I've posted a link below to some gameplay. If you want to see the other parts, just watch it in YouTube and follow the related videos. Did you notice in the gameplay, within seconds of turning on the game, one of the first options is to turn the sound off... now who would want to do that!?
Who created the audio experience? I'm having trouble ascertaining this with certainty, but apparently newer versions than the Apple II 1985 version have a title screen song written by the game composers, Lon Koenig and Larry Phenow. I suppose they could have created the audio for this version as well. If anyone can supply more information, I'd appreciate it.
What is the audio experience? In this version of the game, the music is only a single melodic line at different points in the game, when you start, reach a fort, cross a river, or finish the game. Later versions of the game have much more filled out music with harmony, singers, and simply better sound quality, but nonetheless, the tunes stay the same even in different versions of the game.
How does the music draw the player more deeply into the gaming experience? The tracks are to celebrate milestones in the game-- when you reach various points along the trail. A simple, logical use that I enjoyed it as a kid.
Below's a list of the songs you encounter in the game. While I knew a few more than half of these as I watched, to be honest, it's hard to recognize a song from just a few notes. For help, I used this slightly jumbled and somewhat incomplete credit list from allgame.com, this tiny but complete answer.com list, as well as this excellent playlist of a later version of the game (which actually plays the songs in reverse as you encounter them in the game).
-Leaving Independence, MO: Yankee Doodle.
-Kansas River: I Gave My Love a Cherry. Don't know this at all, but apparently it's in Animal House.
-Big Blue River: Oh Dear! What Can the Matter Be? (Johnny's So Long at the Fair.) Love Marilyn Horne and Martin Katz performing this!
-Fort Kearney: The Campbells are Coming. Here's a cool version of a drum line playing it.
-Chimney Rock: Auld Lang Syne.
-Fort Laramie: Billy Boy. I barely know this song...
-Independence Rock: Wayfaring Stranger. What a beautiful American folk song. Here's Johnny Cash singing it.
-Fort Bridger: Where Has My Laddie Gone? (Blue Bells of Scotland). I've played an Arthur Pryor arrangement of this with Euphonium.
-Green River Crossing: All Through the Night
-Soda Springs: Charlie Is My Darling
-South Pass: Believe Me, Of All Those Endearing Young Charms. Every person my age knows this from those Looney Tune cartoons where the piano is rigged to blow up. I also know this as Fair Harvard from Bernstein's Unanswered Question lectures (A little heady, but this also gives a progression of tonality through musical history... 50:43-55:00)
-Fort Hall: Skip to My Lou
-Snake River Crossing: O Shenandoah. Wish it were easier to upload audio files here; I've conducted a beautiful Erb arrangement this. Here's a performance of it (I'm not involved with this one).
-Fort Boise: On Top of Old Smokey
-Grande Ronde in the Blue Mountains: Long Long Ago
-Fort Walla Walla: Flow Gently Sweet Afton. I know this as an alternate to Away in a Manger from many church jobs.
-The Dalles: Jimmy Crack Corn (Blue Tail Fly)
-Willamette Valley: Viva la compangie (Viva l'amour). How about a macaronic song as an ender?!