The spectral amplitude from 14 shallow-focus events in California and Nevada are used to determine the ground amplification in the 0.4 ≤ T ≤6.0 sec. period range at two sites. The epicentral distances of these events range from 100 to 450 km, and their magnitudes 4.0 ≤ ML ≤ 5.0. The spectral amplitude ratios are formed for an event recorded by a low-gain Benioff system at two mobile stations, in order to determine quantitatively the effect of different subsoil conditions on the recorded signals from the two station locations. The statistical determination of the mean spectral ratios shows that the alluvium-to-granite ratios are higher than the sandstone-to-granite ratios by approximately one-half unit. It is also shown that these ratios vary as a function of frequency.