Delicate Arch Is Standing on Borrowed Time

Delicate Arch stands in Arches National Park, Utah, part of a landscape that holds over 2,000 documented natural stone arches within a fairly small stretch of desert. The concentration exists because of what's sitting underneath it.

A salt bed did the heavy lifting

Millions of years ago, a thick layer of salt formed beneath what's now the park. Salt is unstable under pressure — it shifts and flows over long timescales — and as it moved, it pushed the sandstone layers above it upward and apart, cracking them into long parallel walls of rock called fins.

Fins become arches

Fins are the raw material; erosion does the sculpting. Water gets into cracks, freezes, expands, and widens them. Wind and sand do slower, finer work on the surface. Where a fin was thin or weak enough, the middle eventually wore through completely, leaving an arch standing on two thicker legs of rock.

Freestanding, and temporary

Delicate Arch is unusual even among arches: it stands almost entirely alone, unconnected to a cliff face or fin on either side, which is part of why it reads so cleanly in photographs. It's roughly 20 metres tall and made of Entrada Sandstone, a rock soft enough that the same erosion which carved it is still, slowly, working to take it back down.