Some excellent reference material on the PERRO sessions:
http://www.philzone.com/philbase/perr...

"The Mountain Song - 1" (5' 11"): This is the first of several attempts at what would eventually become a slice of classic Airmachine. However, at this stage, the only fragment of the song they had to work with was the line "Gonna make the mountains be my home" and the chord-sequence that supported it, so it's quite amazing that from such a meager base Kantner, Slick, Crosby and Garcia (possibly with Casady and Hart) are able to conjure 23 minutes of undulating beauty. There's a banjo featured prominently, plus two acoustic guitars and Grace's distinctive piano. The banjo is Paul K.& the touches are so accomplished, it's Kantner on the five- string with Garcia and Crosby on guitars. Surprisingly, there's no trace of Paul's vocal - though the other three take care of that handsomely enough.

Early on, it's Jerry singing the line in orthodox fashion, while Grace embellishes with some improvised lyrics around the theme. Then Crosby takes Grace's place and scats around Jerry's vocal for a while. As you'd expect, the playing is loose and slightly tentative on this first version, but no less affecting for all that.

"The Mountain Song - 2" (5' 17"): Grace is back providing an improvised descant to Jerry's straight vocal at the start here, and she's singing about the sky and the river as he eulogizes the mountains. After a minute or so, Crosby introduces his scat and Grace leaves the chorus to concentrate on her keyboards. Her vocal chords are re-engaged towards the close.

"The Mountain Song - 3" (3' 44"): This version begins with Jerry and David singing the line and Grace gliding around them. Briefly, Crosby supersedes her in this role but soon the two of them are improvising around the structure as Jerry perseveres in the middle.

At the end of this effort, Paul is heard to remark "It sounds like everybody's going in and out of time" to which Crosby responds "No, no, no, it's all working - and it works perfectly." The listener is strongly inclined to agree with him.

"The Mountain Song - 4" (8' 20"): As you'll see, this is the longest version and undoubtedly the most satisfying of the four. This is where Crosby's embryonic "Walkin' In The Mountains" suddenly reemerges and he goes through the verse and various chord sequences as an introduction to "The Mountain Song," to which it bridges seamlessly and beautifully. It's a remarkable segue which makes the listener keenly aware of how the song could have developed in a very different direction had Crosby stayed to contribute throughout its evolution. Speculation aside, what we do have is a return to the familiar pattern of banjo, guitars, bass, piano and percussion. Crosby reverts to his scatted counterpoint before it slips into a stunning instrumental section. Herein, the music weaves a genuinely hypnotic spell as it rolls effortlessly along the bed of Paul's banjo and Grace's piano, with Garcia picking exquisitely. After several minutes of this, the vocal pattern is re-introduced, now in a more restrained vein against instrumentation which has become subdued, with Grace and the Cros gently dancing around Jerry to the finale of a wonderful excursion.