From the back of the book:
"Like the rest of the world, the Cheyenne Mountain facility was devastated by the Big Death over 15 years ago. Originally designed to withstand a nuclear attack, Thunder Mountain became home to NORAD and was later expanded to help in Homeland Defence during the war on terror. Thanks largely to one young boy, Thunder Mountain became a haven in a sea of chaos after the Big Death. Markus Alexander rallied the few children in and around Thunder Mountain and organised them, as the rest of the world collapsed outside. Taking in stragglers over the years, Thunder Mountain only recently began to reveal itself to the world.
This sourcebook for Jeremiah: The Roleplaying Game covers the events that led to the founding of the current Thunder Mountain society, its re-emergence into the world, the creation of the Western Alliance and the key characters that made all this happen."