This ecoregion covers a vast area of northwestern British Columbia and an extreme southern portion of the Yukon. The ecoregion is composed of a complex of rugged mountains, high plateaus, and lowlands. Temperature and precipitation vary with elevation. The climate tends to be more moderate in the western half of the ecoregion and is more continental as one moves eastward. The typical mean annual temperature for the area is approximately -2°C with a summer mean of 10°C and a winter mean of -15°C. The mean annual precipitation ranges 400-700 mm. The vegetation is a complex of ecosystems, ranging from Dryas spp./lichen alpine vegetation and bare bedrock on higher mountain elevations; to alpine fir with some white spruce and deciduous shrubs dominating subalpine forests to middle elevations in the southern Cassiar and northern Omineca mountains; and to closed canopied forests of lodgepole pine, and white and black spruce dominating the boreal forests of the Stikine and Yukon plateaus. A unique feature of this ecoregion is the presence of a number of late Tertiary and Pleistocene volcanoes. The most prominent volcanoes are the great shield volcano of Level Mountains, a low domed mass reaching 2134 m asl, and Mount Edziza, a complex cone reaching 2787 m asl. The Cassiar and Omineca mountains form a belt of massive Palaeozoic and Proterozoic crystalline rocks whose highest peaks carry a number of alpine glaciers. Humo-Ferric Podzolic soils on upland sites in subalpine regions, and Gray Luvisolic with Dystric Brunisolic soils in the boreal forest regions are most common. Permafrost with low ice content occurs sporadically in the northern portion of the ecoregion and is confined to isolated patches in the southwest. Representative wildlife includes mountain goat, Stone's sheep, grizzly bear, moose, ptarmigan, ground squirrel, and caribou. Land use varies from hunting, trapping, and recreation in alpine and subalpine regions to limited forestry and forage crop-based agriculture in the boreal region. The main communities in the region are Atlin, Dease Lake, and Carcross. The population of the ecoregion is approximately 3300.
This ecoregion is part of the Boreal Cordillera ecozone.