The horn area of Hefen is the cradle of early human civilization and the cradle of Chinese civilization for five thousand years. Mount Yun, located to the south of Lvliang Mountain and to the north of Ji Mountain in the horn corner of Hefen, is the place where the ancient people changed from hunting to farming due to its special geographical location as it was Kunlun Mountain. It was also the place where ancient emperors Yao, Shun, Gun, Houji and Xihe carried out activities. Pingyang, capital of Yao, was to the east of Mount Yun, Puban, capital of Shun, was to the south of Mount Yun, and Dayu controlled flood in Longmen which is to the west of Mount Yun. Ji Mountain was the originator of Chinese farming culture, and also the place where Houji taught people to grow crops. Houji was the local farming official of Emperor Yao. That he taught people to farm could not be separated from the four seasons. Emperor Yao ordered Xihe to observe the celestial phenomena at the south foot of Mount Yun. Xihe took the circle of Mount Yun as the high moment in the north, observed sundial and beidou astronomical phenomena and made the summer calendar. The temple and tomb of Xihe lie at the foot of the mountain to the south of Mount Yun. According to the literature records of Xihe, Mount Yun is the place where the Chinese agricultural civilization originated and the summer calendar came into shape.