The flat floodplain of the Rio Grande and a large part of its delta are visible in this synoptic photograph of the southern tip of Texas. The diverse coastal area includes tidal flats; sand dunes; floodplain deposits; and Laguna Madre, whose shallowness allows small waves to keep the sand in suspension, thereby producing a sandy-looking water. The Intracoastal Waterway between Padre Island and the mainland requires constant dredging to keep it and other channels open for ship traffic. The northern part of Mexico’s highly reflective Laguna Madre is visible (lower right corner). The speckled landscape (upper left edge) shows nonvegetated sand dunes; darker areas denote sandy soils where vegetative cover provides some stability for the shifting sands; and the lighter inland areas show the greatest concentration of agricultural activity, primarily north of the United States-Mexico border.