Zep's "In the Light" off PG. I was in my early twenties and doing some car camping in and around the four corners/canyonlands region with my GF. I remember we were driving one morning and crested a cap rock which started a descent into a valley floor and all across the valley and on the horizon were some of the most extraordinary, fantastic and bizarre rock formations I'd ever seen. Off in the near distance on the horizon was a solid white cliff wall which, amongst all the red rock, looked like some sort of ancient, lost temple. I spotted that just as the song began and the light dose of acid we'd taken earlier started to kick in. The spacious, ethereal synth intro created the perfect soundtrack to what I was observing and it remains a vivid memory to this day. That trip was the first of several explorations in and around the desert and mountain southwest....which were profound, life changing experiences (to say the least) and a few of the trips ended up at Dead shows in Vegas (some of their last ones). A very defining episode of my life and that moment coming down into that valley seemed to be the moment that kicked it all off.