Thursday, December 24, 2015

Petrified Forest National Park

Back in the beginning of March, I traveled out West with Ohio University Outdoor Pursuits on a Spring Break trip. The OU Outdoor Pursuits is a department within the Division of Student Affairs at Ohio University which focuses on outdoor adventure and recreation trips. They offer us students an extremely affordable and guided way to travel to new, exciting places and do things like backpacking, rock climbing, hiking, and more.

I've been sitting on my Spring Break trip photos for months and months now, and I've finally decided to get myself in gear and write about it! The main point of the trip was to visit Mammoth Cave National Park and the Grand Canyon National Park, but due to some unforeseen circumstances and flexibility Outdoor Pursuits decided to add a few other national parks on the fly, one of which was Petrified Forest National Park. I'll be making a really big post chronicling the whole trip soon, but for now I'd like to focus on Petrified Forest.

Petrified Forest shrub steppe
We arrived at Petrified Forest National Park on March 1st, 2015. This National Park is located in east-central Arizona. It straddles Interstate-40, a beautiful highway which we traveled nearly 500 miles on. We were all a little stir crazy from being on our two minibuses for about 980 miles straight, and when we pulled into the park we were all ready to see something amazing. The group leaders decided to take the auto-tour of the park, and upon getting onto that park road we were met with the sight above. This is a beautiful semi-desert shrub steppe; at least, I thought it was beautiful. Many of the others thought it was a bit lackluster. But then we rounded a small hill....

Petrified Forest Painted Desert
The view from Tiponi Point. We actually visited on a rare day with rain showers, which you can see in the photo above.
....And the Painted Desert appeared. Various sounds of awe emanated from everyone, and we all stared at the mesmerizing sight before us. As someone who had never been west of Ohio up until this point, I cannot even begin to put into words how I felt when this view appeared. The Painted Desert is a relatively small desert, clocking in at only about 120 miles long and 60 miles wide. As you might guess, the colorful rock formations are the reason behind the name. The Painted Desert is located in the southern portion of the Colorado Plateau, which is a large uplifted region that lies in parts of Arizona, Utah, New Mexico, and Colorado. The very southern tip of the Painted Desert makes up the more northerly half of Petrified Forest NP.

Petrified Forest Pilot Rock

We began our tour in the northern portion of the park. Most of the landscape in Petrified Forest National Park is an example of badlands. Badlands form when soft sedimentary rocks are heavily eroded by water and wind. The best known example of badlands is Badlands National Park in South Dakota, but they occur throughout the world. In the case of Petrified Forest, these badlands are made primarily from layers of soft siltstone, mudstone, and shale. The vast majority of rocks exposed at Petrified Forest belong to the Chinle Formation, a formation which dates to the late Triassic. Select areas of the park also exhibit rocks from the Bidahochi Formation. This formation was formed from a mix of lake and volcanic sediments, but most of it has eroded from the park. Pilot Rock - which is the large, shadowy hill looming on the left side of the horizon in the photo above - is, for example, capped by rocks of the Bidahochi Formation.

Petrified Forest Chinde Mesa
The Chinle Formation is broken up into several sub-units that are called members. Four of these members are exposed in Petrified Forest NP. In the northern Painted Desert section of the park, one can see two members. Essentially everything you see in the photo above are rocks belonging to the Petrified Forest Member of the Chinle Formation. This member consists primarily of siltstone and mudstone, both of which are types of very soft sedimentary rocks. There are a few layers of harder sandstones here and there as well. Also visible in this particular region is the Owl Rock Member. If you look at the horizon toward the center-right in the photo above, you can see a much taller hill called Chinde Mesa. Chinde Mesa is capped by Owl Rock Member layers, while most of the Owl Rock Member has been eroded away elsewhere in the park.

Petrified Forest Black Knoll
As you travel southward through the park, the reds of the Painted Desert fade to various other colors. The view above is from one of the overlooks on a formation called Blue Mesa. These rocks are still part of the Chinle Formation, but belong to a different member called the Sonsela Member. The hill in the background along the horizon is called Black Knoll. Black Knoll doesn't belong to the Chinle Formation, and instead is actually made of hardened basaltic lava. This lava was laid down in the late Cenozoic Era, about 5-1.4 million years ago. The Cenozoic Era is the era after the dinosaurs (the Mesozoic). As I mentioned earlier, the majority of rocks found at Petrified Forest date to the Triassic Period, which is the earliest period of the Mesozoic.

Petrified Forest Blue Mesa Member

Below the Sonsela Member is the Blue Mesa Member. This member is filled with stunning purple hues, as you can see above.

Petrified Wood
Now we are going to get to the namesake of the park. This is a chunk of petrified wood. Petrified wood is a type of fossil formed through the permineralization of wood. Essentially, a dead tree will fall and be quickly buried by sediments. Water containing a large amount of silica will then seep into the ground and begin to seep into the log. Slowly this silica-rich water will then begin to replace the wood as the wood decays. This replacement process takes place at the cellular level, with cavities and other parts of the cells being filled or replaced by minerals. What is left is a fossil in which all the organic material has been replaced by inorganic minerals.

Petrified Forest petrified log
As you might have guessed, there's a lot of petrified logs within the park. A "petrified forest," if you will. To understand why this is, one must go back over 200 million years ago. During the late Triassic, this land was situated near the coast of the super-continent Pangaea. This region was a wet location back then, with major rivers meandering through the area and emptying into the nearby ocean. All of the land in the park was river floodplains and bottomlands. These floodplains and bottomlands were covered in a tall coniferous forest. These tall conifers would die, and sometimes one would fall in the rivers. The rivers would transport them downstream where they would get snagged on rocks or each other, and they would end up being buried by the river sediment and often become petrified. Occasional nearby volcanic eruptions would also knock down trees and cover the land in ash, a perfect medium for petrification to take place. Over hundreds and thousands of years, thousands of logs were fossilized and preserved, causing the land to be littered with petrified logs nowadays. As erosion continues, more and more logs are uncovered. The trees that lived here in the Triassic would have reached upwards of 200 feet in height, but you don't see chunks of petrified wood that long. Oftentimes the pieces are only a few feet long and look like they've been chopped in pieces, like the petrified log pictured above. This is due to past stresses fracturing the logs. The Colorado Plateau experienced millions of years of uplifting, which slowly bent the rock layers. These petrified logs were forced to bend as well, and there would come a point where they simply broke into pieces to relieve that stress.

Petrified Forest Yardang
Since we're on the subject of smaller things within the park, I'd like to talk about this interesting rock above. This is an example of a yardang. Yardangs are streamlined rock formations that have been carved by the wind. Yardangs tend to form in very dry climates (mostly deserts) that experience a strong prevailing wind for most of the year. Bits of sand and silt get picked up by this wind and get blown repeatedly into a rock. Over time this wind erosion eats away at the rock, leaving a long-but-skinny rock formation.

Twin Buttes Petrified Forest

No matter where you go in the park, there's always something magnificent to see. In this photo, the so-named Twin Buttes soar out from a vast, flat steppe that begins when the badlands end. Petrified Forest National Park is an amazing park, but one that doesn't seem to be talked about much. If you're ever out in the area, pay a visit!

Thanks for reading, and stay tuned for more posts from out West!

Wednesday, December 16, 2015

Short-Eared Owls!

This past Sunday I was out chasing a Ross's Goose and two Snow Geese in Lancaster, Ohio. When driving back to Circleville, I noticed that it was approaching dusk. On a whim I decided to drive just south of Circleville to Radcliff Road and see if there were any Short-Eared Owls about. Radcliff Road (and the attached River Drive) cuts through the area that was once the Pickaway Plains, a small section of prairie now all but gone. More recently, a large section of land in this area was put under control of the Conservation Reserve Program. In an attempt to create habitat for wildlife and restore land that was intensely farmed for decades, farmland was converted to a sea of various grasses. This area (including the famous Charlie's Pond) has become well-known to birders for the interesting array of grassland species that call it home.

Short-Eared Owl Ohio
The grasslands along Radcliff Road and River Drive have been known to harbor overwintering populations of Short-Eared Owls for several years. Actual numbers of individuals of vary year to year, and I've personally missed out every time I've gone looking for them here. But this night was different. Just a few minutes after turning onto Radcliff Road, I noticed a Short-Eared Owl on the ground looking at me! Finally, my Short-Eared Owl lifer! I was dancing in my car from excitement and shooting photo after photo. Finally, after a few minutes, I decided to continue on down River Road. Then I noticed the others; there were Short-Eared Owls flying everywhere!

Short-Eared Owl Flying
This is when I really started freaking out from excitement. At least 7 Short-Eared Owls were flying over the grassland. I wasn't really expecting to see any, let alone have them circling my car! The Short-Eared Owl is a medium-sized owl species that can be found on every continent except Australia and Antarctica. In North America, the Short-Eared Owl breeds in Canada and Alaska as well as the north-western quarter of the lower 48. During the winter months they will migrate farther south to overwinter. Their migration isn't quite like the typical migration of most birds, and instead they exhibit more of an irruptive migration. Basically, they follow vole populations. When vole populations crash in the northern section of North America, large numbers of these owls will irrupt southward to find better food sources. Sometimes this results in these northerly owls being found as far south as Florida or northern Mexico and in great numbers. If the vole populations are high in the north, these owls will not go as far south, and might be completely absent in locations they were abundant at a year ago. These irruptive cycles can make them hard or easy to find in Ohio when it comes to a yearly basis, but they always make an appearance throughout the state each winter. There have even been a few records of them breeding in Ohio, including right here in Pickaway County (probably in this location, but I cannot find exact details), but these records are few and far in between.

Short-Eared Owl in Field
Spot the Short-Eared Owl.
The Short-Eared Owl is an inhabitant of grasslands, prairies, marshes, and other open country habitats. They are nocturnal, but they often begin to come out and hunt up to an hour before sunset. These owls were out and about at 4:30, while the sunset wasn't until 5:10 or so. As you might have guessed, the decreasing light made it hard to take decent photos. Telephoto lenses already don't do well in low light, and I have a pretty amateur-level 300 mm telephoto lens at that. Couple that with my Nikon D5100 camera sensor that does okay with ISO (light sensitivity) levels, and it was pretty hard to get a decent, focused photo without a crazy amount of noise. All of these photos were shot at f/8 with a shutter speed of 1/250 seconds and an ISO of 320 and 400. I also shoot in RAW which allows me to be more flexible with exposures. These photos were all underexposed, but Lightroom does a wonderful job at bringing under-and-over-exposed RAW photos under control.

Short-Eared Owl and Northern Harrier
Since the Short-Eared Owls came out while there was still light, they weren't the only ones patrolling the grasses for voles. Northern Harriers, which are essentially the niche-wise daytime equivalent of the Short-Eared Owl, were still out. The two species didn't like this competition though, and some scuffles broke out. The photo above shows a Short-Eared Owl (on the left) chasing a Northern Harrier (on the right). These two frantically chased each other for a bit and occasionally hit each other if one got close enough to launch an attack.

Short-Eared Owl Ohio
These owls are strikingly beautiful. You might be wondering about their name though. The Short-Eared Owl is called such as they have small feather tufts (not actual ears) that stick up from the top of their head, much like a Great Horned Owl. However, these owls only raise these tufts when alarmed or excited. Most of the time these tufts are held down, like in the individual above.

If you want to see these owls, check out Radcliff Road and River Drive in southern Pickaway County at dusk. If you aren't near this location, try checking out nearby hay fields or grass fields at dusk. The roads around The Wilds near Zanesville seem to produce a bunch as well! Thanks for reading!

Tuesday, December 15, 2015

A Ross's Goose with Snow Geese

On Sunday I was browsing Birding Ohio when I saw a report of two Snow Geese and a Ross's Goose in Lancaster, Ohio. The semester had just ended and I was back in my hometown of Circleville, a mere 30 minutes away from Lancaster, so I thought "why not go see them?" I got in my car and headed off to see the three rare geese!

Rare Birds in Urban Areas
I made the drive and arrived at this incredibly wild and biodiverse... retention pond. Okay, maybe not so wild, and not so biodiverse, but sometimes really strange things show up in ponds like this. Take for example the three white geese in the photo above (2 on land, 1 in the water).

Snow Geese Ohio
I pulled up closer to the geese, using my car to act as a blind. People don't always realize how useful of a blind a car can be; animals tend to equate humans with danger, but cars are just those big, quickly moving things that never really bother them. As a result, many animals will allow for a closer approach by car than they would with you trying to sneak up on them. The two white geese pictured above are the Snow Geese in question.

Snow Goose Ohio

The Snow Goose is my favorite goose. It's also a species that's eluded me for years. This year, however, has been different! I recently got my lifer Snow Goose in Athens, which I wrote about here. Now two more Snow Geese! The Snow Goose is a rare, but regularly occurring, bird in Ohio. They breed in the high Arctic and migrate to locations east and west of Ohio. During migration, they use flyways that bypass Ohio completely, and the vast bulk of individuals never visit the state. However, every year a few dozen individuals migrate through Ohio. These individuals end up in Ohio for a variety of reasons; some are blown off course by weather fronts, others might be juveniles who don't have this "migration" thing down yet, and others might be individuals who have some sort of a flaw with the navigating portion of their brain. Birds use various mechanisms to migrate, including Earth's magnetism, star-navigation, and location of sunsets, and if the part of their brain that facilitates navigation is either deformed or injured, you might end up with a bird that knows it needs to migrate, but just doesn't know exactly where to go. Generally speaking though, since we are so close to the flyways Snow Geese use, the ones that show up in Ohio are probably just individuals blown a bit off course by weather.

Ross's Goose vs Snow Goose
The report mentioned a Ross's Goose was also present, and a quick check of all three individuals made it clear who was who. In this photo, the Ross's Goose is the one in the front, while a Snow Goose is behind him. The Ross's Goose looks really similar to the Snow Goose at first glance, right? Further inspection reveals some subtle differences. But first, how do you tell if the white goose you might be looking at is a Snow or Ross's Goose, and not just an escaped white domestic goose? Look at the wing-tips! In a Snow/Ross's Goose, the wingtips will be black, as you can see above, while a white domestic goose will be completely white. Since these guys have black wingtips, how can you now differentiate between the two species? First, notice that there's a nice size difference between the two; the Ross's Goose is only about half the size of a Snow Goose. Obviously size can be deceiving in some circumstances (especially if you don't have a nearby Snow Goose to compare it to), so identification must rely on other characteristics. The most tell-tale field mark, in my opinion, is the beak. Notice how the Snow Goose has a large beak that seems pretty proportional to its head. Now, compare that beak with the tiny, thin beak of the Ross's Goose. If you see a small-looking white goose with a tiny beak, you've probably got yourself a Ross's Goose. Another thing to take into account is the length of the neck. Snow Geese have long necks, while Ross's Geese have shorter, stubbier necks, but once again this can be deceiving in some circumstances.

Ross's Goose Ohio
The Ross's Goose was the more exciting of the two species in question. Although Snow Geese are rare in Ohio, they occur in mind-blowing numbers elsewhere. The Ross's Goose, however, has a much smaller global population, making them uncommon even in places they're supposed to be. Now, couple that with the fact they aren't supposed to be in Ohio, and you've got yourself a very exciting goose! Like the Snow Goose, the Ross's Goose breeds in the high Arctic and migrates to the southern US and northern Mexico. However, the range of the Ross's Goose is much more restricted than the range of the Snow Goose. Interestingly, the Ross's Goose has been expanding in both population and range over the last 40 years, resulting in more and more individuals turning up in places that they normally wouldn't. With this recent trend, it is possible that the Ross's Goose might become a much more regularly-occurring bird in Ohio.

Snow Geese with Canada Geese
It was wonderful to see these geese so close to home. This year has been filled with rare and interesting birds, and hopefully this trend continues into next year.

Thanks for reading!

Friday, November 27, 2015

The Geology of Old Man's Cave

The geology of Ohio is incredibly fascinating, and incredibly varied. One of the most famous geological sites in Ohio is Old Man's Cave in Hocking County. Old Man's Cave is one of the many gorges located within Hocking Hills State Park, one of the most-visited parks in Ohio. Many people think of Ohio as a totally-flat state, but that couldn't be farther from the truth. Although approximately 2/3 of Ohio was glaciated and subsequently flattened in geologically recent times (as recent as 10,000 years ago), the other 1/3 was never glaciated. This region is part of the Allegheny Plateau. The Allegheny Plateau used to be a broad, flat plain that was uplifted before experiencing millions of years of erosion by flowing water (creeks, rivers, etc.). This flowing water cut down into the flat plain, creating the hills that eastern Ohio is known for. This post will essentially be a basic tour of the geology of Old Man's Cave starting from the very beginning of the gorge to the end of the gorge. Note, this is going to be a pretty long post!

Map courtesy of the Ohio Department of Natural Resources. (Link)
Old Man's Cave is located within the highly dissected Allegheny Plateau, but there are some other factors at play that have created the unique Hocking Hills Region. To understand why Old Man's Cave formed, we must first go over some basics. The gorges, waterfalls, and so on of the Hocking Hills occur almost completely within a section of bedrock named Blackhand Sandstone. Understanding this Blackhand Sandstone is completely necessary to understanding Old Man's Cave. Blackhand Sandstone is made up of sand particles which were laid down about 330 million to 345 million years ago during the early Mississippian Period. Now, it used to be thought that this sand was deposited in an ancient delta; however, recent studies have suggested another depositional environment. This 2006 study by Matchen and Kammer puts forth the hypothesis that the sand of the Blackhand Sandstone was actually deposited in an ancient braided stream. Matchen and Kammer put forth a very convincing argument, and I will be sticking with their interpretation. A braided stream is a stream with multiple channels that weave in and out of each other, with shifting sand and other sediment bars in between these channels. These types of streams occur when there is a high amount of sediment in the water. You can see an example of a modern braided stream at this link. If you look at the photo above, you can see the extent of Blackhand Sandstone in Ohio. You can also see that it takes the shape of a wide river floodplain, yet another clue to its braided stream history. The stream flowed south to north, and when it got to the extreme northern section it emptied into a shallow sea.

Now that we have the context down, we can move onto another important factor. Pictured above is a joint. A joint is a type of fracture, or a break in a rock. These are similar to faults, but occur on a much smaller scale, and typically movement doesn't occur along a joint as it does along a fault. A joint is a random break in the rocks which occur when the bedrock faces some sort of stress, such as a compressional force. When a joint forms, it creates a weak area in the rock, which in turn can be more easily eroded by water. This feature is very important when it comes to the formation of Old Man's Cave, as we'll see in a minute.

The parking lot for Old Man's Cave lies within a flat valley. This valley was carved out by Old Man's Creek, the creek which ultimately runs through Old Man's Cave. This creek eroded its way through what is called the Logan Formation. The Logan Formation is a set of relatively soft rock layers, and so the creek was able to erode it easily and carve out a broad valley with no cliffs. Eventually it got down to the Cuyahoga Formation. This is the bedrock group which contains the Blackhand Sandstone. Blackhand Sandstone is much, much harder than the Logan Formation rocks, and so it is harder to erode. Once Old Man's Creek got down to this layer, it couldn't easily erode the sandstone. However, it eventually found a large master joint in the Blackhand Sandstone. The water seeped into this joint and over millions of years slowly widened the joint. This widening joint eventually became the gorge. Looking at the picture above, the rock exposed is the top part of Blackhand Sandstone. This small waterfall is the beginning of the Old Man's Cave Gorge.

Upper Falls
Just a few yards downstream Old Man's Creek cascades over another set of rocks, creating Upper Falls. Right below Upper Falls is a plunge pool. You can see the outline of the plunge pool by looking for the deep turquoise coloration in the water (which signifies deeper water). A plunge pool is a feature that forms below a waterfall. The falling water in a waterfall has a lot of energy, and as this water hits the rocks below it scours out a depression. The eroded sand from the plunge pool is then deposited on the bank of the pool. The creek follows one side of the cliffs and continues on its way down the gorge.

Devil's Bathtub Old Man's Cave

Just a dozen yards downstream, the creek encounters another interesting feature. Pictured above is The Devil's Bathtub, which is actually a pothole. Basically, there was a weak area that the creek found and eroded. Sand and pebble particles in the water fell into this tiny eroded section and the current made them swirl around and around. This swirling action carved a bigger and bigger hole, forming what we now call The Devil's Bathtub. 

Devil's Bathtub Old Man's Cave
This pothole filled up and overflowed, eventually carving out a small notch in the top of the pothole. When the creek has enough water flow (which it does for most of the year, save the dry parts of summer), the water drains from this notch into the tight channel pictured above.

Old Man's Cave

The creek then gently meanders its way down the gorge, like in the section pictured above. Here we can also see many Eastern Hemlock trees. This species, along with other plant species such as Canada Yew and Yellow Birch, are species normally found farther north in cooler climates. During the last glaciation event, Ohio was much, much cooler than it is today. Plant communities characteristic of cooler locations (such as Canada) moved southward in order to survive. As the glaciers receded, most of these plants in Ohio died out and temperate forest plants came back from their Gulf Coast refugia and recolonized the area. However, some of these northerly species remained in a few select areas of Ohio. Deep gorges like this one create a much cooler microclimate, which allows these northerly plants to persist. If you've ever been to Old Man's Cave on a hot summer day, you probably know how nice and cool it is within the gorge.

Sandstone cross-bedding
As always, you can click on the photo to enlarge it!

As we approach the middle of the gorge, I'd like to take a quick tangent and talk a little bit more about some features of Blackhand Sandstone. It's a complex rock formation with many interesting features, such as cross-bedding. Cross-bedding is layering at an angle to the main bedding plane. Essentially, sedimentary rocks have one horizontal layer after another. Cross-bedding is an inclined layering which reflects certain sediment features that were inclined. As I mentioned before, Blackhand Sandstone was originally sand deposited in a braided stream. Braided streams have characteristic sand bars in between the water channels (example). These sand bars were created when the water flow pushed sand up a slight incline before the sand settled down on the downslope of that incline. A diagram at this process can be seen at this link. This results in cross-bedded sand bars. These sand bars were preserved throughout the rock bed, creating very exceptional examples of cross-bedding in the gorge. To recognize these cross-beds, look at the cliffsides and look for angled layers. If you look at the photo above, you can see a part of a cliffside featuring normal bedding along with cross-bedding. On the left side is what it looks like, while on the right I have outlined the different sections along with the direction of incline in order to make the cross-bedding more apparent.

Hocking Hills Conglomerate

Another feature of the Blackhand Sandstone is conglomerate bands. Conglomerate is a type of sedimentary rock that is composed of gravel-sized sediments. In the case of Blackhand Sandstone, these gravel-sized particles consist primarily of quartz. You can see multiple bands of conglomerate running through the sandstone in the photo above. This gravel is typically laid down in the center of a stream channel. Water in the center of a channel is moving the fastest; as a result of this, small particles remain suspended in the water. Larger particles, such as gravel, weigh enough to settle out of the water and deposit on the bed of the stream. Essentially, the faster water flows, the larger the particles that are deposited. Since Blackhand Sandstone was originally deposited as a braided stream with channels and sand bars of assorted sizes, the resulting sandstone consists of varying bands of cross-beds and conglomerate bands along with normal sandstone bedding. These conglomerate bands can be seen throughout the gorge in various locations, so keep an eye out!

Honeycomb Weathering

The previous two features of Blackhand Sandstone had to deal with its depositional environment. This next feature has to do with the subsequent erosion of the Blackhand Sandstone. Pictured above is what is known as honeycomb weathering. Blackhand Sandstone is very porous, meaning water particles can easily seep through the rock. Throughout the sandstone are trace deposits of hard iron compounds. Seeping groundwater has deposited some of these iron oxide particles in pore spaces between sand grains, and that iron then makes the sandstone highly-cemented and very hard to erode. As more groundwater seeps through and erodes the sandstone, you end up getting this honeycomb pattern of cavities (less iron and more easily eroded) and rib-like projections (more iron and less easily eroded). It makes for very attractive sandstone. Anyway, back to the gorge!

Old Man's Cave Waterfalls

Old Man's Cave Gorge can be broken up into 3 regions. There's the Upper Gorge, Middle Gorge, and the Lower Gorge. We're now entering the Middle Gorge. This region begins with a long, gentle cascade of Old Man's Creek down bare rock, a rather abrupt change from the gentle, sandy meander of the creek in the Upper Gorge. These cascades are one of my favorite parts of the gorge!

Old Man's Cave
The cascades eventually lead to a small waterfall called Middle Falls, pictured in the bottom right above. More impressive is the incredibly large recess cave located above it. This recess cave is the "cave" of Old Man's Cave. This recess cave is nearly 200 feet long, 50 feet high, and 75 feet deep! Recess caves form throughout the Hocking Hills region, and they all form due to the same feature of Blackhand Sandstone. Blackhand Sandstone is broken up into 3 separate zones; there is the upper zone, the middle zone, and the lower zone. The highly-cemented upper zone is very resistant to erosion, as is the lower zone; however, the middle zone consists of weakly-cemented particles and highly cross-bedded layers. This makes it relatively soft and easy to erode. As I mentioned before, the sandstone is porous and allows water to seep through it. The upper layer doesn't erode much as groundwater moves through it, but the middle zone easily erodes on the other hand, and as a result this tends to form these large recess caves like the one above. The resistant upper zone forms the roof, while the "cave" part moves farther and farther in as it erodes away.

The Sphinx Old Man's Cave

After the creek cascades over Middle Falls, it comes into contact with the highly-resistant lower zone of Blackhand Sandstone. As a result, it has meandered over this layer while eroding more and more of the middle zone because it couldn't erode down into the lower zone. The result was a gentle widening of the gorge. Another big characteristic of this stretch of the gorge are dozens of large slump blocks. These boulders are actually made up of the resistant upper zone sandstone. As the middle zone eroded, the upper zone remained and formed the roof, like in the previous photo. Eventually, the weight of certain parts would become too much, and this stress would cause a large slump block to break off and fall to the floor below. As this process occurred over millions of years, more and more slump blocks began littering the gorge floor. 

Lower Falls Old Man's Cave
Old Man's Creek continued to flow on top of the resistant lower zone until it found yet another joint to exploit. More erosion occurred, and Lower Falls was born. It is here at the bottom of this recess cave that the Blackhand Sandstone members ends and runs into the so-named Fairfield Shale, a much softer rock. The plunge pool visible was created through the erosion of the Fairfield Shale. From here, Old Man's Creek travels a broad valley until it meets up with Queer Creek. Queer Creek is the stream which created nearby Cedar Falls, yet another section of the Hocking Hills State Park.

Overall, the Gorge Trail at Old Man's Cave is about half a mile long. Over the course of that half mile, the gorge cuts through the entire thickness of Blackhand Sandstone. The thickness of Blackhand Sandstone varies geographically, but in this specific area it's about 130 feet thick, meaning from the very first tiny waterfall to the plunge pool of Lower Falls is about a 130 foot drop. I'm currently on a massive geology kick, so expect to see more geology-themed posts over this winter! Hopefully you enjoyed this long post, and thanks for reading!