Only in America...would you find a boulder dealer

From time to time I see things that just make me think "Only in America...."

So, I'm on my way to work yesterday, traveling on I-80 West, and my eyes turn to a billboard; one of those electronic ones that changes ads in different intervals. The ad had just changed and on the billboard now appeared the following words:

BOULDERS FOR SALE.

Yes, they were selling boulders or big rocks.

Why would you sell rocks? THEY'RE EVERYWHERE! All you need to do is go into the wilderness and find them. You need to hire a truck to collect them or maybe a crane to pick it up but still, why would you go to a rock dealer to buy a boulder?

Are there used boulder dealers? Do people wander around a yard with different boulders lined up and they are inspecting the quality of each boulder?

"Yessiree, this boulder only has 2000 years on it and was crafted through the finest sediment and shale in the Northeast Territory!"

I understand the concept of a stone mason or even a smith of rocks, but still selling boulders freelance seems like something very out there.

"Well Johnny, what do your parents do for a living?"

"My Mommy is a teacher and my Daddy sells boulders."

Right.