Finding Tall Trees
The first area of the game is the MacFarland Ranch, where you learn the different game elements through a series of tutorial missions. After these missions are completed, travel north of the ranch on horseback and look for the waterfall. Near the waterfall is a cliff and when you get to the edge of the cliff, the marker on your screen will say "Tall Trees." This area is technically part of West Elizabeth, so if you are arrested here you will be sent to that territory.
Raising Your Bounty Level
Now that you know how to get to the Tall Trees glitch, you need to get arrested in that area to be transported to the jail in Blackwater, the city in West Elizabeth. First you need to commit some crimes to get the attention of the law, so head to the MacFarland ranch and kill a few ranch hands to get your bounty level high. Escape on horseback and allow the posse to chase you back to Tall Trees.
Blackwater Jail
Once you have lead the posse to Tall Trees, get off of your horse and holster your weapon by letting go of the "L1" button. Wait a few seconds and your character will eventually put his hands up to surrender. You will be sent to jail in Blackwater and have to watch a cut scene as your character serves his time for the crimes committed, unless he has the money to pay off the bounty. Either way, you will have access to all of West Elizabeth afterward.
Back to New Austin
After you have explored West Elizabeth, if you want to get back to New Austin to continue the storyline, there are two ways to do so. Save the game and then let yourself die and you will return to New Austin when the game reloads. The other way to return is to jump the bridge at Thieves Landing with a horse. Build up as much speed as you can before the jump to have the best chances of clearing it.