夷平面是在地壳长期稳定的条件下，起伏的地表受风化和流水的削高补底作用而逐渐变的平坦，后经地壳运动抬升到高处的平坦地形，对面张家界一级夷平面位于海拔1200m左右，形成于始新世晚期—渐新世。When the earth’s crust is in a long-term stable period, the uneven earth’s surface gradually became even because weathering and runoff erosion can cut down higher parts and fill up lower parts. Then the even surface was lifted up by crustal movement and form a flat terrain, which is called the planation surface. This planation surface is about 1,200m above sea level and was formed between the late Eocene and the Oligocene.