What exactly is your goal with the garmin? How do you specifically intent to use the mapping?
Are you just looking to see if the trails appear on screen so you know where they lead?
I personally my 820 to route pre-made courses. I sit down in the Garmin Connect editor, draw a route that i want to ride through the trails i like, then load and follow that route when i get there. Following routes gives you turn by turn routing similar to a car gps as long as you're on known trails. if you wander off or take a wrong turn, it even has back on track routing. I dont use the trailforks applet to do this, rather i just use the direct navigation feature of the garmin unit since it allows me to download and use the created route from my Connect account.
The jorba donation folks are referring to is the *Additional* voluntary donation directly through the trailforks site to allow you to download the full trail gpx files of a riding area. Though not all areas are set up to charge for the trail downloads.
Donate a few dollars to help support Wildcat Ridge WMA trails.
www.trailforks.com