peer reviewed ; The Hoyoux hydrographic basin comprises two regions characterized by karstic phenomena and a rich hydrologic potential. On the one hand, the Condroz, where the Dinantian limestones are in synclinal position in the bottom of depressions, separated from one another by anticlinal crests which are occupied by the Upper Famennian sandstones. On the other hand, the narrow strip of Devonian limestones (of Givetian and Frasnian ages), positioned immediately at the NW of the previous region, separates the Condroz, which is constituted by an alternation of deposits of Famennian and Dinantian (sandstones and limestones) and, the Ardennes Condroz, which consists of lower devonian and eifelian deposits (conglomerates, quartzites, sandstones and schists). Since 2015, the Walloon Public Service's site "WalOnMap", using the ultra-precise digital terrain model "MNT 2013-2014 Hillshade" obtained after a LIDAR scan of the soil surface, offers a remarkable mapping tool essential to geological mapping, in general, and to the cartography and prospection of Karstic phenomena in particular. ; Atlas du Karst wallon