Cenozoic Era (66 million years ago to present)
The Cenozoic Era began about 66 million years ago and consists of three periods: the Quaternary, Neogene, and Paleogene.
Quaternary Period (2.6 million years ago to present)
Glaciers of the Pleistocene Epoch (2.6 million years ago to 11,700 years ago) reached northeast Kansas at least twice, leaving behind unsorted clay, sand, gravel, and boulders. Quartzite boulders, picked up by the glaciers far to the north and deposited in Kansas as the ice retreated, are found on the surface in northeast Kansas today. In some places, thick glacial deposits called glacial drift have formed deep soils.
Volcanic ash blown in from the west during this period is now found under ground. Winds deposited loess (fine silt) over wide areas, and streams flowing south to the Arkansas River carried sand, silt, and gravel eroded from older rocks in the High Plains to the north to form alluvial deposits in south-central Kansas.
Large mammals—including mammoths, camels, saber-toothed cats, and horses—lived in Kansas during the Pleistocene, but most died off during a mass extinction 9,000–12,000 years ago. Bison bones and human artifacts, dating back 11,000 years, have been found together.
During the Holocene Epoch, grasslands became more prevalent and plant and animal species found today began to dominate. Dunes created by strong winds that carried and deposited river sand in western and central Kansas are still visible today. Most are now inactive, or stabilized by grass and other vegetation.
Neogene Period (23 million years ago to 2.6 million years ago)
Streams carried silt, sand, and gravel eroded from the uplifting Rocky Mountains into western and central Kansas, where they formed the porous Ogallala Formation. The Ogallala, now mostly underground, is a major source of groundwater. Winds carried in volcanic ash from the west.
Neogene animals and plants include rhinoceros, tapirs, horses, kangaroo rats, salamanders, elm trees, hackberry trees, and grasses. Trace fossils of animal burrows and ant nests have been found.
Paleogene Period (66 million years ago to 23 million years ago)
Paleogene rocks have not been found in Kansas.