JACKSONVILLE, FLA. A motorboat passes by undeveloped wetlands in cloud reflections on the St. Mary's River, north of Jacksonville. Residents can drive just 10 to 15 minutes from downtown Jacksonville to reach thousands of acres of preserved parkland. The parks offer both paved and backcountry trails through grassy and wooded wetlands. Wildlife observers should fancy the Castaway Island Preserve, a salt marsh ecosystem that features a wooden boardwalk.