Obsidian flake from a archaeological site above the Mad River near Pilot Ridge. A flake is a piece of rock or obsidian that ‘flakes’ off from a larger piece during the manufacture of stone tools. Think spearheads, arrowheads, an knifes. You also produce flakes when sharpening your stone tool. While chert flakes are very common in Humboldt County, I do not come across obsidian very often. It had to travel a long way to get up into the Mad River. The aboriginal people of California traded extensively and that could be how this ended up here. I think the nearest obsidian sources from here are in Lake County. You can date a site if you find a few points, as the type of arrow or spearhead technology is diagnostic of time periods of human habitation, some going back as far as 8,000 years. Its becoming increasingly rare to find a point at a site however, mainly due to a century of people picking up arrowheads.