The next major cultural division is noted in pottery and the use of many materials obtained from distant sources. The Indians seem to have elaborated their material possessions and intellectual life gradually, following a trend apparent through the Midwest. The remains from this period are called Hopewell, a culture dating from 100 B.C. to A.D. 600. Pottery and projectile points collected in the monument show a relationship to certain Hopewellian types. Indians of this period used mica from the Appalachians, obsidian from the Rocky Mountains, seashells from the Gulf of Mexico, and copper from the Lake Superior region.
Several mounds excavated in the monument are of the Hopewellian period.
While certain ones contained traits identified with the Hopewell, the evidence was not as abundant as is usually found in similar centers of Illinois and Ohio. Three of these Hopewellian mounds are adjacent to the visitor center. The Effigy Mounds people occupied the land now within the monument from a time overlapping the Hopewellian period until almost historic times. Their cultural remains indicate they differed from the Hopewellians chiefly in constructing mounds in effigy forms, using copper for tools rather than ornaments and burying their dead with few if any intentional offerings of a lasting nature. Whatever their burial customs, these people probably differed little from their predecessors in terms of economic and everyday life.