By editor
Little Belt Mountains, Judith Basin County
The sapphires of Yogo Gulch formed in an igneous lamprophyre dike that sliced through the Paleozoic limestone of the Little Belt Mountains like a hot knife. These stones require no heat treatment; they emerge from the ground a perfect, uniform cornflower blue. The Yogo sapphire is the only North American gem included in the crown jewels of the Smithsonian.
Visitor Access
The Yogo dike is entirely on private land and is strictly closed to public collecting or viewing. The only way to acquire a Yogo is to buy one from a jeweler. However, visitors can drive the public roads through the surrounding Little Belt Mountains to understand the rugged, limestone terrain that hides the state's most valuable mineral deposit.