Allegheny River Headwaters Watershed Conservation Plan

Allegheny River Headwaters Conservation Plan
Chapter 2. Land Resources
prominent ridge former. Most of the soils are frigid Inceptisols, derived from acidic glacial drift that are
stony, acidic, low in fertility, and often steep (Woods et al., 1999).
The natural vegetation throughout the ecoregion is primarily northern hardwood tree species, such as
sugar maple, yellow birch, beech and hemlock with some intermixed bogs, swamps, and marshes.
Appalachian Oak Forests, primarily containing white and red oaks, also occur. The soils, climate, and
ruggedness make the area well suited to trees and poorly suited for agriculture (Woods et al., 1999).
Rock Types
Within the Allegheny River headwaters region, there are five formations of rocks—Rock Units 7, 13,
14, 15, and 17. Unit 13 comprises shale and siltstone along major waterways, such as the Allegheny
River, Oswayo Creek, and Tunungwant Creek. Adjacent to it is Unit 7, which contains red sedimentary
rocks, such as sandstone, siltstone, shale, and conglomerate. The only exception is along Tunungwant
Creek, where Unit 15—comprised of shale or siltstone with minor amounts of sandstone—splits Unit 7
and Unit 13. Unit 14—comprised of sandstone with minor amounts of shale and siltstone—is adjacent to
Unit 7. Within the watershed, Unit 17 is the least common rock formation, and occurs furthest away from
the tributaries. It occurs in patches that are surrounded by Rock Unit 14. Rock Unit 17 is composed of
mixed sandstone and conglomerate with coal, shale, and siltstone (Berg, Sevon, & Abel, 1984).
Stratification
Sedimentary rocks cover 75 percent of the earth’s surface. They form from weathered, eroded rocks
or dissolved materials that precipitate out of solution. The sequence, or layering, of sedimentary rocks is
known as stratification. The changes in the sequence reflect changing conditions during deposition.
Pennsylvanian-aged rocks are the youngest in the project area, and they underlie the highest
elevations in the southern and western portions of McKean County. Belonging to the Allegheny and
Pottsville groups, they contain a primarily cyclic sequence of shale, siltstone, and sandstone, forming
soils within the Cookport-Hazleton association. Some coal is also found within the Allegheny formation
(Churchill, 1987).
Within the project area, the second-oldest rock is from the Mississippian age. Belonging to the
Shenango and Oswayo formations, these rocks are cyclic sequences of shale, siltstone, and sandstone
located primarily on valley sides (Churchill, 1987).
The oldest rocks within the project area are from the Devonian age and include the Catskill,
Venango, and Chadakoin formations. Rocks in the Catskill formation consist of red siltstone, shale, and
sandstone found in the Buchanan-Hartleton-Leck Kill soil association. The Venango formation is
comprised of gray siltstone, shale, and sandstone with some red shale from the Catskill formation. The
Chadakoin formation consists of gray siltstone, sandstone, and shale. Soils in the Buchanan-Albrights soil
association contain rocks from the Venango and Chadakoin formations.
Soil Characteristics
Soil Associations
Soil associations are landscapes with a distinctive pattern of soils. Typically, they contain one or two
major soil types and a few minor types. They are named for the major soil types in the association.
Different associations may have the same soils, but they appear in different patterns or percentages. The
most dominant soil in each association is identified first. Figure 2-3 displays the 13 soil associations
located within the project area.
2-3