Paleontology and geology
Pleistocene till, clay, gravel, and glacial erratics are common over parts of Missouri north of the Missouri River. A layer of Pleistocene loess (wind-blown silt) of varying thickness covers all of the state except for the highest parts of the Ozark Mountains. Missouri is famous for its fossils of ice age mammals, including two well-known mastodon finds: the Grundel mastodon in extreme northwestern Missouri and the Mastodon State Historic Site south of St. Louis. The present day course of the Missouri River marks the approximate southern extent of glaciation in Missouri.