When most Americans picture the Strategic Petroleum Reserve, they imagine rows of giant steel tanks behind barbed wire. The reality is far stranger—and arguably far more impressive. America’s emergency oil supply is stored inside enormous caverns carved into ancient underground salt domes along the Gulf Coast. It’s a brilliant feat of engineering, but there’s a catch: salt slowly moves. If those caverns stay too empty for too long, the surrounding rock gradually squeezes inward, creating long-term engineering challenges. It’s a fascinating story of geology, infrastructure, and national security—and a reminder that even America’s emergency backup plan isn’t immune to the laws of physics.