The region is part of the Cathaysian fold system and has experienced high volcanic activity and the formation of large fault structures, which were subsequently subject to erosion by water and weathering. The landscape is characterized by beautiful winding river valleys flanked by columnar or dome-shaped cliffs as well as cave systems. Peaks in the western portion of the Wuyi Mountains typically consist of volcanic or plutonic rocks, whereas peaks and hills in the eastern area are made up of red sandstone (particularly in the east) with very steep slopes but flat tops (Danxia landform). Bedrock lithology at Wuyi Shan is dominated by tuff, rhyolite, and granite in the western part. Red sandstone is common farther east. The elevation ranges from 200 m (656 ft) to 2,158 m (7,080 ft). The terrain is rugged with cliffs and high peaks. There are numerous caverns in the mountains, some of which have been explored and opened to the public .