The Proterozoic rocks form a major component of the supracrustal wedge in northern Yukon Territory and western District of Mackenzie. They are composed mostly of sedimentary, clastic rocks of lower greenschist facies and rest with profound unconformity upon crystalline igneous and metamorphic rocks of the Hudsonian basement. The composite thickness of the Proterozoic succession is estimated to be between 30 and 35 km, of which about 25 km are exposed. The Proterozoic succession ranges in age from 1735 to 600 Ma, about twice the time span of the Phanerozoic Eonothem. Four regional unconformities allow its subdivision into three basic tectonostratigraphic sequences, from oldest to youngest: Werneckian (1.7ð1.2 Ga), Inuvikian (1.2ð0.8 Ga), and Rapitanian (0.8ð0.57 Ga). The sequences are homotaxial with the lower Helikian, upper Helikian and Hadrynian respectively. They are separated by major orogenic or epeirogenic events affecting the northern Cordillera and adjacent Interior Platform. The early record of collisional and extensional tectonics of this northwest corner of the ancestral North American plate is contained in these Proterozoic rocks.