Waimea Canyon on Kauai’s west side has unique geologic history. Geologists believe that that a portion of the one of the shield volcanoes which formed the island collapsed and formed a large depression which was then filled with lava flows. The flows pooled in the depression creating the walls of the canyon, and then millions of years of rain and erosion sculpted the canyon. The cliffs on the west side of the canyon are composed of thin lava flows that ran down the surface of the volcano. On the other side of the canyon, the cliff walls are built from thick lava flows that pooled in the depression.