These five specimens were localized in the southeast sector of the deposit, and none occurred deeper than the 12-to-18-inch level. Numerous Phase II projectile points came from this same general area of the site and therefore there is some inclination to assign these specimens to a late position in the Phase I with the probability that they are Phase II. _Abrading Stones_ Two broad classes of abrading stones have been differentiated on the basis of form and inferred function (Treganza and Malamud 1950, p. 147): I. Those that could be held in the hand and rubbed against some article being finished. These have smoothed, even-abrading surfaces that are gently concave to convex. They are clearly distinguishable from manos by their reduced average proportions, and the near consistent lack of pecking as a sharpening measure. That this latter characteristic does not hold without exception seems to be due simply to the fact that some of the abrading stones appear to be reused manos. One of the examples in the above category, originally a broken bifaced mano, has small, half-inch deep depressions at either end. These evidently served as finger-holds, for they effect a good grip on the tool. II. Those that, though quite varied in size, bear one or more grooves on their faces. The furrows vary in breadth and depth and appear to be a function, essentially, of the amount and kind of wear to which the artifact was subjected. Many of these specimens, especially those with narrow, V-shaped longitudinal grooves, would be classed as awl sharpeners had they occurred in sites of later origin. However, bone awls or pointed, worked bone in any form is absent in the Tank Site. It would suggest, then, that this class of abrading stones were involved in conjunction with wood working, the tangible evidence having been lost to us. _Cog Stones_ Cog stones, because of their unique forms and restricted distribution, may be useful as diagnostic elements for future comparative studies. As yet we know little about their function or cultural associations in the rest of southern California. Their temporal position appears to be a middle one, as none occur in positive association with late or historic sites, and conversely, none have been reported for Lake Mohave, coastal San Dieguito, or Oak Grove. The Tank Site specimens represent the earliest known occurrence, and even here their exact position as to Phase I or Phase II is not fully known. Most of our specimens occur in the top levels (0-18 inches), though a single example was found as deep as 32 inches (pl. 23, _b_).