Autumn proved to be the ideal time for me to explore Cape Cod's outer shore near the village of Eastham on the eastern arm of the cape. Fifty years ago, in late October, when I visited, summer crowds had long abandoned the beaches. The nights were cool, and the days stayed mild. The colors of warm-hued leaves and meadows deepened as the days grew shorter.

I was drawn to the grass-covered dunes and sea marshes just south of the Coast Guard Beach Lighthouse. Unlike the western United States, which I later explored and initially overwhelmed my senses, in my earlier black-and-white work along New England’s coast, I sought out intimate places where nature revealed itself in unexpected gestures.

Especially in this marsh, where I found a glacial erratic nearly hidden among the wind-blown salt meadow cord grass. Carried over an unknown distance, this boulder was rolled into its smaller rounded shape beneath mile-deep ice, reaching the eastern edge of a continent-spanning ice sheet.

Ten thousand years ago, the glacier left behind a moraine of sand, gravel, and rocks that formed New England’s outermost shoreline. This embryonic erratic appeared as a softly glowing wonder that seemed to have arisen naturally from this brackish basin.

Years later, storm tides washed out part of the marshland and, with it, swept this rock under the sea. Although I’ve read that a spit of land has once again reemerged as a bay barrier, where this rock is likely buried. Eventually, though, all of Cape Cod will disappear, a temporary headland vulnerable to storms, currents, and the rising sea levels of an encroaching ocean.