The Hartley Mammoth Site is a pre-Clovis archaeological and paleontological site in New Mexico. Preserving the butchered remains of two Columbian mammoths, small mammals and fish, the site is notable due to its age (~37,500 BP), which is significantly older than the currently accepted dates for the settlement of the Americas.
Locality
Situated on the south-eastern corner of the Colorado Plateau, the Hartley Mammoth Site lies on the canyon of the Rio Puerco, which flows into the Abiquiu Lake. Both the river and lake belong to the Chama basin of northern New Mexico. The slope's steepness (~19°) and abundance of sandstone boulders indicates a dynamic environment, discouraging soil formation. This dynamic environment is also evidenced in the poor sorting of sediment grain size. The site is located in a small (1.5m) alluvial channel, formed in the depression of a block of Triassic sandstone (Poleo Formation) slumped over weaker mudstone (Salitral Formation), possibly exacerbated due to the wetter conditions and increased snowmelt of the Late Pleistocene. The Rio Puerco canyon represents around 150,000 years of erosion. The steepness of the slope and nature of the channel was noted as being unusual for a mammoth burial. The site today is of a semi-arid climate, and is occupied by piñon-juniper woodland.
Excavations
The site was discovered on Tim Rowe's property by Gary Hartley in 2013, while he was on a hike. On the surface was a tusk, three ribs, a broken dentary, a heavily reworked obsidian Clovis projectile point, and scattered lithic debitage of pedernal chert and obsidian. Upon excavation, the skeletons of two Columbian mammoths, a young female adult and a calf, were uncovered. The bones were primarily excavated by archeologists from the University of New Mexico, then catalogued for further study at the University of Texas, Austin. The expedition was led by Bruce Huckell, Tim Rowe, Leslie McFadden, and Grant Meyer.
The Hartley Mammoth Site is one of 87 other mammoth sites in New Mexico, with the closest other site nearby, at the La Chama river. The Hartley Mammoth Site is unique, as the mammoths were fully buried, and remained in a stable depositional environment. Most mammoth specimens, in contrast, are poorly fossilized.
Initially, due to the Clovis point, the site was believed to be a Clovis butchery site, rapidly buried by a debris flow. However, further examinations by a 2022 study using both established and new techniques for a Pre-Columbian archeological site, along with radiocarbon dating, led to the conclusion that they were not contemporaneous. Below the exposed tusk and ribs were the disarticulated, intermingled partial skeletons of a young-adult female mammoth (95% of the remains) and a young calf, mostly piled in a meter-thick concentration of broken bones and large cobbles. In total, the adult is represented by 44 broken cranial fragments, an intact upper right second molar and 12 isolated tooth plates, 25 ribs broken into 52 fragments, 3 vertebrae and 15 vertebral fragments, 32 percussion-impact bone flakes, 9 butterfly fragments, 20 unidentifiable bone fragments, and 267 bags of small ‘bone scraps’, whereas the calf's remains are composed of a partial left maxilla and dentary with intact dentitions, three isolated tooth plates, left tibia diaphysis, and 10 rib fragments. In the midst of the pile, lying on top of four broken ribs, was a 23.7 kg boulder interpreted as a hammerstone and/or anvil. The excavations took place at 5 cm intervals, to ensure accuracy.
Although the adult's face and tusks were stacked on top, 88% of the larger (>5 cm) bones and bone fragments in the main accumulation were buried in the lower two-thirds of the excavation. Also recovered were with six chert microflakes, the only excavated lithic remains, preserving evidence of percussion flaking. That two adult vertebral epiphyses remained in articulation with each other suggests that they were held together by an intact joint capsule at time of burial, one of many indications that burial was rapid.