Today is the 50th anniversary of Jefferson Airplane's iconic psychedelic rock album Surrealistic Pillow. The unofficial soundtrack for San Francisco's Summer of Love debuted on Feb 1, 1967 and has since gone on to be ranked #146 in Rolling Stone's list of the 500 Greatest Albums of All Time.

To celebrate the occasion, here are 5 things you probably didn't know about this classic record.

1. Grace Slick's Debut

'Surrealistic Pillow' is the Airplane's sophomore record. But it's the first featuring Grace Slick on vocals. And it's hard to imagine the band without her pipes belting out hits like "Somebody to Love" and "White Rabbit."

2. Jerry Garcia's Cameo

The legendary co-founder of The Grateful Dead is credited on the 'Surrealistic Pillow' album jacket as Jefferson Airplane's "spiritual advisor" -- meaning a go-between that worked with the band and the album's producers to make sure the recording was faithful to the group's artistic vision.

Garcia also allegedly played guitar on tracks including "Today."

3. The Obscure Cover Song

The band's biggest hit of the record -- "Somebody to Love" -- is actually a cover of Grace Slick's earlier work. From 1965-66, she was the singer of The Great Society, who released 'Someone to Love' in February of 1966. Don't let the title fool you: it's the same song but with a much different arrangement. Check out the original version:

4. Raga White Rabbit

Great Society also released an alternate version of Slick singing "White Rabbit" on the 1968 album Conspicuous Only in Its Absence. Recorded during a set at San Francisco's counterculture club The Matrix earlier in their career, the Society's take on "White Rabbit" is almost three times longer than the Airplane version and it has more Indian influences -- much like the era's raga rock.

5. Covers, Covers, Covers

'Surrealistic Pillow' is Jefferson Airplane's best and most-covered album, which isn't shocking given the record's influence. But the covers the artists covering the seminal psychedelic band are often surprising. From The Ramones' punk homage to Somebody to Love (with Traci Lords singing backup vocals), to P!nk's rendition of White Rabbit for Disney's 'Alice Through the Looking Glass'.

But we're going to go off the beaten path and give you The Allman Brothers Band's 1968 cover of 'She Has Funny Cars.'

Banner image: The group in 1966 after Spencer Dryden replaced Skip Spence on drums. (wikipedia.org)