Duvall and Venner ( 1979 : 462 ) examined a sample of Calico artifacts .
Duvall and Venner ( 1979 : 462 ) concluded they were form - selected examples of naturally flaked rocks .
Duvall and Venner ( 1979 : 462 ) examined a sample of Calico artifacts and concluded they were form - selected examples of naturally flaked rocks .