Bumpass Hell is a volcanic area inside Lassen National Park.
You walk on a wooden walkway (the ground is too soft -- and in
some places too hot -- to walk safely) past fumaroles (steam
vents), boiling springs, and bubbling mud pots. The ground
is colored with sulfur and other chemicals.
Oh, and note the romantic self-portraits -- our shadows in
the mists of Bumpass Hell. :-)
Next: Lassen Peak.