Analysis of two separate assemblages of lithic debris from Archaic sites in the Pecos River Drainage (New Mexico) has led to the discovery of what appears to be a noncultural bias affecting flake size, which is believed to be caused by the inherent properties of the flaking material. Graphs of the flake length/thickness ratio versus frequency of ratio occurrence coincide remarkably in their curve characteristics, indicating a nonrandom causal factor. This factor is attributed to the wave pattern created by the blow of the flaking implement and is governed by the physical properties of the medium through which it is passing.