The natural vegetation in the southern tip of Florida consists of mangrove swamp forests, while marsh, broom, saw, and water grasses are typical in the coastal sections of Texas, Georgia, and Louisiana. However, in many areas the natural landscape has been altered by human activity. The region's major crops are rice, grown in southwestern Louisiana and southeastern Texas; sugarcane, in southern Louisiana and the Florida Everglades; and citrus fruits, in central Florida and the lower Rio Grande valley in Texas. Offshore petroleum and natural gas exploration and production are of great economic importance along the coast of Louisiana and Texas. The Gulf Coast also has reserves of sulfur, magnesium, and phosphates. Manufacturing centres are widespread, and the location of important ports at Houston and Galveston in Texas and at New Orleans has contributed to the tremendous economic growth of the hinterland. The Gulf Intracoastal Waterway extends along nearly the entire Gulf Coast. Both commercial and sport fishing are widespread. Tourism is a major component of the regional economy, visitors being attracted by the excellent beaches of Florida, Alabama, Mississippi, and Texas and by such cities as New Orleans.