One of the advantages to the low water level at Lake Oroville is the exposure of some Californian Indian artifacts that are usually 50 feet below water. The divots that you see on the right hand side were created by the Maidu Indians who inhabited this part of California for the past 2000 years. These mortars served the purpose of grinding acorns and other nuts; after drying and grinding the Maidu would use water to leach out bitter tanic acid from the ground food.
Just over the far edge of the stone with the mortars was evidence of a creek where spring rains would naturally flow down the hills (before the creation of the reservoir). One can envision the Maidu brining water up from that creek to leach the contents of these mortars. With the reservoir being so low, the creek had naturally returned for the immediate future.
Many thanks to the local resident who I meet when I stopped at Lake Oroville. He was kind enough to mention to me these grinding mortars and where to roughly find them. He indicated that many of his local neighbors were concerned about the safety of these artifacts. Luckily the rock the mortars were created in is about the size of a small single story house, so it’s unlikely any thieves will run off with it in the middle of the night. If you run across any artifacts like this in your travels, please make sure to respect and preserve them for future generations.