Upper Paleozoic (Pennsylvanian-Permian) silty strata of the northern Pedregosa basin (southern Ancestral Rocky Mountains province) exhibit distinctive features that suggest origin of the silt as eolian dust prior to deposition in marine environments. Studies of mechanisms controlling modern eolian dust accumulation imply that combined marginal-marine-epeiric-sea environments constitute an ideal sink for eolian dust. Accordingly, Pedregosa siltstones may reflect the prevalent mode of eolian dust preservation downwind from coeval ergs, and significant volumes of eolian dust may be preserved within analogous epeiric strata. Because eolian dust reflects conditions of aridity and windiness, it bears on paleoclimatic and paleogeographic reconstructions. Recent studies within several basins of the Ancestral Rocky Mountains suggest an eolian derivation for many siltstones and thus corroborate inferences of increasing aridity and concomitant monsoonal conditions for western Pangea. Further regional analysis may provide valuable insights for refining concepts of the zonal to monsoonal transition that accompanied Pangean assembly.