The Helium Monument, Amarillo, TX

Looks like a 3He monument, but the fourth nucleon is hidden behind the other three. Too bad they don't have a 3He monument, too.

Official Description

If you don't have high enough resolution, the far text reads:

"Amarillo, Potter County, Texas
Helium Capital of the World"

And it's a time capsule!!! And it's a sundial!!! (photo credits: Laura Moore and Marla Miller)