Apparent in this photograph are the Brownsville Ship Channel, extending southwest into the mainland from the Gulf of Mexico, and the east-west-oriented Rio Grande that defines the United States-Mexico border. Most of the land north of Brownsville is used for irrigated agriculture, and Brownsville is obscured by vegetation; however, the bluish-appearing Mexican city of Matamoros (right center ) has much less vegetation. Padre Island and other sandy barrier islands help form Laguna Madre north of the Brownsville Ship Channel. The spoil banks along the western side of Laguna Madre were created by dredging the Intracoastal Waterway. The diverse landscape near the coast consists of tidal flats, lakes, sand dunes, and sandy soils covered by vegetation.