I've been to the Klamath National Forest a few times for backpacking, and it's amazing! One of the…read moreless populated places for camping/backpacking, so you don't need a permit for most trails. I've been to three different wilderness area within the Klamath, and each has their own advantages and disadvantages.
Marble mountains wilderness:
The marble mountains are really nice. I hiked the monument lake trail this past summer, and it is one of my favorites. Despite it being 4th of July weekend, we only encountered one other person on the trail, and often times had entire lakes to our self. We went to Monument lake, one mile lake, and cuddihy lakes. Monument was by far the best, cuddihy was nice, but one mile wasn't worth visiting in my opinion. The water is warm and there's a ton of stuff growing at the bottom of the lake. Fishing is nice at all three lakes.
There is a lot of wildlife at the marble mountains as well. I saw elk, deer, chipmunks, a black bear on the access road, and plenty of insects
Trinity alps:
Came here in fall of 2025 for a short one night backpacking trip on the canyon creeks trail. The trails here were pretty crowded, but it had great views and amazing camping sites. If you hike this specific trail, I'd recommend camping below the lake instead of on it, as it is very cold, windy, and rocky near the lake. Unfortunately, didn't catch any fish here.
Russian wilderness:
Went here this past Labor Day weekend, and it was my favorites! We did the duck lake trail for two nights, which isn't too hard of hike. It was moderately crowded, but it wasn't like you couldn't find a campsite. Not as much wildlife here, although that may be season dependent. We also took the trail up to horseshoe lake, which is a worthwhile hike, horseshoe had the best fishing by far, I caught at least a dozen fish. Also, horseshoe wasn't as corded as the lower duck lakes, which was nice.
The Klamath is a great place to camp/backpack in NorCal!