Casper Bluff Land & Water Reserve is the first site within the Illinois Nature Preserve System to be protected due to significant archaeological features.
Casper Bluff contains the Aiken Mound Group, named for the nearby community of Aiken.
Our knowledge of these mounds stems from 1900, when William Baker Nickerson, an amateur archaeologist who worked for the railroads, documented 51 mounds at this location:
38 long, wall-like structures, 12 conical mounds, and one thunderbird effigy. Nickerson also observed an earth ellipse or hut-ring and two circular depressions.
Nickerson's limited excation of the mounds in 1900 produced pottery fragments, indicating the fill may have come from a nearby habitation site.
Archaeologists from the University of Chicago visited the site in 1926; however, only 40 mounds were observed at that time.
In 2006, Phil Millhouse from the University of Illinois was able to relocate Nickerson’s original map, kept at the Illinois State Museum. Using GIS technology, the location of all 51 mounds documented by Nickerson have been identified.
At the present, however, only 20 mounds can be visually identified on the ground surface. Agricultural cropping and grazing have no doubt affected the integrity of the mounds.
The Aiken Mound Group is part of the larger Effigy Mound culture that existed between A.D. 700-1000 in Wisconsin, Iowa, Minnesota and Illinois.
While most of what is known about the site is based on the mounds themselves, there is a possibility that there may still be intact archaeological features among the mounds.
Skeletal remains from the Aiken Mounds have been found in adjacent crop fields. Habitation sites, while not mapped, were thought to occur in the nearby low-lying fields east of the steep river bluffs where the ceremonial mounds are located.
While the effigy mounds peoples are thought to have abandoned the region after 1000 A.D., as late as 1875 members of the Ho-Chunk Nation performed ceremonies at in the vicinity of Aiken Mounds and constructed a burial mound for the son of their leader, Green Blanket. This burial site is thought to be located one mile east of the reserve within the bottomlands of Small Pox Creek.