Precambrian-Paleozoic(?) Monashee Complex (Group) rocks are exposed in the Thor-Odin gneiss dome, a part of a large domal complex in the central, eastern part of the Shuswap Metamorphic Complex. The dome is characterized by a structural-stratigraphic succession divided into four lithologically distinct zones. These are: the Core Zone, comprising migmatitic and granitic gneisses in the central part of the gneiss dome; the Mantling Zone, well-differentiated metasedimentary rocks ranging from quartzite and marble through calcsilicate gneiss to pelitic schist; the Fringe Zone, in part overlapping, and in part surrounding the Mantling Zone and characterized by large amounts of granitic and pegmatitic rocks; and the Supracrustal Zone that lies outside the gneiss complex, and forms a cover to the gneisses.

In the Mount Odin-Mount Symonds-Mount Fosthall area, paragneisses and schists of the Mantling Zone are present which contain abundant coarse garnet and prismatic sillimanite. Typical exposures occur along the southern branch of Ledge Creek. These gneisses and schists may contain up to 15 per cent sillimanite which is present in the form of prismatic crystals up to 10 centimetres long, and abundant garnet porphyroblasts, up to 2.5 centimetres in size.