Wyoming's Yellowstone National Park, first established in 1872, is a wonderland of deep canyons, majestic mountain ranges, four major rivers, beautiful lakes, impressive waterfalls and a land teaming with wildlife. Best known for its geysers, the park is home to over 10,000 geothermic features, with nearly 300 active geysers. While most are sporadic and small, six geysers erupt on a predictable basis and top 100 feet in height. The remainder of the park's geothermal features consist of boiling pools, steaming fumaroles, hot water seeps and bubbling mud pots.
   Geology, one of the last things on the mind of Yellowstone's visitors, has recently caught the attention national park fans. A new hot spot in the Earth's crust melted an asphalt road along the Firehole River and closed the access to geysers and other thermal features in the area. Little do park guests realize that Yellowstone National Park is centered on one of the world's largest calderas. The Yellowstone Caldera, meaning cooking pot in the Latin form, generates a tremendous amount of heat just a few miles below the earth's surface. Here in a transition zone between the molten magma and the earth's upper crust is a layer of partially molten crystalline rock. Underground tests in 1920 revealed temperatures at 265 feet exceeded 400 degrees Fahrenheit. When water seeps down from the surface through cracks and porous rock, these extreme temperatures produce high pressure steam which looks for the easiest way to escape. Here at the Lower Geyser Basin region, along the Firehole River, hot water and steam rush to the surface as geysers, springs, mud pots, and steam vents.
   While Yellowstone's Old Faithful is the most famous geyser in the Upper Geyser Basin, eight other prominent geysers, named Grand, Lion, Anemone, Giant, Plume, Aurum, Beehive and Giantess, are within view of the Old Faithful Inn and visitor center. Northward, spanning the park road, Midway Geyser Basin, Norris Basin and Lower Geyser Basin reveal some of the largest hot spots in the park. Lower Geyser Basin is the largest geyser basin in Yellowstone, covering about 18 square miles. No other area in the park equals this basin in terms of hot water discharge. At one time, measurements recorded 15,300 gallons per minute.

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