In the area of Grabovača and wider, the oldest sediments are from Upper Cretaceous. Cretaceous period lasts from 144 – 66 milion years ago and is represented with layers of limestone, limestone breccias. They occupy the area around the Old Town Perušić (Turkish tower) and a part, located north from the archaeological site.
Younger Paleogen sediments (breccias, conglomerates and limestones) occupy a smaller part (area northwest from "Turkish tower"). These rocks are gray, grayish-brown or reddish color. The origin of these deposits is associated with strong erosion of the elevated areas, short transport of materials and its rapid sedimentation.
The youngest Quaternary sediments are exposed in the lower parts of the Perušić field. These are mostly brown acid oligotrophic soils that are occasionally covered with a thin layer of humus. Red soil appears only occasionally southeast from Perušić. It is believed that this is secondary effects and that these deposits are formed from primary deposits from Velebit with interference of water in the upper Pleistocene.