Discovered in 1808 by 93-year-old "Aunt" Jess Guernsey, the Flume is now a paid attraction that allows visitors to walk through it from May 10 to October 20.

Nearly 200 million years ago in the Jurassic period, the Conway granite that forms the walls of the Flume was deeply buried molten rock.

As it cooled, the granite was broken by closely spaced vertical fractures that lay nearly parallel in a northeasterly direction.

The basalt dikes eroded faster than the surrounding Conway granite, creating a deepening valley where the gorge is now.

It partially filled the valley with glacial debris and removed soil and weathered rock from the vicinity.