Yellowstone has more thermal features -- geysers, mud pots, and steam vents -- than the rest of the world combined. When you're angling for a good shot of a colorful pool or a belching mud pot, obey the signs -- otherwise, you could find yourself, literally, on shaky ground.
- Old Faithful Geyser: While not quite as faithful as it used to be -- the intervals average 74 minutes but sometimes stretch as long as 120 minutes -- it's still the most predictable geyser on the planet, blasting water 130 feet into the air more than 20 times a day. How could you skip this one?
- West Thumb: This lakeside thermal area is a must-stop for its collection of gemlike hot pools and steaming vents, as well as Fishing Cone, where early visitors poached their catch -- until they realized the scalding water had natural traces of arsenic.
- The Mammoth Hot Springs Terraces: Here you can observe Mother Nature going about the business of mixing and matching heat, water, limestone, and rock fractures to sculpt the area. This is one of the most colorful areas in the park; its tapestries of orange, pink, yellow, green, and brown, formed by masses of bacteria and algae, seem to change colors before your eyes. The mineral-rich hot waters that flow to the surface here do so at an unusually constant rate, roughly 750,000 gallons per day.
