The Chalk Pyramids and Monument Rocks are names for the same group of rock outcroppings, near US-83 in western Kansas. There are signs at the turn off (6 miles of gravel roads). You can see the rocks in the distance from the highway if you know where to look.
Like the Castle Rock Badlands, the Monument Rocks are on private range land, but thanks to the owners, open to the public. The United States Department of the Interior has designated the Chalk Pyramids as a National Natural Landmark.
The 70 feet tall sedimentary formations of Niobrara Chalk were created 80 million years ago when this area was part of a vast inland sea.