The Moosalb rises in the middle of the Palatinate Forest, northwest of Johanniskreuz and flows into the Schwarzbach near Waldfischbach-Burgalben. In the Karlstal valley, the valley of the Moosalbe narrows to only a few meters. The Karlstal became famous especially because of its park-like design at the end of the 18th century by the landscape gardener Friedrich Ludwig von Sckell. The name "Carlsthal" is first documented to have been used in 1817. It is unclear whether the valley is named after Carl Theodor I or after his father Frantz Carl Joseph von Hacke. Originally, it was assumed that Karlstal got its name from the ironworks owner Carl von Gienanth (1818-1890). On a landscape map from 1767, the industrialized Moosalbtal still bears the name "Wüste-Thal".