Landslides prevail in the western mountainous part which consists mainly of the oil-field Tertiary sediments (mudstone), whereas naked peaks and bare slopes which have succeeded to a wide-spread debris-fall owing to snow avalanches, occur in the eastern loftier ridge which a harder volcanic complex, so-called green tuff, has constructed. Stabilizing condition in the meaning of land conservation is kept in the central basin, where younger deposits intercalated by lignite form a lower, hilly land.