About 623 nm — roughly 1h 50m in a midsize jet. 1 leg live on this route right now.
Every price on EmpTleg buys the entire aircraft, not a seat.
San Diego to Aspen & Vail is a different flight with its own aircraft, its own days and its own price: empty legs from San Diego to Aspen & Vail.
Nobody schedules an empty leg. One shows up here because an operator has an aircraft finishing a trip near Aspen & Vail and needs it near San Diego — or needs it home, and this direction happens to be the way home. That is why the flight can be a fraction of a full charter, why it can vanish within hours, and why the return direction is a different flight entirely with its own price and its own aircraft. Watching the route beats searching it once.