Cannonball, concretion

In North Dakota, while crossing the marvelously sculpted badland areas, you can bump into a lot of perfectly spherical reddish concretions called 'cannonballs'. The concretions took their name after the Cannon Ball River and census, in North Dakota. They are greater than one meter in diameter and are made of hard, cemented sandstone popping out unconsolidated host clay, due to differential weathering. This photo was taken within the Theodore Roosevelt National Park, North Unit.