While geyser activity has been minimal in recent times,  there are accounts of geothermal activity similar to that inside the boundaries of Yellowstone National Park in the not too distant past. 

John Colter, an intrepid member of the Lewis and Clark Expedition, gave the first accounts of the area to non-native Americans following his solo journey of 1807-1808. But Colter's descriptions of gloomy terrors, hidden fires, smoking pits, noxious streams and the all-pervading smell of brimstone were too wild for his listeners to believe. They derisively dubbed the imaginary place "Colter's Hell."

It wasn't until Thomas Moran painted the natural features of Yellowstone National Park and William Jackson brought back photographs in 1871 that the American public realized that Colter's accounts were no fantasy.

"While the true Colter's Hell was outside of Cody, it was also erroneously associated with an active geothermal area in the northwestern section of Yellowstone National Park," Michael Rutter points out in Myths and Mysteries of the Old West.

"Hiriam M. Chittenden perpetuated the false mythology in his book Yellowstone National Park. He called the Geyser Basin Colter's Hell. This was an honest error on his part, but the name caught on. For more than a hundred years now, folks have equated Geyser Basin with with John Colter. While he traveled a greatr deal, Colter never actually made it to that sulfurous section of Yellostone National Park. Chittenden corrected the error, incidentally, in his next book, a book worth reading, called American Fur Traders of the Far West. Colter'splace in folklore had already been sealed however, and the legen continues to this day." 

Sources: Grant Teton Natural History Association
                  Yelllowsone Association
                  Colter's Hell and Jackson's Hole