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. _Slate Pendants_ To date, worked slate was represented only by three nonperforated, lozenge-shaped specimens, one of which displays a faint, crude rectilinear design. The second season's activity produced no comparable examples, though it added six pieces to the collection. These can be broken down into three descriptive categories: 1. Four examples, none over 2 mm. in thickness, too fragmentary to warrent reconstruction. Judging by the striations on their surfaces and edges, they were shaped by grinding. On each, one end tapers to a blunt point. 2. A lozenge-shaped specimen containing three broken-out peripheral biconical drilled holes. Average length, 6 cm.; average width, 4.5 cm.; 3 mm. thick.