monument rocks (also chalk pyramids) are a series of big chalk formations in gove county, kansas. it has many fossils. the formations were the first landmark chosen by the us department of the interior as a national natural landmark. the chalk formations reach a height of up to . it includes formations such as buttes and arches. the carbonate deposits were laid down during the cretaceous period in what was then the western interior seaway. it split the continent of north america into two landmasses. they are estimated to have been formed 80 million years ago.