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.
Tongxin County is located in the central and southern part of Ningxia Hui Autonomous region, under the jurisdiction of Wuzhong City. It is bordered by Yanchi County in the east and Huanxian County in Qingyang City, Gansu Province in the east, Yuanzhou District in Guyuan City in the south, Shapotou District, Zhongning County and Haiyuan County in Zhongwei City in the west, and Hongsibao District in Wuzhong City in the north. It is located on the Loess Plateau in the south of Ordos platform and is high in the south and low in the north. There are mainly five types of landforms, such as mountains, loess hills, river valleys and desert lands, with complex topography and crisscross distribution of mountains and rivers. There are Luoshan, Miboshan, Madashan, Laoye Mountain, Qinglong Mountain, Yaoshan and so on, all of which belong to Liupanshan system. In March 2019, it was listed as the first batch of revolutionary cultural relics protection and utilization district and county list.