It's their signature song, but they didn't write it. Dino Valenti did in the mid-sixties and it was recorded earlier by The Byrds and even Jefferson Airplane, before Grace Slick joined them.
I much prefer some of their lesser-known fare, such as: Grizzly Bear; Sugar Babe; Quicksand; Darkness, Darkness; The Wine Song; Sunlight; Euphoria; and this somber gem written by Young:
The song is found on Earth Music, 1967 and the band members are:
Jesse Colin Young (bass, vocals)
Joe Bauer (drums)
Lowell Levinger (piano, guitar, pedal steel, vocals)
Jerry Corbitt (guitar, vocals)