 While most of the White Mountains consist of highly metamorphicized schists and gneisses formed during the Acadian Orogeny, the Pemigewasset Wilderness is part of the White Mountain Batholith and is therefore composed primarily of the igneous White Mountain plutonic-volcanic rock series.The Franconia and Twin Ranges form a massive ring dike in the western half of the White Mountain Batholith made up of a granite porphyry backbone that emerged roughly 170 million years ago.This rock appears pink, red, green or grey, with medium-sized phenocrysts.