A minority of these pieces, thirty-four, are distinguished by the development of a small centralized pit on one or both smoothed faces. In some instances there is a single pit on one surface and two on the other. Many of these pitted examples have been battered on their peripheral edges, suggesting they were either reused rubbing stones or they served a dual function of both smoothing and pecking. We are hesitant to call them "pitted hammerstones" since many are made from a soft sandstone and would be ill adapted to this function. It is of some interest to note that this general type of stone implement occurs in central and northern California throughout most of the entire cultural history of the more advanced industries. It has been suggested that such an artifact may have been used as an "acorn anvil" or in some way related to the preparation of the acorn in the hulling process. Should this prove to be correct, then one might expect it to be an ancient element in native California. For future comparative work it may prove advantageous to make further subdivisions by differentiating between pitted and non-pitted forms. We have made no attempt to do so at the present time. _Core Hammerstones_ Some investigators tend to place core hammerstones in a class with flaked tools, but in the present paper they are classed as an artifact of pecked stone. It is the great quantity of their occurrence which appears significant, rather than how they are classed. Hammerstones may be conceived as having two quite distinct functions: (1) those whose function is primarily to remove a large flake through the percussion method, such as the production of a core itself or a rough blade, and (2) those hammerstones having sharp or semisharp projections used to reduce to some desired shape rocks of a nonconcoidal nature, such as pecking down the surface humps on a mortar or pestle in order to develop symmetry; or the function may not necessarily be one of shaping but merely to periodically rough up a grinding surface on a metate or mano. There naturally remains the possibility that once a specimen of the latter type had lost all of its sharp projections it could then assume the role of the first type and continue as a useful tool (Treganza and Valdivia, 1955, p. 20).