Humans entered the Americas through the Beringia landbridge, and evidence documents their interactions with Columbian mammoths. Tools made from Columbian mammoth remains have been discovered in several North American sites. At Tocuila, Mexico, mammoth bones were quarried 13,000 years ago to produce lithic flakes and cores. At the Lange-Ferguson Site in South Dakota, the remains of two mammoths were found with two 12,800-year-old cleaver choppers made from a mammoth shoulder blade; the choppers had been used to butcher the mammoths. At the same site, a flake knife made from a long mammoth bone was also found wedged against mammoth vertebrae. At Murray Springs, archeologists discovered a 13,100-year-old object made from a mammoth femur; the object is thought to be a shaft wrench, a tool for straightening wood and bone to make spear-shafts (the Inuit use similar tools).