A dike-like body of nepheline syenite, identified from Geological Survey of Canada Map 4-1961, is situated 11 kilometres southeast of the Sullivan River and crosses the valley of Caribou Creek, about 87 kilometres north-northwest of Golden.

The Solitude Mountain nepheline syenite forms an irregular dike-like body a little more than 1.6 kilometres long and less than 304 metres wide, with its long axis trending about 290 degrees. The mid-Paleozoic (?) body cuts irregularly across part of the "Kinbasket limestone". The texture of the nepheline syenite varies from the west to east. In the west, it is coarse grained with closely packed, moderately well-formed crystals of potash feldspar and minor interstitial biotite. Towards the east it becomes fine to medium grained and near the east end is quite variable in texture and composition. Many dike-like tongues extend into the limestone and limy argillite around the eastern end of the mass, and inclusions of limestone within the syenite are common. Most of the syenite is composed of microcline-microperthite, nepheline, biotite and locally carbonate. Amphibole, epidote and garnet are present in coarse-grained lenses near the eastern end of the mass.

Contacts of the syenite with the enclosing limestone are generally well defined but in detail are highly irregular and are gradational over a couple of metres. On the southwest side of Caribou Creek, limestone forming inclusions in or lying along the margins of the syenite is altered to a fine grained greenish rock composed mainly of calcite with interstitial feldspar, clinozoisite and chlorite.