Many of these mounds have been excavated in the past, and the information gleaned from their contents has given archaeologists a picture of Missouri that dates back at least 12,000 years to the Woodland Period and earlier. In 1989, during a construction project along Forum Boulevard, a mound was hit. Carbon dating showed she had lived in the Early Woodland Period, between 850 B. In 1986, Chapman was researching the Rogers Shelter area in the Osage River Basin when he established what he estimated to be an 11,000-year timeline — from about 10,000 B. the unmarked graves were treated as basically abandoned property with no clear ancestry present," he said.