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Geology & Ecology

Your Montour Trail visit can be far more than a walk, run, bike ride or cross-country ski workout. You can experience a trip through geologic time, a retreat from the concrete jungle, or a search for ghost train tracks. Don’t forget to observe the flora, fauna and stunning scenery all along the route!


The sedimentary rocks exposed along the Montour Trail record a time in Earth’s history when coal, limestone, shale and sandstone formed. Geologists name this time the Pennsylvanian Period (318 million years ago to 299 million years ago). Geological processes also formed our fossil fuels: coal, oil and natural gas. Coal formed in ancient peat swamps when Pittsburgh was near the equator, the climate was tropical, and glaciers where at the polar regions.

As the climate warmed, the sea level rose; when it cooled the sea level fell. This affected how sediments were deposited, forming coal on a broad coastal plain with peat swamps, marine limestone in the seaway, sandstone in streams, shale on river banks, and brackish to fresh-water limestone in lakes.

The McDonald oil field, first discovered in the 1890s, produced oil from the 370-million-year old Devonian-age Gordon sand, sited approximately 2,000 feet below the Pittsburgh coal seam.  In comparison, the Marcellus shale natural gas deposit is more than 1.5 miles deep, or about 7,500 feet below the Pittsburgh coal seam.

The modern Ice Age, or Pleistocene epoch, began about 2.6 million years ago and ended about 12,000 years ago. Since the end of the last Ice Age, the warming climate has been slowly changing the modern landscape through stream erosion and landsliding that deposits alluvium sediments. These features can be observed from Mile 0.0 at Coraopolis to MP 25, the highest point at the National Tunnel, and to the end of the trail at Clairton, MP 46.6.

—Albert D. Kollar, Geologist, Carnegie Museum of Natural History


Ecosystems along the Montour Trail primarily comprise deciduous hardwoods and are typical of the Allegheny Plateau. Despite historical coal mining, logging, grazing and heavy industry, the recovering natural areas along the trail are now made up of maturing stands of native species.

Floodplains support a diverse canopy of sycamore, box-elder, black walnut and silver maple trees. Swamps and vernal pools are prevalent and contain a diverse assortment of wildlife including wood ducks, frogs, turtles, salamanders and beaver. Upland forests along the trail include red oak, sugar and red maples, tuliptree and beech. Larger forest stands support many species of birds that require large patches of interior forest habitat. Spicebush is a common shrub along creeks and lower slopes. Wildflowers are prevalent in the spring. Higher up the slope, mountain laurel and lowbush blueberry grow in the understory beneath a canopy of oaks. Wild turkey and white-tailed deer are prevalent.

Aquatic habitats are also recovering. As with most other tributaries to the Ohio River near Pittsburgh, aquatic communities were devastated by industry and human development. Streams still reflect a history of heavy industry, but water quality has improved and the streams are now popular fishing destinations.

Wildflowers and native plants abound along the Trail all year long. Invasive plants — non-native species that harm native plants, wildlife and ecosystems — are a concern. They are especially problematic in areas that support spring wildflowers and can affect regeneration of the forest canopy. Problematic invasive plants include tree-of-heaven, Japanese knotweed and garlic mustard.

—Ephraim Zimmerman, Ecologist, Western Pennsylvania Conservancy