Geology
The range has no single structural or lithological origin but is the result of the alignment of horst, forearc highs and accretionary wedges along Chile's coast. The range was separated from the Andes during the Tertiary rise of the Andes due to the subsidence of the Intermediate Depression.
The range is made of different lithological units. From Valparaíso Region to Lanalhue Fault the bedrock is largely made up of Carboniferous-Permian granitoids. These igneous rocks were once part of a proto-Andean magmatic belt. South of Lanalhue Fault most of the range is an accretionary wedge formed along the subduction zone at South Americas western margin by at least the Paleozoic. From Lanalhue to Pirulil Range the range is dominated by medium grade metamorphic rocks including schists. The analogous granites of the northern part of the coast range are placed inside the Andes in this latitudes.
While during the Miocene regions of the Chilean Coast Range hosted several volcanoes it does not show any sign of volcanic activity at present.
Read more about this topic: Chilean Coast Range