Editing Three Gorges (section)

== Geological evolution ==
Due to the lithological conditions of its different regions, the valleys of the Three Gorges are narrow in some areas and broad in others. Most narrow valleys occur in regions where there is [[limestone]], which is relatively hard and resists erosion. However, water can flow along deep vertical fractures, eroding underneath. As the limestone bed is gradually undercut, parts of it fall into the river along vertical fractures, forming precipitous cliffs. When the river flows through areas of softer [[sandstone]] and [[shale]], which have less resistance to erosion, the erosive effect is increased, carving wide valleys.

There are different theories on how the Three Gorges were formed, but geographers and geologists have generally reached a consensus, believing [[Orogeny|mountain folding]] in the east of Sichuan Province and the west of Hubei Province, including the Wu Mountains ({{lang|zh|巫山}}), were the outcome of the [[Yanshanian]] movement ({{lang|zh-hant|燕山運動}}) around 70 million years ago. The gorges run from southwest to northeast, then turn, and from west to east, with terrain lowering gradually from south to north. The western and eastern parts of the area, between the southern mountains and Bashan Mountain ({{lang|zh|巴山}}), in the north, are comparatively lower; and in the past, the river flowed to the east through the region. As the crust of the locality continued to rise, the river's erosion intensified, and the Three Gorges were carved.