Transverse-barchan dunes, together with flanking sand sheets and whaleback sand mantles, stretch more than 8 kilometers between the Victoria Lower Glacier and the perennially frozen Lake Vida, forming the largest sand accumulation in Antarctica. The cold desert climate, persistent and strong summer easterly winds, thick, sandy ground moraine, and a broad valley train favor dune formation, although ubiquitous snow strata included in the sand deposits may limit movement. The dunes show short-term slip-face movements of up to 12 centimeters a day in mid-summer. Sand from the dunes is generally coarser and more poorly sorted than that from beach-derived dunes, but it is similar to that of many interior deserts. An unusually uniform and generally high degree of roundness of sand grains throughout lower Victoria Valley may be explained by inheritance of round Beacon sandstone grains and/or by a related 8-kilometer-long cyclical grainpath maintained in the valley by the combined action of winter and summer winds.