Treadwell Mine Historic Trail
Nature and industry
Treadwell has a well-documented history of mineral exploration going back to the first gold discovery in 1881. A booklet by Taku Conservation Society, available at the Juneau-Douglas City Museum, describes interpretive sites corresponding to numbered posts along the trails. The emphasis of that booklet is mining technology.
The natural history of Treadwell entwines intimately with the human story. Exploring it, we might ask: What are the geologic underpinnings that led gold-seekers to this part of Gastineau Channel? And how has vegetation responded to the abandonment of this once-bustling company town?
Many of the Treadwell mines were sited on marine sediment (blue stipple below), deposited during times of higher sea level, 9,000 to 14,000 years ago. Tunnels passed through these deposits to underlying bedrock in search of rich veins.
The mountainous crest of Douglas Island is formed of massive greenstones, a term for ancient volcanic rocks extruded as surface flows and later covered by sedimentary rocks, then folded and metamorphosed. This zone is not gold-bearing. Closer to Gastineau Channel, the greenstones are intermixed with slates, phyllites, and limey shales, black and fine-grained. This “black slate” zone is intruded by dikes of 91-million-year-old Treadwell diorite. Two of these pale, gold-bearing dikes were excavated by the Treadwell Glory Hole. The low grade ore could only be mined profitably at a gigantic scale. Those days are long past, but slate for crushed rock was mined from the Crow Hill Quarry above downtown Douglas up until the mid-1990s.
In addition to the glacio-marine sediments blanketing much of the gently sloping lowlands of Douglas Island, this map shows the ancient delta (brown stipple) underlying downtown Douglas. Raised deltas are well-drained and conducive to construction. Like Juneau’s Gold Creek delta, this one formed when sea level was several hundred feet higher. Bear Creek was then a distributary carrying sediment eastward from larger Lawson Creek, the actual source of the Douglas delta materials. Also mapped are the mine tailings (grey stipple) of today’s Sandy Beach.
Why is Treadwell deciduous?
To a naturalist, the most striking feature of the Treadwell Mine Historic Trail is the dominance of deciduous trees. It may take more than a century for these relatively short-lived alder and cottonwood to be over-topped and shaded out by rain-forest conifers.
Alder, cottonwood and willow (Salix spp.) all need exposed mineral soil to germinate. This happens most decisively when a major disturbance like a glacier or flooding river erases the previous forest and even the soils. An abandoned mining town offers similarly raw surfaces, particularly if it burns, as Treadwell did in 1911, 1926 and 1937.
In contrast, on the logged hillsides above Douglas and Treadwell, soils and understory plants were not removed. These hills came back in conifers. Sitka spruce (Picea sitchensis) and western hemlock (Tsuga heterophylla) are better than alders at sprouting in moss, and on stumps and rotting logs.
Deciduous forests of alder, cottonwood and willow attract birds otherwise uncommon in Southeast such as warbling vireo, hammond’s flycatcher, western tanager and downy woodpecker, and exceptional abundances of more widespread species such as myrtle warbler and hermit thrush (shown here). Most nest on or near the ground. Nest success is limited here by dog and cat activity.
In winter, porcupines perch high in spruce trees, ripping off twigs, chewing the needles, and tossing them to the ground. Look for these niptwigs near the trail, and for porky trees with thin, scraggly branches and foliage.
These plant associations are arranged from young to old, each responding to different disturbances.
Uplift meadow Juneau’s beaches are rising from the sea at about 0.5 inches per year–a process known as glacial rebound. Most local uplift meadows have a richer mix of species than Treadwell’s, which are dominated by ryegrass (Elymus mollis). Over time, fireweed (Epilobium angustifolium), cow parsnip, and ultimately forest will grow here.
Sitka willow The willows greeting hikers at the beginning of the Treadwell Historic Trail are already old for their species. Leaning over the path, they require pruning and propping. Look for silky hairs on the underside of the leaves that identify these as Sitka willows (Salix sitchensis).
Red alder Few of the Treadwell alders are older than the great fire of 1926. Once considered by foresters as a “trash wood,” red alder is now widely recognized for its commercial and ecological values. Symbiotic nitrogen fixation within alder roots–and abundant nutritious leaf litter–enriches the lush understory of ferns and berry bushes. These alders are now in “mid-life.” By 2050, the survivors will be majestic and moss-draped, with massive limbs and spreading crowns.
Spruce-hemlock second growth Photos of the hills behind Treadwell in the late 1800s show a 4-mile-long expanse of freshly logged stumps and bleached snags. The recovering forest is spruce-dominated, with interlocking crowns, smooth-textured on the air photos. In contrast, uneven-aged old growth has a rougher, “gappy” texture. The Treadwell conifer second-growth was slow to close canopy, so its relatively lush understory provides more winter deer forage than do most century-old clearcuts.
Hemlock-spruce old growth Upslope from the Treadwell Ditch Trail, bushwackers soon encounter unlogged ancient old-growth forest. Trees are more widely spaced and less uniformly sized than in the second-growth, with more snags and leaners giving an “unkempt” look. A massive hemlock has fallen in the background of this scene. Increased light fosters vigorous growth of blueberry (Vaccinium spp.) and five-leaved bramble (Rubus pedatus), important to deer in winter.
Trail AccessTo Cave-in Cove
Distance: 0.57 miles
Elevation gain: 10 feet
Notes: unusual mature deciduous forest
To Glory Hole
Distance: 0.51 miles
Elevation gain: 100 feet
Notes: climbs to view of the excavation
• Please leave mining artifacts in place for others to enjoy.
• Please do not pick or dig up wild flowers.
• Do not feed wildlife.Pack it out
• Carry out all trash.
• Please pick up after your pet.