See the context of this sign.

Fossil Fumaroles - Crater Lake

The history of the strange rock formations in
front of you began about 7,700 years ago
when the eruptions of Mt. Mazama were reaching
their climax. Torrents of red-hot, gas-charged
pumice poured down Mazama's slopes at speeds
of up to 100 mph (160kph). On top of this came
a flow of heavier rocks called scoria. These
glowing avalanches flooded downslope for many
miles, leaving deep deposits in their wake.

Temperatures in the deposits may have
exceeded 750 F (400 C). Plumes of vapors
appeared, as gasses escaped from the settling
rocks through vents called fumaroles. Minerals
in the gasses, combined with extreme heat,
welded the sides of the fumaroles in the shape
of slender cones. Since then, Annie Creek has
eroded a canyon through the deposits, exposing
the foxxil fumaroles as pinnacles and columns.

The depth of the canyon here at Godfrey Glen
is about 250 feet (75m).

Don't miss the rest of our virtual tour of Crater Lake National Park in 1757 images.