Pretty sweet double track geared towards a beginners needs but simply beautiful way to spen an afternoon. If you decide to explore the falls on bike be careful as the park rangers sometimes don't like it.
Take 290 west out of Austin towards Johnson City, take a right on RR3232, follow till it dead ends take a right then an immediate left in to the park.
http://www.singletracks.com/item.php?c=1&i=1324