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Photo: Mav at English Wikipedia, CC BY-SA 3.0 via Wikimedia Commons
This large area of hydrothermal activity can be viewed by foot along the boardwalk trail at Fountain Paint Pots and by car along the 3 mi Firehole Lake Drive. The latter is a one-way drive where you will find the sixth geyser predicted by the Old Faithful staff: Great Fountain. Its splashy eruptions send jets of diamond droplets bursting 100 - in the air, while waves of water cascade down the raised terraces. Patience is a virtue with this twice-a-day geyser, as the predictions allow a 2-hour (plus or minus) window of opportunity. Fountain Flats Drive departs the Grand Loop Road just south of the Nez Perce picnic area and follows along the Firehole River to a trail head 1.5 mi distant. From there, the Fountain Freight Road hiking/biking trail continues along the old roadbed giving hikers access to the Sentinel Meadows Trail and the Fairy Falls Trail. Also along this path is the only handicapped-accessible backcountry site in the Old Faithful district at Goose Lake.
The geothermal areas of Yellowstone include several geyser basins in Yellowstone National Park as well as other geothermal features such as hot springs, mud pots, and fumaroles. The number of thermal features in Yellowstone is estimated at 10,000. A study that was completed in 2011 found that a total of 1,283 geysers have erupted in Yellowstone, 465 of which are active during an average year. These are distributed among nine geyser basins, with a few geysers found in smaller thermal areas throughout the Park. The number of geysers in each geyser basin are as follows: Upper Geyser Basin (410), Midway Geyser Basin (59), Lower Geyser Basin (283), Norris Geyser Basin (193), West Thumb Geyser Basin (84), Gibbon Geyser Basin (24), Lone Star Geyser Basin (21), Shoshone Geyser Basin (107), Heart Lake Geyser Basin (69), other areas (33). Although famous large geysers like Old Faithful are part of the total, most of Yellowstone's geysers are small, erupting to only a foot or two. The hydrothermal system that supplies the geysers with hot water sits within an ancient active caldera. Many of the thermal features in Yellowstone build up sinter, geyserite, or travertine deposits around and within them.
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This geyser basin is on a hill overlooking the Firehole River. Smaller in size than the other geyser basins in the area, the runoff from its thermal features flows into the river, leaving steaming, colorful trails in its wake. In particular, Excelsior Geyser reveals a gaping crater 200 x with a constant discharge of more than 4000 gal of water per minute into the Firehole River; this geyser once erupted so violently that it may in fact have blown itself up, and no eruptions have since occurred. Also in this surprising basin is Yellowstone's largest hot spring, the beautifully-colored Grand Prismatic Spring. This feature is 370 ft in diameter and is 160 ft deep. The Fairy Falls trailhead provides access to an observation platform on the hill behind the spring that lets you get an elevated view of the entire basin.
Firehole Canyon Drive, a side road, follows the Firehole River upstream from Madison Junction to just above Firehole Falls. The drive takes sightseers past 800 ft thick lava flows. Firehole Falls is a 40 ft waterfall. An unstaffed swimming area here is very popular in the warmest of the summer season. Cliff diving is illegal.
The mountain is part of the lava flows that encircle the Madison Junction area. Near this site, in 1870, the Washburn-Langford-Doane Expedition is said to have camped and discussed the future of the region they were exploring. Legend has it that this was where the idea of the national park was discussed, but there is no evidence of the campfire conversation ever taking place, and there is certainly no evidence to show that the idea of a national park was discussed.
The Madison River is formed at the junction of the Gibbon and Firehole rivers, hence Madison Junction. The Madison joins the Jefferson and the Gallatin rivers at Three Forks, Montana, to form the Missouri River. The Madison is a blue-ribbon fly fishing stream with healthy stocks of brown and rainbow trout and mountain whitefish. The canyon created by the river consists of steep, tree-covered rock walls on each side.
The river derives its name from the steam (which they thought was smoke from fires) witnessed by early trappers to the area. Their term for a mountain valley was "hole," and the designation was born. The Firehole River boasts a world-famous reputation for challenging fly-fishing. Brown, rainbow, and brook trout give the angler a wary target in this stream.
Yellowstone, as a whole, possesses close to sixty percent of the world's geysers, and the Upper Geyser Basin is home to the largest numbers of this fragile feature found in the park, including the iconic "Old Faithful" geyser. Old Faithful, the world's most famous geyser, has large eruptions occurring an average of about once every eighty minutes, although the timing between each eruption varies by as much as an hour and has been increasing over the years. Rangers are able to predict the geyser's eruptions to within about ten minutes, provided the duration of the previous eruption is known. In addition to Old Faithful, this basin contains an additional 150 geysers within a one square mile (0.25 mi2) area; of this remarkable number, the eruptions of Castle, Grand, Daisy, Riverside, and Old Faithful are predicted regularly by the naturalist staff. In addition to geysers the area is home to numerous hot springs. Boardwalks allow access to the most interesting areas. Do not leave the trails; the surface here is thin and unstable and has a real chance of depositing you in a boiling pool of water if you walk where you're not supposed to.