within 5 km of the focal region, no fluctuations in semi-annual mean residuals occurred greater than 0.01 ± 0.06 sec. At a high probability level there is no evidence that the seismic source process at Oroville altered the constancy of P velocities in crustal rocks between the focal zone and the dam.