Here the maar erupted into the Lower Devonian, structureless Ulmen tier with sand-, siltstone and clay slate. Particularities The third-largest maar in the Western Eifel and partly bogged dry maar is located directly at the eastern limits of the village of Mosbruch. To the north is the tertiary, Hochkelberg volcano at 675 m. In the middle of the almost round cone now lie the remainders of a sedge bog. A map from around 1800 (Tranchot map) shows a backed-up pond taking up half the area of the bog. It had possibly been covering the entire cone base since Roman times. In 1838 the lake was drained again and the western portion of the cone used as farmland. In the bog itself peat was cut, especially during World War II. According to botanist Herbert Straka the peat layer is approx. 6 m thick. In 1939 the bog area was made a landscape conservancy, in 1980 a nature conservancy. In line with the EU-Life project “Bogs of the Hunsrück and Eifel” (2011- 2015) this bog is also being renatured into a maar, i.e. removing trees, water-logging, conservation measures, etc. The Üßbach with a length of 49 km has its source in the Mosbruch bog, flows into the Alfbach near Alf, just before that flows into the Mosel.