We compare interferometric synthetic aperture radar displacement maps for Antelope Valley, California, derived for two different satellite orbit geometries to test the common assumption that surface displacements above deforming aquifer systems are purely vertical. This assumption greatly simplifies models of aquifer system deformation related to changes in groundwater flow and storage, permitting the use of one-dimensional codes for characterizing the compaction occurring in the flow model. The analysis is complicated by interferometric phase noise and atmospheric signal contributions. We use a variance-weighted least squares approach to optimally use the information contained in several interferograms. Our analysis of the displacement maps does not identify significant displacement differences for the two acquisition geometries, implying that the motions are indeed nearly vertical. Uncertainties in the interferometric phase measurement and atmospheric delay signals preclude any conclusion regarding the existence of horizontal displacements smaller than ~2 cm. The absence of spatial correlation between the observable differences and the known subsidence field indicates that horizontal displacements are indeed negligible for inelastic aquifer system compaction in Antelope Valley.