In 1991-2 palaeontologists excavated a site near San Diego, California where broken bones had been found. These turned out to be the disarticulated remains of an extinct mastodon. One feature of the site was the association of several large cobbles with bones of large limbs that seemed to have been smashed either to extract marrow or as source of tool-making material. The cobbles showed clear signs or pounding, such as loss of flakes – one flake could be fitted exactly to a scar in a cobble – pitted surfaces and small radiating fractures. The damage to one cobble suggested that it had been used as an anvil, the others being hammer stones. Broken pieces of rock identical to the hammer stones were found among the heap of bones. No other artefacts were found, and the bones show no sign of marks left by cutting meat from them with stone tools. The breakage patterns of the bones included spiral fractures that experimental hammering of large elephant and cow bones suggest form when bone is fresh. Other clear signs of deliberate breakage are impact notches and small bone flakes. Two detached, almost spherical heads of mastodon femora suggest that marrow was the target for the hammering and confirmed the breakage was deliberate.
Since the sediment stratum in which the remains occurred consists of fine sands and silt, typical of a low-energy river system, the chances that the cobbles had been washed into association with the mastodon are very small. The interpretation of the site is that it was the result of opportunistic exploitation of a partial carcase of a young adult mastodon by humans. In the early 1990s attempts were made to date the bones using the radiocarbon method, but failed due to insufficient preserved collagen. That the site may have been much older than the period of known occupation of North America by ancestors of native people (post 14.5 ka) emerged from attempts at optically stimulated luminescence dating of sand grains that can suggest the age of burial. These suggested burial by at least 60 to 70 ka ago. It was only when the uranium-series disequilibrium method was used on bone fragments that full significance of the site emerged. The results indicated that they had been buried at 130.7±9.4 ka (Holen, S.R. and 10 others 2017. A 130,000-year-old archaeological site in southern California, USA. Nature, v. 544, p. 479—493; doi:10.1038/nature22065 – full paper and supplements available free)
Not only is the date almost ten times that of the earliest widely accepted signs of Homo sapiens in the Americas, the earliest anatomically modern humans known to have left Africa are around the same age, but restricted to the Levant. The earliest evidence that modern humans had reached East Asia and Australasia through their eastward migration out of Africa is no more than 60 ka. The date from southern California is around the start of the interglacial (Eemian) before the one in which we live now. It may well have been possible then, as ~14 ka ago, to walk across the Bering Straits due to low sea level, or even by using coast-hugging boats – hominins had reached islands in the Mediterranean and the Indonesian peninsula certainly by 100 ka, and probably earlier. But whoever exploited the Californian mastodon marrow must have been cold-adapted to achieve such a migration. While the authors speculate about ‘archaic’ H. sapiens the best candidates would have been hominins known to have been present in East Asia: H. erectus, Neaderthals and the elusive Denisovans.
Surely there will be reluctance to accept such a suggestion without further evidence, such as tools and, of course, hominin skeletal remains. But these long-delayed findings seem destined to open up a new horizon for American palaeoanthropology, at least in California.
You can find more information on hominin migration here.