The area between the Mureș river corridor to the north, the Sebeș Mountains (Șureanu / Orăștie) to the east, Poiana Ruscă to the west and the Hațeg verge to the south is part of the Strei basin. This northern part of the Hațeg-Strei basin it was once a bay of the Transylvanian Basin.
Sarmatian deposits in the region can reach 500 meters and in Măgura hill, include: conglomerates, sandstones, oolitic, clastic and organogenic limestones, arenaceous marls and sandy sandstones. The geological layers were the main source of stone for the Dacian fortresses in the Șureanu Mountains are located in the upper part of the hill. There are represented by quasi-horizontal levels of oolitic, fossiliferous and clastic limestones, with many subdivisions/varieties. Their genesis is based on a turbulent environment in this edge of the Hațeg sedimentation basin.