and is one of the sources of the Jialing River via the Bailong River, part of the Yangtze River system. Jiuzhaigou's best-known feature is its dozens of blue, green and turquoise-colored lakes. The local Tibetan people call them Haizi in Chinese, meaning "son of the sea". Originating in glacial activity, they were dammed by rockfalls and other natural phenomena, then solidified by processes of carbonate deposition. Some lakes have a high concentration of calcium carbonate, and their water is very clear so that the bottom is often visible even at high depths. The lakes vary in color and aspect according to their depths, residues, and surroundings. Some of the less stable dams and formations have been artificially reinforced, and direct contact with the lakes or other features is forbidden to tourists. Notable features Jiuzhaigou is composed of three valleys arranged in a Y shape. The Rize and Zechawa valleys flow from the south and meet at the centre of the site where they form the Shuzheng valley, flowing north to the mouth of the valley. The mountainous watersheds of these gullies are lined with of roads for shuttle buses, as well as wooden boardwalks and small pavilions. The boardwalks are typically located on the opposite side of the lakes from the road, shielding them from disturbance by passing buses. Most visitors will first take the shuttle bus to the end of Rize and/or Shuzheng gully, then make their way back downhill by foot on the boardwalks, taking the bus instead when the next site is too distant. Here is a summary of the sites found in each of the gullies: Rize Valley The Rize Valley (日则沟, pinyin: Rìzé Gōu) is the south-western branch of Jiuzhaigou. It contains the largest variety of sites and is typically visited first. Going downhill from its highest point, one passes the following sites: The Primeval Forest (原始森林 Yuánshǐ Sēnlín) is a preserved ancient woodland. It is fronted by views of the surrounding mountains and cliffs, including the 500-metre-high, blade-shaped Sword Rock (剑岩 Jiàn Yán). Swan Lake (天鹅海, Tiān'é Hǎi) is a 2250-metre-long, 125-metre-wide lake named for its visiting swans and ducks. Grass Lake (草海, Cǎo Hǎi) is a shallow lake covered in intricate vegetation patterns. Arrow Bamboo Lake (箭竹海, Jiànzhú Hǎi), covering an area of 170,000 m2, is a shallow lake with a depth of 6 m. It lies at an elevation of 2,618 m,