Three isolated remnants of Tertiary strata crop out in the Upper Grey Valley. In Clarke River and at Staircase Creek there is Landon limestone and sandy limestone; between Clarke River and Allan Water an infaulted sequence includes, in upward succession, coal measures, Whaingaroan calcareous siltstone and mudstone, and unconformably overlying breccias and grits, and Waitotaran-Nukumaruan Coal measures.