From 2000 UT on March 17 to 0400 UT on March 18, 1993, when Geotail was in the distant tail, it underwent a series of mantle crossings. These mantle crossings are manifested in the magnetic field and plasma data as smooth excursions between magnetosheath values and lobe values. We test the one-dimensional self-similar MHD slow mode expansion fan model of the mantle by comparing the modeled predictions with the data including, for the first time, magnetic field data. We use the measured speed, density, magnetic field strength, ion and two different electron temperatures to initialize the mantle flow. Using this range of upstream parameters, we show that the model reasonably well brackets the observed variations of both magnetic field and plasma parameters through the mantle. The total pressure through the modeled fan remains constant as the thermal pressure at the outer edge converts into magnetic field pressure at the inner edge. Using the modeled fit, we estimate the mantle to be 10--12 RE thick. ¿ American Geophysical Union 1996