AbstractPatterned ground in the form of large sorted stone-stripes occurs at 450 m altitude in the Rhinog mountains, North Wales. Exposed boulder stripes are separated by vegetated zones, the outer parts of which are composed of boulders with peat or fine earth matrix, the central portions of relatively stoneless fine earth. The width of the pattern is between 5 and 8 m. The stripes are well-preserved relics of Pleistocene periglacial conditions but lack of detailed knowledge of glaciation history of the area prevents precise dating.