0.0

Begin at junction of US Highways 385 and 20 on the West edge of Chadron; drive West.

2.1

Turn North on Highway 385.

Follow Loop 2 route between 385/20 turnoff and Maverick Junction.

49.8

Maverick Junction; turn West on US 385 toward Hot Springs.

54.6

Bypass, US highways 385 and 18.

0.0

Turn left onto US 18 bypass (Mammoth Site turnoff).

1.1

Hot Springs Mammoth Site

1.9

Junction of Highway 18; turn West toward Edgemont and Mule Creek Junction.

48.4

Mule Creek Junction. Junction of Highways 18 and 85; turn North on Highway 85.

82.4

Newcastle; continue North on Highway 85.

Red butte

100.4

Four Corners; junction of Route 585 and US Highway 85; continue North.

127.4

Drive West on Route 585 toward I-90

129.4

Interstate 90

0.0

Turn West on I-90

1.0

Sundance Mountain; exit North to Devil's Tower.

16.0

Devil's Tower and three volcanic remnants.

20.0

Junction of Highways 14 and 24; turn North to Devil's Tower.

20.2

Sundance Formation exposed in the hillside East of highway. The Sundance is Jurassic age and mostly of marine origin.

24.5

Turnout; cliffs on East side of highway. This outcrop is also the Sundance Formation.

25.8

Devil's Tower; turnout on West side of highway.

Devil's Tower is called a volcanic neck, a remnant of the conduit through which magma flowed to the surface in an ancient volcano. The volcano formed by this activity has long since eroded away, but the harder rocks in the conduit remained behind as an erosional remnant.

The rock that makes up Devil's Tower is fractured into dramatic vertical polygons. These polygons are the result of fracturing of the rock by shrinkage as the magma cooled. This texture is typical of volcanic rocks and in intrusive rocks that were intruded near the surface.

26.7

Entrance to Devil's Tower National Monument.

0.0

Entrance; return to Junction of Highways 14 and 24.

6.7

Junction of Highways 14 and 24; turn West. Road curves South to Moorcroft.

16.9

The road cut on the West side of the highway exposes the Cretaceous age Skull Creek and Greenhorn formations. On the East side is exposed the Newcastle Sandstone.

Outcrop on West side

Outcrop on East side

33.0

Highway 14 to Moorcroft.

34.3

Interstate 90

0.0

Turn onto I-90 West

26.0

Gillette exit 128.

37.5

Hillside, unusual red

68.2

Hills North and South of interstate.

82.3

Hills at Crazy Woman Creek

93.5

Hillside North, more unusual red.

96.8

I-90 exit at Buffalo.

0.0

Buffalo exit; drive West to first junction.

2.2

First junction; drive West; road curves South, then West.

2.7

Junction of Highway 16 and Route 299.

6.8

Hill on South. This hill exposes the Eocene age Wasatch Formation.

8.5

Wasatch Formation (equivalent of the Wind River Formation in the Bighorn Basin). The Kinsbury Conglomerate is an exceptionally coarse unit in the Wasatch that was deposited in western Wyoming as a result of gravels being shed off the newly-rising Rocky Mountains.

Fold in Gros Ventre Formation.

Fold in Gros Ventre Formation.

10.7

Gros Ventre Formation (Cambrian) and Big Horn Dolomite (Ordovician).

11.3

Mafic dike of Precambrian age. A dike is an igneous intrusion with a tabular (slab-like) shape and that cuts across pre-existing rock layers. Igneous rocks that contain a high proportion of iron- and magnesium-containing (ferromagnesian) minerals are called mafic.

Fold in Gros Ventre Formation.

18.3

Top of Big Horn Mountain Range.

38.2

Precambrian granite gneiss.

Gneiss is a coarse-grained metamorphic rock that forms as a result of regional metamorphism. It usually shows a high degree of recrystallization of minerals and occasionally signs of melting. The characteristic most useful in identifying a gneiss is banding. Bands are the result of different minerals that form alternating layers in the rock.

This rock is called granite gneiss because it has a composition similar to the igneous rock granite.

51.8

Gallatin Formation

53.5

Big Horn Formation and view down Wind River canyon.

56.0

Madison Formation

58.2

Tensleep Formation

62.5

Downtown Tensleep

64.0

Hillside on North side of road exposes the Gypsum Springs Formation. The Gypsum Springs Formation consists of reddish mudstone and sandstone with beds of gypsum. This combination is typical of sedimentary rocks deposited in an arid environment. Gypsum is an evaporite mineral, formed from precipitation of the mineral out of sea water saturated through evaporation.

Fold in Gros Ventre Formation.

66.7

Hills on South. The rock unit exposed here is the Jurassic Morrison Formation. At many locations in Wyoming the Morrison is rich in dinosaur fossils and has been mined since the late 19th Century by museums around the world.

77.9

The hills on the North side of the highway reveal an outcrop of the Cretaceous Meeteetse Formation. The Meeteetse is also occasionally rich in dinosaur fossils.

84.3

The outcrops on the South side of the road are the Upper Cretaceous Lance Formation. The Lance was deposited during the closing moments of the Cretaceous, and records some of the last dinosaurs to live on Earth.

85.3

Mammoth site sign.

89.9

Worland; junction of Highways 16 and 20; continue West on Highway 16.

110.3

Outcrops of the Cretaceous Mesa Verde Formation.

115.1

Cliffs East of highway.

Lance (Cretaceous) and Fort Union (Paleocene) formations.

The Lance and Fort Union formations were deposited at the end of the Cretaceous and beginning of the Tertiary by streams flowing out of the rising Rocky Mountains. Meandering rivers and broad swamps in a tropical or subtropical setting left behind a complex package of sandy and muddy sediments and coal.

120.5

Bluff West of Highway. Sundance or Cloverly Formation.

123.1

Hot Springs State Park

0.0

Hot Springs State Park

0.1

Sulfur fountain

The tower surrounding this spring is a tufa tower, formed by crystallization of calcite and other minerals carried in the hot spring waters. As the water cools, it is not able to retain these minerals in solution and they crystallize out.

This tufa tower consists mostly of the mineral calcite. Colors are due to trace minerals in the hot waters and algae and other microorganisms living on the tower. The waters that deposit these minerals have a certain amount of dissolved hydrogen sulfide, the source of the "rotten egg" smell.

0.8

Hot Spring pools are located on the North end of the park, Dinosaur is located on the Southern end.

These flat-topped terraces are being formed by precipitation of minerals out of hot springs water. Hot water is capable of dissolving much more mineral matter out of the rocks it flows through than cold water. But when hot springs water reaches the surface it cools suddenly and is no longer capable of holding its large dissolved mineral content. Therefore, minerals, mostly calcite, are deposited.

The rock formed this way is called travertine.

1.5

Pools above the Big Horn River. The Nugget Formation (Jurassic age) is visible on the cliffs in the background.

0.0

Return to highway; drive West into Thermopolis.

0.6

Thermopolis; junction of Route 120, US 20, and Route 789; continue South.

4.5

Chugwater Formation (Triassic).

The Chugwater Formation is equivalent in part to the similar-looking Spearfish Formation in the Black Hills.

5.7

Phosphoria Formation (Permian).

Fold in Gros Ventre Formation.

7.3

Amsden Formation (Pennsylvanian).

Fold in Gros Ventre Formation.

9.8

Big Horn Dolomite (Ordovician)

Fold in Gros Ventre Formation.

15.4

Gros Ventre Formation (Cambrian).

Fold in Gros Ventre Formation.

16.9

Dike in Precambrian rock.

17.6

Third tunnel in Wind River Canyon, campground on the East. View looking back into the canyon.

Wind River Canyon was cut by the Wind River in its passage between the Wind River Basin to the south and the Bighorn Basin to the north. The river changes its name to the Big Horn River as it enters the Bighorn Basin.

Wind River is a good example of a superposed stream. It cuts right through the Owl Creek Mountains as if they were not there. This seeming paradox can be explained by imagining the landscape after formation of the Owl Creek Mountains and the other Rocky Mountain ranges. After uplift of the Rockies ended, near the beginning of the Eocene, about 40 million years ago, weathering of the uplifted rocks had created enormous volumes of sediment, which buried all but the highest peaks. Thus, at that time, the mountains would not have been as spectacular as today. Streams would have flowed across relatively flat plains with the mountains buried beneath.

Beginning in the Oligocene Epoch, 30 million years ago or so, western North America was uplifted again, but this time as a sort of gently-rising plateau. Rivers cutting through this plateau were rejuvenated, that is, their gradients increased, and they began to cut downward and form canyons. The Wind River was one of those. As it cut downward, it gradually eroded its canyon through the top of the Owl Creek Range. Later, most of the sediment fill that had buried the mountains was eroded away, leaving the high-relief topography we see today.

Flathead Formation East of highway.

19.3

Dinwoody Formation on South side of highway.

Fold in Gros Ventre Formation.

20.7

Dinwoody Formation

23.5

Highway passes between outcrops of Wind River Formation (Eocene).

25.9

Hills East of highway; Boysen Reservoir on the right.

33.9

Shoshone; junction of Highway 26, Route 789, and Highway 20.

0.0

Junction 26/20/789. Drive South on 20/789.

2.3

Cliffs on West.

Wind River Formation North of Boysen Reservoir.

3.9

Boysen Reservoir and cliffs.

6.1

Hills East of highway

22.7

Riverton; intersection of Main and Federal streets; continue South on Highway 26/Route 789.

29.1

Hills on East.

37.6

Hills on West.

40.4

Hills on both sides of highway. Hudson; continue South.

41.9

Hudson/Lander hill.

45.1

Cliffs East of highway.

Chugwater (Triassic) and Nugget (Jurassic) formations (above). The Wind River Range is visible in the background.

45.8

Cliff East of highway.

48.1

Junction of Highway 287 and Route 789 in Lander.

End of Loop 3.