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.
Guangyuan City, a prefecture-level city under the jurisdiction of Sichuan Province, borders Gansu Province and Shaanxi Province in the north; Nanchong City in the south; Mianyang City in the west; Bazhong City in the east; on the northern edge of Sichuan, the mountain is in the transition zone to the basin, belonging to the subtropical humid monsoon climate; the city has a total area of 16314 square kilometers, with 3 districts and 4 counties under its jurisdiction; and there are 3.0262 million registered residents in 2017. Guangyuan City has been an important passageway into Sichuan since ancient times. It is the old place of Guo, the fortress of entering Shu, and the important town of the three Kingdoms. Guangyuan has a profound cultural heritage, especially the bright red gene handed down from generation to generation. Guangyuan is the concentrated display of pre-Qin ancient plank road culture and Chinese Shu road culture, the core corridor of the history and culture of the three Kingdoms, and the birthplace of the only female emperor Wu Zetian in Chinese history. It is also the core area of the former Sichuan-Shaanxi Soviet area and the later stage of the Red fourth Front Army.