Preparation for Tall Trees
To take full advantage of the Tall Trees features, it's best to have completed Bonnie's "Wild Horses, Tamed Passions" mission, which rewards the lasso needed to rope wild horses, and Marshall's "Political Realities in Armadillo" mission, which opens the bounties for the money needed to purchase better weapons.
Entering Tall Trees
Locate the train tracks running to the north of the MacFarlane Ranch and follow them to the east until reaching the unfinished bridge. To the north lies a waterfall with a path leading up the mountain. Follow this path up and to the edge of the cliff to enter Tall Trees. The location message will pop up on the screen when entering the area. Look to the south to find people riding horses into the ranch. Shoot the horse but not the rider. The rider will run off to report the shooting and lawmen will come. Stay near the waterfall to keep from their sight and fire into the air so they'll remain interested while leading them up the cliff. When one gets within 10 to 15 yards surrender to the arrest. Once released in Blackwater the entire northern area is open.
Auto-Save
Since the easiest way to return from Tall Trees is to die, it's necessary to save the game or any horses and weapons gained are lost. To trigger an auto save complete a mission, start a bounty, change horses or shoot a horse and use the deed to summon it again. As well, auto-save can be engaged by changing any audio settings in the game's options.
Returning
Once the game has been saved with any new items, find a way to die, such as drowning. The character automatically reverts to the nearest respawn point. If no property has yet been purchased in Manzanita, the character transports back to New Austin. If Manzanita property has been purchased then use a fast horse, like the American Standardbred, and head to the unfinished bridge in the southeast corner of West Elizabeth. Take a long, running start to leap off the bridge. Land underneath the bridge and then move left to reenter New Austin.