The coastal plain transitions to the Piedmont region along the Atlantic Seaboard fall line, the elevation at which waterfalls first appear on streams and rivers. The Piedmont region of central North Carolina is the state's most populous region, containing the six largest cities in the state by population. It consists of gently rolling countryside frequently broken by hills or low mountain ridges. Small, isolated, and deeply eroded mountain ranges and peaks are located in the Piedmont, including the Sauratown Mountains, Pilot Mountain, the Uwharrie Mountains, Crowder's Mountain, King's Pinnacle, the Brushy Mountains, and the South Mountains. The Piedmont ranges from about in elevation in the east to about in the west.