Recommended reading (FREE)
Note: We know more today about the Mound Builders than the scholars of the 19th and early 20th century. I provide links to these books because they are excellent, free resources with maps and illustrations of many of the known mounds and earth works.
MacLean, J.P. The Mound Builders. Cincinnati: Publisher, 1893. Print.
Shetrone, Henry Clyde. The Mound-Builders. New York: D. Appleton-Century Company, 1936. Print
Squier, E.G., A.M. & Davis, E.H., M.D. Ancient Monuments of the Mississippi Valley Bartlett & Welford, 1848. Print