Sawmill Geyser

Sawmill geyser is a small fountain-type geyser in the Upper Geyser Basin. It is the largest geyser in the Sawmill Group and is located approximately 10 feet off the boardwalk near Churn, Spasmodic, Penta, and Tardy geysers.

Eruption Pattern
The geyser has an irregular pattern of eruption due to the underground structural interconnectivity which is characteristic of geyser complexes. Often, Sawmill will erupt after the nearby Spasmodic Geyser, but only if Penta Geyser, another significant geyser in the complex, does not erupt first. If Penta erupts before Sawmill, Sawmill is cut off from water, and cannot erupt until the basin is recharged, indicated by an eruption by Spasmodic. Another eruption indicator is when Sawmill fills with the rest of the geyser's water in the Sawmill Complex or starts to overflow, bubbles tend to rise to the surface. This indicates that an eruption is near. Sawmill drains after its eruptions, and if it had a large eruption prior, unusual behavior can occur in other geysers in the area.

History
Sawmill geyser was named by Antoine Schoenborn of the Hayden Geological Survey of 1871. It was named for the whirring sound it makes during its eruption.

In 1993, several observations of the geyser indicated no signs of eruption.

Current Activity
Sawmill erupted regularly and frequently in recent years prior to January 2017, when eruptions suddenly ceased. Sawmill's last observed eruption occurred during the morning hours of January 29, 2017.

As of 2019, observations of the water level were being made frequently, with notes made in July and August 2019 indicating that the level was fluctuating above and below the orange bacterial line ("bathtub ring") inside the pool.