I stumbled across the '75 studio sessions last night on the archive. If you haven't heard these they're really worth listening to. Of special interest to me was on 3-17-75, where keyboardist Ned Lagin and David Crosby hung out with Phil, Jerry, and Kreutzmann and just messed around and jammed all day. There's a transcript of a radio interview somewhere out there with Ned Lagin talking about that day. From all the giggling and diologue in the background I can only assume they were all tripping, lol. There's a lot of really cool jams, including some based on the theme of Crosby's tune "Low Down Payment" but there's one track in particular that sticks out, a 25:00 or so jam that starts out very spacy but ends up turning into a lot of rhythmic and harmonic interesting-ness by 10-12 minutes in. Very cool. Sound quality is pretty great, too. Check it out!