The water in Sponge Geyser
often completely fills the raised cone, which is formed of grey-brown sinter with an uneven surface, resembling a sponge. Like Pump Geyser
on the opposite side of the trail, Sponge Geyser is generally very active, throwing water 1 or 2 feet in the air over a period of up to one minute, with a similar interval between eruptions. In recent years the spring has become less spectacular, however, the water rising and falling but not being ejected. The large cone partly obscures two other small geysers behind, Plate and Slot.
Back to map of the Upper Geyser Basin