Alaska. Polygonal ground on a mountaintop east of Rex Dome in the Alaska Range. The clay-rich centers swell and collapse sufficiently from freezing and thawing ice that they destroy the roots of any plants that grow on them. Plants gain footholds only along the relatively clay-free borders, which do not heave as much as the centers. Plate 2, figure 11, U.S. Geological Survey Professional Paper 482.
Digital File:wah00136