The 8 foot diameter pool of
Spa Geyser contains two separate vents and is filled with clear blue water, ringed by thin-layered ledges of sinter, partly broken. The geyser lies close to the trail, beside the junction with the short loop to the viewing area for
Riverside Geyser; water from its eruptions flows east 200 feet into the Firehole River. Activity is tied to that of
Grotto Geyser to the south; Spa produces jets of water up to 40 feet high, though usually much lower, and eruptions last from several minutes to several hours.
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map of the Upper Geyser Basin