Grotto Geyser is named for the interesting cavern-like shape of its "cone". I put the terms in quotes because what you see when you look at the geyser cone is only partially the cone itself; the standing formations are actually trees, which over the course of many years, have been covered in sinter forming the intricate structure of the geyser.

Grotto is a very active geyser, often spurting, gurgling and splashing for hours at a time. It only reaches a maximum height of 20 or 25 feet; this image shows one of the biggest splashes I saw when we were there.