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Hell Creek
The Hell Creek Formation is a set of river and swamp deposits in Montana and the Dakotas, laid down in the last couple of million years before the dinosaurs vanished. Hell Creek is the single most important locality for deciding whether dinosaurs were in decline before the impact or were taken abruptly. The question is unsettled, but the density of finds right up to the boundary argues against a drawn-out extinction. The formation has also yielded most known T. rex specimens, and it is the arena for a continuing dispute over ownership of fossils on private land — a conflict that in practice decides whether scientifically important finds reach museums or auction houses.
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