A brief review is given of the state-of-the-art and the theory involved in the influence of geology on seismic response. Several field experiments are described which were performed to determine the dynamic amplification of seismic response by alluvium. In the Dry Lake area (saturated alluvium) resonant depths of alluvium were observed at 500 feet and 1400 feet. This is in approximately the harmonic ratio as predicted by theory. In the Hidden Valley area (dry alluvium) the resonant depth of alluvium was observed at 300 feet. The ratio of 500 feet to 300 feet for the two areas is in fair agreement with the ratio of 7000 feet to 5300 feet for the velocities of the alluvium in the two areas as determined by the refraction surveys.