Evident in this color infrared photograph is the flatness of the south Texas coastal plain with sand dunes, sandy soils covered by scrubby trees and grass (darker areas), tidal flats, and some lighter rectangular field patterns. Visible are the southern end of the Intracoastal Waterway, identified by linear deposits of dredged material near the shoreline of the mainland, and Laguna Madre, which separates Padre Island from the mainland of south Texas. Because of blowing sands, two other features—a dredged channel perpendicular to Padre Island (left edge) and a section of the dredged Brownsville Ship Channel (upper right corner)—require constant dredging to keep the channels open for shipping.