Nabesna Road Geology

The Nabesna Road provides opportunities for beautiful views and interesting geology

 

Mile 0
Turnoff from the Glenn Highway, also known as the Tok Cutoff.

Mile 0.2
The Slana Ranger Station is on the south side of the road. Be sure to stop by for current road conditions, maps, and park information.

Mile 1.7
Slana River Bridge. The Slana River drains southward off of the Mentasta Mountains. It empties into the Copper River just two miles downstream from this bridge. Looking straight down the road, the glaciated summit of Noyes Mountain can be seen 25 miles away. At an elevation of 8,235', Noyes is the highest peak in the Mentasta Mountains; its summit is on the park's northern boundary. The Mentastas run in a northwest/southeast direction from Mentasta Pass to the Nabesna River. From there the slightly higher Nutzotin Mountains continue into Canada. These two mountain ranges are the eastern edge of the Alaska Range which arches across the state. Mt. McKinley and Denali national park are also in the Alaska Range, but a few hundred miles to the west.

 

The first several miles of the Nabesna Road traverse relatively flat landscape underlain by accumulations of relatively young sediment. Much of this material is stream sediment, but a good deal of it, especially the beds of silt and fine sand, was deposited in huge glacial lakes which formed when glacial ice blocked off the stream valleys. Additionally, you will see many deposits of coarse gravel that were laid down by the glacial ice itself.

Mile 5.0
You are entering the Park/Preserve at this point. You may notice that many of the culverts beneath the road have small diameter pipes extending from both ends. These are installed to solve a problem that occurs in permafrost areas such as this. Each fall and winter, the culverts freeze full of ice. This is not a problem during winter, when there is no running water through the culvert. As temperatures warm each spring, however, melting snow sends water down the drainages where it is impounded behind the solidly frozen culverts. Such waters flood the road and may cause damage by erosion or ice. To avoid this, highway maintenance crews connect truck-mounted steam boilers to the small pipes to melt the ice and open the culverts.

 

Mile 15-18
Along this stretch of road there are several points from which prominent peaks of the Wrangell Mountains can be seen. All of these peaks are built up of the Wrangell Lavas, the general term for lava flows and volcanic rocks of this area. Ages of these rocks range from 10 million years to very recent. The conspicuous high glaciated conical summit to the southwest is Mount Sanford, the fifth highest mountain in the United States with an elevation of 16,237'. It shows the typical form of a strato-volcano (sometimes called a composite cone).

Mount Wrangell is the more distant, rounded and glacial covered dome southeast of Mount Sanford, with its summit of 14,163'. It is the park's only active volcano and occasionally steam plumes can be seen rising from its summit. Mount Wrangell's broad, gentle form is an excellent example of a shield volcano, in fact, it is the largest andesite shield volcano in North America. Stratovolcanoes form from thick, sticky, viscous lava that does not flow readily. Because of its thick nature, development of the volcano is through infrequent, but violent explosive eruptions. The resulting ash, cinders, and lava form steep slopes as they pile up. Shield volcanoes develop from more fluid lava. Because the lava flows more easily, shield volcanoes have more frequent, but less violent eruptions. These eruptions produce only limited amounts of ash and cinders, but large volumes of lava that flows into gentle slopes.

 

Mount Sanford (16,237') as seen from the Nabesna Road.

 

North of Mount Sanford and nearer to the road is the jagged prominence of Capital Mountain, with a summit elevation of 7,731'. The jagged dark colored ridge north and east of Mt. Wrangell is topped by 9,240' Tanada Peak. Capital Mountain and Tanada Peak are both remnants of once large shield volcanoes like Mount Wrangell, but their volcanic activity ceased and their summits have been heavily eroded and sculpted by the force of glaciers. Geologic studies and potassium-argon dating have indicated that the entire Tanada Peak shield volcano was formed between one and two million years ago and eroded to its present shape only during the last million years. On a clear day, Mount Jarvis can be seen over the right shoulder of Tanada Peak. It too is composed of lavas between one and two million years old, and its summit rises to 13,421 feet.

Flowing northward from the great ice fields of Mount Wrangell is the Copper Glacier. Its meltwaters give rise to the Copper River which flows northward off the mountains, and then westward along the end of the Wrangell Range. From there is turns southward and finally reaches Gulf of Alaska near Cordova. It is the only stream that cuts through the coastal barrier of the Chugach Mountains. Along much of its length, the Copper River marks the western boundary of Wrangell-St. Elias National Park and Preserve.

 

Mile 24.7
Watershed Divide. This is the highest point along the Nabesna Road with an elevation of 3,320'. Waters flowing west and south from here are carried into the Copper River and ultimately the Gulf of Alaska. Waters flowing easterly from here are carried by Jack Creek into the Nabesna River and on through the Tanana River to the Yukon River which empties into the Bering Sea.

 

Mile 27
Toward the northeast in the Mentasta Range is a conspicuously multi-colored mountain. The lower slopes are made up of dark reddish-brown and greenish-gray rock unit known as the Nikolai Greenstone. On top of these dark rocks rests a light colored (gray and tan) limestone. Both rock units date to the Triassic. Stream and gravity transport of limestone rubble down valleys and gullies has produced the prominent light stripes extending down the mountain slopes.

Mile 28
The ridges north and south of Twin Lakes are composed of gravels deposited along the margins of glaciers. Such glacial rock dumps are called glacial moraines. These moraines were formed during the Wisconsin Glaciation. This was the last great ice age; it reached its maximum advance 18,000 years ago when ice covered much of Alaska, almost all of Canada, and extended well into the northern states.

 

Mile 29.4
Trail Creek Crossing. Because this creek changes course frequently and carries a huge amount of sediment and debris, it is not practical to install a bridge or culverts...so the stream must be forded. Although the stream bed usually provides a fairly solid gravel footing, be very careful to avoid sandy or muddy areas. High water levels are sometimes produced by rain or hot weather that accelerates melting upstream. During high water, 4-wheel drive is highly recommended.

Low clearance vehicles can make this crossing when conditions are favorable, but exercise extreme driver caution.

Mile 30.8
Lost Creek Crossing. Same as previous crossing. Use extreme caution.

 

Use caution when water is crossing the road.

 

Hiking the Skookum Volcano Trail

Mile 32.5
The two flat topped hills south of the road are composed of the Wrangell Lavas partially mantled by rock debris and soils that contain permafrost. During summer thaws of this frozen terrain, surface materials are slowly transported downslope by creep and semi-fluid flow. The hummocky area at the base of the western hill was produced by an ancient landslide.

Mile 41-46
The jagged peaks south of the road are dominated by volcanic rocks ejected from the Skookum Creek Volcano. Volcanic Ash and hot gasses formed a fiery cloud which flowed down the flanks of an ancient volcano to produce the tan and light gray, conspicuously bedded rocks. Lava which issued from several nearby volcanic vents flowed downslope and solidified to produce the more massive pinkish-tan rocks. Radioactive dating of these rocks by USGS investigators shows that Skookum Creek Volcano was active between two and four million years ago. Deep canyons and steep slopes show that erosion has been very effective in wearing down the land during the last two million years. The trailhead for the Skookum Volcano Trail is located at mile marker 36.2.

 

Mile 42
Devil's Mountain Lodge and Airstrip. This is the end of the state maintained Nabesna Road. From here on, the road is privately maintained for access by four-wheel drive vehicles to the privately owned Nabesna Mine. Obtain permission from the mine owner prior to visiting private property.

The Nabesna Mine went into production in the early 1930's and had produced over $1,870,000 in gold by the time that large scale mining ceased in 1940. Limited, small scale mining has continued since then. The mine entrance is on a very steep slope high up on White Mountain, so ore had to be transported hundreds of feet by aerial tramway down to the processing plant at the base of the mountain. The primary ore materials are gold-bearing pyrite and chalcopyrite which occur in limestone along with other metallic minerals such as magnetite, pyrrhotite, and pyrite. These mineral deposits probably formed when metal and quartz-rich fluids migrated from an underground chamber of molten material into nearby limestone where they cooled and solidified.

 

Nice views from above the Rambler Mine

 

Continue on foot:
Miles 42 to 46 of Nabesna Road make for interesting hiking and the mine buildings and tailings are visible from the road. Drive to the end of the maintained road, and drive through the Devil’s Mountain Lodge property. About 1/3 mile further, there is a gravel parking area. This is the best place to park your car.

Approximately 1/3 mile past the parking area, a trail leads south towards the remains of the abandoned Rambler Mine, an area that was active after WWII, but never patented, and now part of the park. The trail is steep, but the effort rewards you with superlative views of the Nabesna River and Nutzotin Mountains.