At 3,472 square miles—over 2.2 million acres—Yellowstone is larger than the states of Rhode Island and Delaware combined. The vast majority of its territory is situated in Wyoming, but it also creeps into neighboring Montana and Idaho. Though not the largest of the United States’ national parks, it is noteworthy for its dense concentration of geysers, mudpots, steam vents and hot springs. According to UNESCO, which has designated Yellowstone a World Heritage Site, half of all the known geothermal features on the globe are nestled within the park.