Try horsetraildirectory.com for ideas on places to ride in your area - I'm not at all familiar with the riding in that region, but I know people who have been there and enjoyed it.
If you have access to an arena with any kind of jumps/rails/standards, you could always create some trail-like obstacles to prepare you and your horse for things you might encounter. While a jumping course is measured and things are supposed to be evenly-spaced, Mother Nature is much more random. Your horse may have to pick its way through uneven footing or roots, and learn how to step over logs, weave through trees, etc.
Nothing you do in an arena can really substitute actual trail time, but it is good to at least be sure your horse is prepared and responsive to you.
Relax, have fun, and enjoy. Don't push your horse or yourself too much the first time out. It's better to take a shorter ride and end on a good note, at least the first rides. See how it goes. If possible, ride with a buddy on a seasoned trail horse - that can do wonders for a horse that has had limited trail experience when it comes to boosting confidence.
"Parelli horsemanship is just like painting by the numbers. You need absolutely no skill. You just put this color here and this color there, and when you're done, you have ... a mess no one wants." mp