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.
Hongya County is located in the southwest edge of Sichuan Basin, under the jurisdiction of Meishan City. The geographical coordinates are 102o 49 & #39;-103 °32 & #39;, 29 °24 N & #39;-30 °00 & #39;, is located in the triangle zone of Chengdu, Leshan and Ya'an, bordering Jiajiang County and Emeishan City in the east, Hanyuan County and Jinkou District in the south, Yucheng District and Yingjing County in the west, Mingshan District and Danling County in the north, 147km away from Chengdu, 55km from Leshan, 50km from Meishan and 62km from Ya'an. The highest elevation of the county is 3090 meters, and the lowest elevation is 417.5 meters. It covers an area of 1896.49 square kilometers and has a total population of 350800 (2016). The county people's government is stationed in Hongchuan town. Hongya County