According to Beautypically, the Rocky Mountains result mainly of Paleozoic sediments, including more or less extensive masses of precambric stratified zones, and, to a lesser extent, also Mesozoic basins: wherever it has been possible to control it, the contact between this formation and the Cretaceous of the foothills that follow towards E. appears well defined by faults and fracture lines. It is even more evident towards the West, where a long furrow of the same origin (intermontane trench) can be followed without interruption from the top Liard (and perhaps by the Yukon) to the Kutenai (upper courses of Columbia, Fraser, Parsnip and Finlay). In addition to being wider, the S system is more complex, divided as it is into parallel beams (Purcell Range, Selkirk Mountains, Gold Range), which continue with peaks sometimes exceeding 3000 m., At least up to the upper course of the River of Peace; on the outermost alignment, which to the South. of this marks the watershed towards the Pacific, the highest crests of the Canadian Rocks rise (M. Columbia m. 4300, M. Alberta m. 4115, M. Forbes m. 4084). Proceeding towards N., the powerful bulwark loses in elevation what it gains in width: in general, however, it presents itself with less harsh and accentuated forms than our Alps, whose characters it recalls only in the rugged area of British Columbia. The sides of the mountains, covered with magnificent forests, become bald and rocky on the eastern edge facing the foothills (hence the name, because the penetration of the Whites proceeded from here); on the opposite side the ancient and recent glaciation assumes considerable importance, averaging around 2300 m. the limit of the eternal snows.
No less majestic is the mountain landscape in the two series of reliefs that fringe the coast, divided one from the other by a partially submerged valley furrow (Hecate Strait, Strait of Georgia); partially submerged is the same western chain of which the Alexander Archipelago, the Queen Charlotte Islands and the Vancouver Island are only fragments (and which could therefore be called island chain). The second, innermost bastion is sometimes also called the Cascade Mountains, but geologically and orographically it has nothing to do with the rise of the same name that crosses Oregon and Washington, resulting from a powerful dioptic mass, intruding, in the Jurassic age. -cretaceous, within piles of layers of the Trias, or even more ancient, such as those that form the backbone of Vancouver Island. On the other hand, considerable extensions of postcretaceous land are enclosed in the actual coastal chain, which continues, rising, along the Alaskan coast. Where it touches the border, there are also the highest heights of the Canadian section (M. Logan, m. 5955), characterized, throughout its course, by an intricate complex of fjords and islands, which together certify its recent lowering and intensity of the Quaternary glaciation. To this currently corresponds a considerable development of glaciers. The limit of permanent snow falls on the coast up to 500 m .; yes, even taking into account the climatic conditions, the analogy with the west coast of Norway could not be more evident.
The regressive erosion of the watercourses descending to the Pacific – very intense, given the heavy rainfall of the entire coastal district – has carved the crest line of the innermost mountain range (Catena Costiera) in several points: along the Stikine courses, of the Skeena and the Fraser it is thus possible to penetrate within the vast region that the Cordillera itself and the Rocky Mountains close together, from British Columbia to the middle Yukon. This is a plateau consisting essentially of paleozoic and mesozoic, corrugated and fractured assizes, with more or less large areas of marine depositions and volcanic formations of the recent Tertiary, the latter prevalent in S., where they represent the most characteristic element of the Columbia territory British. Its average width fluctuates around 1500 km., its height around 1000 m., but only for limited extensions or if considered as a whole, we can speak of level uniformity. In fact, the surface of the plateau, which gradually degrades towards the N., is rather moved, mostly due to the effect of the incisions that the rivers have opened, while the powerful cap of the Quaternary glaciers left its footprints, streaking it with cavities now filled with lakes. About 55 ° 30 ‘N., a series of fairly well accentuated reliefs, which exceed 2500 m. high (and which could rejoin, in the absence of more certain determinations, the group of M. Cassiar), closes the area of British Columbia towards N .; further on, the plateau assumes an even greater regularity, in the upper and middle Yukon basin, and continue beyond the Alaskan border. To its geological and morphological individuality, the internal plateau joins that which the particular conditions of the climate (rainfall) give it: especially towards the S., in British Columbia, the region takes on the appearance of a steppe zone (artificial irrigation). A small strip of Canadian territory, where Vancouver rises, falls, morphologically, into the unit that takes its name from Puget Sound: terminal element, to the North., of the great depression that returns to submerge much further to the South., in the Gulf of California.