I find most of my points here on the Columbia River by walking the banks after the water level drops .Opening & closing of the dams cause a fluctuation as much as 5 feet, which doesn't sound like much, but makes a huge difference in the amount of exposed river bank. Anyways, it is my understanding that the Indians heat treated a lot of the materials they used in point making. Petrefied wood was commonly used, and it is extremley hard as far as rocks go, so they would heat treat them. The way it was explained to me at the museum was that they would dig a pit, then they would get a good layer of red hot coals, then they would ad a layer of sand on top of the coals, then they would add a layer of point making material, then another layer of sand, then the rest of the pit was filled in with the dirt originally taken out of it. The Coals would usually burn all day long. The reason for this process was to slowley heat up the material, and then slowley cool it. The sand was the key to the process, it acted as an insulator, and insured that the material wasn't heated to quickly (that would cause cracking of the materials), and it also slowed the heat loss during toe cool down period. This whole process was to "Soften" up the material so it was easier to "Knapp"..........Sorry this post is so long, but it may explain the "Heating" of the lithic materials you are finding. I have only ever found one of these pits while gold dredging on the river, it still had unworked blanks in it.
Paul