Walking across the dunes outside the coastal port of Provincetown on a rare, calm, sunny winter morning was like crossing an arid wilderness, devoid of vegetation, open and flat. It was a place that inspired me to look down as I walked in order to take in the patterns in the sand. Eventually, I came across one that, at first, made no sense.

Eighteen thousand years ago, clay, rocks, and sand deposited by receding glaciers formed what would become Cape Cod. As sea levels rose to near present-day levels, the outer part of the cape took on the shape of a forearm. The northernmost reach of the cape (the fist) is where wind and ocean currents transported sand, forming a sandbar that expanded in size and height.

Originally covered by forests, the area was cleared by early settlers. As Henry David Thoreau noted in his 1854 book “Cape Cod,” “the sands began to invade the land more and more, until finally they had entire possession from sea to sea…” Since the 18th century, Cape Codders have planted beach grasses. Today, the dunes are mostly grass-covered, and the extensive stretch of pure sand in this picture from fifty years ago no longer exists.

Describing the character of this desert, Thoreau wrote, “None of the elements were resting. On the beach, there is a ceaseless activity, always something going on, in storm and in calm, winter and summer, night and day.” In winter, these dunes are buffeted by winds that move the sand. Snow is often covered with sand blown in from the surrounding dunes and beach. Surface cracks and dimpled hummocks form as the snow beneath alternates between melting and freezing.