The Rock Springs Run, a 10-mile (16 km)-long tributary of the Wekiva River, has its source near the northern boundary of Kelly Park.
Much of the park is shaded by temperate-zone trees such as red maple, American sweetgum, several species of hickory and oak, and one of the southernmost natural populations of tulip tree.
The forests are supported by poorly drained soils which have developed from marine sands and clays.
The topsoils are usually dark gray or black fine sands which are acidic (slightly so in some cases).
The park's largest animals are alligator, white-tailed deer and possibly black bear.