Sounds like you're referring to a place called a few different names in the book: Atlantis, Mulligan's Valley, Galt's Gulch.
" A secluded refuge in a valley of Colorado where the men of ability have retreated after relinquishing participation in American society. Nicknamed "Galt's Gulch" by its inhabitants, it is in fact the property of "Midas" Mulligan, one of the early strikers to follow John Galt's call. This call was to the great men of mind and action to abandon the increasingly slave-state inclinations of a decaying United States - to go on strike - thereby withdrawing the only thing supporting the parasites and looters.
Sarcastically nicknamed Midas in the press because everything he seemed to touch turned to gold, Mulligan adopted the nickname during his explosive investment career before dropping out of sight. He had purchased this land among his far-ranging speculative endeavors, and subsequently retreated to it upon his disappearance. Other strikers soon followed him there, including John Galt, renting or buying land for summer retreats as a respite from continuing their search for fellow strikers among the increasingly collapsing American society. Eventually, a society develops in Galt's Gulch as more people live there year-round as the outside world becomes virtually unsafe to visit.
We are introduced to Galt's Gulch in the final section of the Novel, in the first chapter, entitled Atlantis. The people live with each other in completely free society and embody everything which is the thesis of the Novel, the appropriate values for a society of Mankind: philosophical, moral, economic, legal, aesthetic, and sexual, among others too numerous to mention."
http://www.answers.com/topic/things-in-atlas-shrugged
