Jesse Stavro's Doorway by Marshal Tenner Winter

Jordan is looking for his friend, Jesse, who is in hiding from the government. Picking up the trail, he discovers that Jesse is following the Grateful Dead on tour, but as Jordan immerses himself into the "deadhead" culture, he learns that Jesse is not currently in the same decade as those searching for him. The world is full of doors and logic is an illusion in this drug-fueled, time-travel adventure tale.