On this barren desert hillside, in strata laid down 200,000 years ago, deep excavations have revealed what may be crude scrapers and choppers made by very ancient humans. These people lived on the game-rich shores of a lake that occupied lowlands to the east and south. The site offers an excellent introduction to the physical organization and technical aspects of a major archaeological dig.Artifacts found here lend credence to a theory that an earlier species of man may have inhabited the Americas before Homo sapiens, thought to have entered the North American continent via the Bering land bridge as long ago as 20,000 BC. Louis S.B. Leakey, who uncovered some of the world's oldest human remains in East Africa's Olduvai Gorge, believed the Calico site was a stone tool workshop. Begin at the small, rustic visitor center, where several excavated artifacts are on view. Tours led by site archaeologists depart from the miner's shack that Leakey used as his field headquarters, and continue on to three large and several smaller pits, some as deep as 30ft.