The mountain's castellated, or castle-like, appearance is a result of erosive processes acting at different rates on the peak's alternating layers of softer shale and harder limestone, dolomite and quartzite.

[4][5] Castle Mountain's upper sections, including its cliff faces, consist of late Pre-Cambrian and Cambrian age sedimentary rocks such as limestone and shale along with some metamorphic quartzite.

The agreement ended an outstanding claim dating back to the 1880s when land located at Castle Mountain was set aside as a timber berth for the use and benefit of the First Nation.

After this we reached the first of the cliff ranges that are so conspicuous from the valley below; it was composed of quartzite, passing into a conglomerate of pebbles of milk quartz and other rocks.

The mass of the mountain, which yet rose more than 2,000 feet above us, seemed to be composed of thick-bedded limestones, and these breaking away as the soft shales below them have been destroyed has given rise to the castellated appearance.

News of Healy's ore soon spread; others began to arrive and the settlement of Silver City, situated near Castle Mountain, quickly developed.

At a meeting of the Ottawa Canadian Club in January 1946 at which World War II general Dwight D. Eisenhower was a guest speaker, Prime Minister Mackenzie King renamed Castle Mountain in his honour.

[11] A change of name was already planned by 1976, but its implementation was delayed to avoid causing offense on account of the United States Bicentennial commemorations taking place that year.

[9][19] While the peak presents a formidable challenge to climb when viewed from the highway, the mountain can be ascended by first hiking to Rockbound Lake which is located on the easier backside.

[20] The Castle Mountain Hut on the southern side could be used but requires technical rock climbing skills and possibly a rope to access it.

If pressed for time or a different objective, Helena Ridge is basically a scree slog straight up although a lingering snowfield in the gully above the big hill may provide some relief.