Yellowstone National Park contains over half the world's active geysers, with more than 700 within its 3,472 square miles. The most famous geyser is Old Faithful, named in 1870 during the Washburn-Langford-Doane Expedition. In 1871, the US Geological and Geographical Survey, led by Dr. F.V. Hayden, reached the Upper Geyser Basin. In just over a day, the explorers witnessed eruptions of many geysers still seen today, including Giantess, Beehive, Grotto, Castle, and Old Faithful. Yellowstone became the first National Park in 1872. Since then, visitors have come in increasing numbers to witness the unique geysers, numerous wildlife, and spectacular scenery.