Volcanology
Your question is a popular one! For more about becoming a National Park ranger, check out this answer from our partners at the Association of National Park Rangers.
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Don't miss Mammoth Hot Springs, the geysers, especially Old Faithful, the Grand Canyon of Yellowstone and wildlife in the Lamar Valley!
Some great tips from other visitors are available here: http://www.ohranger.com/qa/15619/how-many-days-do-we-need-see-most-yellowstone-national-park
If you're interested in seeing wolves at Yellowstone, get expert tips here: http://www.ohranger.com/yellowstone/oh-ranger#comment-151



