Archeologists call this area "the Great Plains" because it was here that they found most of the prehistoric ruins and artifacts. Parts of this region has been used as farmland for thousands of years, so you won't find any relics left behind from ancient civilizations like those in Mexico or Peru. Instead, you'll see evidence of early Americans: Neanderthals and Homo sapiens. Neanderthals went extinct about 4000 years ago, but scientists still know a lot about them because they've found many skeletons still wearing clothes and tools made from rock and bone. Homo sapiens (modern humans) appeared about 200000 years ago and replaced Neanderthals as the dominant species in Europe and Asia.