Geology - Pennsylvania Highlands

Geology

The Pennsylvania Highlands are the foothills of the Appalachian Mountains.  The irregular ridges and deep valleys of this unique landscape feature common themes that reflect the region’s geology, which in turn has influenced local history and land use.

Although the geology of the Highlands is complex, two types of rock are common to the erosion resistant, largely forested ridges: diabase (basalt), and granitic gneiss and quartzite. The diabase areas in particular have created natural limitations for agriculture and land development. As a result these areas feature large contiguous woodlands such as Hopewell Big Woods and Unami Hills.

The high iron content found in the gneiss and quartzite rock ridges provided the raw material for the region’s industrial legacy of iron and steel. This legacy is reflected in the names of towns, historic sites and parks found throughout all thirteen counties of the Pennsylvania Highlands region: places such as Durham Furnace, Coventry Forge, Hopewell Furnace, Johanna Furnace, Cornwall Furnace, and Pine Forge Furnace. The unique combination of forests, rocky hills, historic sites, industrial towns, and fertile limestone valleys makes for a compelling story to be told through interpretive signage and online tools, enhancing the experience of trail users.