Old Faithful has not always been faithful. Mineralized wood on its mound suggests a long silence centuries ago, and a bathhouse pool at the Upper Basin accidentally turned a quiet spring above Geyser Hill into a geyser that still runs. Both stories play on the road east of the interchange.
Has Old Faithful always done that? It has not. Lodgepole pines don't grow on active geyser mounds, yet mineralized wood from Old Faithful's own mound dates to between the years twelve thirty-three and thirteen sixty-two. Trees were growing on it. So a study suggests that about six hundred fifty to eight hundred years ago the geyser wasn't erupting, during a severe and sustained drought. For a long stretch it may have been a quiet hill with pines on top. Even its rhythm moves. In the eighteen seventies explorers noted sixty to seventy minutes between eruptions, and earthquakes have stretched it since, including Hebgen Lake in nineteen fifty-nine. Geysers can start as well as stop, and one of them started over a swimming pool. In nineteen fifteen Henry Brothers opened his Geyser Baths at the Upper Basin, fed by wooden troughs from Solitary Spring, above Geyser Hill. Lowering the spring's level let the water boil at depth, and the spring began to erupt. The pool's long gone and the water level has been restored. It kept going anyway. Solitary Geyser still erupts, mostly about three feet high, all from a pool that charged fifty cents a swim.
Photo: NPS Photo / William Keller, 1964 · Public domain (NPS; PD-USGov-NPS)