**Narrative Descriptions for the**

**Ecoregions of Alaska and Neighboring Territories**

**G. Nowacki (USFS), P. Spencer (NPS), T. Brock (USFS),**

**M. Fleming (USGS) and Torre Jorgenson (ABRI).**

**FINAL DRAFT 6-1-00**

**Map Contributors: Lee Anne Ayers (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), Mike Vivion (USFWS), David Brew (USGS), Alisa Gallant (USGS)
and Mark Shasby (USGS).**

**GIS Work: Gary Fisher (USFS) and Kari Youkey (USFS).**

# 1) Ahklun Mountains

This **coastal group of rugged steep-walled mountains** spans two
extensive 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 and carved **many broad U-shaped
valleys**. On the south side of the mountains, these valleys
subsequently filled with water forming **large "finger" lakes**. These
lakes have resident rainbow trout and nurture abundant runs of sockeye
(red) 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 and 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. Great numbers of gregarious **walruses and sea
lions haul out** in along the rocky beaches while seabirds patrol the
skies. The climate is moist polar with some moderation 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 toward 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
volcanoes on the continent are here. The **Pleistocene glaciation**
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, glacially 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 are on
mountaintops.

# 3) Alaska Range

A series of accreted terranes conveyed from the Pacific Ocean 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 the Alaska Range's 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 the glacier's 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 crustal plate subducting, or descending, beneath the North
American crustal 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-round 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 are dominated by low shrubs of willow, birch, and alder
interspersed with ericaceous-heath, *Dryas*-lichen, and grass
communities. Alpine tundra and glaciers are on mountains. This island
chain demarcates the southern boundary of the Bering Sea and is
important 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 supply important fertilizing nutrients
by splattering these islands with their guano.

#  

# 5) Alexander Archipelago

The rugged area consists of a series of accreted terranes of Pacific
origin heavily scoured in the past by 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 and piedmont glaciers overrode the land.
High, steep-sided, angular mountains (i.e., former nunataks), some still
sporting alpine glaciers, area above the reach of these overriding
glaciers. Rebound after the withdrawal of the continental ice sheets,
together with tectonic movements, have both raised and lowered marine
terraces, giving rise to rich coastal lowlands and estuaries. A **cool,
hypermaritime climate** dominates with minor seasonal temperature
variation and extended periods of **overcast clouds, fog, and
precipitation**. Snow, though abundant in some 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 allows. 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 and steelhead trout, and all five
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 the freshwater and
terrestrial systems which bore them life. Streams become increasingly
littered with spawned-out carcasses as brown and black bears, bald
eagles, and sea gulls feast on returning salmon from late spring to
early fall.

# 

# 6) Beaufort Coastal Plain

This **treeless, wind-swept plain** gradually ascends from the Beaufort
Sea coast southward to the foothills of the Brooks Range. This flat to
undulating coastal plain is underlain by unconsolidated deposits of
marine, fluvial, glaciofluvial, and eolian origin and lacks bedrock
control. A **dry, polar climate** dominates throughout the year, with
short, cool summers and long, cold winters. Proximity to the Arctic
Ocean and abundant sea ice contribute to the cool, frequently foggy,
summers. Annual precipitation is low and mostly falls as snow during the
winter. Due to low temperatures, **permafrost is continuous** across the
region, except under large rivers and thaw lakes. Permafrost and frost
processes contribute to a large variety of surface features such as
pingos, ice-wedge polygons, and oriented thaw lakes. The presence of
permafrost prevents surface drainage so soils typically are saturated
and have thick organic horizons. Due to the abundance of thaw lakes
(covering up to 50% of the surface) and saturated soils, nearly the
entire region supports **wetland communities**. Vegetation is dominated
by wet sedge tundra in drained lake basins, swales, and floodplains, and
by tussock tundra and sedge-*Dryas* tundra on gentle ridges. Low willow
thickets grow on well-drained riverbanks. Although drainage over most of
the area is poorly integrated, there are numerous large, braided rivers
that originate in the Brooks Range and drain northward to cross the
coastal plain. **Anadromous arctic cisco, broad whitefish, least
cisco,** and **Dolly Varden char** overwinter in these larger rivers and
migrate to nearshore waters for the summer. Smaller streams often dry up
or freeze completely during the winter. The coastal plain supports
**large caribou herds** and is an important calving area. Important
hervibores include muskoxen, lemmings, and arctic ground squirrels,
while important predators include arctic foxes, gray wolves, and brown
bears. **Polar bears** occasionally den on the coastal plain. The region
also is important for breeding waterfowl, including a wide variety of
shorebirds, ducks, geese, swans, and passerines.

# 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
breakup. Thin to moderately thick 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 on these islands today possesses
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 seabirds** (cormorants, kittiwakes,
murres, puffins, and auklets) and **marine mammals** (northern fur
seals, ribbon seals, and sea lions) inhabit 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 nunataks. Summer
meltwaters accumulate and flow across these icefields and glaciers,
often plunging into deep, icy crevasses called moulins. Meltwaters
coalesce at the bottom of glaciers forming a vast sheet of water that
gushes out along glacier termini. 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 five 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** mainly comprised of **glacial
till and outwash** deposited by various Pleistocene glaciers from the
surrounding Ahklun Mountains and the 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 contain 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 bears, 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 ground covers. The climate is maritime polar with substantial
moderation by the southern Bering Sea and the north Pacific Ocean. At
this latitude, ice occasionally spans the Bering Sea in winter admitting
for cold Siberian air.

**10) Brooks Foothills**

**Gently rolling hills** and **broad exposed ridges** form the northern
flank of the Brooks Range. Narrow alluvial valleys and glacial moraines
and outwash are interspersed among long linear ridges, buttes, and mesas
comprised of tightly-folded sedimentary rocks. Most of the surface is
mantled with colluvial and eolian deposits. A **dry polar climate**
dominates the land, but is somewhat warmer and wetter than the Beaufort
Coastal Plain. The surface is underlain by **thick continuous
permafrost** and slope-related periglacial features, such as
solifluction lobes and stone stripes, are common. Because the permafrost
impedes drainage, soils in the active layer are usually saturated and
have fairly thick organic horizons. The lower foothills tend to be
calcareous, whereas the upper foothills are frequently acidic. **Many
braided streams and rivers** with highly variable seasonal discharge are
present -- their clear waters teem with arctic char and arctic grayling.
Lakes are infrequent. Some streams freeze solid to their bottoms,
causing large aufeis deposits that last well into summer and provide
refuge for caribou from voracious mosquitoes. Vegetation is dominated by
vast expanses of **mixed shrub-sedge tussock tundra**, interspersed with
willow thickets along rivers and small drainages and *Dryas* tundra on
ridges. Calcareous areas support sedge-*Dryas* tundra. The area is
important to **caribou, muskox**, arctic ground squirrels, peregrine
falcons, wolves, and brown bears.

**11) Brooks Range**

This **east-west trending range** represents the northern extension of
the Rocky Mountains, and includes the Brooks Range and British and
Richardson Mountains. Accreted terranes originating from the Arctic
Ocean underlie most of this range, ending at the Kobuk-Malamute fault
system along its southern boundary. The high central portion possesses
**steep angular summits** of sedimentary and metamorphic rock **draped
with rubble and scree**. To the west and east, the topography becomes
less rugged -- for instance the Richardson Mountains have flat-topped
summits flanked by stepped slopes reflecting bedrock conditions.
High-energy streams and rivers cut through narrow ravines with steep
headwalls etching a **deeply-incised, dendritic pattern** into the
terrain. During Pleistocene Epoch, mountain glaciers coalesced to cover
the higher portions of the range -- here only a few remnants in the form
of small cirque glaciers still exist. The Richardson Mountains were
ice-free during the last ice age and blocked the continental ice sheet
advance from the east. The **dry polar climate** has short, cool summers
and long, cold winters; and air temperatures decrease rapidly with
rising elevation. Valleys and lower mountain slopes on the north side of
the range are covered by mixed shrub-sedge tussock tundra with willow
thickets along rivers and streams. **Alpine tundra and barrens**
dominate at higher elevations along the entire crest of the range. On
the south side, lower mountain slopes and valleys possess sedge tussocks
and shrubs. The arctic tree line skirts across the range in Canada and
is restricted to the south side of the range in Alaska. Here, sparse
conifer-birch forests and tall shrublands occur in larger valleys.
**Dall sheep, gray wolves, brown bears, marmots, and caribou** inhabit
the mountains. **Arctic grayling** are found in groundwater fed springs
and streams.

# 12) Chugach-St. Elias Mountains

Arcing terranes of Pacific origin have been thrust onto the North
American continent forming a **rugged ice-clad mountain chain**
surrounding the Gulf of Alaska. This is the largest collection of
icefields and glaciers found on the globe outside the polar regions.
These towering mountains of faulted and folded sedimentary rocks
intercept an **abundance of maritime moisture**, mainly in the form of
snow. **Huge icefields, snowfields, and glaciers** surround steep
angular and cliffy peaks that are mantled with hanging glaciers;
isolated small peaks called nunataks poke up sporadically in the middle
of the broad glaciers. In the summer, glacial meltwaters form rivulets
and plunge down vertical ice shafts called moulins to join vast amounts
of water flowing along the base of glaciers. 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 sheer height of these mountains
together with their expansive icefields, 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. Glaciers and
icefields have receeded, leaving b**road U-shaped valleys**, many with
sinuous lakes. Here, deeper soils have formed in unconsolidated morainal
and fluvial deposits underlain by isolated pockets of permafrost. Alder
shrublands and mixed forests grow on lower slopes and valley floors
where moose and brown and black bears forage.

# 13) Cook Inlet Basin

This gently-sloping lowland was buried by ice and flooded by proglacial
lakes several times during the Pleistocene. As such, the basin floor 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 prevails 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** that support
**black spruce** forests and woodlands. Ericaceous shrubs are dominant
in open bogs. Mixed forests of white and Sitka spruce, aspen and birch
grow 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 bears, beavers, 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** grows in
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 be 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, paper
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. These mountains are home to moose, bears, wintering caribou,
and various furbearers.

# 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 through time. Common forest animals include
black and brown bears 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 five 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 grow sporadically
where soil drainage affords (e.g., moraines, stream levees, and uplifted
beach ridges). Rare dusky Canada geese and trumpeter swans nest on these
wet flats where brown bears, 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 rain shadow** of the
St. Elias Mountains whereby moisture from the Pacific Ocean is
effectively wrung from the atmosphere as weather systems rise over these
towering peaks. Deformed sedimentary and volcanic rocks of the
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** occur. **Permafrost is discontinuous** with the presence of
frost action features such as solifluction lobes, ice-wedge networks,
and patterned ground. Vegetation is principally **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 bears, caribou, moose, wolves, and wolverines.

# 18) Kobuk Ridges and Valleys

A series of **paralleling ridges and valleys** radiate southward from
the Brooks Range. 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. Thin
to moderately thick permafrost 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 the 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 on ridges. Trees become increasingly sparse,
less robust, and restricted to lower elevations in the west -- here
forests are slowly invading along rivers and streams (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 this island group is still recovering from the last
glaciation. For instance, trees did not survive the last Pleistocene
glaciation, and only recently have Sitka spruce and black cottonwood
managed to regain a foothold. Today **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**. A seemingly
endless stream of moisture blows in during the fall from repeating 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 otters, 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 nest on the islands' rocky shoreline
cliffs.

# 20) Kuskokwim Mountains

This **subdued terrain** is comprised of **old, low rolling mountains**
that have eroded 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 composed 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. These mountains support abundant moose, bears, beavers, and
scattered caribou herds.

# 21) Lime Hills

The Lime Hills are **glacially dissected mountains** descending from the
west side of the Alaska Range. The effects of **heavy glaciation** are
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, while 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 are confined to valley bottoms and mountain
toeslopes. These habitats support moose, bears, caribou, and various
furbearers.

# 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, more moist, 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
modest elevation, most of these hills have been spared from recent
glaciations and were part of the ice-free Beringia corridor linking
North America and Asia. 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
ranges from thin to moderately thick. Ecological affinities to Asia
exist to this day with the presence of Eurasian birds (gray-headed
chickadee, yellow and white wagtails, bluethroat), fishes (Alaska
blackfish), and flora. Vegetation patterns generally follow the terrain,
with *Dryas*-lichen and sedge-ericaceous shrub tundra on hilltops,
grading into short, then tall, willow-birch-alder shrublands and
eventually spruce and birch woodlands at progressively lower elevations.
Moose, brown bears, caribou, arctic foxes, and Alaska hares are common.
Ribbon seals and walruses comb the coastline, and huge summer runs of
pink salmon ascend the Unalakleet drainage.

# 24) Ray Mountains

The Ray Mountains are an **overlapping series of compact, east-west
trending ranges** underlain by the 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. 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 somewhat moist, warm summers. The vegetation is
dominated by **black spruce woodlands**, while white spruce, birch, and
aspen usually are restricted to warm, south-facing slopes. Floodplains
are dominated by white spruce, balsam poplar, alders, and willows. Shrub
birch and *Dryas*-lichen tundra prevail at higher elevations. Forest
fires occasionally occur in the summer. The clear headwater streams are
important habitat for **arctic grayling** and of minor importance to
king, chum, and coho salmon. Moose, brown bears, wolves, red fox, lynx,
and marten are common land dwellers.

# 

# 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 ranges
from thin to moderately thick. Soils are often wet, shallow, and organic
because of 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 Chukchi Sea and
Bering Strait afford very little climatic moderation since ice spans
these waters over much of the year allowing direct passage of bitterly
cold air from Siberia. Persistent cold, windy conditions occur in the
winter and fog blankets the coastlines in the summer. At its height,
Pleistocene glaciation covered only the highest 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 with the presence of Eurasian birds (gray-headed chickadee,
yellow and white wagtails, bluethroat), fishes (Alaska blackfish), and
flora. Streams occupy all larger valleys, and many lakes lie in 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. Bears, caribou, snowy owls, arctic foxes, and
Alaska 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. The undifferentiated sediments of fluvial and glaciofluvial origin are capped by varying thicknesses of eolian silts and organic soils. Sand dune fields and glacial moraines occur in some areas. 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, patches of impermeable permafrost, and poor soil drainage. Permafrost is thin and discontinuous, and temperatures are near the melting point. **Collapse-scar bogs and fens** caused by retreating permafrost are frequent and related to climate warming since the Little Ice Age. Streams flowing across this north-sloping plain ultimately drain into one of two large river systems \-- the Tanana or Kuskokwim. Groundwater-charged seeps and springs are common in gravel deposits. **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 south-facing slopes. The coldest, wettest areas on permafrost flats support birch-ericaceous shrubs and sedge tussocks. Tall willow, birch, and alder communities are scattered throughout. The mosaic of habitats supports moose, black bears, beavers, porcupines, trumpeter swans, and numerous other waterfowl.

# 27) Wrangell Mountains

This **volcanic cluster** **of towering, ice-clad mountains** is at the
northwest edge of the St. Elias Mountains. This exceedingly steep,
rugged terrain is the result of the ongoing collision of the Pacific and
North American tectonic plates. Here, relatively recent volcanic flows
and debris form a carapace over the Wrangellia terrane. 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 sheer height of the Wrangell Mountains allows
interception of moisture-laden air emanating from the north Pacific
Ocean. The abundant maritime snows feed **extensive icefields and
glaciers** interspersed by **dull gray ridges** draped with **rock shard
slopes** and patches of **alpine meadows**. The climate grades to 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 grow along larger drainages. The Wrangell Mountains are
highly dynamic due to **active volcanism, avalanches, landslides,
glaciers, 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 is associated with the lower stretches of the Yukon and Koyukuk Rivers in west-central Alaska. Although this area was unglaciated, meltwater flushes deposited vast quantities of sediment within these riverine corridors during glacial retreat. As such, deep deposits of undifferentiated sediments underlie these floodplains and adjacent lowlands. A seasonally moist continental climate prevails with cool, moist summers and cold, dry winters. Permafrost is absent along the younger floodplains, but is thin, discontinuous, and relatively "warm" on the abandoned floodplains in the adjacent lowlands. Poor drainage caused by permafrost contributes to the prevalence of wet, organic-rich soils. Collapse-scar features from thawing permafrost are common. Water levels drop in the Yukon River and its tributaries in early fall during freezeup and remain low until spring breakup when substantial ice-jam flooding can occur. The vegetation along the major rivers is highly productive and supports vigorous stands of white spruce and balsam poplar. Active floodplains and riverbars support tall stands of alders and willows. Robust wet sedge meadows and aquatic vegetation reside in infilling sloughs and oxbow ponds. The adjacent permafrost-dominated lowlands support black spruce woodlands, and birch-ericaceous shrubs and sedge-tussock bogs. Many flat organic surfaces are pockmarked with dense concentrations of lakes and ponds. These areas support large populations of moose and black bear, the oxbow sloughs and thaw ponds support abundant waterfowl, and the lowland forests are important to furbearers. The large rivers support important runs of chinook, chum, and coho salmon. 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 delta** as
they fan out to meet the Bering Sea. The delta was formed from a
combination of heavy sediment load carried by glacial runoff and from
stabilization of sea levels after an initial rapid rise during
deglaciation. The unconsolidated sediments are comprised principally of
marine tidal flats, beach deposits, and alluvium. Isolated basalt hills
and volcanic cinder cones jut up in places. 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. Permafrost is discontinuous, moderately thick to thin,
and relatively "warm." Impeded subsurface drainage caused by the
permafrost contributes to **shallow** **organic soils**. Thermokarst
lakes are abundant across the delta. **Many low-gradient streams
meander** dynamically across the surface. Coastal vegetation is
dominated by highly productive brackish marshes and wet meadows. Inland,
permafrost-dominated landscapes support low birch-ericaceous shrubs and
sedge-tussock and sedge-moss bogs. Willow thickets occur along rivers
and on better-drained slopes. The diverse and abundant wetlands support
**exceptional populations of waterfowl** (including brant, emperor
geese, and tundra swans), sandhill cranes, shorebirds (Sabines' gulls,
black turnstones, western sandpipers). Whales, walruses, and bearded and
ribbon seals patrol its shore while black bear, moose, and wolves roam
the land. Arctic char, sheefish, and all five 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
**depositional fans, terraces, pediments, 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 eolian 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
floodplains**. Opaque with glacial silts and shoreline mud, the Yukon
River forms an **aquatic maze** of islands, sandbars, meander sloughs,
and oxbow lakes as it crisscrosses the lower flats. The rich aquatic
habitats support tremendous concentrations of **nesting waterfowl** (in
the millions!) 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 **broad, rounded mountains** of moderate height are underlain by
the metasedimentary Yukon-Tanana terrane. This terrane is a composite of
transported crust blocks that includes former volcanic island arcs and
continental shelf deposits. Most surfaces are comprised of bedrock and
coarse rubble on ridges, colluvium on lower slopes, and alluvium in the
deeply incised, narrow valleys. **Climate is strongly continental** with
warm summers and very cold winters. The region is underlain by
discontinuous permafrost on north-facing slopes and valley bottoms. In
valley bottoms, permafrost is thin, ice-rich, and relatively "warm."
Vegetation is dominated by white spruce, birch and aspen on south-facing
slopes, black spruce on north-facing slopes, and black spruce woodlands
and tussock and scrub bogs in valley bottoms. Floodplains of headwater
streams support white spruce, balsam poplar, alder, and willows. Above
treeline, low birch-ericaceous shrubs and *Dryas*-lichen tundra
dominate. This area has the **highest incidence of lightning strikes**
in Alaska and the Yukon Territory, causing frequent forest fires.
Caribou, moose, snowshoe hares, marten, lynx, and black and brown bears
are plentiful. The area's abundant cliffs are important to peregrine
falcons. The clear headwater streams are important spawning areas for
chinook, chum, and coho salmon.