A tectonic framework that was established in the northern and eastern parts of the northern Canadian Cordillera in the late Proterozoic persisted generally until mid-Devonian time. Late Palaeozoic deposition was strongly influenced by a late Devonian and (or) early Mississippian orogeny, which produced coarse clastic sediments in the northern and western parts of the region, and by a late Pennsylvanian (?) orogeny evident in northern Yukon. The Cassiar and Coast geanticlines were established at least by late Triassic time and controlled the distribution and character of Mesozoic strata southwest of Tintina and Rocky Mountain Trenches.Metamorphism and granitic intrusion were concentrated along Cassiar and Coast Geanticlines. During the Mesozoic and early Tertiary, plutonic activity appears to have occurred at intervals of about 30 million years and was accompanied generally by deformation and development of regional unconformities. Crustal shortening has been much less in Mackenzie Mountains than in southern Rocky Mountains; a marked change in structural style of the eastern Cordillera occurs near Liard River. Many phases of deformation and intrusion have affected rocks in the southwestern part of the region; their differentiation is as yet incomplete.

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