Anybody know why 8 miles is significant? As well as the Byrds' song '8 miles high', the phrase crops up in Mickey Newbury's 'Just dropped in', and I've come across half a dozen or so examples in 60's counter-culture music, although right now I can't remember where....
Thankyou very much, mattk. Following your suggestion I found that the lower reaches of the tropopause (on the boundary between the troposphere and the stratosphere) is reckoned to be about 9 miles up, offering an answer which is well within a stoner's judgemental faculties.