A considerable part of the range is made of various Mesozoic rocks. The central part and the main ridge are made up of non-resistant rocks (slates) and the relief is softly modeled (Ploská, Ostredok). The southern and south-western part is formed by resistant limestone and dolomite with rocky walls and reefs. The ridges are usually separated by canyon-like valleys. The most important ones are Gader Valley (Gaderská dolina) and Blatnica Valley (Blatnická dolina). The longest valley is the Ľubochňa Valley (Ľubochnianska dolina) at 25 km. Numerous karst formations are located in this area and the Harmanec Cave is one of the best known caves in Slovakia.