Tulsa, the second largest city in Oklahoma, is obvious in this northeast-looking, low-oblique photograph. A principal financial, commercial, and transportation center in a major oil producing region, Tulsa is also the home of some of the best medical facilities in the United States. Important to the city’s economy are aircraft and aircraft components, electronic components, oil field equipment, machinery, cement, glass, canned goods, gas and oil wells, oil refineries, and coal mining. Tulsa became an inland port with the opening in 1971 of the McClellan-Kerr Waterway, a 440-mile (708-kilometer) system linking the city with the Mississippi River and the Gulf of Mexico. Visible is the Arkansas River as it leaves Keystone Lake and flows southeast past Tulsa.