A small mass of nepheline syenite is exposed along the old Big Bend Highway about 2 kilometres southeast of the Sullivan River. The original road has been flooded and is now under the water of Columbia Reach, about 100 kilometres north-northwest of Golden.

The nepheline syenite body is located from Geological Survey of Canada Map 4-1961, and is mid-Paleozoic (?). The rock is mainly medium grained, light grey with a vague gneissic banding. Feldspar and small amounts of amphibole and locally biotite can be recognized. Thin sections show a high proportion of plagioclase, lesser microcline-microperthite, and scattered grains of feldspathoid. Where exposed in roadcuts, the contact of the nepheline syenite with wallrocks is concordant and gradational. Wallrocks are mainly mica schists which locally have calcareous interbeds. The northwestern part of the nepheline syenite and its western contact are beneath the river flats (Minister of Mines Annual Report 1959, page 103).