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.
Youyi County is located in the western part of Shuangyashan City, Heilongjiang Province, under the jurisdiction of Shuangyashan City. The geographical location is 46 °28 °14 "~ 46 °59 °38" N and 131 °27 °50 "~ 132 °15'E. It is located in the hinterland of Heilongjiang, Songhua River and Wusuli River. It is adjacent to Baoqing County in the east, Shuangyashan City in the south, Jixian County in the west and Fujin City in the north. The terrain in Friendship County is flat and low-lying, with hills in the southwest and lowlands in the northeast, tilting from southwest to northeast. In 2012, Youyi County has a total population of 125000. The total area is 1888 square kilometers. Youyi County has a mid-temperate continental climate, with an average annual temperature of 2.5C, an average annual rainfall of 500mm, an average of 2730 hours of light, and a frost-free period of 120.1.