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.
Wensu County, which belongs to Aksu region of Xinjiang Uygur Autonomous region, is located at the southern foot of Tomur Peak in the middle of Tianshan in the west, the northwest edge of Tarim Basin, the border with Baicheng and Xinhe counties in the east, the city of Aksu in the south, the Tashkent River and Wushi County in the west, and the Kyrgyz Republic, the Republic of Kazakhstan and Zhaosu County in Yili Kazakh Autonomous Prefecture of Xinjiang in the north. It is between latitude 40 °52 mi 42 °15 N and longitude 79 °28 Mel 81 °30'E. it is 171km long from east to west and 158km wide from north to south, with a total area of 14569.3 square kilometers. Wensu is a place name in the western region of the Han Dynasty, and the Uyghur language is called "Aksu Kuona Xiehai", that is, the meaning of the old city of Aksu. Wensu is the 36 country of the ancient western region.