There are several tectonic provinces collectively called as crystalline providences.
Explanation:
The geology of Appalachians consists of Blue Ridge, Piedmont, Adirondack, and the New England providences. They are known as Crystalline provinces.
The sinking of the oceans continued about 270 million year ago due to which a huge mass of rocks was pushed westwards along the margins of North America and piled up to form the mountains.
The Sierra Nevada is the youngest mountain range on the west coast of the United States.
The Great Leap resulted in tens of millions of deaths, with estimates ranging between 18 million and 45 million deaths, making the Great Chinese Famine the largest in human history.