radiocarbon dated ash beds

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The LSU campus mounds, with construction beginning at ∼11,000 BP, are the oldest known extant man-made structures in the Americas
Brooks B. Ellwood, Sophie Warny, Rebecca A. Hackworth, Suzanne H. Ellwood, Jonathan H. Tomkin, Samuel J. Bentley, Dewitt H. Braud and Geoffrey C. Clayton

American Journal of Science June 2022, 322 (6) 795-827; DOI: https://doi.org/10.2475/06.2022.02