Lassen Volcanic National Park was the last place I hit prior to heading up the coast and back to Washington. It’s kinda tucked back in the middle of nowhere in California, and was kind of annoying to get to. Once there it immediately reminded me of a VERY small scale Yellowstone… mainly due to the pleasant aroma of sulfur in the air. The features here are no where near the scale of Yellowstone, and has far fewer hydrothermal areas.
Although you won’t get the same experience as a Yellowstone, there’s also a much smaller population of assholes to bother you while you’re adventuring around the park. We rarely ran into other hikers, or even cars, the entire time we were there. It just felt very peaceful, and the nature surrounding the area was even prettier in areas. The color of the water was stunning, but unfortunately my camera couldn’t quite capture the depths of the colors as well as I had wished (much like at Crater Lake National Park).
If you’re in this area of California I would suggest visiting Lassen Volcanic to anyone, although if it’s out of the way (and especially if you’ve already seen Yellowstone), you can safely skip this national park. You’re not going to see anything new here that you can’t see on a much grander scale in Yellowstone, or hikes around the Washington/Oregon areas. It’s a beautiful place, but isn’t worth the effort to get there unless you’re as obsessive as I am about seeing all of the national parks.