The stoss face of a large parabolic dune at Dillon Beach, California, is being actively eroded by wind action. The result is formation of a lag deposit consisting largely of shells of Helminthoglypta arrosa (Gould), a heliciform, terrestrial gastropod. Wind velocities up to thirty miles per hour serve to orient many of these sand-filled shells with the aperture away from the prevailing wind direction. In addition, sandblasting by saltating grains produces a wedge-shaped abrasion or decortication pattern on the spire of the shell with the wedge pointing downwind. Wind-oriented gastropod shells and decortication wedges may be useful criteria for determination of paleowind directions in ancient dune deposits.