Old Faithful, the world's most famous geyser, is one of 25 named geysers in Yellowstone's Upper Geyser Basin. The Upper Basin holds the largest collection of geysers in the world and spreads out for almost three miles along the Firehole River. This area of hot springs, geothermal pools and lively geysers is one of the most active hot spots on earth. Yellowstone National Park surrounds an active volcano, with molten lava lying as close as three miles below the surface. Rain and snow melt seep into a myriad of cavities and crevices, providing water to power these huge steam jets and fountains.
   The Castle Geyser cone, pictured here, is thought to be thousands of years old. This geyser keeps a fairly regular schedule, such as Old Faithful, and shoots out a 75 foot stream that lasts almost 20 minutes. The nearby Grand Geyser is the worlds tallest, predictable fountain geyser, sending out a burst up to 200 feet.
   Although all of this thermal activity is exciting, Yellowstone National Park is more than geysers and fumaroles. The park road weaves through majestic mountain ranges, alongside major rivers and lakes and traffic is quite often stopped for bison, bear, elk and moose.

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