Erhai Lake is located in Dali City, Dali Bai Autonomous Prefecture, Yunnan Province. It was called Kunming Pool, Erhe River and Yeyuze in ancient times. Because of its earlike appearance, it is named Erhai Lake, which belongs to the Lancang River system. It is the second largest lake in Yunnan after Dianchi Lake, and the 7th largest freshwater lake in China. Erhai Lake was formed at the end of the Ice Age. Its main cause is subsidence erosion. It is a faulted lake with plateau structure. It covers an area of 251 square kilometers and has an elevation of 1972 meters. To the west, Cangshan (also known as Cangshan) lies in a row like Ping. It is the main peak at the southern end of Yunling Mountains. It consists of 19 peaks from the north to the south. Butterfly Spring, one of the scenic spots along the coast, is situated at the foot of Cangshan Yunlang Peak, 24 kilometers north of the ancient city of Dali. The springs are gathered in a pond of more than 40 square meters, surrounded by marble railings and engraved in the middle with the words "Butterfly Spring" inscribed by Guo Moruo. The spring water is green and clear, surrounded by green trees. There is an ancient double fragrant tree, commonly known as "butterfly tree", which spans the spring and reflects the water. With the change of sky light and tree shadows, the landscape changes endlessly. There are also Butterfly Museum, Guanquan Pavilion, Wing Butterfly Monument, Xu Xiake Stone Sculpture and so on.