Abstract Mountains in the Yukon and Northwest Territories within the belt lying east of the Rocky Mountain trench are principally the product of the Laramide orogeny, but earlier orogenic periods have contributed materially to the structure in a number of areas. Evidence indicating late Precambrian, Caledonian, Hercynian, and Nevadan orogenies has been observed. The region under study can be divided into two parts on the basis of structural history and structural type. The southeastern segment comprises the Selwyn, Mackenzie, and Franklin Mountains, and adjacent plateaus. Numerous reverse faults characterize the western part of this area. Intrusive bodies are common near the Rocky Mountain trench. Farther east, simple folds are the predominant structural type. The eastern margin of the belt is in most parts of the area marked by a high-angle reverse fault. Pre-Cretaceous movements have contributed relatively little to the overall structure. The northwestern part of the region is characterized by a complex structural history and a variety of structural types. It comprises the Richardson, Barn, British, Keele, and Ogilvie Mountains, and adjacent highlands and basins. Structural belts widely divergent in trend and consisting of structures ranging from simple folds to complex imbricate faults characterize this area. The principal geologic features distinguishing mountainous regions in the Northwest Territories and Yukon from those making up the Canadian Rockies to the south are the higher degree of structural activity through time, the greater breadth of the mountainous belt, the greater breadth of the region in which thick late Precambrian sedimentary rocks occur, and the presence of intrusive rocks in considerable quantity in the interior ranges.