English: On December 22, 2019, the Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Aqua satellite acquired a true-color image spanning parts of Southeastern Texas and Northeastern Mexico. The folded ridges in the west belong to the Sierra Madre Oriental, a mountain range formed of shales and limestones. Situation on the eastern side of the Mexican Plateau, these mountains run roughly 700 miles (1,100 km) in length, roughly aligned from north to south. The large flat plain is the lower Rio Grande Valley. Despite the name, this region is a floodplain rather than a valley created by the Rio Grande and its meanders over time. The Rio Grande flows through the floodplain, forming the border between North America (north) and Mexico (south). The Gulf of Mexico sits in the east.