Our journey from Columbia, Missouri, to Littleton, Colorado, climbs through geologic time. In greater Columbia and along I-70 to its immediate west, outcrops of Mississippian limestone are evident, deposited in shallow seas some 320 million years ago (MYA). By the time we reach western Missouri, we are riding atop Pennsylvanian sedimentary rocks, about 300 million years old; this strata continues into eastern Kansas.
West of Topeka and to the eastern outskirts of Junction City, I-70 undulates across the Flint Hills, where Permian sediments, including thin seams of coal, outcrop along road-cuts and stream valleys; these rocks were deposited about 220 MYA as Earth's Continents were merging into Pangea. West of Junction City and throughout Central Kansas, the highway crosses Cretaceous limestones, shales and sandstones, deposited in and along a broad seaway that stretched from coastal Texas to southwest Canada when Tyrannosaurus rex roamed the planet, some 100 MYA.
Throughout the High Plains of western Kansas and eastern Colorado, Tertiary deposits lie atop the Cretaceous sea bed, eroded from the Front Range of the Rockies or blown in from pockets of volcanism throughout the American West. This erosional debris, carried eastward by braided rivers, began to accumulate early in the Tertiary (60 MYA), following the initial rise of the Rockies, but increased dramatically during the Miocene-Pliocene Uplift (20-5 MYA) of the Colorado Plateau and Rocky Mountain corridor. Finally, during the Pleistocene (2.5-0.01 MYA), wind-blown loess, from continental glaciers to the north and mountain glaciers to the west, coated some regions. Along the South Platte and Arkansas Valleys, the Tertiary veneer has been removed, exposing the underlying Cretaceous sea deposits (primarily Pierre shale) upon which the rivers drop their own cargo of Quaternary sand and gravel.
