For a while I was most well known for that [the Janis Joplin album cover], and for Keep on Truckin'. That was a drawing that came out of LSD trips, and the words came from a Blind Boy Fuller song from 1935. I drew it in my sketchbook and then for Zap. It sort of caught the popular imagination. It became a horrible popular thing.

"R. Crumb, The Art of Comics No. 1", The Paris Review, Summer 2010, No. 193.