The granite rock that makes up the walls of the flume was formed many millions of years ago in ancient geological time. At a later period, dark-colored lava in a molten condition was pushed up from below, filling a great crack and smaller side cracks that had been formed in the granite. This lava solidified, and as ages passed the main dike was worn away, leaving the flume gorge. The original flume thus formed has been further altered, but the remaining inscription is not legible.