In the 21st Century, civilization crumbles as the Shiva Virus touches off a series of small nuclear wars in South Asia that soon spreads and eventually consumes the world in a great nuclear holocaust killing 'billions'.
In the South-West United States a few areas remain unscathed, one of them being the Hoover Dam Garrison built inside The Grand Canyon province - the area having become completely self-sufficient by 2051 due to GlobalTech dealings. Survivors gradually begin to migrate to this area and attempt to survive, doing whatever they can to exist.
The Shiva Virus is released upon the world in 2054 - hitting those in The Grand Canyon by 2056, and by 2057 around 90% of the population in that area is wiped out...the Hoover Dam Garrison loses all contact with the outside world, and it is assumed that this is the last safe refuge of humankind. A final few survivors straggle into the area from Las Vegas in 2058.
As diverse as ever, the general populace around The Grand Canyon area slowly rebuilds, separating into six socially defined factions - CHOTA, Travelers, Techs, Enforcers, Lightbearers and Vistas - all with very different views on how humanity should construct their society in this new, fractured world.
The current year is now 2156.