It can be said that Spinal Tap might've risen from the ashes of Lenny & the Squigtones, the pre-fab band Michael McKean & David Lander formed on Laverne & Shirley. Christopher Guest introduced his ST persona as Nigel Tufnel when he sat in with the Squigtones on American Bandstand in 1979. Five years later, Spinal Tap is brought to life in the mockumentary, "This is Spinal Tap", directed by Rob Reiner (ex-All in The Family).
McKean is David St. Hubbins opposite Tufnel and Derek Smalls (Harry Shearer), and is the band's lead singer. The trio also wrote the movie with Reiner and wrote the songs, including this soft rock track, purported to be from 1967, "Listen to the Flower People".
Having never seen the movie, I have to say I'm impressed.