Appalachian Highlands

Although the mountains are formed from ancient rocks more than one billion years old, geologically, the 160-mile wide dome area, called a massif, is relatively new.

It is theorized that there is a "hotspot" beneath the region, which causes continued uplift at the rate of 1.5-3 cm annually.

The plateau is composed of sedimentary rocks, including sandstones, conglomerates, and shales, that were deposited during the late Paleozoic Era.

[9] This province is about 580 miles long and consists of northern and southern physiographic sections, which divides near the Roanoke River gap.

[11] The mountains are made of highly deformed metamorphic rocks, largely developed during the Precambrian age over 541 million years ago.

The mountains include schists, gneisses, slates, and quartzites, and are extensively intruded by igneous bodies.

The province starts in Rockland County, New York near South Mountain on the west side of the Hudson River.

The east side of the Piedmont runs along the Hudson, parallel to Manhattan, New York City, through New Jersey, and then along a line near Philadelphia, Baltimore, Washington, D.C., Richmond, Virginia, Raleigh, North Carolina, Columbia, South Carolina, Augusta, Georgia, Macon, Georgia, and Montgomery, Alabama.

The west side of the Piedmont runs through lesser populated areas, from south of Harrisburg to Lake Martin in Elmore County, Alabama.

The oldest rocks in the Piedmont are gneisses and schists that formed more than a billion years ago during the Grenville orogeny.

During the Mesozoic era, the Piedmont was covered by shallow seas that deposited layers of sandstone, shale, and limestone.

Some of these aquifers, mainly in the western portion of Vermont, consist of carbonate rocks (primarily limestone, dolomite, and marble).

These consolidated rocks yield water primarily from bedding planes, fractures, joints, and faults, rather than from intergranular pores.

Most of the northern border of the St. Lawrence Valley province is adjacent to a physiographic division in Canada that is not part of the Appalachian Mountains in that country.

[24] The province is a series of northeast-southwest trending synclines and anticlines composed of early Paleozoic sedimentary rocks.

Limestones and shales are more susceptible to erosion and make up much of the valleys, whereas more resistant sandstones and conglomerates form the ridges.