The Piedmont Mountains are outlying mountains, sometimes called “low mountains”, that typically occur in the western Piedmont near the Blue Ridge, The Piedmont is part of the greater Appalachian Mountain Range and is also referred to as the Appalachian Plateau, it's a series of rugged, high plains located on the western side of the which location?
Appalachian Highlands
Title: Appalachian Plateau
Passage: The Appalachian Plateau is a series of rugged, high plains located on the western side of the Appalachian Highlands.  The Appalachian Highlands are a mountain range that run down the entire east coast of the United States.
Title: Piedmont Mountains
Passage: The Piedmont Mountains are outlying mountains, sometimes called “low mountains”, that typically occur in the western Piedmont near the Blue Ridge.  Most of the features within the Piedmont physiographic region of North America lie either on the eastern border where the plateau plunges onto the Coastal Plain at the Fall Line, in the broad valleys of the river systems, or on the western border where Piedmont Mountains likely occur.  Occasionally, due to diverse rock formations, folds and outcroppings, these mountains can rise at various locations across the Piedmont like the Uwharrie Mountain Range in North Carolina or the Pine Mountain Range in Georgia.  Most of these mountains, or hills, are what is left of ancient eroded mountains.  Some, like Stone Mountain in Georgia, are solitary rock domes called Monadnocks which become further exposed with erosion.  The Piedmont is part of the greater Appalachian Mountain Range and is also referred to as the Appalachian Plateau.  The French definition of piedmont in itself translates as foothill; however, a Piedmont Mountain may be that of greater significance or prominent elevation.
Title: Catoctin Mountain
Passage: Catoctin Mountain, along with the geologically associated Bull Run Mountains, forms the easternmost mountain ridge of the Blue Ridge Mountains, which are in turn a part of the Appalachian Mountains range.  The ridge runs northeast/southwest for about 50 mi departing from South Mountain near Emmitsburg, Maryland, and running south past Leesburg, Virginia, where it disappears into the Piedmont in a series of low-lying hills near Aldie, Virginia.  The ridge forms the eastern rampart of the Loudoun and Middletown valleys.
Appalachian Plateau Piedmont Mountains