The bottom of the magnetized crust determined from the spectral analysis of residual magnetic anomalies is generally interpreted as the level of the Curie point isotherm. This paper studies the spatial variation of the Curie point isotherm level in Yellowstone National Park with the help of aeromagnetic data. A very shallow isothermal surface at a depth of only 5--6 km below sea level is associated with the central part of the Yellowstone caldera. It seems to extend along a narrow corridor toward the southwestern and eastern edges of the map. Except in a few localized spots, the isotherm deepens considerably in the areas outside the caldera. Because the caldera encloses most of the areas of hydrothermal alteration, fumaroles, and boiling springs in the park, this study indicates a strong correlation between the spatial variation of the Curie isotherm level and the concentration of subsurface geothermal energy.