Erie's bedrock is Devonian shale and siltstone, overlain by glacial tills and stratified drift. These are unconformably overlain by the Ridgeway Conglomerate Formation. These are conformably overlain by peperite and the basaltic and andesitic Lorne plateau lavas. The lava flows are overlain by thin alluvial deposits. The lava flows are overlain by thin alluvial deposits along the Kham and Sukhana river. This is overlain by marine clay or stony sandy loam glacial till. After initial deposition of the fan, the deposits are commonly overlain by clay/marl sediments. The bioregion is made up of sandstone and shale overlain by basalt. Each of the structures consists of Carboniferous limestone overlain with Millstone Grit. It is commonly overlain by shale, which thickens northwards. These are overlain by Eocene back arc tholeiitic Pugo Metavolcanics. The turquoise is found in sandstone that is, or was originally, overlain by basalt. They are mostly overlain by laterite clays. Its activity appears to be heavily concentrated on low, broad ridges overlain with sandy soils. It is overlain by the Bearpaw Formation.