You may have noticed a few large rocks around here - they have escaped from somewhere nearby. I can see the conversation going something like this -
"Boss, what are we going to do with these rocks?"
"What Rocks?"
"These big ones over there."
"Just push them over to the side of the road. Someone will use them to hide a cache one day."
And they did. You are looking for a 100mil container in a slightly sneaky hide.