The Gran Desierto dune field is only partially composed of quartz-rich sands from the ancestral Colorado River. Local sources have been previously underestimated as a major source of sand because previous remote-sensing studies were limited in their capability to detect silicate minerals. Compositions of sands were evaluated in this study using a combination of laboratory thermal emission spectroscopy and thermal remote-sensing data acquired from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument. The spatial interpolation of sample compositions allowed visualization of the sand transport pathways from feldspar-rich local sources by revealing gradients of composition between the dune field and surrounding local sources. The laboratory data were comparable to the remote-sensing retrievals of quartz and feldspar abundance. The mineralogical maturity of the Desierto dunes could be determined by the quartz/feldspar ratio, therefore providing a context for understanding the provenance of the Gran Desierto in relation to other Mojave and Sonoran dune fields. The composition of a previously undescribed group of dunes east of the Pinacate, the Sonoyta dunes, was measured as higher in potassium feldspar relative to the rest of the dune field. The composition of Sonoyta dunes is characteristic of other Mojave dune fields, which are more isolated near local feldspar-rich sources. South of the Pinacate, quartz-rich sand from the west admixes with feldspar-rich sand from the Sonoyta dunes to the east. The northern margin of the Gran Desierto is similarly enriched in feldspar from alluvial fans, and the coastal sand is influenced by carbonate sand that does not appear to survive transport to the inland dunes.