San Diego (/ˌsæn diˈeɪɡoʊ/ SAN dee-AY-goh, Spanish: [san ˈdjeɣo]; Spanish for 'Saint Didacus') is a city on the Pacific Ocean coast of Southern California located immediately adjacent to the Mexico–United States border. With a 2020 population of 1,386,932, it is the eighth most populous city in the United States and the seat of San Diego County, the fifth most populous county in the United States, with 3,338,330 estimated residents as of 2019. The city is known for its mild year-round climate, natural deep-water harbor, extensive beaches and parks, long association with the United States Navy, and recent emergence as a healthcare and biotechnology development center. San Diego is the second largest city in the state of California, after Los Angeles.
Huanglong County, which belongs to Yan'an City, Shaanxi Province, is located in the hilly and gully region of the Loess Plateau, in the north-central part of Shaanxi Province, on the southeast edge of Yan'an City. It is bordered by Luochuan in the west, Baishui in the south, Chengcheng and Heyang in the south, Hancheng in the east and Yichuan in the north. It is located between latitude 35 °24 °05 north latitude and longitude 110 °16 °49 east longitude, between north and south longitude 69.754 km long, east-west width 62.195 km, and total area 2752 square km. The skull fossils of the "Huanglong Man" unearthed about 50,000 years ago in Huanglong County filled a missing ring in the history of human development in China, and discovered the largest giant stone stone in the Neolithic Age in China.