Alum Bluff: Fossil Hotspot of the Apalachicola River

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Last October (2025), The Florida Geological Survey bestowed two designations on Alum Bluff. FGS Director Harley Means made the bluff Florida’s ninth Geological Site, and first ever Invertebrate Geological site. Alum Bluff is Florida’s largest geologic outcropping, and it has rich fossil deposits.

I know Alum Bluff from my adventures on Apalachicola RiverTrek. It sits at mile marker 84 on the Apalachicola River, as in 84 river miles from Apalachicola Bay. As the crow flies, it’s about fifty miles from the coast. And yet, it preserves coastal and offshore ecosystems that occupied this space millions of years ago.

This is a geologically and biologically unique region, known as the Apalachicola Bluffs and Ravines. While fossils preserve ancient north Florida on the bluff, rare and endemic plants and animals preserve it in ravines. As a native south Floridian, I’m still in awe that such a landscape exists in our state.

I keep coming back to this area for stories, and I felt that it was time for a deep dive. Welcome to the Alum Bluff/ Apalachicola Bluffs and Ravines edition of Coast to Canopy.

Meet our guests

In this episode, we talk to three researchers who have extensively studied Alum Bluff and the Apalachicola Bluffs and Ravines region:

Harley Means, Florida’s State Geologist and the Director of the Florida Geological Survey.

Roger Portell, Invertebrate Paleontology Collection Director at the Florida Museum of Natural History in Gainesville.

Dr. Bruce Means, former director of Tall Timbers Research Station and founder of the Coastal Plains Institute.

Coast to Canopy blog posts are curated transcripts. My notes appear in italics.

Alum Bluff: Florida’s First Invertebrate Paleontological Site

Harley Means: As the state geologist, one of the many neat things I get to do, is I get to designate places in the state that are significant geologically and/ or paleontological. It turns out Alum Bluff is one of those unique places where both things are true.

So, Alum Bluff was just a natural place for me to designate, not only a State Geological site, but also the first state Invertebrate Paleontological site. Now, there are others around the state that I may designate at some point in the future. But Alum Bluff is so well known in the geological literature, and known to geologists in the southeastern US that it really warranted the first designation.

Roger Portell: There’s constant erosion on the bluff, and so, whenever we come, we find new things. In addition to the invertebrates, we also find vertebrate fossils and plant fossils. I’ve come out here with the plant folks are paleobotanists and we’ve collected, and recently they’ve begun publishing, after a hundred year hiatus, the fossils from Alum Bluff, the fossil plants.

Can we collect fossils at Alum Bluff?

Rob Diaz de Villegas: Does this receive extra protection that it didn’t before? As far as is it being a fossil site?

Harley Means: Statutorily it does. Its designation in statute, it does say that if people go there to collect, they are required to actually have the written permission of the State Geologist.

Now, what I would say is that’s probably not reasonable. Since the bluff is an erosional feature and it’s constantly cutting in and it is eroding out fossils and those fossils eventually get deposited in the river and broken up and transported.

If you go to Alum Bluff, we would just ask that, you know, be respectful, don’t don’t dig into the bluff and cause a huge blocks to tumble down and be eroded. If you want to pick up a fossil or two that have already eroded out, that’s probably okay.

But, it is recognized now as a state invertebrate paleontological site. It is afforded a little more protection.

Geological Units at Alum Bluff

We can see four distinct geologic units at Alum Bluff. Each has distinct characteristics, and preserves a snapshot of a specific environment at a specific time.

1. Chipola Formation

Early Miocene epoch (~18,000,000 years ago)

Harley Means: the oldest unit that you can see at Alum Bluff, when the river stage is low enough, is what’s called the Chipola Formation. It was deposited during what we call the Miocene epoch, and it’s about 18 million years old. What’s really impressive about it are the abundance of marine fossils that you find there.

It’s from those fossils that paleontologists are able to tell us something about the age of that unit.

The Chipola Formation is really quite incredible. It occurs, not only here at Alum Bluff where we’re talking about, but also further to the west. You can find exposures of it along the Chipola River, which is where it was named from.

Paleontologists estimate that it has in excess of probably about 1100 species of marine mollusks that have been identified in it. That’s a huge diversity of mollusks and taxa. What it’s indicative of is a time when it was it was more tropical in north Florida. In fact, that was really probably the last time north Florida really saw a tropical climate. That’s reflected in all those amazing marine fossils we see and we see fossil corals and fossil echinoids (a class of marine animals that includes sea urchins and sand dollars).

The Richest Deposit of Miocene Invertebrate Fossils in the State

Roger Portell: This is probably the richest bed of Miocene invertebrate fossils anywhere in the state. because there’s so many varieties, plus there’s just a great abundance.

I’ve described a number of species, some of which are from Alum Bluff, but some from other portions of the Chipola Formation. The Chipola Formation occurs in Liberty County and Calhoun County. And so I’ll collect the Chipola River and some of the creeks in addition to the sites on the Apalachicola River. And together we’re able to piece this material together and find new species and describe new taxa, and mostly from these areas.

I’ve described echinoderms, the sand dollars, sea biscuits, sea urchins; and mollusks, the snails and clams. The next one that I’ll work on is the long kuphus tubes that we find. Those are two meters long. And so, we’ve extracted several of them, and it turns out it’s a new genus. So we’ll be describing the new genus, and of course, they’ll have a new species associated.

The process of describing new species

Bruce Means will also talk about describing species later. This is the process researchers use to determine whether a species is new to science.

Roger Portell: Having museum collections, and especially older collections, we search those collections and we try and identify all of the various species that we find (in the field). Sometimes we can’t. And it’s when we can’t identify them, based on collections at the Florida Museum of Natural History or the Smithsonian or the Philadelphia Academy, then we we think that they they’re probably new to science.

And so then we’ll do comparisons to similar taxa: the same genus, same family. Eventually, we’ll get down to the point where this has not been described. It is unknown to science. Then we’ll write a description and describe the species in a formal sense, and then publish it in a formal publication that’s peer-reviewed.

2. Alum Bluff Undifferentiated

Miocene epoch (~15,000,000 years ago)

Harley Means: We call it undifferentiated, as geologists, because we haven’t assigned it to a formation within the larger Alum Bluff group. So we just call it the Alum Bluff Group Undifferentiated unit.

And it’s also a really interesting unit because… the fossils in it are quite a bit different. They’re not marine. In fact, they’re terrestrial plant remains. It’s probably one of the most impressive assemblages of plant fossils in Florida. Plant fossils are pretty rare in our state.

You can find neat things like big palm fronds and nuts and seeds of plants that grew back, probably some 15 million years ago. So again, it is another Miocene unit.

It is younger than the one underneath it. And, it’s it’s indicative of a time period when the climate was more temperate. And we know this from the fossil flora that has been identified from that unit.

3. Jackson Bluff Formation

Late Pliocene epoch (3.6 to 2.58 million years ago)

Harley Means: Sitting on top of that unit, there’s quite a big gap in time. But the next unit up is called the Jackson Bluff Formation. And it is, again, a marine unit. You can tell that as you walk along the bluff, because you see a huge assemblage of marine fossils that come out of that unit.

Now, it’s a little different in that it was deposited in a different kind of a marine environment than the Chipola Formation. You can notice that not only from the fossils that are in it, but also the color and type of sediment that comprises that unit. It’s kind of dark and organic rich, and it is indicative of an estuary.

So it’s more of a nearshore marine environment than the underlying Chipola Formation was, and it was deposited about 3 to 3.5 million years ago during what we call the Pliocene epoch.

Ecphora: Ancient snails doing what modern snails do

Harley Means: I think my favorite fossil from Alum Bluff is actually a mollusk. It’s a gastropod, and it’s called Ecphora. That’s its genus. It’s a really unique ribbed gastropod snail that was probably a predatory snail that ate and feasted on other snails. Just the uniqueness of its shell. It’s a pretty coveted fossil shell.

Harley’s description of predatory snails brings me back to the very beginning of the WFSU Ecology Blog. We started in estuary environments. In one seagrass bed called Bay Mouth Bar, our research partners studied a diverse assemblage of predatory snails that eat each other, and the many clams there.

Harley Means: You’re right, Rob. What’s neat about it is, here in Florida, you can stand at Alum Bluff and you can look at one of these paleo-estuary deposits. Then you can go fifty miles to the south and see a modern analog that looks very similar to what was going on 3 million years ago in this area.

Three million years ago, Megalodon swam here

Harley Means: At Alum Bluff, you can find shark teeth, but you can even find the shark teeth of what was once the largest marine predator to have ever lived: Megalodon

They’re not common. But, occasionally you can find a Maegalodon tooth there. What kid is not super excited or amazed when they look down and see that little triangular shark tooth fossil? I certainly was as a kid.

Megalodon teeth can reach more than six inches in length. That’s a really, really large example. They don’t all get that large. Most of them are smaller than that. The largest one I have seen from Alum Bluff is probably no more than about five to five-point-five inches in length.

There are multiple species of sharks where the teeth have been found in the deposits at Alum Bluff. Primarily, they come out of the Jackson Bluff Formation. It’s not unheard of to find one in the underlying Chipola Formation, but they’re certainly not as common.

Fossil evidence of ancient killings

Harley Means: You do find vertebrate remains there. Most of the vertebrates that you find are the vertebrate remains of marine mammals, which makes sense because it’s a marine deposit. Many of those bones are broken up and tumbled. But, many of them could show evidence of what might have happened to them.

That evidence comes in the form of cut marks and other other marks that are left as a signature of maybe a marine predator that might have attacked this marine mammal while it was alive. Or it could be a scavenger that jumped on the animal after it perished.

Occasionally you do find ribs and vertebra and other parts of these marine mammals that have those signature marks on them. And paleontologists can take a look at those and use that as evidence for what may have been happening at that time with that particular animal.

4. Citronelle Formation

Late Pliocene epoch (~3 to 2.5 million years ago)

Harley Means: Sitting on top of the Jackson Bluff formation is something that stands out. You really see it, both from standing on top of the bluff and coming at it from the river. It is this thick package of, basically, sand and gravel. For the most part, quartz sand. And it’s from a formation called the Citronelle formation.

That’s something that’s kind of near and dear to my heart, because it’s what I did my master’s thesis work on in the panhandle. Essentially, it is a big deposit of quartz sand and gravel that was reworked and brought down by rivers and streams, and at some point it met the nearshore marine environment. Probably not at Alum Bluff, [but] further to the south.

It’s really not terribly distinctive, at least across its extent, because it’s got so much quartz sand and gravel in it. It does not have much in the way of fossils. The important character about it at Alum Bluff is that it’s unconsolidated there. It’s sand and gravel and it’s not cemented together or stuck together with any clay or any other kind of material.

When it starts to erode, it can easily slump. And that’s important for the formation of features at Alum Bluff and other places in that part of Florida that are unique geomorphic features called steepheads.

The Geology of Steephead Ravines

While most ravines erode away from above, from rainfall, steepheads erode from underneath.

Harley Means: I mentioned the term steepheads. Steepheads are unique geomorphic features that form in areas where you’ve got a deep sandy deposit, like the Citronelle formation, which is an unconsolidated quartz sand.

That sits on top of the Jackson Bluff Formation. The Jackson Bluff Formation is clay and clay sand. So it’s fairly impermeable to the downward percolation of groundwater. We all know Florida gets quite a bit of rainfall. And when that rain hits the land surface, part of what hits the land surface can percolate down and get into the underlying sediments. And that’s what we call our aquifers. That’s where we get our recharge.

But at Alum Bluff and in areas adjacent to that where that Jackson Bluff Formation occurs, that groundwater can no longer percolate downward, and it has to migrate laterally. As it migrates laterally, it eventually will bleed off into the Apalachicola River valley. When it does that, you start to get headwater erosion.

The green tree-shaped features are steephead ravines. North of the largest of these ravines, we see much more green. These ravines rot the north are mostly gully ravines, with the possible exception of Crooked Creek (the subject of an earlier Coast to Canopy episode).

Bruce Means’ longtime connection to steepheads

In the 1960s, Bruce means started exploring ravines by the Apalachicola River. At the time, he was a graduate student studying salamanders.

Bruce Means: Halfway between Torreya State Park and Bristol, there is a big stream called Sweetwater Creek. That is the beginning of where the seepage occurs, south of that.

Over the years and after, even into my doctoral work, I explored as many steepheads as I could, and I discovered they were also prominent and common elsewhere west of the Apalachicola Bluffs and Ravines, especially on Eglin Air Force Base and on other streams that were about the same latitude as those in the area of the Apalachicola River.

I got into the literature and discovered that one of Harley’s predecessors was the first geologist to recognize that a steephead was a geomorphologicaly distinct geological phenomenon.

So the geologists discovered steepheads and identified their unique geomorphology and how the bleeding, or the sapping they called it, of the of the groundwater created a steephead. Well, then, as a biologist, I think I’m the first biologist to recognize how cool they were. And I published several papers in semi technical and semi popular literature early on to try to bring the focus on to steepheads and how neat they were.

The steephead ecosystem

Bruce Means: They’re biologically fascinating because… their aquatic environment is almost completely perennial, meaning it never dries up. And the reason for that is there’s this huge perched aquifer that is bleeding into these steepheads.

You can imagine the aquifer during our 50 or 60 inches of annual rainfall. That water, a lot of it percolates down and builds up this underground lake that is bleeding into the steepheads.

It takes a long time for that lake to get exhausted. Meanwhile, it’s being restored by more rainfall… so that means that the animals and plants that live in a steephead environment are always experiencing the moisture in the soils and the creek.

Apalachicola Bluffs and Ravines endemic species

Bruce Means: There are some fishes that go up those steepheads, some quite, quite interesting ones. But there’s a fireback crayfish that’s only known from the Apalachicola ravines, and that includes the steepheads as well as the gully-eroded ravines.

And then that salamander I was so keen on studying, I discerned years ago it was a unique species, only known from the Apalachicola River system. But it’s found both in the steepheads as well as in the gully-eroded ravines. But it’s a unique species in that stream system.

Then we got the plants. Plants require moisture, too. So in a steephead, especially those that migrate, that are aligned east and west on the north side of their slopes, the sun coming in from the south dries the slope out more than on the south side.

The south side is in a sun shadow. It turns out the Torreya, the rare yew, and Taxus (floridana, the Florida yew tree), the other rare yew, both of them, they’re endemic species just found in the Apalachicola ravines (Florida Torreya and Florida yew are both in the yew family). Both in steepheads as well as a gully-eroded ravines, and not found anywhere else on Earth.

And there’s even an herbaceous plant called Croomia that’s really ancient. And its closest relative is over in Asia, like the like the yew trees.

A little more about the Apalachicola dusky salamander

Bruce Means: The salamanders I was interested in belong in a big genus called Desmognathus. And it turns out they’re notable for being extremely variable. A given population of the same species will have dark adults and colorful females and colorful juveniles and then if you go downstream, you can get into another group of animals that are variable also.

I determined that there was a population of salamanders in the Apalachicola Bluffs and Ravines that was at the headwaters, up at these steepheads itself.

Every steephead had that population… As you go downstream, the streams, of course, get bigger and bigger. Eventually they get so big during rainy periods that they over overtopped their banks and they create a little floodplain. And when the water goes back down, that floodplain is wet and has swampy, mucky places in it.

That’s where I found another salamander (the southern dusky salamander) that was being confused with the Apalachicola dusky (the salamander at the headwaters). And then eventually I named the Apalachicola dusky (in the late 1960s). And it has held up to DNA scrutiny. It’s only found in our Apalachicola ravines, actually.

Also in the Ochlcokonee ravines. That’s because the Ochlockonee River was probably connected to the Apalachicola River through Telogia Creek at one time.

The southern dusky is found throughout Florida. The Apalachicola dusky is only found in Apalachicola ravines, but, before Bruce studied them, researchers thought they were also southern dusky salamanders.

Apalachicola Dusky Salamanders are Ice Age Refugees

Apalachicola duskies and southern duskies are in the same genus and are found in the same ravine systems. However, Apalachicola dusky salamanders’ closest relatives are hundreds of miles away.

Bruce Means: The closest relatives are up in the southern Appalachians. The reason why that’s so easy to understand is the Apalachicola River and the ravines in our own Torreya State Park and Bluffs and Ravines area, those [gully] ravines occur all the way up the river Chattahoochee River, all the way into the headwaters, which are in the southern Appalachians of North Georgia.

There has been a corridor of ravines going from North Georgia mountains all the way to our bluffs and ravines, allowing plants and animals to migrate upstream or downstream during climate changes of the Pleistocene, the glacial ages.

Sea level was 300 or more feet lower, and a lot of things that were up north had come down and populated our ravines down here. And things have changed, gotten warmer, and who knows what’s going to happen to them now, because getting warmer and warmer.

Anyway that that’s there’s no other stream system in Florida whose headwaters are outside of the coastal plain. The Apalachicola River is the only one whose headwaters drain the Blue Ridge of the southern Appalachian Mountains.

Means Creek

Bruce Means: I’ll tell you how I got name Means Creek. When Florida Natural Areas Inventory (FNAI) got started, I had a couple of contracts with them. One of them was to identify rare and unusual environments. And one of the environments that I discovered, other people I’m sure I’ve seen it, was this thing they have called Means Creek, after me.

We’re talking about all the steepheads you encounter there in that sandy Citronelle. And but then you get above Sweetwater Creek, you start getting the clays…

Harley Means: They’re part of the Torreya formation, and then ultimately the Chattahoochee Formation, which is the lower part. Means Creek has eroded down into that.

Bruce Means: What I thought was so special about Means Creek is the water that it gullies down, it has hit limestone. And what what does acidic water do when it hits basic limestone? It dissolves it. So it’s dissolved its lower part of its valley into limestone. When you walk up the stream, you can walk on a hard rock bed and you put your hands on and touch vertical lime rock sidewalls that are having seepage come down out of the overlying material above.

And the seepage is creating these wonderful rock faces that are wet and full of mosses and liverworts and salamanders and all kinds of good stuff. So I proposed that. When you go further north, you don’t get that. That one stream is unique in that regard.

Three things I learned from this podcast that I’ve had totally wrong

I love Coast to Canopy because it allows me to really delve into a topic. Doing so on this episode helped me refine my understanding of a few points, things I’ve misunderstood to different degrees. So, here goes:

1. The Cody Escarpment does not reach Alum Bluff

Many maps on government and educational websites show the Cody Escarpment running from just north of Gainesville, and over to the Apalachicola River. The Escarpment is an ancient coastline, a place where high and hilly starts to transition to a flatter Florida. Alum Bluff is also higher place and an ancient coastline, but a different formation than the Cody Scarp.

Harley Means: The Cody Scarp, you don’t see at Alum Bluff or in the vicinity of it. The Cody Scarp kind of pinches out in Leon County. But it’s more prevalent in Jefferson County, where it was actually named for the little town of Cody there.

What’s spectacular about that area, and why it was named there, is because there’s quite a bit of an elevation difference between the area to the north, which is what we call the Tallahassee Red Clay Hills region. And you go over this escarpment, this big hill down and on to the Woodville Karst Plain. And the reason you have that big escarpment there is because sea level has stood at much higher levels than currently.

During times when sea levels were higher, the ocean would actually lap into and cut into and erode away those sediments. And so what you’re seeing is what we call a marine escarpment. So it’s where a higher sea level once stood.

There are some maps that put it there [at the Apalachicola River], but it doesn’t make it all the way over there. It becomes more difficult to trace as you go further to the west. Now, it’s not to say that there are not other escarpments that you can identify over further west. It’s just the Cody Scarp itself, kind of… transitions into a feature that’s less discernible.

2. Steephead Ravines may not have formed in paleo-barrier islands

This one is a little more of a scientific disagreement between Bruce and Harley. Bruce maintains that steephead ravines form in ancient beach dunes, that were likely once barrier islands.

Harley Means: Well, in some areas, yes, but that sand has been transported down here. Actually, all of the quartz that we have in Florida ultimately was transported down here from the erosion of the Appalachian Mountains. Rivers and streams have been carving and cutting down into those mountains.

The reason we have quartz sand down here and not some of the other minerals is because quartz is so hard. So, it’s really about the only thing that survives a trip through that distance in a river, tumbled along for many hundreds of miles to be deposited down here in Florida.

Some of the quartz sand deposits in Florida were deposited as barrier islands and dunes. And we see that across Florida’s landscape, we have quite a few, and we call them paleo dunes and paleo barrier islands

At Alum Bluff, per se, that’s probably not the case, except for maybe a little bit of the very uppermost part, of the sand deposits that exist there. So you couldn’t say all of that is the Cironelle formation is a barrier island deposit.

Bruce Means: He’s the Florida state geologist, so I will not… In my opinion, I thought the most of that was a barrier island based on a guy named Tanner. But that’s what happens in science. You don’t always agree, even though he’s my son.

3. Torreya Trees are not ice age refugees

Many plants and animals in the Apalachicola Bluffs and Ravines are ice age refugees. These include many endemic species, but some endemic species have much older origins.

Bruce Means: The Torreya and the yew and the Croomia are part of an ancient Miocene, Arcto-tertiary geo-flora that used to occur more widely all over the southeastern United States. And the last remnants of them are found in the Torreya ravines area. So we have that as a refuge sort of a situation, going back, what 18 or more million years?

Harley Means: With you saying that about the Miocene connection, it might be interesting to take a look at the fossil flora that we know is found in the Alum Bluff group, undifferentiated sediments, and see if there are representatives in there.

Here, Harley brings it full circle. Alum Bluff preserves ancient north Florida in fossils. The steephead ravines that flow through the bluff and into the Apalachicola River preserve an ancient past in living plants and animals. Torreya trees are only found along a twenty mile stretch of the Apalachicola, on one side. They evolved from more widespread ancestors whose fossils might be on that bluff.