 The lower gorge is cut in part through late Silurian age Raglan Mudstone Formation which forms the lowest part of the Old Red Sandstone.At the eastern end of its catchment is Rhos Goch Common National Nature Reserve.Another notable nature reserve within its catchment is Llan Bwch-llyn Lake, a stream draining which, enters the Bachawy as a right-bank tributary below Llanddewi.