Maui is made up of two volcanoes, one now extinct and the other dormant, which erupted long ago and joined into one island. The resulting depression between the two is what gives the island its nickname, the Valley Isle. West Maui's 5,788-foot Puu Kukui was the first volcano to form, a distinction that gives that area's mountainous topography a more weathered look. Rainbows seem to grow wild over this terrain as gentle mists fill the deeply eroded canyons. The Valley Isle's second volcano is the 10,023-foot Haleakala, where desertlike terrain butts up against tropical forests.