The bedrock in Pelister National Park is primarily Paleozoic and Mesozoic in age, with few glacial and fluvioglacial overlays dating from Quaternary. Among the Paleozoic rocks, the series of green shale are the oldest and most ubiquitous stratigraphic unit. Typical for the Park is the “Pelister Granite”, Paleozoic alkaline-granite dating from the Ordovician, some 456 millions years ago, and usually embedded within the Paleozoic shale. Other Paleozoic rocks found in the Park include quartz- and quartz-sericite schists. The gabbro is the most ubiquitous among the Mesozoic rocks, found in several places, including a large mass with a surface area of 5 km², situated south-east of the village of Malovishta. Other Mesozoic complexes are also found, such as diabase and mermekitic granite and dolerite veins. Due to the nature and compactness of the bedrock as well as the vegetative cover and lack of human activities the erosion in the Park is negligible.