Iowa is his childhood. It's where he became the man that he is now, good and bad, and he's been running from it for eight years, since he first stepped onto that shuttle and never looked back. Bones grumbles about the weather, too much rain and too hot and too this or too that, and bitches about their motel room, too small and the bed's too hard and the shower is too cold, but Jim knows he's mostly doing it out of habit. It's comforting, in a twisted way, to hear Bones being grumpy, and Jim needs that familiar connection to his present as he faces his past.
It's when they're walking in a cornfield that he used to sneak into to hide as a child that he realizes why this is important to Bones. Jim knows everything about Bones, his past and his marriage and his father and all of it, mostly from asking and refusing to give up until Bones finally answers all his questions. But Jim is just as stubborn, maybe more so, and he never gives up when Bones asks. His past is mostly a blank space for twenty-two years, as if his life never really started until they met on that shuttle. In a fucked up way, it's the truth. But Bones deserves more than that. They've been best friends for eight years and something more for five of those, and Jim can't see himself in the future without Bones beside him.
He stops walking and makes Bones lie down beside him in the middle of the cornfield. When Bones starts bitching about dirt and sunburn, he puts his fingers over his lips to stop the words and begins talking. He talks about his childhood, about George and Mom and Frank, remembering good times that the bad ones always overshadow and managing to talk about those bad ones without feeling guilty or ashamed or hurt because Bones listens without judging. He just accepts him completely, like he always has, and that unconditional love makes Jim talk even more as a warm breeze rustles the corn stalks surrounding them.