Both of these photos illustrate a geologic phenomenon known as a "pothole", but not the kind that ends up in the asphalt along the highway. Potholes form along exposed bedrock where there is often swift and turbulent water movement. Streams carry small rocks into a depression in the bedrock and, as the rock swirls around the depression, it scours a hole into the bedrock. This continuing abrassion, over time, eventually can create potholes of varrying sizes.

Trenton Falls, New York. Ordovician Rust Fm of the Trenton Group

Little Falls, New York. Precambrian Grenville Fm