An aeromagnetic survey of central Utah has given improved resolution of a regional anomaly previously recognized from satellite magnetometer data. The anomaly consists of a gradient from a high over the Colorado Plateau to a low over the Basin Range province. Magnetic profiles are fit by a model in which the Curie isotherm deepens eastward in a belt up to 80 km wide, whose western side is about 50 km east of the Basin Range physiographic margin. The magnetic profiles could also be fit be a change of average crustal susceptibility instead of Curie depth. In either case we conclude that the major lateral change between Basin Range and Colorado Plateau crustal geophysical parameters occurs not at the Fenneman physiographic boundary but more than 50 km eastward of it. This suggestion is found to be consistent with data from seismic refraction, geomagnetic variation, geochemistry, and geologic structures.

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