From offshore, the northwest half of the range appears as a long ridge sloping gradually downward and ending in low bluffs near Kahuku Point. The entire range has a very jagged appearance and is cut on its windward side by deep gorges and valleys. The peak is on the east side of Nuuanu Valley and overlooks the famous Nuuanu Pali at the head of the valley. On the south-southwest side of the Koolau Range the land is mostly low and rolling. The second mountain range, Waianae Range, parallels the southwest coast for nearly the entire distance between Barbers and Kaena Points.
Several spurs extend from the range toward the shore forming short valleys.
The range has numerous high peaks. The highest is Kaala at 4,020 feet high, the highest point of land on Oahu, and is located 13 miles northwest of Pearl Harbor. Between the two mountain ranges is an extensive plain which extends from Pearl Harbor on the south to Haleiwa on the north. The plain rises to an elevation of about 1,000 feet at Wahiawa. Prominent headlands on Oahu are Makapuu Point, Koko Head, Diamond Head, Kaena Point, Kahuku Point and Mokapu Peninsula.