Chinese civilization emerged on a land shaped like three massive steps, each marked by distinct and highly complex natural conditions. The first step, the highest region in China, is the Qinghai-Xizang Plateau, often referred to as the “roof of the world.” The second step, with the Loess Plateau at its center, lies west of a mountain chain running from northeast to southwest, including the Greater Khingan Mountains, Taihang Mountains, Wushan Mountains, and the mountain ranges in western Hunan.