Narrative Descriptions for the
Ecoregions of Alaska – The Next Generation
Version 5.1

G. Nowacki (USFS), P. Spencer (NPS), T. Brock (USFS) and M. Fleming (USGS)

DRAFT 4-25-00

Map Contributors: Torre Jorgenson (ABRI), Lee Anne Ayers (formerly ADFG, now USFWS), Keith Boggs (AHNP), Dennis Demarchi (BCMELP), Charles Roots (GSC), Mary Beth Cook (NPS), Lois Dalle-Molle (NPS), Bill Eichenlaub (NPS), Penny Knuckles (NPS), Danny Rosenkrans (NPS), Sara Wesser (NPS), Mark Clark (NRCS), Darrell Kautz (NRCS), Scott Smith (PAFRC), David Banks (TNC), Dean Davidson (USFS), Rob DeVelice (USFS), Connie Hubbard (USFS), Beth Schulz (USFS), Michael Shephard (USFS), Ken Winterberger (USFS), Jonathon Hall (USFWS), Janet Jorgenson (USFWS), Fran Mauer (USFWS), Ken Rice (USFWS), Susan Savage (USFWS), David Brew (USGS), Alisa Gallant (USGS) and Mark Shasby (USGS).

1) Ahklun Mountains

This coastal group of rugged steep-walled mountains spans two expansive wetland complexes (Yukon-Kuskokwim Delta and Bristol Bay Lowlands) along the southern Bering Sea. Here, strongly-deformed sedimentary and volcanic rocks are cut by great northeast-trending faults including portions of the Denali Fault. Here, mountain glaciers coalesced during the Pleistocene ice age and carved many broad U-shaped valleys. On the south side of the mountains, these valleys have subsequently filled with water forming large “finger” lakes. These lakes have resident rainbow trout and nurture abundant runs of sockeye salmon during the summer. Mountain soils have formed in very stony and gravelly colluvium over bedrock, whereas valley soils have formed in glacial till. Dwarf shrub-lichen tundra dominates mountain crests and upper slopes where permafrost is discontinuous. Shrubs (willows, birches, and alders) become progressively more abundant and robust at lower elevations as permafrost becomes more fragmented. In valleys, shrublands are punctuated by sedge-tussock tundra meadows (on very wet areas) and mixed forests. Moose, beavers, and Arctic hares thrive in these shrubby habitats. Gregarious walruses and sea lions haul-out in great numbers along the rocky beaches while seabirds patrol the skies. The climate is moist polar with some moderation afforded by the Bering Sea. At this latitude, ice normally spans the Bering Sea in winter allowing access for cold Siberian air.

2) Alaska Peninsula

The Aleutian Range serves as the spine of this peninsula which divides Bristol Bay from the North Pacific Ocean. The Alaska Peninsula narrows progressively towards the southwest as the range becomes increasingly submerged. The folded and faulted sandstone bedrock is dotted with symmetrical cinder cones clad with ice, pumice, and volcanic ash. Earthquakes are common and some of the most active volcanos on the continent occur here. The Pleistocene Glaciation has produced strongly contrasting topographies along this peninsula with smooth glacial moraines and colluvial shields on the north side and rugged deeply-cut fjordlands on the south side. In turn, glacial-fed streams flowing northward have low-energy, shallow channels whereas those flowing southward have high-energy, deeply-incised channels. Along the north side, huge lakes have filled behind young glacial moraines that act as dams. The peninsula is free of permafrost, however sea ice occasionally forms in Bristol Bay demarcating the northern extent of sea otters. The coastline habitat supports numerous shorebirds and sea mammals. Many Steller sea lion rookeries and haul outs are present. Large populations of brown bears survive on abundant pink, chum, and silver salmon runs. A cool maritime climate prevails with moderate seasonal temperatures, abundant year-around precipitation, and foggy and overcast conditions. Dominant vegetation is low shrublands of willow, birch, and alder interspersed with ericaceous/heath and Dryas-lichen communities. Alpine tundra and glaciers occur on mountaintops.

3) Alaska Range

A series of accreted terranes conveyed from the Pacific Ocean have fused to form this arcing mountain range. In turn, these towering mountains harbor a complex mix of folded, faulted, deformed metamorphic rocks. Landslides and avalanches frequently sweep the steep, scree-lined slopes. Discontinuous permafrost underlies shallow and rocky soils. Because of its height, a cold continental climate prevails and much of the area is barren of vegetation. Occasional streams of Pacific moisture are intercepted by the highest mountains and help feed small icefields and glaciers. At their termini, swift glacial streams with heavy sediment loads course down mountain ravines and braid across valley bottoms. Alpine tundra supports populations of Dall sheep and pikas on mid and upper slopes. Shrub communities of willow, birch, and alder occupy lower slopes and valley bottoms. Forests are rare and relegated to the low-elevation drainages. Brown bears, gray wolves, caribou, Dall sheep, and wolverines are common denizens in the Alaska Range.

4) Aleutian Islands

These fog-shrouded islands represent volcanic summits of a submarine ridge extending from the Alaska Peninsula to the Kamchatka Peninsula. The Aleutian island arc and deep sea trench are products of the Pacific plate subducting beneath the North America plate. It is one of the most seismically and volcanically active areas in the world. The topography features glaciated and rubble-strewn volcanic cones indented with fjords and bordered by sea cliffs or wave-beaten platforms. These islands are free of permafrost, covered by volcanic-ash soils, and dissected radially by short, swift streams. A cool maritime climate with abundant year-around precipitation prevails over these permafrost-free islands. Terrestrial warming is subdued by incessant cold ocean winds and perpetual overcast clouds and fog which limits solar insolation. The flora is a blend of species from two continents, grading from North American to Asian affinities from east to west. Mountain flanks and coastlines dominated by low shrubs of willow, birch, and alder interspersed with ericaceous-heath, Dryas-lichen, and grass communities. Alpine tundra and glaciers occur on mountains. This island chain demarcates the southern boundary of the Bering Sea and are important grounds for marine mammals (northern fur seals, Steller sea lions, and sea otters), waterfowl (Aleutian Canada geese, emperor geese) and seabirds (various species of auklet, red-legged kittiwakes). With their vast numbers, seabirds serve as important nutrient suppliers by splattering these islands with guano.

5) Alexander Archipelago

The rugged area consists of a series of accreted terranes of Pacific origin heavily scoured by past ice sheets. This island-rich fjordland formed when the glacier-carved landscape filled with seawater after deglaciation. Exceedingly deep waters exist where thick rivers of ice flowed along geologic faults. Today, humpback whales, orcas, seals, and sea otters patrol these waters. At the head of fjords lie broad U-shaped valleys that have steep, deeply-incised side walls draped with hanging glacial valleys. Rounded mountains with rolling till plains occur where continental glaciers overrode the land whereas angular mountains (possessing unglaciated peaks called “nunataks”) exist where continental glaciers did not. Glacial rebound has raised marine terraces where rich coastal lowlands and estuaries now exist. A cool, hypermaritime climate dominates with minor seasonal temperature variation and extended periods of overcast clouds, fog, and precipitation. Winter snow, though abundant in locations, is ephemeral at sea level. Lush, lichen-draped temperate rain forests of hemlock and spruce blanket the shorelines and mountain slopes where soil drainage affords. Open and forested wetlands occur on poorly-drained soils especially on compact glacial tills, marine terraces, and gentle slopes. On upper slopes, forests progressively give way to shrublands, landslide and avalanche tracks, and alpine tundra. Numerous short and swift streams support Dolly Varden, steelhead trout, and all 5 species of Pacific salmon. The land and the sea are intimately connected as spawning salmon return to their native streams and, in the process, cycle tremendous amounts of nutrients back to aquatic and terrestrial systems from which bore them life. Streams become increasingly littered with spawned-out carcasses as brown and black bears, bald eagles, and seagulls feast on returning salmon from late spring to early fall.

6) Beaufort Coastal Plain

This treeless, wind-swept plain gradually ascends from the Arctic Ocean to the foothills of the Brooks Range. Unconsolidated deposits of marine, fluvial, and glacial origin overlay thick layers of continuous permafrost. There is a lack of bedrock control so the physiography is flat. Local topography contains many permafrost-related features such as pingos, ice-wedge polygons, and oriented lakes. A dry, polar climate dominates throughout the year, with short cool summers and long cold winters. The cold is reinforced by sea ice which is along or near the shoreline year around. Even though annual precipitation is minimal, surface water is abundant since soils are fine textured and largely impermeable due to permafrost. Surfaces are pockmarked with high concentrations of thaw lakes connected by poorly-integrated drainages and interspersed with wetlands. Many species of seabirds and waterfowl thrive in these habitats. Streams originating from the Brooks Range course across the plain – most of the smaller ones dry up or freeze completely during the winter. Anadromous Arctic cisco, broad whitefish, least cisco, and Dolly Varden char over winter in larger river systems and migrate to nearshore waters for the summer. The moist and wet sedge tussock tundra is comprised mainly of sedges, herbs, and mosses. Low shrubs occur mostly in small drainages where microtopography allows deeper rooting. Arctic foxes, muskoxen, gray wolves, and caribou roam these plains, polar bears canvass its pebbly shorelines and adjacent ice floes, and golden eagles patrol its skies.

7) Bering Sea Islands

These rocky volcanic islands are scattered thoughout shallow portions of the Bering Sea. Here, a peculiar mix of polar and maritime climates exist dependent on season. In winter, ice encapsulates these islands ushering in dry polar air from Siberia. These conditions are replaced by cool, moist maritime conditions after spring ice break up. Thin to moderately think permafrost underlies mainly thin, rocky soils. At the height of the Pleistocene glaciation, these islands were mere hills within a vast seabed plain of the Bering land bridge. Not surprisingly, life residing on these islands today possess affinities to North America and Asia. Moist tundra communities of sedges, grasses, low shrubs and lichens are surrounded by rocky cliffs and shorelines. Millions of sea birds (cormorants, kittiwakes, murres, puffins, and auklets) and marine mammals (northern fur seals, ribbon seals, sea lions) descend on these rocky outposts during the summer. Wintering flocks of rare spectacled eiders congregate in small polynyas (or openings) in the sea ice south of St. Lawrence Island.

8) Boundary Ranges

A northwest-southeast trending batholith of resistant granite and granodiorite underlies this portion of the Coastal Mountains. Abundant maritime snows feed huge icefields and glaciers that form an undulating matrix around exposed, rugged peaks called nunutaks. Summer meltwaters accumulate and flow across these ice fields, oftentimes plunging into deep icy crevasses called moulins. During the Pleistocene massive ice sheets formed along these ranges and spread across surrounding lands. Today, the southern most extent of tidewater glaciers on the North American continent occurs here. Only a few large rivers (Taku and Stikine Rivers) manage to breach this mountain range from the Interior. These, together with smaller streams, support large salmon runs of all 5 Pacific species. Alpine tundra habitats of sedges, grasses, and low shrubs support mountain goats, brown bears, hoary marmots, and ptarmigans.

9) Bristol Bay Lowlands

This flat to gently-rolling lowland is comprised mainly of glacial till and outwash deposited by various Pleistocene glaciers from the surrounding Ahklun Mountains and Aleutian Range. This basin is underlain with mixes of glacial, alluvial, and marine sediments all cloaked with varying amounts of loess. Regardless of substrate, these lowlands harbor large concentrations of lakes, ponds, meandering rivers, and wetlands that serve as important staging and migration areas for an abundance of waterfowl. This habitat supports the largest run of sockeye salmon in the world which, in turn, sustains large populations of brown bear, eagles and osprey. Permafrost occurs in scattered isolated masses. Wet organic soils support low and dwarf shrub communities of willow, birch, and alder. Mosses and lichens are abundant groundcovers. The climate is maritime polar with substantial moderation afforded by the southern Bering Sea and the North Pacific Ocean. At this latitude, ice occasionally spans the Bering Sea in winter allowing access for cold Siberian air.

10) Brooks Foothills

These dissected hills and ridges form the northern flank of the rugged Brooks Range as it descends toward the Beaufort Coastal Plain. Undulating plains of alluvial, colluvial, glacial and aeolian deposits spread from long linear ridges, buttes, and mesas comprised of tightly-folded sedimentary rocks. A dry polar climate dominates over the land. The surface is underlain by thick continuous permafrost and display ice-related features such as pingos, solifluction lobes, ice-wedge polyons, and stone stripes. Soils in the active permafrost layer are fairly wet. Many swift, braided streams and rivers with Arctic char and Arctic grayling are present, but lakes are infrequent. Some streams freeze solid to their bottoms, causing large aufice deposits that last well into summer and provide refuge for caribou from voracious mosquitoes. Moist tussock sedge tundra spans across the landscape interspersed with willow communities along river corridors. Past glaciation has been confined to areas immediately adjacent to the Brooks Range. Large herds of caribou migrate across the Brooks Foothills between calving grounds on the Beaufort Plain and winter habitats in the Brooks Range.

11) Brooks Range

This rugged, east-west trending range represents the northern extension of the Rocky Mountains. Accreted terranes originating from the Arctic Ocean underlie this range and end at the Kobuk-Malamute fault system along its southern boundary. Exposed angular summits of sedimentary and metamorphic rock are draped with coarse rubble. During Pleistocene ice ages, mountain glaciers coalesced to cover the entire range -- only a few remnants in the form of small cirque glaciers still exist. The dry polar climate coupled with underlying permafrost make growing conditions difficult for plant life, particularly at high elevations or on steep slopes with active scree movement. Alpine, moist, and tussock tundra of lichens, sedges, and ericaceous plants exist where conditions permit (lower summits and mountainsides). The arctic tree line enters larger drainages along the south portion of the Brooks Range. Here, taller shrub communities fringe these forested valleys. High-energy streams and rivers cut through narrow ravines with steep headwalls etching a deeply-incised, dendritic pattern into the terrain. Arctic char are found in groundwater fed springs and streams and Dall sheep, grey wolves, brown bears, and caribou inhabit surrounding mountains. Golden eagles are common in the sky.

12) Chugach-St. Elias Mountains

Arcing terranes of Pacific origin have been thrusted onto the North American continent forming a rugged ice-clad mountain chain that surrounds the Gulf of Alaska. This is the largest collection of ice fields and glaciers found on the globe outside the polar region. These towering mountains of faulted and folded sedimentary rocks intercept an abundance of maritime moisture, mainly in the form of snow. Huge ice fields, snowfields and glaciers form a continuous matrix over these mountains interrupted occasionally by rock cliffs and small exposed peaks called “nunataks.” In the summer, meltwater accumulates atop the ice fields and glaciers forming rivulets that eventually plunge down vertical ice shafts called moulins. Where they exude onto coastal flats, glaciers spread to form expansive lobes that gush water at their edges. Some glaciers run all the way to tidewater. Ice sheets swelled during past glaciations, inundating surrounding lands along the coast as well as the Interior. The steer height of these mountains together with their expansive ice fields forms an effective barrier for Interior species except along the Alsek and Copper River corridors. Thin and rocky soils exist where mountain summits and slopes are devoid of ice, snow, and active scree. Here, alpine communities of sedges, grasses, and low shrubs grow which, in turn, support Dall sheep, mountain goats, hoary marmots, pikas, and ptarmigans. Broad U-shaped valleys, many with sinuous lakes, occur where glaciers and ice fields have pulled back sufficiently. Here, deeper soils have formed in unconsolidated morainal and fluvial deposits underlain by isolated pockets of permafrost. Alder shrublands and mixed forests occur on lower slopes and valley floors where moose and brown and black bears forage.

13) Cook Inlet Basin

This gently-sloping lowland has been buried by ice and flooded by proglacial lakes several times during the Pleistocene. As such, the basin is comprised of fine-textured lacustrine deposits ringed by coarse-textured glacial tills and outwash. Numerous lakes, ponds, and wetlands attract large numbers of waterfowl (including trumpeter swans) and shorebirds. Dolly Varden and white fish occur in fresh waters. Several river systems support recovering salmon runs and resultant bear and raven populations. The basin is generally free of permafrost. A mix of maritime and continental climates prevail with moderate fluctuations of seasonal temperature and abundant precipitation. This climate coupled with the flat to gently-sloping, fine-texture surfaces give rise to wet, organic soils clothed with black spruce forests and woodlands. Ericaceous shrubs are dominant in open bogs. Mixed forests of white and Sitka spruce, aspen and birch occur on better-drained sites and grade into tall shrub communities of willow and alder on slopes along the periphery of the basin. A mixture of wetland habitats supports numerous moose, black bear and muskrats.

14) Copper River Basin

This mountain basin lies within the former bed of Glacial Lake Ahtna on fine-textured lacustrine deposits ringed by coarse glacial tills. The basin is a large wetland complex underlain by thin to moderately thick permafrost and pockmarked with thaw lakes and ponds. A mix of low shrubs and black spruce forests and woodlands clothe the wet organic soils. Cottonwood, willow, and alder line rivers and streams as they braid or meander across the basin. Spring floods are common along drainages. Arctic grayling, burbot, and anadromous sockeye salmon are common fishes. Black and brown bears, caribou, wolverines, and ruffed grouse are present throughout these wetland habitats. The climate is strongly continental, with steep seasonal temperature variation. The basin acts as a cold-air sink and winter temperatures can get bitterly cold.

15) Davidson Mountains

Along the south flank of the eastern Brooks Range lie rugged mountains dissected by broad floodplains of glacial origin. The mountains are draped by course rubble whereas river valleys and floodplains are lined with unconsolidated glacial and alluvial sediments. Continuous permafrost from thin to moderate thickness underlies most of the area. Boreal forests cover much of the terrain with black spruce in bogs, white spruce and balsam poplar along rivers, and white spruce, white birch and trembling aspen on uplands. Tall willow, birch, and alder communities also occur. Forest fires are frequent. A strong continental climate prevails with long cold winters and short cool summers.

16) Gulf of Alaska Coast

Lush, lichen-draped temperate rain forests of hemlock and spruce interspersed with open wetlands blanket the shorelines and adjacent mountain slopes along the Gulf of Alaska. A cool, hypermaritime climate dominates with minor seasonal temperature variation and extended periods of overcast clouds, fog, and precipitation. Snow is abundant in the winter and persists for long periods at sea level. Permafrost is absent. Tectonic events have raised and submerged various portions of the coastline over time. Common forest animals include black and brown bear and Sitka black-tailed deer. Bald eagles, common murres, Bonaparte’s gulls, Steller’s sea lions, harbor seals, and sea otters teem along its endless shorelines. Numerous streams and rivers support Dolly Varden, steelhead trout, and all 5 species of Pacific salmon. Salmon spawning runs deliver tremendous amounts of nutrients to aquatic and terrestrial systems. A fjordal coastline and archipelago exists around Prince William Sound and points west where continental ice sheets repeatedly descended in the past. Here, fjords formed where glacier-carved terrain filled with seawater after deglaciation. At the head of fjords lie broad U-shaped valleys that have steep, deeply-incised side walls draped with hanging glacial valleys. A coastal foreland extends from the Copper River Delta southeast to Icy Point fringed by the slopes and glacier margins of the Chugach-St. Elias Mountains. Here, unconsolidated glacial, alluvial, and marine deposits have been uplifted by tectonics and isostatic rebound to form this relatively flat plain. Because of its geographic position, the foreland is water-drenched through persistent maritime precipitation and overland runoff from the mountains. The organic soils shed water slowly and are blanketed with wetlands among meandering and braided silt-laden streams. Temperate rain forests of hemlock and spruce occur sporadically where soil drainage affords (e.g., moraines, stream levees, uplifted beach ridges). Rare dusky Canada geese and trumpeter swans nest on these wet flats where brown bear, Sitka black-tailed deer, and moose roam.

17) Kluane Range

The Kluane Range encompasses the drier interior portion of the St. Elias Mountains spanning from the ablation zone (area where glacial ice melts faster than it accumulates) eastward to a fault line scarp along the Shakwak Valley. It is generally ice-free except for occasional glaciers extending from the St. Elias icefields. The area has a dry continental climate. It lies within a partial rainshadow of the St. Elias Mountains whereby moisture from the Pacific Ocean is effectively rung-out of the atmosphere on its accent over these towering peaks. Deformed sedimentary and volcanic rocks of Wrangellia and Alexander terranes underlie this area. The high-relief topography has been exposed to mass wasting, stream erosion and glacial scouring. Thin and rocky soils have developed in the colluvial veneer that covers most surfaces. Swift streams cascade down steep mountainsides where scree movement, rock falls, landslides, and soil creep actively occur. Permafrost is discontinuous with the presence of frost action features such as solifluction lobes, ice-wedge networks, and patterned ground. Vegetation is comprised principally of alpine tundra and barrens of lichens, prostrate willows, and ericaceous shrubs. Taller shrub communities occur at mid elevations. White spruce is found on lower slopes and valleys along the eastern boundary. Alpine and subalpine habitats support an abundance of Dall sheep, mountain goats, brown bear, caribou, moose, wolves, and wolverine.

18) Kobuk Ridges and Valleys

A series of paralleling ridges and valleys radiate southwards from the Brooks Ranges. This diagnostic feature is created in part by high-angle reverse faults and interceding troughs. This area was overridden by past ice sheets descending from the north. Today, immense U-shaped valleys harbor large rivers that originate in the Brooks Range. The broad valleys are lined with alluvial and glacial sediments whereas the intervening ridges are covered with rubble. Permafrost of thin to moderate thickness underlies most of the area. A dry continental climate prevails with long cold winters and short cool summers. Frigid conditions are reinforced during the winter as the valleys serve as cold-air drainages for the Brooks Range. Forests and woodlands dominate much of valley bottoms and mountainsides with black spruce in wetland bogs, white spruce and balsam poplar along rivers, and white spruce, white birch, and trembling aspen on well-drained uplands. Tall and short shrublands of willow, birch, and alder communities occur in ridges. Trees become increasingly sparse, less robust, and restricted to lower elevations in the west – here forest succession is slowly progressing along rivers (e.g., lower Noatak River).

19) Kodiak Island

This rugged, fjord-carved island complex is a geologic extension of the Chugach Mountains with a similar suite of folded and faulted sedimentary rocks of Pacific origin. During past glaciations, a solid ice sheet spanned Shelikof Strait connecting this group of islands with the mainland. Ice engulfed most of the islands except for the highest mountains (nunataks) and some seaward coastal plains that provided refugia for plant and animal life. Today, high sharp peaks with cirque glaciers and low rounded ridges overtop glacially-scoured valleys covered with till or lacustrine deposits. Large terminal moraines occur offshore where many former glaciers extended onto the continental shelf. The flora of island group is still recovering from the last glaciation. For instance, trees did not survive the last Pleistocene glaciation and only recently has Sitka spruce and black cottonwood managed to regain a foothold on the northeastern portion of this island group. At present, luxuriant forb/grass meadows and willow and alder thickets cover the majority of these islands. Some alpine tundra exists at higher elevations. The climate is a cool wet maritime with minimal seasonal temperature variation and extended periods of overcast clouds, fog, and precipitation. Snow blankets these islands during the winter from lows sweeping eastward along the Aleutians. These islands are entirely free of permafrost. Offshore waters are rich with deepwater fish such as halibut and cod and marine mammals including sea otter, Stellar’s sea lions and a variety of whales. Small, swift rivers and streams radiating from the highlands harbor abundant salmon runs. These runs funnel tremendous amounts of nutrients to these islands and help support populations of the largest land carnivore in the world – the Kodiak brown bear. Puffins and auklets perch on its rocky shoreline cliffs.

20) Kuskokwim Mountains

This subdued terrain is comprised of old, low-rolling mountains that have eroded down largely without the aid of recent past glaciations. A continental climate prevails with seasonal moisture provided by the Bering Sea during the summer. Mountains are composed of eroded bedrock and rubble whereas intervening valleys and lowlands are comprised of undifferentiated sediments. Thin to moderately thick permafrost underlies most of the area. Boreal forests dominate grading from white spruce, white birch, and trembling aspen on uplands to black spruce and tamarack in lowlands. Tall willow, birch, and alder shrub communities are scattered throughout, particularly where forest fires burned in the recent past. Rivers meander through this undulating landscape following fault lines and highly eroded bedrock seams.

21) Lime Hills

The Lime Hills are glacially-dissected mountains descending from the west side of the Alaska Range. The affect of heavy glaciation is etched in the surface topography through a repeated sequence of sharp mountain ridges with steep headwalls and broad U-shaped valleys. The ridges and mountainsides are covered with colluvial rubble whereas the valleys contain glacial moraines and outwash with some alluvial deposits along rivers. The continental climate is moderated somewhat by maritime influences of the Bering Sea and North Pacific Ocean. The area is underlain by isolated masses of permafrost. Vegetation is predominately tall and low shrub communities of willow, birch, and alder. Spruce forests and woodlands confined to valley bottoms and mountain toeslopes.

22) North Ogilvie Mountains

This terrain consists of flat-topped hills and eroded remnants of a former plain. This area represents the western extent of the North America stable platform onto which terranes radiating from the Pacific and Arctic oceans have attached. Sedimentary rocks, especially limestone, underlie most of the area. Ridgetops and upper slopes are often barren with angular, frost-shattered rock outcrops (resembling castellations) surrounded by long scree slopes. These are characteristics of an unglaciated area that has undergone long periods of erosion. Shallow soils have developed in rocky colluvium on mountainsides where landslides, debris flows, and soil creep frequently occur. On lower slopes, soils are deeper, moister, and underlain by extensive permafrost. Low shrub tundra of willow, alder, and birch and aspen and spruce woodlands occur at lower elevations. These mountains are the source of many streams that eventually feed the Porcupine, Yukon, and Peel rivers. Lakes are relatively rare. A strong continental climate prevails, with prolonged frigid winters lasting from October to May and cool, short summers. Brown bears, wolverine, Dall sheep, caribou, lemmings, and pikas are common inhabitants of these mountains.

23) Nulato Hills

These low-rolling hills are the remains of an ancient mountain range after extended periods of downcutting, weathering, and erosion. East of Norton Sound, these hills ripple inland in a southwest-northeast orientation with streams flowing in intervening valleys. Due to their low elevation, most of these hills have been spared from recent glaciations. Indeed, during the last glaciation, these hills were part of the ice-free Beringia corridor linking North America and Asia. Ecological affinities to Asia exist to this day with the presence of Eurasian birds (gray-headed chickadee, yellow and white wagtails, bluethroat) and fishes (Alaska blackfish). Vegetation patterns generally follow the terrain, with alpine Dryas-lichen tundra and moist sedge-tussock tundra on hilltops grading into short then tall willow-birch-alder shrublands and eventually spruce woodlands at progressively lower elevations. The climate is best classified as moist polar. The Bering Sea affords some climatic moderation, however, at this latitude, ice spans the sea early every winter allowing direct passage of bitterly cold Siberian air. Permafrost is continuous but oscillates from thin to moderately thick. Moose, brown bears, caribou, Arctic foxes, and Alaskan hares are common. Ribbon seals and walruses are observed in Norton Sound.

24) Ray Mountains

The Ray Mountains are an overlapping series of compact, east-west trending ranges underlain by Ruby terrane. The metamorphic bedrock is usually covered with rubble and soils are subsequently shallow and rocky. The Kobuk-Malamute fault essentially separates the Ray Mountains from the Brooks Range to the north. A number of thrust faults occur in the southern portion of the Ray Mountains. The area was largely unglaciated during Pleistocene ice ages, except for alpine glaciers that capped the highest peaks. Permafrost is generally discontinuous and ranges from thin to moderate thickness. The climate is strongly continental with dry, cold winters and moist warm summers. Open scrubby forests of spruce and aspen interspersed with tall shrublands prevail over much of the area. Low shrubs and alpine tundra progressively dominate at higher elevations. Forest fires are common in the summer.

25) Seward Peninsula

This cold, wind-swept landmass jutting out into the Bering Sea represents the southernmost haunt of polar bears on mainland Alaska. Sedimentary, metamorphic, and volcanic rocks intertwine to form a landscape mosaic of coastal lowlands, expansive convex hills with scattered broad valleys, and small, isolated groups of rugged mountains. Vegetation is principally tundra, with alpine Dryas-lichen tundra and barrens at high elevations and moist sedge-tussock tundra at lower elevations. Patches of low-growing ericaceous and willow-birch shrubs occur on better-drained areas. Permafrost is continuous but oscillates from thin to moderately thick. Soils are often wet, shallow, and organic due to permafrost. Ice-related features such as pingos and patterned ground (raised polygons outlined by rock-filled ditches) are present. The climate is best classified as moist polar. The cold Bering Sea affords some climatic moderation, however, at this latitude, ice spans the sea early every winter allowing direct passage of bitterly cold Siberian air. Persistent cold, windy conditions occur in the winter whereas fog blankets the coastlines in the summer. At its height, Pleistocene glaciation covered only the higher mountains. Back then the peninsula was part of an important ice-free migration corridor between North America and Asia. Strong ecological affinities to Asia remain to this day – such as the presence of Eurasian birds (gray-headed chickadee, yellow and white wagtails, bluethroat) and fishes (Alaska blackfish). Streams occupy all larger valleys and many lakes occur within broad inland valleys. Dense concentrations of lakes and ponds support abundant waterfowl (including the rare Arctic loon) and nesting birds (e.g., spectacled eiders and ruddy and black turnstones) occur within coastal plains. Brown bear, snowy owls, Arctic foxes and Alaskan hares are common. Ribbon seals and walruses are often observed along shorelines and adjacent ice floes.

26) Tanana-Kuskokwim Lowlands

This alluvial plain slopes gently northward from the Alaska Range. A mosaic of undifferentiated sediments of fluvial and eolian origin underlies the mosaic of floodplains, lowlands, and intervening hills. Glaciofluvial deposits occur adjacent to the Alaska Range where ice lobes pushed down during past glaciations. Streams flowing across this north-sloping plain ultimately drain into one of two large river systems -- the Tanana or Kuskokwim. A dry continental climate prevails with cool summers and cold winters. Even though a rain shadow exists due to the neighboring Alaska Range, surface moisture is rather abundant due to the gentle topography and poor soil drainage due to underlying permafrost. Boreal forests dominate the landscape with black spruce in bogs, white spruce and balsam poplar along rivers, and white spruce, white birch, and trembling aspen on hills. Tall willow, birch, and alder communities are scattered throughout. An abundance of waterfowl, moose, furbearers are attracted by this area’s rich aquatic habitats.

27) Wrangell Mountains

This volcanic cluster of towering, ice-clad mountains occurs at the northwest edge of the St. Elias Mountains. This exceeding steep, rugged terrain is the result of the ongoing collision of the Pacific and North American tectonic plates. The Wrangell Mountains possess a peculiar mix of climates because of their size and geographic location (i.e., on the Interior-side of the Coastal Mountains). The shear height of the Wrangell Mountains allows interception of moisture-laden air emanating from the North Pacific Ocean. The abundant maritime snows feed extensive ice fields and glaciers interspersed by dull gray ridges draped with rock shard slopes and patches of alpine meadows. The climate grades to a dry continental at lower elevations where the Wrangell Mountains abut the cold-air basin of the Copper River. Shrublands of willow and alder with scattered spruce woodlands ring the lower slopes. Spruce and cottonwood occur along larger drainages. The Wrangell Mountains are highly dynamic due to active volcanism, avalanches, landslides, and stream erosion. Soils are thin and stony and underlain by discontinuous permafrost. Its best-known denizen, the Dall sheep, roams throughout the area along with mountain goats, brown bears, caribou, wolverines, and gray wolves.

28) Yukon River Lowlands

An expansive wetland system occurs along major rivers coursing through central Alaska. Although this area was not overridden by recent glaciations, meltwater flushes has deposited vast quantities of sediment within these riverine corridors during glacial retreat. As such, deep deposits of undifferentiated sediments underlie these floodplains, lowlands, and intervening hills. Surface moisture is abundant due to the gentle grade, poor soil drainage, and presence of permafrost. A seasonally-moist continental climate prevails with cool moisture summers and cold dry winters. Water levels drop in the Yukon River and its tributaries in early fall during freeze up and will remain low until spring break up when substantial flooding can occur. Boreal forests dominate the landscape with black spruce in bogs, white spruce and balsam poplar along rivers, and white spruce, white birch, and trembling aspen on hills. Tall willow, birch, and alder communities are scattered throughout. Many flat organic surfaces are pockmarked with dense concentrations of lakes and ponds. An abundance of waterfowl, moose, wolves, brown bears, and furbearers are attracted by this areas rich aquatic habitats and associated salmon runs. This unit is distinguished from the Tanana-Kuskokwim Lowlands by having lower elevations, a slightly wetter climate, and more robust vegetation.

29) Yukon-Kuskokwim Delta

The Yukon and Kuskokwim rivers nourish this vast marshy plain as they fan out to meet the Bering Sea. Although ice sheets did not override this area per se, their indirect effects were immense as glacial meltwaters washed incredible amounts of sediments onto the delta. Marine sediments and alluvium principally underlie this flat, lake-studded lowland. Together with its many rivers, estuaries and tidal flats, this area supports exceptional populations of waterfowl (including tundra swans, emperor geese, and sandhill cranes), shorebirds (Sabines’ and mew gulls, black turnstones) and furbearers (wolverines and mink). Isolated basalt hills and volcanic cinder cones jut up in places. Moderately thick to thin permafrost underlies wet and shallow organic soils. Many low-gradient streams meander dynamically across the surface. Moist tundra communities of sedge, herbs, grasses and lichens predominate with shrubs occurring near rivers and on hills. The climate is moist polar ameliorated somewhat by the Bering Sea. At this latitude, sea ice spans the Bering Sea every winter allowing direct passage of cold Siberian fronts. Whales, walruses, and bearded and ribbon seals patrol its shore while black bear, moose, and wolves roam the land. Arctic char, sheefish, and all 5 species of North American Pacific salmon are common fishes in rivers, streams and surrounding sea.

30) Yukon-Old Crow Basin

This gently-sloping basin along the Porcupine River is comprised of terraces, hilly moraines, and mountain toeslopes that ring the Yukon and Old Crow Flats. The surfaces surrounding the flats are largely unglaciated and products of millions of years of weathering of the surrounding mountains. Here, deep deposits of colluvial, alluvial, and wind origin are underlain by continuous masses of permafrost. The marshy flats have developed in deep alluvial and glaciolacustrine deposits underlain by discontinuous permafrost. The poorly-drained flats and terraces harbor vast wetlands pockmarked with dense concentrations of thaw lakes and ponds. On the flats, water levels of lakes are often maintained by spring flooding rather than precipitation. Active fluvial processes are etched throughout the topography featuring deltaic fans, terraces, and broad floodplains with meander scars and oxbow lakes. Opaque with glacial silts and shoreline mud, the Yukon River forms an aquatic maze of islands, sandbars, and back sloughs as it crisscrosses the lower flats. The rich aquatic habitats support tremendous concentrations of nesting waterfowl (1.5 million!) and other migratory birds and an abundance of moose, bears, furbearers, northern pike and salmon. A dry continental climate prevails with considerable seasonal temperature variation. Arctic high-pressure systems prevail during the winter bringing clear and frigid weather. In contrast, summers are short but relatively warm. Vegetation varies with soil drainage grading from wet grass marshes and low shrub swamps to open black spruce forests to closed spruce-aspen-birch forests on better-drained uplands. Summer forest fires are common.

31) Yukon-Tanana Uplands

These dissected mountains of moderate height are underlain by the metasedimentary Yukon-Tanana terrane sandwiched between the Tintina and Denali Faults. This terrane is a composite of transported crust blocks that includes former volcanic island arcs and continental shelf deposits. The topography of smooth-topped ridges deeply incised by narrow valleys is indicative of a lack of glaciation in the past. Most surfaces are comprised of bedrock and coarse rubble and underlain by discontinuous permafrost. Surface deposits consist of colluvium (gravity-transported materials) due in large part to soil creep and debris flows. Permafrost is discontinuous but widespread, and is particularly abundant on moist lower slopes and valley bottoms. Climate is strongly continental with warm summers and very cold winters. There a slight rainshadow affect from the towering Wrangell and St. Elias Mountains to the south. This area straddles treeline with vegetation ranging from alpine tundra on ridges and upper slopes to boreal forests on lower slopes and valleys. Stunted black spruce woodlands occur on cold, north-facing slopes whereas mixed forests (spruce, aspen, birch, poplar) occur on warm south-facing slopes. This area includes the highest incidence of lightening strikes in the Yukon and forest fires are consequently frequent. Caribou, moose, snowshoe hares, marten, lynx, black bear, and wolverine are abundant mammals.

U.S. Department of the Interior | U.S. Geological Survey
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