Long period magnetotelluric (MT) data is being collected as a component of the USArray covering the continent of North America at a quasi-regular grid. Data from 250 MT stations were acquired covering the north-western part of the United States of America (USA). Dimensionality analysis was applied using Swift skew, Bahr skew and ellipticity. Results show a 1-D/2-D character for the short periods (< 1 sec) for the shallower structures, while the longer periods (> 1 sec) shows a 3-D character for the deeper structures. Two dimensional Occam inversion was applied for a set of E-W trending profiles to map the regional electrical resistivity distribution to a depth up to crust/mantle transition zone. 2-D resistivity structures were obtained by inverting both the transverse electric (TM) and transverse magnetic (TM) modes. Results show a resistive upper crust with a decreasing resistivity for lower crust. To the west, the subudcting Gorda plate was mapped as a relatively higher resistivity body nearly equal to the Wyoming basin to the east. Thick resistive lithosphere was mapped under Wyoming to the east. The results of this research shows the distribution of the electrical resistivity with adequate details for the shallow depth, while 3D inversion is necessary for the larger depths.