Activity of Mortar Geyser
is closely related to that of adjacent Fan Geyser
; they are situated on the east bank of the Firehole River (west of the path), surrounded by well established sinter formations. Mortar has three vents, one enclosed by a three foot cone, the other two lower down to the east. It is the smaller erupting of the two geysers, emitting water to a height of 80 feet, during a performance that lasts for around 45 minutes. Eruptions are still very forceful, however, made more impressive by the river running just beyond, and the pair of geysers would be more well known were it not for the rather long distance (1.6 miles) from the start of the trail at Old Faithful.
Back to map of the Upper Geyser Basin