The stations which recorded the GNOME explosion in the continental United States can be arranged into 8 more or less linear profiles centered on ground zero. The P wave velocities in an area within 300 km of the explosion yield the following results: 5.55 km of layer 1 --- velocity 4.86 km/sec, 17.85 km of layer 2 --- velocity 6.20 km/sec, 20.84 km of layer 3 --- velocity 6.64 km/sec, the velocity of the underlying material is 7.81 km/sec. The velocities of Pn along the profiles are : 8. 37--8. 43-- 8.49-7.99-7.86-7.82--8.00 and 8.12 km/sec as the azimuth of the profiles changes counterclockwise beginning from the east. These observations strongly suggest regional variations in the mantle material. P velocities show the same trend as the Pn velocities. Travel times at stations west of Sierra Nevada show delays caused by mountain roots.