The Antigorio Nappe is a tectonic nappe of the Western Lepontic (Toce Culimnation) consisting mainly of Variscan granitoids. In its northwestern part, this basement is surrounded by an autochthonous Mesozoic–Paleogene sedimentary cover, which could be connected to the cover of the Verampio Nappe via an early thrust syncline. Late folding is responsible for two multi-kilometer-scale isoclinal structures: the Alpe Bosa-Wandfluhhorn fold and the Ziccher fold.

The Mergoscia Zone is a heterogeneous tectonic unit of the Western Lepontic (Toce Culimnation). It is composed of ortho- and paragneisses, metapelites, calcschists, metabasites and meta-ultrabasites. Both metabasites and meta-ultrabasites contain rare relics of high-pressure metamorphism (retrogressed eclogites and garnet-metaperidotites). This zone, displaying a high degree of deformation, is also interpreted as a mélange rather than as an originally stratified framework.