Fan and Mortar Geysers

Fan and Mortar Geysers are two geothermal formations in the Upper Geyser Basin that discharge hot water and steam from multiple vents near the Firehole River. The water temperatures reach about 48 degrees Celsius (120 degrees Fahrenheit), creating a dynamic landscape with active thermal outlets and mineral deposits around their bases.

The area was discovered during early explorations in the 1870s when surveyors and naturalists began documenting the geyser region. These formations received their names from early explorers who studied the geothermal landscape and its distinctive features.

These geysers represent the geological forces that led Congress to establish Yellowstone as the first National Park in 1872 to protect natural phenomena.

You can view both geysers from a bridge and boardwalk that leads to a larger thermal pool area. Wear sturdy shoes since the ground is uneven and can be slippery from mineral deposits and moisture.

Beneath the ground, the two geysers are connected through an underground channel system that sometimes causes them to erupt in sync. This subsurface link makes their eruption patterns unpredictable and means no two visits display the same behavior.