The early Devonian Greywacke Conglomerate Formation of the Lanark Basin, south-western Midland Valley of Scotland, has been exposed by a new road cut in the Glenbuck area, East Ayrshire, enabling, a high-resolution sedimentological analysis of this unusually high-quality section. This study provides a facies analysis of the sedimentary rocks exposed in the Glenbuck area, and comparison with contemporaneous bedrock sections from across the Lanark Basin and adjacent Southern Upland High. Eleven lithofacies are identified, grouped into five associations: aggradational talus cone, progradational talus cone, debris flow lobe, fan surface aqueous-alluvial deposits, and gravel barform deposits. These comprise medial and proximal alluvial fan deposits, controlled by autogenic scour and avulsion along with general fan progradation. Contemporaneous sediments are present around Silurian inliers in the Lanark Basin and adjacent regions of the Southern Upland High. Whilst deposits in the Lanark Basin are genetically similar, contemporaneous deposits of the Southern Upland High preserve a distinctly more angular clast assemblage indicating textural immaturity relative to those in the Lanark Basin.