Polygonal patterned ground is a dominant geomorphic feature in the McMurdo Dry Valleys, Antarctica. In central Beacon Valley, polygons are considered to be ancient expressions of stagnant surface processes and are thought to be stable for millions of years. However, the actual rate at which these polygons form and alter is not known. We describe a detailed cross section of a polygon, make several depth profiles of meteoric 10Be along this cross section, and use optically stimulated luminescence to date a few key samples at the center of this polygon. While confirming conclusions of previous studies that the polygon shoulders are stable on a 100 k.y. time scale and experience little vertical sediment mixing, our results also give clear evidence of eolian transport to the polygon center, leading to a sediment accumulation rate of 3 cm k.y.−1 over the past 15 k.y. Moreover, the data suggest that the accumulated material is locally derived, and, hence, surface erosion of the polygon shoulders must exist that cannot be recorded by meteoric 10Be. We conclude that polygon modification and soil accumulation under the apparent frozen conditions of Beacon Valley is an active and ongoing process.