The south west tail of the Fintona Hills flanks the line of the Tempo River valley on its north western side. The hills are the landscape reflection of the underlying Topped Mountain Sandstone Formation and the high summits are separated by east/west cols hosting 3 small rock and diamict floored lakes, Skale, Topped Mountain, and Derrin Loughs. A further feature of the area is a series of isolated ridges and mounds of diamict, a rock type consisting of everything from clay to boulders. These features tend to hug the contours and at Curraghnakeely there is an exposure revealing a sandy diamict with a wide range of particle sizes including boulders up to 60 cm in diameter. The particle shapes range from blunt-edged to roughly rounded. One shattered limestone boulder is surrounded by a shell of Old Red Sandstone (Devonian) and quartzite pebbles.
These deposits are thought to be the remnants of mass flow diamict deformed by ice margins. The crude layering of large particles combined with thin beds of well-sorted sands would tend to support this view. Professor Charlesworth suggested that the ice sheet retreated westwards over these uplands as the Tempo and Clogher valleys cleared. The diamict mounds and ridges provide good supporting evidence.
