Introduction to the Lower Geyser Basin: The Lower Geyser Basin covers approximately 12 square miles and is the largest fountain area in Yellowstone Park. The timing of the fountains in this area is unpredictable. Only the Great Fountain Geyser erupts every 9 to 15 hours. In addition, the Fountain Paint Pot is a swamp-like spring that boils due to geothermal heat. Braving the hot mud bubbles, it really lives up to its name; other sights include: Firehole Lake Drive, White Dome Geyser, Imperial Geyser, Pocker Basin Mud Pots, etc.