In the photo above, Sam Ascah is standing on sand and gravel in a pothole, where a stream swirls during the short but intense thunderstorms of Zion National Park. And next to that stream, the other picture shows the sandstone and the hang-on-so-you-don't-fall-over-the-cliff chain along the trail. A likely interpretation of these features is:

The grooves behind the chain have been cut over decades by motion of the chain as hikers grabbed it, and the potholes were cut by water swirling rocks around during the rare floods over much longer times.

Explanation:

In the question above, we can see that the physical action of some factors found in this environment, such as the movement of the currents and the movement of stones in the water, which managed to cause some changes in the environment, building a totally new scenario, which would not occur if these factors did not exist.

By reading the question and imagining the scenario described, we can conclude that the grooves behind the chain have been cut over decades by motion of the chain as hikers grabbed it, and the potholes were cut by water swirling rocks around during the rare floods over much longer times.