Longmen is located about 65 kilometers south of Hukou Waterfall, at the southernmost tip of Shanxi-Shaanxi Canyon. To the south of Longmen is the open and flat Guanzhong Plain. The water of the Yellow River suddenly entered the wide riverbed from the narrow Longmenkou, and the river property changed greatly. The formation of the Longmen is that the Longmen Mountain in the east and Liangshan Mountain in the west extend out of the ridge and close to each other, forming a narrow mouth with a width of only 100 meters, which is like a giant clamp, binding the river and forming a swift current. Every flood season, because the water level in the gorge is high, the river valley suddenly widens and the water level suddenly drops after leaving the canyon, so there is an obvious water level difference in Longmen, so there is a saying that "Longmen falls into water three times". The story of "carp jumping at the dragon gate" passed down from generation to generation refers to the water falling here. The story tells that small carp are not afraid of dangers and obstacles, and they jump the gate on the road to Jackie Chan one after another. If they can jump over the past, they will become Jackie Chan. Only those indomitable little carp can finally become Jackie Chan. For thousands of years, this story has also inspired the descendants of the Chinese people to work hard and struggle endlessly. Ancient people felt incredible about the formation of Longmen Gorge, a natural wonder, and imagined it as a gorge cut by Dayu, so Longmen was also called "Yumenkou".

2. The legend of Dayu's water control. Legend has it that during the reign of Emperor Yao, floods often occurred in the Yellow River basin. In order to stop flooding and protect agricultural production, Emperor Yao once called a meeting of tribal leaders to solicit experts in water control to quell water disasters. Gun was recommended to take charge of the work. After accepting the task, Gun used dikes to block the water, making a city of three blocks, that is, enclosing the residential area with simple dikes to block the flood, which failed for nine years, and finally he was exiled to Yushan and died. After Shun Di ascended the throne, Yu Zhi, the son of Gun, was appointed to control water. Yu summed up his father's experience in water control, and changed Gun's "blocking barrier" into "dredging and guiding stagnation", that is, using the natural trend of water flowing from high to low, consequent relief dredged the congested stream. The flood was introduced into dredged rivers, depressions or lakes, and then connected to the four seas, thus quelling the flood and enabling the people to move back from the highlands to Pingchuan to live and engage in agricultural production. Later, Yu became the first king of the Xia Dynasty, and was called "Shen Yu" and spread to later generations.

In the process of Dayu's water control, he left many touching deeds. According to legend, with the help of the original measuring tools invented by himself-yardsticks and rules, he traveled all over the river, split Longmen and Yizui with a magic axe, and cut through Jishi Mountain and Qingtongxia to make the river unimpeded. He lived away from home 13 years, but he didn't enter the house for three times. Even his newborn child didn't have time to caress, and he took the lead in hardship, and the hair on his legs was polished in labor. He is the first hero who successfully managed the Yellow River flood in the history of China.