The Beaver Street Wall is a radiolarian chert, a hard sedimentary rock comprising fine silica crystals originating from the shells of radiolaria, tiny ocean-dwelling plankton, that settled to the sea floor millions of years ago.
Large areas of the rock appear smooth and shiny, a feature known as a slickenside, which suggests that the rock sat on one side of a geological fault line. Sliding against rock on the other side of the fault over many years has left a polished, glassy surface in places.
