The geology of the region is certainly as complicated as the terrain. For several decades it has been a domain of research geologists, and a full discussion is inappropriate here. However, some points are of general interest.
The Badshot Group contains a great arc of steeply dipping sedimentary rocks (now metamorphic) containing the Badshot Limestone (early Cambrian). Numbers of the big peaks are composed of this not quite ideal limestone. It is shot through with mineral veins and the ore grade is often high, but the veins are often offset by faults which make locating the remainder of the veins difficult. Also, even though rich, the total amount of ore was not great.
The Goat Group is a complex one. It is made of an anticlinal structure which has been thrust faulted and folded. It contains a steeply dipping thick limestone bed (passing east of Cascade Mt) which is of later age than the Badshot Limestone. The group has pieces of accreted island arc volcanics which have been slowly added to the ancient B. C. coast by motion of subducting oceanic plates. The highest peak (Mt Cooper) is of a middle Jurassic granite which has subsequently been metamorphosed. A good cross section of structure in the Goat Group is on the north face of Mount Stubbs.
The Kokanee Group is simpler. A middle Jurassic granite intrusion comprises most of the group, but the northern part is largely covered by older volcanic rocks. It is here, just east of New Denver and Silverton, where large amounts of lead, zinc and silver were mined from approximately 1900 to recent times. When Earl Whipple first visited this area in 1966, there was still an operating mine which employed an electric locomotive.
It is characteristic of potassium feldspar (orthoclase) in the Kokanee Group that its crystals grew in the granite partial melt and incorporated small needles of hornblende (black). The needles attached themselves to some faces of the orthoclase crystals (along their lengths) during growth. One can often find orthoclase crystals with a square of long black hornblende crystals framing the centre of the crystal face.
The Valhallas, to the west of the Kokanee Group, are what is known as a “gneiss complex” (pronounced “nice”). The word “complex” is appropriate. It is a group of sedimentary rocks which has been heated and changed, and folded by tectonic movements. In places, the heating proceeded to near the melting point and the rock then shows the appearance of granite (except for the partial alignment of crystals, or the segregation of the crystals in bands). The Mulvey Group, in these rocks, is probably the gem of the whole area. The Valhallas are separated from the eastern groups by a fault which runs along Slocan Lake, and are utterly different than the other groups except the Valkyr and Norns Ranges. For the most part, gneiss complexes are barren of mineral resources.
The Northernmost Purcells are composed of late Proterozoic (Pre- Cambrian) rocks. Stratigraphically above these is the Hamill Quartzite, the excellent quartzite exposed at Glacier, the age of which straddles the Proterozoic-Cambrian boundary (about one half billion years). A hidden fault in the Beaver River-Duncan River trench separates an uplifted block on the east (Purcell Range) and a sunken block on the west (Selkirk Range; with the Hamill Quartzite; Sir Donald as seen from the Dogtooth Group). This quartzite has been worn away in the Northernmost Purcells (uplifted), leaving the poorer quality Pre-Cambrian rocks, but reappears on the big peaks of the Southern Purcells. In places, as in the Dogtooth Group, the rocks have been thrust faulted, also exposing a few lower Paleozoic rocks. (It is “all sliced up”.)
There is a mining district in the Spillimacheen, Carbonate and Vermont Groups. Farther south, a granite intrusion in the Hatteras Group provides the best rock climbing in this part of the Purcells.
Despite some destruction, the beauty of the Columbia Mountains is mostly intact, and with a bit of care can remain so. The Columbia Mountains defend themselves better than the Rockies because of the high growth rate of vegetation and resultant difficulties of entry. To the proponents of this area, the difficulties are part of the game.