Twenty Mile

The Twenty Mile Inventoried Roadless Area covers 198,775 acres within the Chugach National Forest in Alaska, occupying a broad reach of the western Chugach Mountains along Turnagain Arm. The area takes its name from the Twentymile River, which originates in glaciated high terrain and drains toward the head of Turnagain Arm. Major glaciers — including Raven Glacier, Milk Glacier, Twentymile Glacier, Crow Glacier, Lowell Glacier, and Learnard Glacier — feed headwater drainages that converge into named creeks: Peterson Creek, California Creek, Glacier Creek, Kern Creek, Winner Creek, Raven Creek, Milk Creek, Crow Creek, and Placer Creek. Carmen Lake, Crystal Lake, and Glenn Lake occupy glacier-carved basins within the watershed. Named landforms include Crow Peak, Jewel Mountain, Barnes Mountain, Goat Mountain, Hibbs Peak, Summit Mountain, Maynard Mountain, Boggs Peak, Raggedtop Mountain, and Begich Peak, with Crow Pass and Glacier Gulch marking key passages through the range.

The area's vegetation shifts with elevation and moisture conditions across its varied terrain. At lower elevations, Sitka spruce (Picea sitchensis) and black cottonwood (Populus trichocarpa) form the canopy of riparian corridors, giving way to mountain hemlock (Tsuga mertensiana) on mid-elevation slopes. Wet understories along stream margins support yellow skunk cabbage (Lysichiton americanus), devil's-club (Oplopanax horridus), and salmonberry (Rubus spectabilis). Subalpine zones are characterized by segmented luetkea (Luetkea pectinata) and purple mountain saxifrage (Saxifraga oppositifolia), with oval-leaf huckleberry (Vaccinium ovalifolium) and Alaska blueberry (Vaccinium alaskaense) forming open heath communities. Boggy depressions support bog rosemary (Andromeda polifolia), bog buckbean (Menyanthes trifoliata), and tall white bog orchid (Platanthera dilatata), within a moss layer dominated by stairstep moss (Hylocomium splendens) and lanky moss (Rhytidiadelphus loreus).

The Twentymile River watershed supports runs of pink salmon (Oncorhynchus gorbuscha), sockeye salmon (Oncorhynchus nerka), coho salmon (Oncorhynchus kisutch), chum salmon (Oncorhynchus keta), and chinook salmon (Oncorhynchus tshawytscha), which in turn sustain brown bear (Ursus arctos) and American black bear (Ursus americanus) at stream margins during spawning. Bald eagles (Haliaeetus leucocephalus) gather along salmon-bearing corridors. Rocky mountain goat (Oreamnos americanus) occupy steep terrain on upper ridges, while thinhorn sheep (Ovis dalli) range the high rocky ground of the Chugach Mountains. Among the area's confirmed bird species, the marbled murrelet (Brachyramphus marmoratus), classified as endangered on the IUCN Red List, depends on large-diameter old-growth conifers for nesting. The horned grebe (Podiceps auritus, IUCN: vulnerable) uses lakes and ponds within the watershed. Portions of this area fall within the potential range of several federally listed species; see the Conservation section for details.

A person following the historic Crow Pass Trail from Glacier Gulch moves through dense riparian Sitka spruce and cottonwood, where American dipper (Cinclus mexicanus) work the current of Crow Creek, then climbs into open subalpine heath where nootka lupine (Lupinus nootkatensis) and western columbine (Aquilegia formosa) color the margins of snowmelt runnels in summer. At the pass, vegetation drops below the knee as views open across Raven Glacier to bare rock and ice. Descending toward the Twentymile River drainage, the landscape shifts back through montane hemlock into riparian corridors thick with devil's-club and salmonberry.

The lands constituting the Twenty Mile Inventoried Roadless Area lie at the head of Turnagain Arm, where the Twentymile River flows to tidal waters in Southcentral Alaska. Indigenous people lived and occupied these territories for more than 10,000 years before European contact [2], including the Dena'ina and Alutiiq/Sugpiaq peoples, whose presence is attested by oral history and archaeological findings [1].

The first European contact with Alaska came in 1741, when a Russian expedition led by Vitus Bering arrived in the region [1]. Captain James Cook journeyed into Turnagain Arm and Prince William Sound in 1776 [2]. Russian commercial activity expanded across what became known as Russian America until the United States purchased the territory in 1867 for $7.2 million, a transaction in which Indigenous peoples were neither recognized nor consulted [1].

The Klondike Gold Rush brought a surge of prospectors to Southcentral Alaska in 1896. James E. Girdwood traveled north that May and staked placer ground on Crow Creek, adjacent to what is now the Twenty Mile area [5]. He established his base at Glacier City, a small distribution settlement on a trading and transportation route over the Chugach Range [5]. His Crow Creek Alaska Hydraulic Gold Mining Co. was operating some of the largest hydraulic plants in the Turnagain Arm region by June 1904 [5], and about 50,000 yards of gravel were removed in 1905 in pursuit of placer gold [5].

Rail access was essential to the region's extraction economy. The Alaska Central Railway, reorganized as the Alaska Northern Railway in 1909, laid standard gauge track north from Seward along Turnagain Arm [4][6]. By 1911, the railroad's end of track stood at Twenty Mile River, mile 65 from Seward, where boats met trains to offload freight and passengers bound for the gold-bearing Hope, Sunrise, and Knik districts [4]. Maintenance costs proved unmanageable, and the line never reached the interior coal fields it had targeted. In 1915 the federal government purchased the Alaska Northern — 71 miles of track — at roughly 25 cents on the dollar, incorporating it into what became the Alaska Railroad [6][3].

Federal land administration in the region predated the gold rush. In 1892, President Benjamin Harrison established the Afognak Forest and Fish Culture Reserve as a precursor to the Chugach National Forest [2]. The Chugach National Forest was formally established by presidential proclamation in 1907, protecting vast tracts of Southcentral Alaska [1][2]. An early test of that protection came in 1910, when Forest Service Chief Gifford Pinchot was dismissed by President Taft following a dispute over Chugach land and mining interests [2]. The Alaska National Interest Lands Conservation Act of 1980 added nearly two million acres to the Chugach National Forest [1]. Today, the 198,775-acre Twenty Mile area is protected under the 2001 Roadless Area Conservation Rule within the Glacier Ranger District.

Vital Resources Protected

Cold-Water Stream Integrity and Salmon Habitat

The roadless condition of the Twenty Mile area preserves an unaltered drainage network of exceptional scale. The Twentymile River and its tributaries — Crow Creek, Kern Creek, Winner Creek, Placer Creek, Raven Creek, Milk Creek, and Peterson Creek — drain directly from glaciers including Raven Glacier, Milk Glacier, Twentymile Glacier, Crow Glacier, and Learnard Glacier. Without road crossings, these streams maintain uncompacted streambeds and undisturbed spawning gravels that support Pacific salmon runs. Intact riparian corridors buffer water temperature and filter sediment, conditions critical to anadromous fish productivity across the entire watershed.

Old-Growth Structural Complexity and Forest-Dependent Species

The roadless forests of the western Chugach Mountains provide nesting habitat for species requiring structurally complex, unfragmented old-growth stands. The marbled murrelet (Brachyramphus marmoratus, IUCN: endangered) is the clearest indicator: the only North American seabird that nests inland, laying a single egg directly on the large-diameter branch of an old-growth conifer, sometimes miles from the ocean. This species does not use structurally simplified or young-growth forests. The roadless condition of the Twenty Mile area maintains interior forest blocks large enough to preserve the murrelet's nesting-to-foraging connection between old-growth stands and marine feeding areas on Turnagain Arm.

Subalpine Ecosystem Integrity and Elevational Gradient Connectivity

The full elevational gradient — from glaciated peaks through subalpine heath to riparian bottomland — remains uninterrupted by road infrastructure across this 198,775-acre area. Thinhorn sheep (Ovis dalli) and rocky mountain goat (Oreamnos americanus) move seasonally between high rocky terrain and lower feeding areas along undisrupted corridors. The white bog orchid (Platanthera dilatata, IUCN: vulnerable) and other subalpine wetland specialists depend on undisturbed hydrological function — intact snowmelt seep and bog communities that road drainage modifications sever. Species with narrow climate tolerances depend on continuous elevational gradients to shift their ranges as temperatures change; the roadless condition preserves that connectivity.

Potential Effects of Road Construction

Sedimentation and Spawning Substrate Disruption

Road construction on the steep slopes of the western Chugach Mountains generates chronic sedimentation through cut-slope erosion, drainage diversion, and culvert installation. In glacially fed streams, where spawning gravels are composed of well-sorted material from glacial outwash, road-derived fine sediment embeds those gravels, reducing intergravel oxygen flow and lowering egg survival rates. Restoration of streambed substrate complexity is technically difficult and rarely complete once a watershed has been altered by road-related disturbance.

Fragmentation of Old-Growth and Edge Effects on Forest-Dependent Species

Road clearing creates forest edges that penetrate interior stands, altering light conditions, wind exposure, and the structural character old-growth specialists require. For the marbled murrelet, fragmentation increases the proportion of edge habitat relative to interior and exposes nesting sites to elevated predation from corvids that follow road corridors. Because marbled murrelets rely on trees that take centuries to develop nesting-quality branch structure, old-growth lost to road construction cannot be replaced on any management-relevant timescale.

Invasive Species Establishment via Disturbed Corridors

Road corridors in subarctic environments function as invasion vectors for non-native plant species, which colonize disturbed mineral soils along cut slopes and rights-of-way before spreading into adjacent native communities. In the wet subalpine and riparian zones of the Twentymile River watershed, invasive colonization can displace native plant communities and alter nutrient cycling and soil moisture dynamics. Once established, invasive species in these low-disturbance systems are extremely difficult to eradicate.

Hiking and Backpacking

The Twenty Mile area is reached from several trailheads near Girdwood and Portage, with a trail network covering terrain from riparian corridors to glaciated passes. The Crow Pass Trail (Trail 101), accessed from Crow Pass Trailhead, runs 4.2 miles on native material through Glacier Gulch to Crow Pass, passing Raven Glacier en route. The trail is part of the Iditarod National Historic Trail (INHT) and continues across the mountains toward Eagle River — the full crossing is a challenging multi-day route. The Upper Winner Creek Trail (Trail 131, 8.4 miles, open to hikers and bikes) branches from Winner Creek Gorge Trailhead and follows the drainage deep into the roadless interior. Shorter hikes include the Kern Creek Trail (Trail 120, 0.8 miles), the Peterson Creek Trail (Trail 132, 0.8 miles), and the Eagle Glacier Crow Creek Trail (Trail 110, 2.3 miles). The Monarch Mine Trail (Trail 108, 0.9 miles) follows the INHT alignment near the area boundary. Dispersed camping is available throughout the roadless interior; designated facilities include Black Bear Campground and Williwaw Campground.

Fishing

The drainages within the Twenty Mile area support all five Pacific salmon species. Pink salmon (Oncorhynchus gorbuscha), sockeye salmon (Oncorhynchus nerka), coho salmon (Oncorhynchus kisutch), chum salmon (Oncorhynchus keta), and chinook salmon (Oncorhynchus tshawytscha) run through the Twentymile River, Crow Creek, Kern Creek, and Winner Creek drainages. Eulachon (Thaleichthys pacificus), a small smelt species that runs in large spring aggregations in glacially influenced drainages, are also documented in the watershed. Access to named streams is available from the trail system; Crow Creek and Kern Creek are reachable via their respective trails. Alaska Department of Fish and Game regulations apply; anglers should confirm current season and retention rules before fishing.

Wildlife Observation and Birding

The Twenty Mile River mouth is one of the most productive birding locations in Southcentral Alaska, with 130 confirmed species and 278 eBird checklists documented. Trumpeter swans (Cygnus buccinator), harlequin ducks (Histrionicus histrionicus), and common mergansers (Mergus merganser) use the estuary and lower river. Bald eagles (Haliaeetus leucocephalus) concentrate along salmon-bearing corridors during run periods. The Crow Creek Road corridor and lower Winner Creek Trail are active birding routes with 64 and 72 species confirmed, respectively. Along Crow Creek, American dipper (Cinclus mexicanus) work the current year-round; golden eagles (Aquila chrysaetos) and peregrine falcons (Falco peregrinus) patrol cliff faces and ridgelines above Glacier Gulch.

Brown bear (Ursus arctos) and black bear (Ursus americanus) move through riparian corridors during salmon runs; standard bear awareness practices apply throughout. Mountain goat (Oreamnos americanus) and thinhorn sheep (Ovis dalli) are visible on upper rocky terrain above Crow Pass. Moose (Alces alces) use lower riparian vegetation along the Winner Creek drainage.

Access and Conditions

The trail network connects to the Girdwood area approximately one hour south of Anchorage via the Seward Highway. Primary access points include Crow Pass Trailhead, Winner Creek Gorge Trailhead, Trail of Blue Ice Trailhead, and Five Fingers Trailhead. Trails are open year-round; snow covers high routes including Crow Pass from late fall through spring, and conditions can change rapidly at elevation. Avalanche terrain is present above timberline.

The roadless condition of the Twenty Mile area is directly tied to the backcountry character of these trails. Without road infrastructure penetrating the interior, the trails remain quiet, the stream corridors are undisturbed, and the wildlife movement patterns — particularly salmon runs and bear activity along those drainages — continue unaltered. Fishable streams accessible only on foot, and birding sites productive because the estuary and river corridors remain intact, are the direct product of the area's roadless designation.