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).
One problem of classification arises when we combine the process of manufacture and the concept of use. If we assume a rough piece of source material was purposely flaked down to produce a core to be used solely as a hammerstone, the artifact by definition becomes a flaked tool. However, at this point it bears no resemblance to a hammerstone, but looks more like a chopper or just a plain core and frequently may be classed as such. Once this core is used as a percussion instrument and has its sharp margins battered back, it begins to take on the characteristics of a hammerstone or a used core tool. If battering continues, the final result is an angular nodule whose irregular, worn margins mark the former presence of sharp bifacial flake edges. A well-worn core hammerstone is also a worn-out specimen, at least in the light of its original function.
Of the 1,478 specimens from the Tank Site it is our opinion that their resultant form is derived through means of their own function—that of pecking. That such an implement was much in demand is evidenced by the pecked surfaces of numerous grinding tools. We doubt seriously if hammerstones of this type were manufactured as such, but rather we assume any suitable core, rejected scraper plane, or chopper could have served as a starting point, and an over-all examination of our specimens supports such a thesis.
Emergent is the correlation of core hammerstones and the presence of manos and metates. Noteably both these grinding elements are rare in the coastal San Dieguito and in the Lake Mohave area but do occur among the Shoshonean and Yuman groups who occupied the areas corresponding to these ancient lithic cultures.
Cobble Hammerstones
Cobble hammerstones tend to be oval or egg-shaped and exhibit abrasion on one or both ends. None exceeds fist size, and many are slightly smaller. A number evidence additional use as a rubbing stone.
A varient of this form is slightly thinner and contains small bifacial depressions that have been pecked into the more flattened sides and presumably served as finger grips.