These are the Cannonball Concretions in the North Unit of Theodore Roosevelt NP. How could you miss seeing these rock formations, which were not more than 100 yards from the main road driving in? We did, at least on our first pass by. We were looking for the picnic area, which was on the other side of the road.
People are easily distracted, which is one reason why it is important to be intentional in our daily lives.