Gravels from Guadalupe River north of Victoria by flintknapper and archeologist Glenn T. Goode. Notice the brown piece in the center. That was once an artifact that subsequently became part of the gravel load of the river. Its original flake scares can still be seen, but they are abraded by stream transport. One likely explanation for the occurrence of this piece is that it represents a discarded failed tool, a "thick biface," that some prehistoric flintknapper discarded while sitting on a gravel bar upstream trying to make stone tools. Speculative, of course, but reworked stone tools can be found in the gravel bars of most of the rivers in the region, if you know what you what to look for.