Grand Prismatic Spring
The largest hot spring in the United States and the third largest in the world. About 110 metres across, it has a deep blue centre and a rainbow-like ring of yellow, orange and red microbial mats. The boardwalk overlook offers the best panorama.
Grand Prismatic Spring sits in the Midway Geyser Basin. It is about 110 metres across and 50 metres deep, making it the largest hot spring in the United States. The water at its centre is about 70°C, and the deep water looks deep blue because it absorbs red light. Moving outward, the water cools, and different heat-loving bacteria and algae grow at different temperatures, forming concentric rings of green, yellow, orange and red. Seen from above, it looks like a coloured eye. There are two ways to view it. The first is a loop boardwalk of about 1 km from the Midway Geyser Basin car park, passing the huge Excelsior Geyser crater and reaching the edge of the spring. Here you can feel the heat and see the colours, but only the outer ring is visible from eye level. The second is to go to the Fairy Falls trailhead car park about 1.5 km to the south. Walk about 1 km along the trail and then climb to the Grand Prismatic Overlook, which is about 1.3 km one way. This is the only place to photograph the classic full-colour rings, so it is worth doing both. Continuing along the Fairy Falls trail leads to the 60-metre Fairy Falls (about 8 km return).
Tips: The car park is often full between 10:00 and 16:00 in summer, so arrive before 9:00 or after 17:00. The steam drifts in the direction the wind blows. Colours are best on clear, dry afternoons. Never leave the boardwalk, as the ground around hot springs is very thin. It is about 13 km from Old Faithful.
Opening hours
Open all day (road open about late April–early November)
Nearby sights
- Fairy Falls Trail & Grand Prismatic Overlook
- Fountain Paint Pot
- Upper Geyser Basin & Morning Glory Pool
- Old Faithful
- Old Faithful Inn
- Firehole Canyon Drive & Firehole Falls
- Lone Star Geyser
- Gibbon Falls