You might want to go to Lassen in September or early October at the latest. Just a word to the wise, unless you are ready for the chance of the blizzard. We'll be there with hiking friends in September, so if you are there then, let me know if you want to meet. The group is finishing a bunch of hikes we didn't get to do; two of them were done in snow back in the original group camp in late June.We are working on this also. Up to 55 as of now. Redwood and Lassen in October. Only 7 left after that.
We went in late June 4 years ago and almost froze two nights. Mid/Late October might be pushing it, but then you might be lucky! Go to Redwoods after Lassen (we hikers went to Redwood the year before COVID; I was responsible since I'd always wanted to go there.)