Riyue Mountain (Sun-and-Moon Mountain), part of the Qilian Mountain Range, is located in the west of Huangyuan County, Qinghai Province. In the past, it was a vital communications center between Central China and the southwest frontiers as well as the west regions. In 420, the first year of the Shengui reign under Emperor Mingdi in the Northern Wei Dynasty (386-534), the monk Song Yun left Luoyang City for India to learn about Buddhism via Riyue Mountain. Later on, Princess Wencheng passed Riyue Mountain when she was going to marry Songtsen Gampo, king of the Tubo tribe.    

Riyue Mountain was called Chiling Range (Russet Ridge) during the Tang Dynasty (618-907) because of its grassless russet mountaintop. Legend has it that when Princess Wencheng left for Tubo for her marriage, she passed the Chiling Range. At the thought that she would enter a remote land, she took out the Sun-and-Moon Treasure Mirror given by her mother at departure, and saw her homeland Chang'an (today's Xi'an City). For the cause of the unity of the two nationalities, she threw the mirror onto the mountain. The mirror turned into the Qinghai Lake, and her tears flowed into a river named Daotang River (flowing back river). To commemorate the princess, the mountain was renamed the Sun-and-Moon Mountain, and the Princess Wencheng Temple was built at the foot of the mountain.  

Riyue Mountain divides Qinghai into agricultural area and pastoral area. To the east is the Huangshui Valley; to the northwest is the Qinghai Lake; to the southwest are continuous rolling mountains, vast grassland and scattering tents; 40 km from Riyue Mountain, at the foot of the West Hill, is the famous Daotang River; and tens of kilometers to the south is the Yellow River and the Longyang Gorge.