A boundary condition on temperature at depth in the continental crusts can in principle be obtained by mapping of the Curie isotherm where it forms the base of the magnetic crust. An approach to mapping magnetic crustal thickness using satellite magnetic anomly data is described. Because magnetic srustal thickness is small with respect to satellite altitude, inversion of the anomaly data yields magnetization models expressing regional variations in the vertical integral of magnetization. This parameter is inversely correlated with regional heat flow in the western United States, suggesting that areas of low apparent magnetization are areas of thin magnetic crust resulting from a shallow Curie isotherm. For a simple model of a uniformaly magnetized magnetic crust (or intra-crustal layer), Curie depth is linearly related to apparent magnetization. If the relation can be calibrated by two or more Curie depth estimates, regional apparent Curie isotherm configuration can be mapped. In an alternative approach, a family of Curie depth models can be computed using assumed magnetization values. In each case, the Curie depth configuration is used as a boundary condition in a thermal model. That model is selected which gives a heat flow distribution best fitting observations. Conductive heat flow models for a traverse across the Rio Grande Rift using a finite element technique and for a map grid using a one-dimensional thermal model approximation are given as examples.