You can't actually get any more '70's than an album cover or painting by Roger Dean.
Dragon's Dream published Views, a best-of combination portfolio / book in 1975, and I snapped it up, even though we already had most of those triple-gatefold albums around the house, my dad being massively into prog rock in general, and Yes in particular at the time.
Some of this stuff is literally amazing, and really does give you the feeling of entering another world, much like Moebius or Caza.
It's also good to look at work like this through fresh eyes occasionally, some of these images being so familiar that you can almost take them for granted. But this is the kind of art you can wallow in.
My favourite's probably the multi-armed priest / prophet that used to adorn Dave Greenslade's solo albums, mainly 'cos I always wanted him to get his own comic strip.