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.
Changyi District, which belongs to Xi'an City, Shaanxi Province, formerly known as Huan County and Huxian County, is located in the southwest of Xi'an, Qinling Mountains in the south and Weihe River in the north, with a total area of 1282 square kilometers. It is one of the three deputy central cities of Xi'an international metropolis, 18 kilometers away from the main city of Xi'an, and is located in Xi'an "half-hour economic circle". As of March 2019, Changyi District has jurisdiction over 8 streets, 6 established towns and a scenic spot management bureau. On November 24, 2016, the State Council approved the revocation of Huxian County and established Xi'an City's Fengyi District. On September 9, 2017, Qianyi District was officially unveiled as the 11th district of Xi'an. It is the hometown of modern Chinese folk painting, Chinese poetry, national civilized county, national health county and national go. 2018, Changyi District