I have found one just like the last one posted near a spring with several Indian bowls with the grinding stones still in them in Mariposa county, almost perfectly round with the two flat sides. I'm sure it's a tool but I don't know enough about it to be certain. I'll post a pic or two when I get a chance
A Rock! Come on up to Montana with a dump truck or two, or three....., and I am absolutely sure that we could fill them up with the same type of rock. We got lots of them.
I am referencing to your (this) rock that you originally posted. Please understand that I commenting on your first set of pictures and not on later added photo's. It might help if don't add other possible artifacts to the question.