This is the Pacific Grand Canyon. Waimea Canyon was formed as the island of Kauai settled and old rift zones developed into fault lines on the island. The original shield failed and the main fault slipped forming a low valley which with weathering and erosion created this canyon.
I hiked to a waterfall which it turns out you cannot see because you are standing at the top of it. The river that feeds this waterfall has leptospirosis in it, so you really do not want to touch it. The ledge you see is part of the path you walk on and where I had my picture taken. I am not so fond of heights so I stayed back from the edge.