P and S wave amplitude data from digital, three-component seismograms of local earthquakes recorded on a temporary seismic array have been used to tomographically invert for the three-dimensional attenuation structure in the upper crust of Long Valley caldera, California. Differential attenuation (∂Q-1) values are obtained through the use of a spectral ratio technique that minimizes the site effect on the spectral ratios. The spectral ratios are inverted for ∂Q-1 using the LSQR algorithm. Zones of high, positive P wave ∂Q-1 (greater P wave attenuation) are observed at a depth of 4--5 km beneath the east flank of Mammoth Mountain and at 6--8 km beneath the southwestern edge of the resurgent dome. A region of positive S wave ∂Q-1 is seem at 7--8 km beneath the southern edge of the resurgent dome, whereas at 6--7 km, the S wave results are near average. The region of positive S wave ∂Q-1 at 7--8 km beneath the resurgent dome may indicate the roof of a magmatic system. The positive P wave ∂Q-1 at 4--5 km beneath Mammoth Mountain and 6--8 km beneath the resurgent dome may be due to the presence of a compressible fluid such as supercritical water. These zones may represent some of the source regions for the Long Valley geothermal system.