There are a lot of references on the internet of places claiming to be the filming location for Return of the Jedi. A lot of them are wrong, but they did film in several locations.

Most of the big action sequences and stuff with the principal actors were filmed on private property owned by Miller-Rellim Lumber Company in the Smith River Tract north of Crescent City. They needed a secluded area that they could have for a long period of time and where they could blow stuff up which ruled out national parks. This land has since been logged so it doesn't look anything like it did in the movie anymore.

The steadycam shots for the speeder bike sequences were filmed at Owen Cheatham grove in Grizzly Creek Redwoods State Park. I was able to find shots from the movie that lined up perfectly when I visited there.
http://www.starwarslocations.com/mediagallery/album.php?aid=55&page=1

I had a chance to ask Dennis Muren a question about the Endor scenes a few years ago and he recalled shotting from the back of a truck in the Avenue of the Giants to get the side views of the speeder bikes zooming by the trees.

The only other areas used that I can think of were for the Ewok television movies. I don't exactly where those were filmed but I'm sure they were shot much closer to Skywalker Ranch to save on production costs.

Bill