These Dakota sandstone concretions are related to the same natural phenomena that created the spherical Moeraki Boulders and Bowling Ball Beach in California.

Coming into existence when parts of Kansas where covered by an Inland Sea, these formations were the product of a type of natural cement. Known as concretion, over millions of years natural concrete binds tiny particles into massive round boulders, forming what are known as "cannonball concretions". Originally thought to be corals, glacial boulders, or a handful of other geological phenomenon, the rocks were eventually recognized as calcite-cemented concretions, the softer sandstone eroding away from the calcite cement leaving the banded, free-standing boulders. 

About 200 of the formations are in the 5-acre park, some nearly 30 feet across. The park claims that this is the largest collection of spherical concretions in one place.