Crumbproducts.com has three of the autobiographical pieces written by R.Crumb as introductions to The Complete Crumb series. They're worth a read! Someone should collect together all Crumb's written pieces and interviews into one place... that would be a great book as he's always entertaining.
Anyway, they have :
"Minds are Made to be Blown" Crumb reflects on 1966-'67
"Roughing It" Crumb in the early '70s
"Dealing With Reality" Looking Back at Work and Music in 1972–73