The Schwellenburg nature reserve covers 22 hectares and is located in the border area of the city of Erfurt and the district of Sömmerda. It comprises a total of seven gypsum-skeuper hills: Schwellenburg and the smaller hills to the northwest: Kippelhorn, Hühnerbiel, Marolsberg, Steinberg, Ringelberg and Edelberg. The hills are characterised by karstification processes, some of which are still active today. In past centuries, gypsum rock was quarried throughout the area, which can be found as grey or reddish stone in the walls of the surrounding villages. Of the dry grasslands found in the reserve, a large part is formed as steppe grassland. Aerial photographs from 1953 show at that time only about 11% of these dry grasslands were used as arable land and are therefore currently to be classified as secondary dry grasslands. Their occurrence can be easily recognised by the distribution of spring pheasant's eye (Adonis vernalis) and tor-grass (Brachypodium pinnatum), which only grow on somewhat deeper soils.