The island of Kauai is oldest of the primary Hawaiian islands, giving it extremely weathered features on its exposed areas like the north shore. This exposure has built some of the most dramatic cliff faces (pali) around.
Add to that copious amounts of rain and warm temperatures that combine to create a tropical environment and you get the green and red Na Pali.
From the Photographer:
“It was so much fun cruising around the north side of Kauai. This is the Na Pali Coast. These rugged cliffs are up to 4,000 feet high and drop straight down into the rough seas below.”