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.
Saga County, which belongs to Xigaze City, Tibet Autonomous region, is located in the southwest of Tibet Autonomous region, northwest of Xigaze City, located in the northern foot of the Himalayas and the southwest edge south of the Gangdise Mountains. Saga County is one of the border counties with a length of 105 kilometers. It is the center of the three counties (Zhongba, Saga and Jilong) in the west of Xigaze City, bordered by Angren County and Nyalam County in the east, Jilong County and Nepal in the south, and Zhongba County in the west. The north is connected with Cuoqin County in Ali area. The upper reaches of the Brahmaputra River. The "219" national highway runs through the east and west of the county, and it is also the main road from Lhasa to Aripland. The county covers a total area of 25500 square kilometers and has jurisdiction over seven townships and one town and 38 administrative villages. The total population is 12600 (2003). The average elevation of the county is more than 4600 meters, and the climate is high and cold.