Lepper, Bradley T.; Duncan, James R.; Diaz-Granádos, Carol; Frolking, Tod A. (August 2018). "Arguments for the Age of Serpent Mound". Cambridge Archaeological Journal. 28 (3): 433–450. doi:10.1017/S095977431800001X. S2CID165819360.
Lepper, Bradley T.; Duncan, James R.; Diaz-Granádos, Carol; Frolking, Tod A. (August 2018). "Arguments for the Age of Serpent Mound". Cambridge Archaeological Journal. 28 (3): 433–450. doi:10.1017/S095977431800001X. S2CID165819360.