I recently spent a weekend at Lake Almanor in Northern California.
These images were from Bumpass Hell. It is a 1.5 mile hike to get to this area where you can walk on boardwalks to see many different volcanic features. It smells very strongly of rotten eggs, but it was pretty cool to see all bubbling water and steam.
We hiked in on a Saturday so the trail traffic was very heavy. I would advise if you have a choice check out Bumpass Hell on a weekday to avoid the crowds.