The Upper Orobic Nappe is the uppermost and oldest thin-skinned thrust sheets of the eastern South Alpine domain. It consists of an around 5 to 7 km thick basement sheet, arranged in a series of en-échelon anticlines. The thrusts associated with the Upper Orobic Nappe ramped into the sedimentary cover, creating several duplexes that occur in a belt of klippes. The distribution of these erosional remnants reflects the later deformation by the basement ramps of the underlying younger local thrust sheets and imbricates (Lower Orobic Imbricates).

The Val Colla Zone is a Variscan tectonic unit representing, together with part of the Strona-Ceneri Zone, the basement of the Upper Orobic Nappe. It consists mainly of paragneisses, hornblende-epidote schists and metagranites. These Variscan, originally amphibolite-facies metamorphic rocks, were retrogressed to the greenschist facies, possibly during Mesozoic rifting and associated exhumation of the basement rocks.