The Cooper's Ferry archaeological site, located on a terrace above the Salmon River in western Idaho, has yielded a range of stone tools and other material dated to between 16 000 and 13 200 years before the present. This assemblage includes several stemmed points, a type of stone point presumed to have been used to tip an arrow, javelin, or spear, which are currently the oldest known such points from the Americas.
This material comes from a palaeosol (fossil soil) horizon within a glacial loess (rock groundings produced by the action of a glacier) layer, which has been dated to between 16 450 and 14 160 years before the present, and which has itself been truncated by the erosion of its upper surface. The loess layer within which the palaeosol was found also contains a three pits, from which a variety of bone fragments, a partial tooth from an extinct species of Horse, debitage and flake tools, plus a hearth feature were found; charcoal from the hearth yielded a radiocarbon date of 14 660 years before the present. Other charcoal and bone fragments recovered from the loess layer have yielded radiocarbon dates of between 15 660 and 14 650 years before the present. Debitage and flakes, bone fragments, and a fire cracked rock have also been found within the loess below the level of the bottom of the pits, although no formal tools or dates have been recovered from this deep; in the absence of such data, models have been used to predict that the Human settlement of the area probably began between 16 560 and 15 280 years before the present.
In a paper published in the journal Science Advances on 23 December 2022, a team of scientists led by Loren Davis of the Department of Anthropology at Oregon State University present the result of excavations at a new site at Cooper's Ferry, to the east of the original site.
The lowest layers from the new excavation site yielded radiocarbon dates of between 16 675 and 15 617 years before the present, dates which support the modelled earlier dates for the occupation of the first site. This site also yielded 14 broken and intact stemmed projectile points, as well as a variety of other stone tools, lithic debris, and Animal bones. These new stemmed projectile points are thousands of years older than the oldest known Clovis points in the Americas (which can be dated to about 13 000 years before the present) and about 2300 years older than the stemmed projectile points from the original Cooper's Ferry excavation site.
This means that the Cooper's Ferry tool assemblage is now quite large, overcoming a problem found at many pre-Clovis sites in North America, and enabling the archaeologists to develop a picture of the technology and tool making culture, by the comparison of multiple similar tools. These tools show cultural similarities to tools manufactured in northeast Asia, particularly Japan, during the Late Upper Palaeolithic, around 21 400 to 16 170 years ago.
The new excavations were carried out at a site named Cooper's Ferry Area B. Here a series of alluvial (river-derived) gravel and sand deposits, identified as lithostratigraphic units 1 and 2 (LUB1 and LUB2) are overlain by the glacial loess layer, LUB3. The area was disturbed by an exploratory trench in the 1960s, but the sediment infill was easily identified, and excluded from the study.
The site overlooks the Salmon River, and is overlain by a palaeochannel of the Rock Creek. This makes the sequence above the loess layer more complicated than at Area A, with different erosional and depositional conditions. Despite this, the lower layers, containing the archaeological material, can be traced between the two sites. A total of eleven lithostratigraphic layers are present, as well as an occurrance of the palaeosol layer, which is referred to as the Rock Creek Soil. The unconformity produced by the erosion of the upper surface of the loess layer is also present at Area B, with more material apparently removed here than at Area A.
The loess layer at Area B, LUB3, was found to contain three cylindrical pits, identified as Features 78, 108, and 151 (F78, F108, and F151). Feature 78 is 105 cm in diameter and 50 cm deep, and contains four intact and fragmentary stemmed projectile points, as well as a possible fragment of a the base of a fifth point, a fragment of a bifaced tool, a burin spall, a small edge fragment of a core, 250 pieces of debitage, seven pieces of fire-cracked rock, two pieces of charcoal, and 226 fragments of Animal bone. The top of this pit lies within the loess layer, LUB3, with the pit fill sediments contrasting visibly with the loess. Feature 108 lies to the north of Feature 78 at the same elevation, and is roughly 90 cm wide and 40 cm deep. This pit has an infill of carbonate material with Animal remains, and contains seven complete and fragmentary stemmed projectile points, 53 pieces of debitage, and 21 fragments of Animal bone. Feature 151 is roughly 75 cm long, 60 cm wide, and 50 cm deep. The upper layer of this is again below the upper surface of the loess layer LUB3, and is particularly notable, as this pit has been topped off with a layer of pebbly sandy loam sediments, which contrast with the surrounding loess, and resemble the material of a small cairn found on top of a pit feature at Area A. This pit also has a carbonaceous infill, within which were found eight pieces of debitage and 16 Animal bone fragments. The stone tools and bone fragments from these pits had a layer of carbonate material on their lower surface.
Composite stratigraphy of Area B. Drawing of stratigraphic units exposed along the a-a’ easting profile (A). Looking north into the deposits arranged near the a- a’ stratigraphic transect–pits F151 and F108 are positioned behind pit F78. To show this arrangement, the fill of F78 is made partially transparent. Plan view of Area B’s deepest excavation units showing distribution of pit features and trench excavation placed by Butler (B). Excavation unit numbers and quadrant designations are shown in each 1 m by 1 m square (e.g., 23-SE). Davis et al. (2022).Two radiocarbon dates were obtained from an Animal bone fragment within pit F78, 15 882-15 719 years before present and 15 914-15 740 years before present. Radiocarbon dates were also obtained from two Animal bone fragments from pit F108, giving dates of 15 970-15 600 and 15 975-15 590 years before the present. Three dates were obtained from different Animal bones in pit F151, giving ages of 15 772-15 617 years before the present, 15 970-15 790 years before the present, and 16 675-15 598. These ages appear to indicate that the three pits were in use at about the same time.
Comparison of stratigraphic profiles along the a-a’ transect, Area B. Cleaned stratigraphic profile exposed along the a-a’ transect in 2012 (A). Stratigraphic boundary lines overlain on cleaned profile (B). Composite stratigraphic drawing showing stratigraphic units, pit features, and radiocarbon ages (C). Dashed black box in (C) shows orientation of stratigraphic profiles shown in (A) and (B) relative to the composite stratigraphy drawing. Davis et al. (2022).The loess layer external pits also yielded archaeological material, albeit somewhat less. These comprise 10 pieces of debitage, six animal bone fragments, and two stemmed projectile points. One of the projectile points (specimen number 73-49277) was about 15 cm lower than the upper surface of pit F78, indicating that this object was deposited some time before the pit was dug. The second point (specimen number 73-54105) came from directly above pit F108, in the upper layers of the remaining loess, indicating that it was deposited some time after the pit was filled in, but before the onset of the erosion event that removes the uppermost part of the loess.
Projectile points from LUB3 sediments, pit F78, and pit F108. Catalog numbers are shown beneath each point (e.g., 73-54185). Dashed lines show estimated extents. A small fragment of a probable stemmed point base found in F78 is not shown here. Davis et al. (2022).In addition to the pit features originating within the loess layer (LUB3), four pit features were found at Area B originating from layers above, given the numbers F96, F99, F59, and F111. These higher pits do not intersect the LUB3 pits, so the material in them can be confidently assumed to be later in origin. Material from these pits included an array of stone tools, including stemmed projectile points of a different design to those from the later pits, several fire-cracked rocks, and a large amount of debitage and Animal bones. One of the later pits, F59, contained the partial skeleton of a Wolverine, Gulo gulo, and was capped by a hearth. Organic material derived from these pits five produced accelerated mass spectrometry ages, with the oldest being 11 610 to 11 240 years before the present, and the youngest being 11 075 to 10 595 years before the present. Unlike the lower pits, none of the material from these pits had a carbonate layer covering them.
Davis et al. remodelled the chronology for Cooper's Ferry Area A, including 94 new radiocarbon dates from Mussel shells within layer LUB6. The new model placed the start of LUB3 at between 16 500 and 15 250 years before the present, and the end at between 13 450 and 11 800. This gives a total duration for the bed's deposition of between 2070 and 4195 years, with a 68.3% confidence that it was deposited over between 2300 and 3500 years.
At Area B, LUB3 was modelled to have started between 16 045 and 15 725 years before the present. This is compatible with the estimated start of the layer at Area A, but gives a narrower age range. All of the features found within LUB3 at Area B were found to be between 15 955 and 15 625 years old, and the uppermost sediments from this layer are estimated date from between 15 845 and 15 530 years ago, again a much tighter window than at Area A, and considerably earlier. Layer LUB3 is overlain by layer LUB4, which is in turn overlain by layer LUB5. The lowermost part of LUB5 is estimated to date from between 12 695 and 11 240 years before the present.
Most of the dates obtained from layer LU3 at Area A were derived from the upper part of the loess, while many of the dates from LUB3 come from close to the base of the deposit, providing a better dating structure for the cultural artefacts.
Twelve of the fourteen projectile points recovered from loess layer LUB3 and pits F78 and F108 were made from a cryptocrystalline silicate, while the other two were made from a fine-grained volcanic rock. Both of these materials are available within about 10 km of the site. Most of these items are small, and made by the bifacial reduction of elongate flakes. Four larger flakes appear to have been made by the reduction of larger bifacial platforms. These tools are either biconvex or planar-convex, and all show signs of some reworking. The smallest point resembles a similar tool from Gault in Texas, which has been dated to 16 000 years ago, at a site where it was overlain by later layers containing material from a Clovis technology. Many of the points from Pits F78 and F108 resemble material from the Friedkin site, also in Texas, which has been dated to 15 500 years before the present. and the Santa Isabel Iztapan site in Mexico, which has been dated to 14 500 years ago. The points from both sites at Cooper's Ferry appear to develop more pronounced shoulders and straighter stems over time, possibly showing an evolutionary progression. This may be present at other sites in the Pacific Northwest, and merits further investigation.
The excavations at Area B increase both the tool assemblage and the amount of dated material available. This supports the modelled initial occupancy of the site being between 16 045 and 15 725 years before the present, with at least intermittent occupation of the site continuing till between 13 450 and 11 800 years ago. The features left during this occupancy include a hearth, five pits used for storage and/or refuse disposal, and a possible food preparation surface. The tools recovered from the site include 16 whole or partial stemmed points, 30 other stone tools, and 482 pieces of debitage. Other items found include 355 fragments of Animal bone, eight pieces of fire-cracked rock, and a partial Mussel shell. Radiocarbon dates from tools deposited before the palaeosol layer was deposited confirm the site was in use by Humans between approximately 16 000 and 15 600 years ago, while dates obtained from Animal bones within the pits associated with stemmed points suggest Human occupation of the site between 16 045 and 15 725 years before the present; with artefacts beneath the pit layer indicating Humans were present before this.
This significantly increases the range of confirmed dates for the early Human occupation of the Americas, as well as the known tool assemblage associated with these people. The earliest Americans are thought to share a common ancestry with the peoples of southern Siberia and northeast Asia, probably becoming isolated from these people by 25 000 years ago, and reaching the Americas bu about 19 500 years ago. However, genetic studies cannot at this time tell us whereabouts in northeast Asia these people came from, making comparison of their technology an important tool in understanding their origins. The material from Asia which most closely resembles the Cooper's Ferry assemblage comes from the Late Upper Palaeolithic of Hokkaido and northern Honshu, Japan, and dates to between approximately 32 000 and 20 000 years ago. This is well before the occupation of the islands by the Jomon people, thought to be ancestral to the modern Japanese, about 14 700 years ago. Previous studies have established that the Jomon were not ancestral to the earliest Americans, but this does not have any baring on the relationship between pre-Jomon peoples and early Americans. Davis et al. suggest that the technological similarity between the Cooper's Ferry people and the pre-Jomon Japanese may give some indication as to where the ancestors of these people originated.
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