. . . "Cretaceous and Paleocene rocks of the northern Great Plains"@en . . . . . . . . "Chart showing geologic stratigraphy of American states and Canadian provinces on the Great Plains. Shows layers by series and stage ; used to show potential oil producing layers in the region."@en . . . . . . . . . . . . "Correlation chart of Cretaceous and Paleocene rocks of the northern Great Plains"@en . "Charts, diagrams, etc"@en . "From 55 to 140 million years ago" . .