[2] Palaeozoic and Mesozoic sedimentary rock forms the western portion of the ecozone, whereas Precambrian granite is the dominant feature in the east.

A permanent layer of permafrost may be up to one kilometre thick, and lies under a shallow stratum of waterlogged active soils that cyclically freeze and thaw, creating patterned ground.

This ecozone can be further subdivided into seven ecoprovinces:[5] The region is extremely cold, with temperatures rising above the freezing point only in July and August.

[4] Despite the low precipitation, the permafrost's ability to prevent water from draining through the soil, and the abundant snow and ice cover throughout the zone ensure that the climate is usually moist.

[4] The northern waters are permanently frozen, but coastal areas in the south may open in the summer, though numerous large ice floes persist.