The state has a coast of 590 km (370 mi)[2] and the width of the state varies between 11 and 121 kilometres (7 and 75 mi).[3] Geographically, Kerala can be divided into three climatically distinct regions: the eastern highlands; rugged and cool mountainous terrain, the central mid-lands; rolling hills, and the western lowlands; coastal plains.[4]: 110 Pre-Cambrian and Pleistocene geological formations compose the bulk of Kerala's terrain.[5][6] A catastrophic flood in Kerala in 1341 CE drastically modified its terrain and consequently affected its history; it also created a natural harbour for spice transport.[7] The eastern region of Kerala consists of high mountains, gorges and deep-cut valleys immediately west of the Western Ghats' rain shadow.[4]: 110 41 of Kerala's west-flowing rivers,[8] and 3 of its east-flowing ones originate in this region.[9][10] The Western Ghats form a wall of mountains interrupted only near Palakkad; hence also known Palghat, where the Palakkad Gap breaks.[11] The Western Ghats rise on average to 1,500 metres (4,900 feet) above sea level,[12] while the highest peaks reach around 2,500 metres (8,200 feet).[13] Anamudi in the Idukki district is the highest peak in south India, is at an elevation of 2,695 m (8,842 ft).[14] The Western Ghats mountain chain is recognised as one of the world's eight "hottest hotspots" of biological diversity and is listed among UNESCO World Heritage Sites.[15] The chain's forests are considered to be older than the Himalaya mountains.[15] The Athirappilly Falls, which is situated on the background of Western Ghat mountain ranges, is also known as The Niagara of India.[16] It is located in the Chalakudy River and is the largest waterfall in the state.[16] Wayanad is the sole Plateau in Kerala.[17] The eastern regions in the districts of Wayanad, Malappuram (Chaliyar valley at Nilambur), and Palakkad (Attappadi Valley), which together form parts of the Nilgiri Biosphere Reserve and a continuation of the Mysore Plateau, are known for natural Gold fields, along with the adjoining districts of Karnataka.[18]