Leaflet No. i

On the front cdver:

A view of the Gregory-Houe from the River-'Note the floodpiainsurface andithe tree roots eiposed by erosion of the rivei bank.

Inside-thelbackcoveari

Map of Torre4 a State Parkshiowingi pint ieoloic interest.

Prepared by the'

FLORIDA BUREAU I W!$GEOLOGYDIVISTON OF RESOURC -MwAGEMENT

FLORIDADEPARTMENTOFl _ ;iESO CES

1982

THE GEOLOGY OF TORREYA STATE PARK

by

Kenneth Campbell and Ronald W. Hoenstine

The pristine forest of Torreya StatePark stands overlooking the ApalachicolaRiver. Visitors to the park are greatlyimpressed by the natural beauty of thisrecreational area that is situated inthe physiographic zone known as theTallahassee Hills. This zone includesthe higher elevations in the easternFlorida Panhandle. A great deal of thepark's appeal is attributed to itsrugged topography, with elevationsvarying from a low of approximately 50feet above MSL (mean sea level) at theriver to a maximum of 252 feet above MSLin the park's interior. The unspoilednatural setting is enhanced by numerousstreams which traverse the park; many ofwhich carry water only during heavyrains or sustained wet periods.

THE PROCESS OF EROSION

The rugged landscape of TorreyaState Park, which is due to the processof erosion, vividly illustrates the dra-matic changes that can occur as a resultof the combined effects of such diverseweathering agents as water, dissolution,gravity, and wind on Florida'slandscape. Although water has played anessential role in developing the beautyof the park, it can also presentproblems. The clayey sands, which formthe highlands, retard infiltration ofprecipitation and enhance runoff.During periods of heavy rains, thenumerous dry streams encountered inhikes through the park may quickly fill

with rain water collected along thehigher ridges and steep slopes. Thesestreams can become "torrents of water"rushing downstream, uprooting trees, andcarrying roots and debris along withvast quantities of soil. This erosionis an ever-changing dynamic process, theresults of which are visible in thepark.

Runoff is not necessarily confinedto the stream beds. It may flow downthe sides of steep slopes causingslumping. Slump scours, channels cut inthe steep slopes, can be seen below theGregory House. The newly exposed sedi-ments become susceptible to additionalweathering and erosion. Eroded soil androck continue their journey downslope,ultimately being transported by theApalachicola River downstream to theGulf of Mexico where the material isdeposited.

THE RIVER

The present location of theApalachicola River serves as a boundaryseparating two areas with differentnear-surface geology. West of theriver, carbonate rocks (limestones anddolomites) are found near the land sur-face, while east of the river, carbonaterocks are overlain by a thick sequenceof sands and clays with some limestonebeds. These sands and clays form themajor portion of the bluffs at TorreyaState Park.

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RIVER EROSION

The effects of river erosion aredramatically evident along the bluffsviewed from the campground, the GregoryHouse, and the Apalachicola BluffsTrail. This trail, which starts at theGregory House, follows along the bluffand down to the river. The bluffs are atopographic feature which can be foundon the east side of the ApalachicolaRiver from Lake Seminole at the north tothe town of Bristol at the south, adistance of approximately 20 miles.Rising up to 150 feet in height, thebluffs have formed from a combination ofgeologic conditions and geomorphic pro-cesses (those which shape landforms)that have been dominated by theApalachicola River. The ApalachicolaRiver cuts into these highlands,widening its floodplain by the processknown as lateral planation. In thisprocess, rock and soil materials areeroded from the outside and downstreamsides of river bends (meanders) whilematerial is deposited on the inside andupstream sides. The result is a slowwidening of the meander belt as well asa slow downstream migration of the mean-ders. Part of the floodplain can beseen starting below the Gregory Houseand extending downstream on the parkside of the river. In addition, thereare shallow channels cut in thefloodplain that can be seen along theApalachicola Bluffs Trail just to thewest of the Gregory House. These arefloodplain scour routes which may be theinitial stage in the development of anew river channel, or may be the finalremnant of an old channel.

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Geologic conditions influence theriver as the channel migrates and widensthe floodplain. The rocks in this areadip to the southeast and cause the riverto migrate slowly eastward as it cutsits channel. The lowlands, swamps, andriver deposits on the west side of theriver are remnants of former high ridgeareas that have been eroded and loweredby the river over the years.

LIMESTONE EXPOSURES

As a result of these erosionalforces and the subsequent removal ofsoil, park visitors can see theunderlying limestone exposed at severalsites in the park. The first exposureis encountered in the vicinity of theConfederate gun pits which are locatedon the bluff along the nature trailbelow the Gregory House (see map). Thislimestone, which formed from the hardshells of animals that died and accumu-lated on an ancient sea floor, is justvisible at the ground surface. Otherlimestone exposures can be seen whilehiking along the river bank below theGregory House and near the River BluffPrimitive Camp. These outcrops, whichare very prominent during extended dryperiods and associated low river stages,are generally submerged and hidden fromview by the river during years of normalprecipitation.

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A view of the limestone exposed at Rock Bluff near the River Bluff Primitive Camp.

FOSSILS

Torreya State Park offers a uniquesetting for an impressive array ofplants and animals, some of which can beseen in the park's fossil record. Thisrecord, in part, has been preserved inthe limestone which underlies the park.A cursory examination of this limestonemay show little detail; however, whenviewed under a microscope, thislimestone is found to contain tinyfossil plants and animals. These relicsof past life have enabled geologists todate the deposition of the sediments ashaving been laid down approximately 15million years ago during a period oftime known as the Miocene Epoch. Inaddition, an analysis of these micro-fossils enables a reconstruction of thepark's environment during that period oftime millions of years ago. Though itmay be difficult to imagine, thelimestone, which is exposed near the topof the Bluff, was, in fact, part of anancient seafloor. The microfossilscontained within the limestone arerelated to those that occur in a presentday marine coastal setting. It is anindication that the present park areawas covered by a relatively shallowocean during this period of Florida'spast. This interpretation is compatiblewith other studies which have indicatedthat much of Florida was covered bywater during the Miocene Epoch.

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UNIQUE OPPORTUNITY

Torreya State Park offers visitorsthe opportunity to experience the beautyand natural wonder of a unique setting.As you walk along the numerous trailsand paths within the park, we hope yourenjoyment is enhanced by an increasedunderstanding and awareness of thegeologic forces that have molded andshaped this magnificent landscape overthe millennia.

View of Rock Bluff (looking north) near the River Bluff Primitive Camp.

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Geologists from the Florida Bureau of Geology examine the limestone out-crop at Apalachicola Bluffs, just upstream from the Gregory House. Thisnutcrop It covered by the river except dutring vary low water.

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TORREYA STATE PARK

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Map of Torreya State Park showing points of geologic interest.

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