Falling In Love
Joe fell in love with Oliver the "moment [he] saw him." But before that, Joe fell in love with Oliver's mother. It's important to start here because in many ways Oliver is the redeemed part of Joe's failed marriage. Out of the heartbreak of his wife's infidelity came a beautiful gift in Oliver, and despite not being Joe's son by blood, "being [his] father" means everything to Joe.
The first hint is the fact Joe somehow ended up on the east coast for work, perhaps from where he sent those "fifteen years worth of [unanswered] letters marked 'return to sender,'" only to return home to Colorado to retire. Along with missing the mountains, Joe "missed [Oliver]," "spending time with [his] long lost son" a primary goal of his retirement. Then upon returning to Denver, Joe spends much of his time out in the woods hiking alone. Oddly enough, this prevents Oliver from reaching Joe the few times he did try and reach out to his father.
Apparently venturing into the mountains isn't a new thing for Joe. Recall that after Oliver's mother passed, Joe went into the mountains to watch the sunset, only to find himself seeking "a reason that the sunrise was worth waiting for," the answer once again rooted in being Oliver's father. The question becomes what is prompting Joe's more recent and more frequent returns to the wilderness? Hold onto that inquiry for a bit---it's definitely worth an answer. What's notable here is how Joe's separation from his son created a void that he is still in many ways struggling to fill.
During their trip, you get the sense Joe has an alternative purpose for taking Oliver to the woods, a motive which comes into focus as Joe confronts Oliver with "the little boy deep down inside of [him] that still believes" his mother's abandonment was his fault, releasing him of all responsibility, and encouraging Oliver to "leave [the hurt] on the mountain," and "go back and start over." While trying to help his son, Joe is also trying to heal his own hurt---and even guilt---associated with what happened that day, and the impact he sees it had on Oliver given "how long it took [him] to come back to the forest."
When Oliver declares at the hospital that "there's been too much leaving in this family. Let's not do that anymore," it speaks to not only Joe's near-death experience in the woods, but also to the abandonment experienced by them both. It seems Oliver might finally be getting a sense of how important his father is to him, and ready to make proactive attempts to connect with him, the kind of relationship Joe has always wanted.
Joe's love for Oliver has been a driving force in his life. In Oliver's absence, Joe suffered an identity crisis, which subsequently manifested itself in him wandering first to the east coast for work, and again in the wilderness once he retired to Colorado. It's only once he and Oliver connect during their trek in El Dorado canyon that the hurt and guilt Joe carries comes into focus, simultaneously presenting an opportunity for healing.
Into The Details,