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.
Yongji County is one of the five counties under the jurisdiction of Jilin City, Jilin Province. It is located between longitude 125 °48 "9" ~ 126 °40 "1" east and latitude 43 °18 "7" ~ 43 °35 "00" north. It is located in the central and eastern part of Jilin Province, bordering Fengman District of Jilin City in the east, Huadian and Panshi in the south, Shuangyang District in Changchun City across the Yinma River in the west, and Jiutai City, Chuanying District in Jilin City and Qianerdao Township in Fengman District in the north. It is 20 kilometers away from the main city of Jilin City. At the end of 2011, Yongji County had jurisdiction over 7 towns, 2 townships and 2 development zones. In 2013, Yongji County has a total area of 2625 square kilometers and a total population of 420000. Yongji County has Beida Pot Ski Resort, one of the first national AAAA scenic spots in China. On October 22, 2018, Yongji County was selected for 2018.