Meandering along the Utah/Arizona border, Buckskin Wash is an ephemeral stream that flows through a broad valley before draining into a long, constricted canyon. In some places, the gulch is so narrow that I could stretch my arms out and touch both sides of its nearly vertical walls.

Ancient dunes, compacted by weight and cemented by minerals once dissolved in groundwater, lithified into a thick layer of sedimentary rock that was uplifted into a plateau that covers much of Utah and portions of adjoining states, and has since eroded into "slot canyons" such as Buckskin Gulch.

This deep ravine has been scraped and polished into an exotic (if claustrophobic) wonderland, offering the chance to discover unusual details in nature. This scoured pocket in a sandstone wall is a perfect example. The midday light leaked through an opening in the canyon rim, briefly illuminating the contours of an oval feature.

At first, I couldn't tell whether it bulged inward or outward. Just above the line of mudded sediment from the last flash flood, I wondered, had previous erosion sanded this concave pocket out of weakly cemented sandstone? Or was it a soft, rounded imprint left by a concretion of hardened sandstone that was swept away by a flood? Either way, the canyon's subtle lighting lent this mysterious feature a radiant glow.