You are on the Upper North Side Trail traversing the north side of the ridge not far below the ridgline. The massive rock formation that forms the ridge is readily seen beside the stairway here, which leads up to the Ki‘i Mo‘o (lizard image) and eventually the very top (Kilohana or "lookout").

This massive rock and the many large boulders that have rolled down the slope are the remains of a lava lake that formed in the prehistoric Ko‘olau volcano caldera—the central part of that eruptive event that created the eastern half of the Island of O‘ahu. At its greatest height, this volcano rose over 10,000 feet above the sea surface in a process of building that lasted several million years and ceased perhaps 2 million years ago.

So, you might ask, if this place is near the middle of the Ko‘olau volcano, where is the northern part of that volcano? The answer is, at some point in the far distant past, the northeast face broke away and slid down into deep water. It is now a debris field with the largest piece—the Tuscaloosa Seamount—some 60 miles distant to the northeast.