Slope gradients are generally from 0 to 5 in the lowlands and hills, but typically from 5 to 15 in the mountains. Geologic parent materials include Paleozoic sediments and metamorphosed volcanic rocks, and Precambrian volcanic rocks. Highland areas are possible Cenezoic uplifts of these formations. An extensive area of Quaternary or Tertiary volcanic rock occurs in the northeastern portion of the ecoregion. Permafrost is continuous throughout the ecoregion, ranging from a thin to moderately thick layer.
Streams draining interior basins travel through narrow canyons across broad uplands.
Lowlands have numerous thaw lakes, but lakes are rare in the highlands. Except for the highest elevations, the region was unglaciated during the Pleistocene epoch. Soils Predominant soils are Histic Pergelic Cryaquepts, Pergelic Cryaquepts, Typic Cryochrepts, Pergelic Cryumbrepts, Lithic Cryorthents, and Pergelic Cryorthents. Soils are generally poorly drained and shallow over permafrost. Soils on hillslopes and ridges formed in very gravelly residual materials over weathered bedrock.