Mike Keller has studied Yellowstone’s thermal features and volcanic underworld since high school, and when he’s not busy directing operations for the park’s concessioner, he spends most of his free time geyser gazing. As the president of the Geyser Observation and Study Association, Mr. Keller possesses both an extreme passion and an extensive knowledge about all things geothermal.

Seasonal migrations offer special opportunities to see wildlife herding and flocking, leaving, passing through, and arriving in our national parks.

Winter long has been regarded as the slow season for national park visits, and that's a good thing if you prefer to have the parks to yourself. With most travelers confined by school schedules to the summer months, and many convinced winter is a bad time to be outdoors, you can savor the best of the parks from coast to coast in winter. Here are some snapshots of wintry fun in the parks that bear that out.