|Boiling mud pot at Sulphur Works.|
It was a clear day, and we drove into the park from the south, taking Highway 36 to Highway 89 north (AKA the Main Park Road), up past the newish Kohm Yah-mah-nee Visitor Center, past Emerald Lake, past the turnoff to Bumpass Hell, past Lake Helen, past the Lassen Peak trailhead, and over the pass a little ways until we turned back around (map of the park).
We had stopped at Sulphur Works on the way up to note the ways in which the hydrothermal activity had changed since our first official visit to the park sometime in the early 2000s. (Earlier visits of mine/ours prior to this more recent era have faded into a distant non-digital past.)
As far as I know, this boiling mud pot came into existence in late 2007, and it grew considerably by early 2008. We remember from earlier trips that the main roadside attraction (besides a side trail that is now closed due to a shifting in the location of hydrothermal features) had been across the road: an active fumarolic area with several vents, and possibly with a mud pot. These fumaroles were barely steaming on our recent trip, though fumarolic activity can vary with air temperature and other factors.
My somewhat shaky mud pot video.
If anyone knows anything more definitive about the history of this mudpot, please let me know.
UPDATE 21Oct2012: Google Street View shows several fumaroles but no mud pot in this location in photos dated 2007.