Midway Geyser Basin
The primary geothermal feature of the Midway Geyser Basin is the Grand Prismatic Spring. It’s brilliant red, orange, yellow, green, and blue colors match the rainbow dispersion of white light by an optical prism, producing the beautiful hot spring that has become one of the most famous icons of Yellowstone National Park. With a diameter of approximately 370 ft/113 m (and a depth of 121 ft/36.9 m), it is the largest hot spring in the park and in the United States.
A wheelchair accessible boardwalk begins at the east end of the parking lot and crosses a bridge over the Firehole River where you get to see streams of runoff (4,500 gallons per minute) from Excelsior Geyser rushing down the hill and directly into the Firehole River. The path then climbs slightly upward via a switchback until at the level where you pass by Excelsior Geyser Pool/Crater (now a dormant fountain-type geyser, but in the late 1800’s was an active geyser with eruptions ranging from 100 to 300 feet in height and width). Here the path splits providing a loop where you will also pass by Turquoise Pool and Opal Pool in route to or from the star of the show, the Grand Prismatic Spring. However, if you want to see the Grand Prismatic Spring in all its glory, from the vantage point of its overlook, you will need to access that trail from a parking lot located a mile further down the road on the Grand Loop drive. It is a hike worth taking. (See Trailhead to Grand Prismatic Overlook and Fairy Falls). The basin has a large parking lot with many spaces for vehicles including RV’s and buses. However, during peak season a waiting line is often created. Adjacent to the parking lot are four single restrooms and trash dumpsters.