The crescentic sand-dune formation known as the "barchan" occurs extensively in the desert coast of southern Peru. Quantitative measurements were made on 75 of these to determine relationships between height, width, and length of horns. A consistently longer west horn was measured in most of the barchans, but this distortion cannot be readily explained. Mechanical analyses of the dune sand were performed on samples taken from the Pampa de Clemesi and the principal barchan deposits in the Pampa de la Joya, as well as from deposits further downwind from La Joya. There is a consistent increase in the proportion of the fine material in the samples taken farther from the Pampa de Clemesi. The bulk specific gravity also decreases with distance from Clemesi. Bulk specific gravity varied with dune height. Mineralogical analyses of these same samples indicate a decrease in the heavier minerals with increasing distance from the Pampa de Clemesi, and an increase in the volcanic, fibrous glass. This evidence indicate...