Framed by the dark Pacific Ocean, Oahu appears as an emerald oasis. The green, heavily forested slopes of the Koolau Range on the northeast side of the island are separated from the higher but smaller Waianae Range near the southwest coast by a small, cultivated valley. These three physiographic landforms are aligned in a general northwest-southeast direction. Apparent on the south of Oahu are Honolulu International Airport, Pearl Harbor, Honolulu, and Diamond Head Crater.