Kauai is geologically the oldest of the main Hawaiian Islands. With an area of 562.3 square miles (1,456.4 km2), it is the fourth-largest of these islands and the 21st largest island in the United States. Known also as the "Garden Isle", Kauai lies 105 miles (169 km) across the Kauai Channel, northwest of Oahu. This island is the site of Waimea Canyon State Park.(Wikipedia)