In 1952, a large bone bed was discovered at this location containing the remains of extinct mammoth, tapir, bison, and horse, along with the weapons and tools of the Indians who had killed and butchered these animals. The bones and weapons date back 11,000 years. Ed Lehner discovered the bone bed on his ranch after observing bones eroding from the banks of a side drainage of the San Pedro River near his home. In 1955 and 1956, archaeologists from the Arizona State Museum led by Dr. Emil W. Haury uncovered the bones and found 13 Clovis spear points and 8 cutting and scraping tools. Further excavations in 1974 and 1975 by Dr. C. Vance Haynes, Jr., also from the Arizona State Museum, uncovered butchering and cooking areas. The site is one of the best preserved mammoth hunting sites in the New World. Because of its importance, it was designated a National Historic Landmark in 1967. Ed and Lynne Lehner donated this land to the people of the United State, and it became part of the San Pedro area to be preserved and interpreted for the public by the Bureau of Land Management.