Ziegfield's Wall

Where the rivers burn and the air turns poisonous, where the Smoking Tops exhale gases that kill anything foolish enough to breathe them, Ziegfield's Wall has found the perfect hiding place. The terrain that murders outsiders shelters the faithful.
  This is not a stationary fortification. Ziegfield's Wall is a mobile unit of Diesel Jocks devoted to the Cult of the Fallow Hopes, and their strength is measured in treaded Iron Horse rides that swarm through the mountain passes like predators through familiar hunting ground. The deadly landscape of burning rivers and lethal gases serves as natural cover; no pursuing force can follow them without suffering losses that make the pursuit pointless.
  Chaplain Erica Steelframe leads this growing war tribe alongside her wife Joanna. Together they organize with faith, ruthlessness, and a motivation that borders between insanity and brilliance. The tribe's numbers increase daily. Outsider Diesel Jock tribes willing to bend to the faith are absorbed. Those that refuse are raided into submission or scattered. The equation is simple: join or be broken.
  All of this serves a larger purpose. Once enough troops and vehicles are gathered, the entirety of Ziegfield's Wall will ride south to join the Retribution Outpost for a siege of Vegasia. The Final Knights do not yet know this force exists, hidden in mountains that deter all casual exploration. When the Wall finally moves, it will arrive with an army that was assembled in secret, hardened by terrain that would kill lesser forces, and led by two people who consider mercy a liability.