Introduction to the Houjiayao site: The Houjiayao site is located 1,000 meters southwest of Houjiayao Village, Dongjingji Town, Yangyuan County. In 1973, it was discovered by Jia Lanpo and Wei Qi from the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences. It was discovered and officially excavated in 1976. 16 human fossils were discovered, as well as a large number of vertebrate fossils. 14,041 stone products were discovered, including 1,079 stone balls. The largest weighed more than 1,500 grams and the smallest weighed less than 100 grams. They were "flying rope stones" used by ancient humans for hunting, which are rare in the world. Its geological age is 100,000 years ago. The ancient human fossils unearthed at the Houjiayao site are comparable to those of Peking Man to a certain extent in terms of distribution scale and burial content.