In recent work by Herring and by Frisch and Morrison, a classical model of a high temperature, spatially inhomogeneous semiconductor has been used to study the nonsaturation of the magnetoresistance at high magnetic fields. We have studied a quantum mechanical reformulation of this model which is valid in the region where the ratio, a, of the Landau level spacing to the mean electron kinetic energy is less than unity. The electrons, still treated in the effective mass approximation, are statistically described by a quantum mechanical transport equation for the one-electron density matrix. The effective potential arising from a more or less random distribution in space of inhomogeneities, whose scale may now extend to atomic dimensions, is included in the electron Hamiltonian. The electron-phonon interaction is described by an appropriate stochastic, relaxation type collision term first employed by Gross and Lebowitz to study dipole relaxation. To obtain the magnetoresistance we require only the local current and density of electrons. These are obtained from a positive, quasi-classical electron distribution function which arises when we consider the expectation value of the density matrix (Husimi transform) in a state in which both position and velocity of the electron are highly localized. We show explicity, at least for the case of a stratified medium, that to leading terms in inverse powers of the magnetic field strength the current and thus the magnetoresistance, given previously by Frisch and Morrison are correct to order a. We briefly discuss and illustrate by examples certain aspects of the use of Husimi transforms in related problems.