0.0

Begin at Junction - Highway 287/Route 789 at Lander, Southeast.

2.5

Salinization on West side of highway.

If the weather is dry, the soils in the valley next to the road will have a white coating of salt. This salt encrustation, or salinization is caused by evaporation of water containing dissolved salts. The soil is not permeable enough to allow the water to infiltrate, so it accumulates on the surface and evaporates in the desert sun.

8.6

Junction of Highway 287, Route 789, and Highway 28; continue South.

10.5

An exposure of the Cretaceous age Mowry Shale. The Mowry is distinctive in that it contains silica as a cement, making the rock harder than most shales and giving it a silvery color when weathered. The shale tends to have an abundance of fish scales

13.0

Cloverly and Morrison formations.

14.8

Slump West of highway.

A slump is a form of mass wasting, or slope failure, in which partly water-saturated material moves downhill on a curved surface. The top of this surface is usually marked by a small break in slope called a scarp. If the slump occurred recently, its scarp will look fresh, but with time vegetation covers slump scarps and they become indistinct. The lower parts of slumps frequently experience flow of water-saturated soil and soft sediment called earthflow.

16.2

The Jurassic Sundance Formation is exposed in the hillside West of the highway.

17.1

Cliff on North side of highway with exposure of the Nugget Formation.

18.0

An outcrop of the Triassic age Chugwater Formation. A limestone layer stands out in the middle of the Chugwater redbeds.

18.7

Red Canyon cliffs on the North and Phosphoria Formation on the South.

23.1

Roadcut on West side of highway exposes the Pennsylvanian Tensleep Formation.

25.1

The northern end of Limestone Mountain contains an outcrop of the prominent Bighorn Dolomite of Ordovician age.

25.9

Mountain side, West and opposite of Limestone Mountain. The Bighorn Dolomite is also exposed here. It is overlain by the Mississippian age Madison Limestone.

27.2

Roadcut on East side of the road with outcrop of the Cambrian-age Flathead Formation.

27.4

Atlantic City Iron Ore Mine

34.9

Rock Shop

48.7

Sweetwater River rest stop

72.0

The badlands-like outcrops next to the road are made of the Wasatch Formation of Eocene age.

78.6

Farson; junction of Highways 28 and 191; turn South on Highway 191.

86.6

Turn to Boars Tusk, just South of Eden.

0.0

To Boars Tusk and Red Desert. This route starts out on an blacktop old highway going Southeast and then turns into a gravel road going East.

3.7

The hillside on the North exposes the Eocene Green River Formation.

The shales and thin, slabby limestones of the Green River Formation were deposited as muds in a series of huge lakes that occupied this part of Wyoming and adjacent parts of Wyoming and Utah. In some places these shales are rich in fossils of many kinds of fish, invertebrates, and plants. In fact, they have been "mined" for years by commercial fossil collectors, who sell these fossils in shops around the world.

The Green River shales are also rich in kerogen, a petroleum precursor that can be processed into oil, gasoline, and other petroleum products. But the cost of mining and processing the oil shale has always exceeded the cost of conventional petroleum sources. Future economics, however, may indicate exploitation of these deposits.

8.9

Sand dunes are visible from the road. Boars Tusk is also visible.

Turn South

10.4

The hills on the West expose the Green River Formation. These exposures contain fossils.

Boars Tusk off to the East. You will need an all-wheel drive vehicle if you want to drive from here to the volcanic remnant.

Boars Tusk is a volcanic neck, the preserved remnant of the conduit through which magma spewed on the way to the surface. Typically, this rock is much harder and resists weathering better than the fragmental volcanic rock thrown from the volcano's vent. Thus, the internal workings of the volcano are more likely to be preserved as a topographic feature than the volcanic cone itself.

0.0

Return to Highway 191, North

8.0

Farson; continue North.

44.6

South Pass turnoff, East.

47.0

Louis Lake and Loop Road to Lander turnoff. Drive West.

78.2

Return to Lander; junction of Highway 287 and Route 789.

0.0

Lander; junction of Highway 287 and Route; turn Southeast.

8.6

Junction of Highway 287 and Route 789; turn East to Jeffrey City.

9.3

Hills on the East showing exposures of the Cretaceous Mowry Shale, the Jurassic Cloverly/Morrison, Sundance and Nugget formations, and the Triassic Chugwater. The rocks here are folded and dipping steeply into the hillside.

10.3

Hills on East

19.3

Hills on the North with exposure of the Upper Cretaceous Lance Formation.

28.3

Hill on the North side of the road exposing the Eocene/Oligocene age White River Formation.

82.8

Junction of Highway 287, Route 789, and Route 220.

0.0

Turn North on Route 220.

12.5

Precambrian - Devil's Gate.

19.2

Independence Rock

Independence Rock is a good example of an exfoliation dome. Granite, like all igneous intrusive rock, forms at depth under great pressure. Uplift, followed by millenia of erosion, were necessary to bring this huge body of rock to this place. Now, it is under very different conditions from those under which it formed. Granite frequently forms dome-shaped mountains like this one as a result of spalling off -exfoliation-of huge sheets of rock as the pressure of overlying rock is released.

38.3

Hills on West with outcrops of the Eocene Wagon Bed Formation.

55.6

Cliffs on East side of the road.

57.0

This photograph of the mountain side was taken on 1 July 1997; a forest fire occurred here just 9 days later.

57.3

Fire on the West ridge. This photograph shows the fire in progress on 10 July 1997.

59.1

The Triassic Alcova Limestone, a member of the Chugwater Group, is exposed on the West side of the highway. The distinctive Alcova is a prominent marker bed in central Wyoming.

59.9

Roadcut on West side of road.

60.1

Outcrop on the East side of road. This is the West slope of Casper Mountain.

60.3

Hills on the West. Fossil plants are found in this outcrop.

67.1

Casper Junction - CY Ave./Route 220

75.0

I-25 at Casper

0.0

East on I-25

17.4

Outcrop on North side of road. Cretaceous Mesa Verde or Cody formation.

17.5

Outcrop on South

55.6

Landscape East of the highway. Here the Miocene-age Harrison Formation is exposed. This is the same stratigraphic unit that contains the fossils at Agate Fossil Beds National Monument.

Orin Junction; junction of I-90 and US Highways 18 and 20.

0.0

Turn East on Highway 18/20 to Lusk Junction and from there continue East on Highway 20.

65.9

Nebraska/Wyoming state line.

66.8

Landscape North of highway.

75.1

Junction of Highway 20 and Route 29. This is the turn to Agate Fossil Beds National Monument. Continue East.

92.7

Roadcut on the North side of the highway.

93.7

Roadcut exposing the Harrison Formation.

100.9

Cliffs above Fort Robinson.

100.9

These cliffs are exposures of the Miocene-age Arikaree Group, containing the Gering and Monroe Creek formations.

102.3

Crawford; junction of routes 2/71 and US Highway 20; turn North, then East.

Trunk Butte. This landmark South of the highway contains good exposures of the Oligocene Brule Formation.

Chadron

125.8

End of Loop 4