A valley in Wyoming.
The Purifiers had a secret HQ there (exact location: 44º50'34"N, 105º50'W), but when they kidnapped Magma, they were tracked there by the New Mutants and later by the Hellfire Club. Both teams raided the Complex, laying it to waste, not to mention that it was no longer secret. The Purifiers relocated in the High Evolutionary's submarine.
Points of Interest
Purifiers' Complex (44º50'34"N, 105º50'W)