A mesa is an isolated, flat-topped elevation, ridge or hill, which is bounded from all sides by steep escarpments and stands distinctly above a surrounding plain. Mesas characteristically consist of flat-lying soft sedimentary rocks capped by a more resistant layer or layers of harder rock, e.g. shales overlain by sandstones. The resistant layer acts as a caprock that forms the flat summit of a mesa. The caprock can consist of either sedimentary rocks such as sandstone and limestone; dissected lava flows; or a deeply eroded duricrust. Unlike plateau, whose usage does not imply horizontal layers of bedrock, e.g. Tibetan Plateau, the term mesa applies exclusively to the landforms built of flat-lying strata. Instead, flat-topped plateaus are specifically known as tablelands.
Yulin, known as "Shangxun" in ancient times, began in the Spring and Autumn and warring States period, flourished in the Ming and Qing dynasties, and was stationed in Yansui Town (also known as Yulin Town), an important town on the nine frontiers of the Ming Dynasty. Emperor Kangxi engraved a stele of "two isolated cities and a thousand years of loyalty and courage". There is a good reputation of "the ancient city of Taichung in the north of South Tower, the sixth floor riding the street all over the world". Such a strange urban construction is rare in China, which is also an important symbol of Yulin as a national historical and cultural city. Yulin is located in the northernmost part of China's Shaanxi Province, at the junction of the Loess Plateau and Maowusu Sandy Land, which is the transitional area between the Loess Plateau and the Inner Mongolia Plateau. Facing the Yellow River and Shanxi Province in the east, Ningxia and Gansu in the west, Yan'an in the south and Ordos in the north, it is the border of Shaanxi, Gansu, Ningxia, Mongolia and Jin. It has jurisdiction over 2 districts, 1 county-level city and 9 counties, with a resident population of 340