A compilation of aeromagnetic and new earthquake data is used to characterize the current tectonic activity and crustal properties of the Yellowstone hot spot. Earthquakes located during detailed surveys from 1972 to 1976 occurred west and northeast of the Yellowstone caldera along east-west zones and south of the caldera in north-south zones. The change in trend suggests that Yellowstone is at a vertex of the contemporary tectonic patterns. Seismicity showed variations of maximum focal depths from ~20 km outside the Yellowstone caldera to ~5 km inside the caldera. The frequency of earthquake occurrence was markedly lower within the caldera. Fault plane solutions showed general north-south extension west of the caldera, a suggestion of radial compression near the western caldera rim, and northeast to southeast extension south of the caldera. Spectral analyses of aeromagnetic data indicate the Curie isotherm to be 10¿3 km below sea level at the periphery of the caldera. These data support the hypothesis of a magma source within the crust for the Yellowstone hydrothermal activity, but they do not bear on the definition of a deep mantle source for the Yellowstone hot spot.