Bert Loper built this boat and then died in it at the age of 79 while running 24.5 mile rapid in 1949. He was a pioneer of running whitewater and likely knew his time was about up before leaving on his last trip. His companions found this boat farther downstream and moved it up above the high water mark to where it rests today. Bert's bones were found a bit later on farther down the river.
This is just speculation, but I imagine the tendency of the redwall layer to act as an aquifer is what leads to these caverns being created. Water comes through the cliffs in many places and must have taken advantage of a weakness in the cliff face here. Whatever the cause, there are many of these large caverns in the canyon in this layer.
