Steve,
Richardson's Grove is good.
So are Hidden Springs and Albee Creek... They are listed at
http://www.humboldtredwoods.org/
( Might want to click on "Other Nearby State Parks... about 14 others listed, not to mention all the county parks)
Go
Here for Humboldt County Parks...16 I think.
You don't have to drive far to find a campground in Humboldt County...
One thing I like about Albee Creek, although the trees right in the campground are kinda dinky, is that it's just past Bull Creek.
Take the road to Honeydew at the Founders Tree and enjoy the Bull Creek area in the Rockerfeller Forest on your way to Albee Creek.
Bull Creek is about my favorite place as far as photographing the trees.
See my kids???
BTW- If you're heading farther North afterwards for a day or two, might wanna try Jed Smith park along the Smith River on 199 just past Crescent City... I think it's the most beautiful river in the world...clad in giant redwoods "a coarse".
Heck... You may as well just move here.
