-- US 301 N approx..10 miles

-- Park Entrance on the left

The Hillsborough River State Park is one of Florida's oldest parks, established in 1938 through the efforts of the Civilian Conservation Corps. The park preserves an inland section of the Hillsborough River, one very different from the section you have observed at Lettuce Lake Park. The goal of this field exercise (other than touring a very cool place) is to examine a typical Florida river system, and to learn what you can of the region's underlying geology. Unusually enough for Florida, rock outcrops do occur in the park, and particularly along the river.

-- Mosquito repellant (you'll need it!)

-- Water (fountains and a concession stand are available in the park, but

they're pretty spread out, and not along the trails.)

-- A hat

--Comfortable walking shoes

-- Umbrella or rain gear (for the chance storm, though in the summer heat, rain's actually sorta pleasant!)

Stop #1: Parking area for Rapids Trail. You will walk down the trail to the rapids, and along the river westward to the suspension bridge, and loop back, about 1.5 mile of easy walking along well maintained, shaded (if buggy) trail.

--Note the vegetation around you: slash pine, and sabal palm are the primary trees, along with abundant saw palmetto. This is called Pine Flatwoods, and it tells you that the land you're walking through doesn't spend very much time under water during the year.

Question 1: Nonetheless, water is standing amongst the pines on the right (beware mosquitos!) Given that usually this is dry land, what can you say about the composition of the soil beneath this section of woodland? (ie., which of the three size constituents of soil might it be rich in, given the fact that water remains standing here?)

--Follow the trail to the Rapids. Here, the Hillsborough River flows over and around outcrops of the Suwanee Limestone, a unit which is a major member of the Floridan Aquifer, from which many of us pump our drinking water. Note the tea-color of the river water: this is due to high concentrations of dissolved and suspended organic matter derived from the Green Swamp (the headwaters of the Hillsborough) and other wetlands which drain into it.

Question 2: A geologic cross section of Florida is relatively simple: just a thick body of limestone overlain by sand. How thick is the sand layer that overlies the Suwannee Limestone here along the riverbank? (Hints: did you see any limestone outcropping on the trail to the Rapids? How high above the river are you standing at the Rapids observation stop?)

Question 3: Compare the thickness of the sand layer here to that which you encountered at Lettuce Lake Park, or the other park you have visited. In which park is it thicker? Why? (i.e., what can you say about sand thicknesses at these parks, based on your field exercise there?)

--Assuming that surface elevations are more-or-less the same at both parks, what do your inferences suggest about the subsurface topography of the limestones in this region of Hillsborough County?

Thought Question 1: The Recharge Zones of aquifer rocks are sites where those rocks are close enough to the surface to receive inputs of downward percolating Meteoric Waters (i.e., surface-derived water). As such, the Rapids, and much of this stretch of the Hillsborough River, must be considered local recharge sites for the Floridan aquifer. Is this a good thing? (Note the "no swimming" signs and their explanation for this prohibition). Where might pollutants in the Hillsborough River at this location be coming from? (Hint: where does fecal coliform come from?)

--Follow the trail along the river downstream from the rapids. Note that you are walking on high ground along the river, and that the land elevation declines away from the river before rising again. This high ground is called a Natural Levee, and they form commonly along rivers.

Question 4: Referring to the chapter on rivers and drainages, how do natural levees form?

Question 5: Note the vegetation (trees) along the river: what are they (Hint: look for signs on boardwalks, and read the literature they give: this is not a botany class!). This vegetation is typical of the wetter areas along rivers and in Florida wetlands.

Thought Question 2: Presumably, the entirety of the Hillsborough River State Park (and Lettuce Lake park, for that matter) lie within the Floodplain of the Hillsborough River. What observations could you make that would help you define the boundaries of this floodplain (hint: these can be anything: slope changes, vegetation changes, whatever. What would you think might work, and why?)

--walk along the river until you come to a bridge across a small tributary creek. You also crossed this same creek on your way to the Rapids. Note the Meander Pattern of this creek, as compared with that of the Hillsborough River (which rounds a bend at this location as well).

Question 6: Your textbook describes stream meanders and how they form. Does the tributary creek appear to be doing what the book says its doing? How about the Hillsborough River? (If you are not sure about the Hillsborough River, pull out a Florida map and take a look at it - does it meander as per our textbook?)

Question 7: This creek parallels the Hillsborough River for some distance before finally emptying into it. Why does it do this, as opposed to draining directly into the river? (Hint: refer to the natural leveee description above. How might a levee affect a tributary stream?)

Question 8: On another topic, all along this trail, you see clearly man-made blocks which are being used to support the bank below. What natural process are they trying to inhibit? Why is this process in need of inhibition (i.e., what's been happening along this stretch of river?)?

Thought Question 3: Look at the attached map of the Hillsborough river through the park, and also check out a map of Florida, so you can follow the river's path from this park to Lettuce Lake Park. The Hillsborough makes a lot of right angle turns, with river flow switching from West to South and back again. Could there be a Geologic Feature (i.e., a property of the limestone rock below) that might explain these unusual bends? (go and check the chapter(s) on the deformation of rocks for help here!)

-- Between this point and the Suspension Bridge, there are several small trails which cut a few tens of meters inland (see attached park map) Walk inland along one of these, and note the abrupt depressions which occur behind the natural levee. Cypress trees are common here, and the land level is almost at river level in these low spots.

Question 9: There are two possible explanations for these depressions:

a) meanders which have been cut off by a change in river flow direction, producing an Oxbow Lake or its equivalent.

b) a sinkhole near the river.

Tell me which is the more reasonable explanation here, and why. Provide evidence why your choice is correct, AS WELL AS why the other choice is incorrect.

--Return to the trail along the river, and follow it to the suspension bridge.

Question 10: Near the suspension bridge is a sign for a Stream Gauging Station. What does a stream gauging station do? How high was the highest flood level along the Hillsborough River since this station was establshed (see signs!)?

Question 11: From the Suspension Bridge, walk in toward the picnic areas you can see to the left. Several small creeks cross this picnic area. In one, country rocks are exposed. Find this creek, take a look at some of this rock and tell me what it is, and what it is made of. (be specific about the things which comprise it, if you can recognize them!)

Stop 2: You have a choice here. Either walk a short stretch of the Bayard Nature Trail, or the Florida Trail (both accessible from the Picnic Area/Concession area on the map across a footbridge), or of the Wetlands Restoration Trail (far side of the park on the right, past the campgrounds), and describe for me in about 1/2 page three geologically and/or environmentally significant things that you saw (stuff related to this class!). This can take you 10 minutes, or five hours: your call. If it's fun, play!

Stop 3, and Question 12: On your way out, on the left just before the exit road, you will see a pulloff and an information sign for Flatwoods Pond. Get out of the car and read the sign and look at the pond. They give two explanations for the origins of this pond on the sign: a nearshore feature (coastal sand transport) or a sinkhole. Based on your observations and you knowledge of both from our class, which do you think is most likely, and why? (you can be brief here!)