Suhl sits on the southern edge of the "Suhler Scholle," an upthrust granite complex that is streaked by numerous dikes. This is part of the Ruhla-Schleusingen Horst that defines the southwest side of the Thuringian Forest. The southwest side of the "Suhler Scholle" abuts horizontal sedimentary layers, Buntsandstein (sandstone from the Triassic period) over Zechstein (evaporite deposits from the Permian period). The granite of the "Suhler Scholle" is capped with Permian sediments and igneous deposits. The higher hills to the northeast are part of the "Beerberg Scholle", an irregularly cracked mass of quartz porphyry from the later Permian period.