Here's an odd one from the Cisco, California area my dad found on a insulator hunt back in the late 80's early 90's. For a long while, we had no idea what it was. We weren't even sure if it was even insulator related. We asked a lot of people and stumped almost all of them. Then an insulator guru showed us a picture of a complete ramshorn in it's glass sheith. We had found out what it was and were very suprised of it's origin! To think...we weren't even looking for anything ramshorn!!!

EDIT: It wasn't the Auburn area like I thought...