The catchment's bedrock geology is characterised by alternating bands of limestone, sandstone and a combination of limestone, sandstone, siltstone and mudstone. This area is well known for its ridges of crags and columns that form the Great Whin Sill. It is the geology that results in the long linear river network (running east to west), for example the Caw Burn, before it bends south towards the town of Haltwhistle. Recent and unconsolidated deposits (superficial geology) are typically peat and glacial till.