The time of first arrival of seismic waves generated by 4 underground nuclear explosions at the Nevada Test Site (NTS) and recorded along a line extending north into southern Idaho is expressed as T0 = 0. 00 + Δ/3.0 (assumed), T1 = 0 .40 + Δ/6.03, and T2 = 6.15 + Δ/7.84, where time is in seconds and the shot-detector distance (Δ) is in km. Assuming constant velocities and horizontal layers, crustal thickness in the vicinity of NTS was determined to be 28 km. Delays in the traveltime segment T2, which represents Pn, indicate that the crust may thicken to 32 km in northern Nevada. A third phase, expressed as T3 = 14.48 + Δ/7.84, was also recognized and has arrival times appropriate for SPS. Amplitudes of Pn were determined at 7 places from recordings of seismic waves from one underground nuclear explosion (ANTLER).