This, in my opinion, is one of the more interesting parks in the US. Located in the northern region of California the park encompasses large areas of a once active volcanic zone where erosion still has not had its full impact and volcanic rocks are visible everywhere and more interestingly undergrond lava tubes can be accessed easily.
My trip with a friend took place in August 1988 for about a week. A troublsome task that we had to endure was the continuous removal of small volcanic pebbles that would fall into our hiking boots no matter how much care we took to close the tops. Another was the dust that occured whenever the winds got a bit stronger.
An enjoyable diversion was the exploration of the undergournd laval tube of which there are numeorus scattered around the park. One that we explored was almost as mile long and looked as if we were going down the throat of a monster similar to that in Star Wars that lived on an asteroid. (image of tube)
Water was not as much a problem as at first seemed. There are smaller to larger lakes scattered around the park though it may be a day's hike from one to the other.
As a final note: a climb up Mt. Lassen is well worth the effort since the views present a beautiful mosaic of barren lava rock, pristine forests, and emerald blue lakes. Mt. Shasta is also clearly visible and with luck will have a ??? (that ring cloud, as JS) cloud around its top.
The images below are from an earlier trip where the group I was with entered a laval tube that was below two other ones. As you can see there is a small frozen pond, this during the middle of August! What happens here is that during winter the cold air moves down the lava tubes and collect at the bottom of the lowest one. The air being below zero any water that reaches this lower level is frozen. Then during summer the colder air is basically traped and keeps the water frozen year round, the lava acting as an efficient insulator. Quite an interesting sight.
I don't quite recall where the location was but that it is underneath a small road that passes through the park.