The 4-Mile Trail isn't a terribly interesting trail, so go hike to the Pedernales Falls first, and also do the Wolf Mountain Trail. The most exciting thing about the trail is the start, where you have to wade across the Pedernales on a low water crossing that can be slippery or thigh-deep in water. Be safe! Ask a ranger for current conditions of the river, because it can easily sweep you away.
Once you cross the river, the 4-Mile Trail goes up the rocky river side to a typical Hill Country juniper woodlands. There isn't much to really see on the 4-mile trail, so just enjoy yourself and keep an eye out for wildlife. Very few visitors to the state park ever use this trail, so you'll probably have it to yourself.
