Culbertson

The Fort Union Formation was deposited not long after the dinosaur extinction, about 65 million years ago. Rivers originating in mountains to the west and south carried abundant sediment to the nearby shallow inland sea to the east, crossing the subtropical, swampy coastal plain of eastern Montana on their way. As the rivers shifted, the swamp vegetation and peat were covered with thick deposits of sand, silt, and clay. In time, it compacted to form coal. The sand, silt and clay cemented and compacted into sandstone, siltstone, and mudstone. Eastern Montana has an estimated 200 billion tons of coal that developed from the vegetation of these swamps. Geologists classify much of the coal buried in northeastern Montana as lignite, which has a low energy content. Most of the coal is buried under layers of the soft rock in the Fort Union Formation, but is locally exposed in hill and road cuts. The scattered red rock of the Fort Union Formation is clinker. Clinker forms when lightning strikes, wildfires, or spontaneous combustion cause the coal to ignite and burn. The intense heat of burning coal bakes the adjacent sedimentary layers creating the dense, hard red rock.

Northeastern Montana is part of the Williston Basin, a slightly irregular, round depression centered in North Dakota that slowly subsided over hundreds of millions of years. Sediment that accumulated in the depression is now up to 16,000 feet deep in the basin. The Williston Basin is a major oil and natural gas province because it has all the right components and conditions for oil and gas formation: organic-rich deposits such as black shale to generate the oil and gas, reservoir rocks where it accumulated such as porous sandstone, and geologic traps. The traps are faults, folds, and lateral changes in the rocks that keep the oil and gas from moving out of the area of accumulation.

Geo-Facts:

• Oil is typically generated for organic-rich marine sedimentary rocks. It is accumulated in any porous and permeable rock. The reservoirs are most commonly found in limestones and sandstones deposited in a variety of environments.

• Oil and natural gas exploration has continued in the Williston Basin. In 2008, the Montana Board of Oil and Gas Conservation reported oil production of about 34 million barrels from the Williston Basin and about 1900 active producing wells.

• The Fort Union Formation is named for Fort Union, an American Fur Company trading post located near the confluence of the Missouri and Yellowstone rivers.

The post was active from 1828 to 1867 and is now a National Historic Site.

Geo-Activity:

• Keep a look out for the red rock and soil that can be found throughout eastern Montana; remember that the red color comes from coal seam fires which baked the surrounding rock.

Erected by Montana Department of Transportation.

Wherever you are in Montana, you stand in the pathway of Lewis and Clark. Their 1804-1806 expedition was a grand adventure to investigate the people and resources of the newly acquired Louisiana Purchase and to seek a navigable passage across the Rocky Mountains to the Pacific. Like the French and Spanish who made similar voyages across North America, the Corps of Discovery brought back information that would change life in this land forever.

Nations in Transformation

The 19th century brought tumult to North America. Indian nations, recovering from five waves of smallpox, pushed west as Europeans raced to conquer more territories. Though others had explored, traded and trapped in the Northern Plains, Lewis and Clark were the first to come for military, scientific and economic development reasons. Their expedition defined agendas and relationships that people of the West are still sorting out - between different cultures, and between people and the land.

Montana Legacy: Many Cultures, Many Landmarks

The Corps of Discovery included Indians, French, Euro-Americans, men of mixed European and Indian decent, one black, a woman and a baby. Indian people of many nations fed, guided and helped the Corps with few violent altercations. Montana today is a land of many cultures, and its diversity is part of our region's identity.

In what we now call Montana, Lewis and Clark explored 1,900 miles of wilderness, catalogued 63 species of plants and animals new to science, and charted significant geographic features. Seven the these are National Historic Landmarks and Monuments: Pompeys Pillar, the Great Falls Portage, the Three Forks of the Missouri, Lemhi Pass, Lolo Pass, Traveller's Rest, and the Upper Missouri Breaks.

There are still places in Montana where you may see landscape, wildlife and native plants just as the Corps described in their journals: rich, raw and full of possibilities. You can also see evidence of cultural cooperation, conflicts and collisions in values that have defined the West for two centuries.

Discovery, for all travelers, is a deeply personal and universally human experience. In the larger sense, Montana is continually discovered, its cultures are always transforming, and each of us is explorer, witness and storyteller.

Montana welcomes you to make discoveries of your own in this rich landscape. Please respect private property, help preserve out public lands and abundant wildlife and celebrate with us the mix of people who call Montana home.

Erected by Montana Department of Transportation.