Houston, the fourth most populous city in the United States, is featured in this east-looking, low-oblique photograph. A channel dredged within Galveston Bay, whose average depth is 12 feet (4 meters), allows merchant ships and tankers to enter the Port of Houston, the third-busiest port in the United States. Galveston is discernible at the east end of Galveston Island at the entrance to Galveston Bay. Visible are reflective areas northwest of Galveston that identify large oil refinery and petrochemical plants in Texas City; rich agricultural lands of the coastal plain on either side of Galveston Bay and south of Houston; and a large smoke plume from an oil refinery fire north of Baytown in the small community of Mont Belvieu.