There's a cliff and a waterfall in the far northern regions of New Austin -- just above the MacFarlane Ranch. Enter this area and you'll see "Tall Trees" appear on your screen. If you can manage to get arrested here you'll get carted off to Blackwater. From here you can access the full northern map. You'll need to auto save (see 'Save Anywhere' cheat) and die to return to the southern areas. If you buy the property in Manzanita, it will prevent you from doing this. However, it is possible to hop the unfinished bridge in Thieves' Landing to get back.