Last week, I shared a post about a little quirk we’ve encountered with the collection of negatives in the Bell Museum of Natural History records. A set of negatives, contained within the last six drawers of the 56 drawers that the negatives are stored in, are numbered differently than the negatives contained within the earlier drawers. They are not sequential (like in the first 50), and have no discernible organization. Also, a large portion of the negatives are labeled with a number that is preceded with an “M.” What the “M” stands for remains a mystery.

For this week’s Mystery “M” Number, we travel to Lake Minnetonka, where at some point in time, and for some particular reason, a pile of rocks was photographed:

?