Sal's sorrow becomes stronger: farewells aren't the exciting launching points they were before, but moments of contemplation. Movement--parting and change in life--is not a choice, but inevitable: the "too crazy world vaulting us." There is nothing to be done about it but to accept it, and lean toward the next destination.
Sal's views of the landscape also become less euphoric and more contemplative. Instead of describing definitively, he asks, "what is" the Mississippi? He thinks of what the river is physically, and where it goes. When they drive through the South, the landscape parallels Sal's frame of mind at this time: it is mysterious, dark and deep--even ominous, as when they see the fire at night. There are a lot of cars parked by the side of the road there. It could be a "fishfry"; it might be anything else.
In a way, the road is the only place Sal and Dean belong. Both misfits--Dean in his actions, Sal in his thoughts--the road is where people pass by each other with tolerance. Or at least disbelief: when Dean is jumping around naked at a roadstop, Sal mentions that some tourists see him but don't believe it. Dean and Sal and Marylou can drive naked and shock the truckdrivers, but they never have to be confronted by more than passing reactions, have to answer for themselves. On the road, everything might be a mirage, and there are no consequences to actions (Dean's) or lack of action (Sal).
Also in this section for the first time, Kerouac suggests for the first time that the women in this story might have deep and complex feelings. He describes Marylou watching Dean intensely, with an "envious and rueful" love-a surprising observation of someone who up until now has only been presented as a compliant bimbo. It suggests that others in this story may be experiencing something quite different from what Sal describes. (For one woman's perspective of this time, see Carolyn Cassady's ["Camille's"] memoir, Off the Road.)
Sal's moment standing on the sidewalk in San Francisco, feeling bliss, imminent death and an awareness of past lives, should be understood in the context of Kerouac's later interest in Buddhism. Naturally, the ideas of detachment from the world, solitude and peace appeal to Sal, who is in a kind of spiritual pain, but these qualities are in direct conflict with the unabashed Hedonism and impulsiveness that he admires in Dean. Kerouac would continue to struggle with these conflicting impulses in his later work, and in his life as well.