The fact that these are to be found mainly in areas which have been exposed for a large part of the Tertiary and over soils considered "relictos", supposes a great antiquity for such groves. The harsh climatological conditions, with the surface of the ground undergoing processes of alternate freezing and thawing (cryoturbation), makes difficult the development of elevated brush. In their regressive stages, they tend toward hummocky thickets of "cambrones" ("Genista pumila") or tomillares "y prados de diente dominados por" dwarf shrubs and dog's tooth grass. At lower altitudes, these groves can also alternate with "espliego y aliaga."