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.
Gansu District, which belongs to Zhangye City, Gansu Province, is located in the middle of Qianhe West Corridor, between 100 °6km east longitude and 100 °52m north latitude, 38 °32' north latitude between Ganzhou District-39 °24', south by Qilian Mountain and north by Alashan right Banner in Inner Mongolia. Ganzhou District has a continental climate. There are 4 major rivers and 26 seasonal rivers in the territory, with a runoff of 1.66 billion cubic meters, groundwater reserves of 990 million cubic meters and arable land of 686200 mu in 2012. In 2012, Ganzhou District completed a GDP of 2.531 billion yuan, accounting for 78.8% of the planned GDP, an increase of 10.1% over the same period last year, including 808 million yuan for the primary industry, 766 million yuan for the secondary industry and 766 million yuan for the tertiary industry.