Region 1: Inland Basin
The Allegheny Plateau dominates the Inland Basin topographically. The Plateau is deeply dissected by many streams, eroding through the bedrock to create relief throughout the area. The rugged peaks of the Adirondacks, composed of uplifted Precambrian rock, tower above the surrounding Lowlands of Lakes Ontario and Erie, and the St. Lawrence and Mohawk Rivers.
Region 2: Appalachian/Piedmont
Traditionally, the Appalachian/Piedmont region is divided into the Valley and Ridge Province, characterized by distinctive long, narrow ridges and valleys; the Precambrian ridges, which make up the rugged Precambrian rock core of the Appalachians and includes the Blue Ridge province of Pennsylvania and Maryland; the Triassic Rift Basins, formed as Pangea ripped apart; and the Piedmont, an area of rolling hills at the foot of the Appalachians. Within these divisions lie other distinctive topographic features, such as the Great Valley that extends nearly the entire length of the region, and the Taconic Mountains, pushed to their present position from the east when a volcanic island arc collided with the continent in the early Paleozoic.
Region 3: Coastal Plain
Topographically, the Coastal Plain is a relatively flat region. Underlain by a wedge of unconsolidated sediments deposited over the last 100 million years (which is recent in geologic time), the Coastal Plain is easily eroded and remains fairly level, with a slope of less than one degree.
Region 4: Exotic Terrane
The Exotic Terrane region is known as the New England Uplands because of the dominance of north-northeast trending mountainous and hilly terrain in the region. Resistant metamorphic Silurian and Devonian rocks dominate the region, cross cut by intrusions and volcanic rocks from the Taconic and Acadian mountain-building events. There are a few notable exceptions to the general highland nature of the region, including the Boston and Narragansett Basins, the Connecticut Valley Rift Basin and the New England Coastal Lowlands.