I took this photo next to a small waterfall while hiking along Healy Creek in Banff National Park. I couldn't help but notice dozens of rock formations much like the one pictured below. After some research, I discovered the reason for these holes with rocks in them. They are called rock cut basins. Fast moving water below the waterfall creates vortexes and spin smaller sized rocks. These rocks, over many years, erode the softer rock below and create cylindrical depressions or holes.
I also took pictures of two other rock cut basins and including this one, I framed the set of three which is now for sale in a local art gallery.