Here's some other second hand finds.
My betterhalf's grandmother found this when she was a kid in northern Mexico along the Conquistidor Trails... about 70 years ago. Sadly it has a big chip in it. She also found this pestle a few years later miles away. Gave them to me for my collection.
On a side note, I have one very similar that was a personal find (in NE Alabama) without any chips, also found the pestle a few feet away. Perfect shape! Someone told me that these where strictly of Spanish origin. That being said, mine from NE Alabama... Desoto?
And check out this petrified log I found. How cool is that?