Guana River State Park features 10 miles of hiking trails near St. Augustine, FL.
From the South: Take I-95 North and exit East on SR 207. About 7 miles later you'll need to head north on US 1 and then north on SR A1A. From the North: Take I-10 to I-95 South. From I-95 South, exit on SR 202 and head South on A1A from Ponte Vedra. There are several signs for Guana River State Park, but you want the main entrance (not the beach area). Pay the entrance fee and park on the west side of dam. No, there's no shade.
http://www.tripleblaze.com/trail.php?c=3&i=1226