Johnston Creek cuts through layered limestone walls formed from marine sediments hundreds of millions of years ago, leaving the narrow gorge, falls and overhangs beside the path. The strata are easiest to notice where the canyon walls squeeze close around the creek.
Local accounts connect the canyon’s name to William “Billy” Johnston, a trapper turned prospector associated with the Silver City gold rush of the 1880s. The story says he returned from the upper canyon claiming to have found gold nuggets; when other prospectors could not repeat the find, he headed west for British Columbia. Treat it as a local prospecting story, not a reason to expect gold in Johnston Creek.