Cooper's Ferry/Nipéhe, stratigraphic integrity, and confirming early inland dispersal: Evaluating peopling of the Americas modeling.

At Cooper’s Ferry/Nipéhe, Idaho, 5-centimeter elevation bins used for the Apparent Stratigraphic Integrity Index (ASI) do not match artifact stratigraphic positions, so ASI cannot support claims of large-scale vertical mixing.

• Why it matters: Statistical peopling models rely on assumptions about postdepositional mixing, but their credibility depends on whether indices like ASI truly measure stratigraphic integrity.
• What they did: The study evaluates ASI’s binning logic against independent chronological, stratigraphic, pedogenic, archaeological, and excavation evidence for the Late Pleistocene deposits at Cooper’s Ferry/Nipéhe.
• The result: Multiple independent lines of evidence support the integrity of an approximately 16,000-calibrated-years-before-the-present occupation and provide early inland evidence expected under coastal-migration models.

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