Paul,
Thanks for that.

Anyone interested in evidence for early man in the Americas should take notice of Steve Holen's paper: Taphonomy of two last glacial maximum mammoth sites in the central Great Plains of North America: A preliminary report on La Sena and Lovewell

These sites are located in Northcentral Kansas and Southwestern Nebraska with bone colagen dates in the range of 18,000BP. No significant tool finds, but he found stacked, spirally fractured mammoth bones which as Holen points out could only have been caused by humans harvesting marrow.