Features
Glacier and Badlands byways: reading rock signs where plains meet peaks
Going-to-the-Sun Road and the Badlands Loop Road show how brown byway markers and wayside panels explain glacial and sedimentary rock across one long drive.
What to take away
- Going-to-the-Sun Road runs 50 miles across Glacier National Park and cuts Precambrian Belt rock: mudstone, argillite and dolomite.
- Badlands Loop Road, signed as South Dakota Highway 240, runs about 31 miles through Cretaceous shale, an ancient soil, and Oligocene fossil beds.
- Brown recreational signs and byway markers tell you which route you are on. Wayside panels do the geological explaining.
- Sign names such as Jackson Glacier Overlook and Yellow Mounds Overlook are literal labels for the ice and rock in front of you.
- Vehicles longer than 21 feet are barred from Going-to-the-Sun Road, so a big rig belongs on the Badlands loop instead.
Where plains meet peaks and the rock changes
Glacier and Badlands national parks sit at two ends of one long corridor. US 2 and Interstate 90 carry a driver from the Northern Rockies out onto the South Dakota plains.
The rock changes completely along the way. Glacier's cliffs are very old sedimentary layers, later lifted and carved by ice. The Badlands are much younger sedimentary layers, cut by rivers and rain. Mixed grass prairie covers the ground between them.
Signage is often the only guide you get. Brown guide signs mark recreation and cultural sites, a standard described in the Manual on Uniform Traffic Control Devices.
Byway markers do a second job. They confirm that a route is part of a recognized program, and the National Scenic Byways Program lists which roads qualify and how they are signed.
Before you drive either route:
Where plains meet peaks
- Carry a paper map, because cell service is thin on both roads.
- Fill the tank before turning onto the loop road.
- Check the park road status, since Logan Pass closes with snow.
Reading the signs on Going-to-the-Sun Road
Going-to-the-Sun Road is 50 miles long and crosses the Continental Divide at Logan Pass, 6,646 feet up. Crews built it in the 1920s and early 1930s. It holds National Historic Landmark status.
The rock beneath the pavement is Belt Supergroup, laid down as sediment more than a billion years ago. Altyn Formation dolomite and limestone cap Logan Pass. Grinnell Formation argillite gives nearby slopes their red and green stripes.
Wayside panels at Logan Pass explain stromatolites, the layered structures that ancient algae built in shallow water. Jackson Glacier Overlook names a glacier still visible from the pullout. Triple Divide Peak sends water toward three ocean drainages.
Signs here also carry rules. Vehicles longer than 21 feet are not permitted over the pass, so large RVs must use another route.
Badlands Loop Road markers and the layers below
Badlands Loop Road is signed as South Dakota Highway 240 and runs about 31 miles between Interstate 90 exits 110 and 131. Roughly 14 overlooks carry names.
Each marker names a landform or a rock unit. Yellow Mounds Overlook marks a fossil soil that weathered into yellow and purple. Pinnacles Overlook looks over spires cut into Brule Formation siltstone.
The wall sequence reads from the bottom up. Dark Pierre Shale is Cretaceous sea floor. The yellow mounds sit above it. Gray green Chadron claystone and pale Brule beds follow, both rich in Oligocene mammal fossils.
Fossil Exhibit Trail is a quarter mile boardwalk with casts of oreodonts, three toed horses and nimravid predators. Above the walls, mixed grass prairie feeds bison and hides prairie dog towns.
Example: matching each sign to the rock beneath
Matching each sign to the rock beneath
| Sign or marker | What it names | Rock or process behind it |
|---|---|---|
| Logan Pass wayside | Continental Divide crossing | Altyn Formation dolomite and stromatolites |
| Jackson Glacier Overlook | A shrinking glacier | Pleistocene ice, still carving rock |
| Yellow Mounds Overlook | Yellow and purple slopes | Fossil soil developed on Pierre Shale |
| Fossil Exhibit Trail | Mammal fossils | Chadron and Brule river deposits |
| Prairie Wind Overlook | Grass and sky | Mixed grass prairie on old soil |
Read the sign, then look for a color change in the wall. Color is the fastest clue that you have stepped onto a different rock unit.
A National Scenic Byway label signals that a state nominated the road and the federal program accepted it, and the designation itself shapes the marker you see at the entrance.
Comparing with other rock byways
Granite and volcanic rock tell a different story. Drivers who want that contrast should compare the granite signs in the Black Hills with the Cascade Lakes route near Bend, where the pavement sits on lava.
For a third kind of rock, red rock byway signs in Utah and New Mexico mark sandstone corridors where the layers are younger, drier and far more orange.
Common questions
How far apart are the two parks by road?
They sit more than 700 miles apart on US 2 and Interstate 90. Plan an overnight stop, often near Billings, Montana or in the Black Hills.
Which signs are brown, and which are not?
Brown guide signs mark recreation and cultural sites under the MUTCD. Numbered route markers, including South Dakota Highway 240, keep their own shapes and colors.
Can a large RV drive Going-to-the-Sun Road?
No. Vehicles longer than 21 feet are not allowed over Logan Pass. Park shuttles and smaller vehicles are the usual workaround.
Is the Badlands Loop Road paved?
South Dakota Highway 240 is paved. The connecting Sage Creek Rim Road is gravel for part of its length and can close after heavy rain.
