Northern CA.If one goes to the OR,CA border there is a lot more obsidian and arrow head type artifacts.
If you happen to be in the Tulelake area of Nor. Cal, head out to Medicine Lake and check out Glass Mountain and the HUGE obsidian lava flow. It's a little hard to find but once you do, prepare to be amazed, At one point, the road follows the flow and it's easy to access.
