 Hello, good afternoon. Hello everyone. Hello. Hi. Hi. My name is Penny. I'm a librarian here at the library. And I just want to welcome you all here. What a great turnout. And just want to remind you all to turn off your phones. Or at least turn them down. And I'm not going to take much of your time. I just wanted to give you all a welcome. And we are super excited to be partnering today with the Boulder County Heart and Open Space. I want to make sure I said that right. And with that, I will pass the mic over to David, who will be doing our presentation today. Thank you. Are you ready? Thanks so much for coming on the first warm sunny day in Hawaii over here. I almost didn't want to come inside myself, but I did. So I'm David Copeland. And I'm a volunteer naturalist with Boulder County Parks and Open Space. How many people have done a program with Boulder County Parks and Open Space in the past? Well, that's great. We have all kinds of stuff going on. In addition to talks, we have a lot of hikes and outdoor programs at all our different open space programs. Sites. And at the end, I'll show you how to find those programs and register for them. So today we're going to talk about story in the rocks, the spectacular geology of Boulder County. And, okay, let's begin. So really what we're going to talk about is the geologic history of Boulder County. But what I want to focus on is interesting geologic features you can see in the parks. And looking at these things, you can ask, how did that happen? And to me, this enriches my appreciation and joy in the outdoors, when you can see things and say, oh, there's that thing. And I understand how that formed. Okay, so just a word about my background. Geology was my field of study in college and grad school. But it didn't actually work as a geologist. My first job was with a small company doing oil gas and mineral exploration using Landsat satellite data. And I ended up kind of bearing off into the image processing side of things. And first day of my career, I did image processing and machine vision. And then the second half, I did education. I led a small nonprofit, educational nonprofit. And then I taught high school science for 13 years. So without a lot of science and teaching, and now I'm so happy to go and combine that being a volunteer naturalist. I'm pretty new to Colorado, but I'm trying to get up to speed on what's going on around here in terms of the geology. One of the great things about Boulder County is that many great things is that they have really fascinating geology here. So here's an outline of what we're going to talk about. Just going to go over a few key ideas from geology, probably things that way, way back you may have learned in school. And then we're going to kind of work through time here. First, how did Colorado form? Because Colorado wasn't here forever. Before Colorado, there was no continent here. And then we'll talk about sedimentary rocks in the foothills and plains. The rise of the modern Rockies and finally the glacial geology of the area, which is quite interesting. So just kind of make this a little interactive and keep you on your toes. Once in a while I'll show a picture with a question mark. And if you know where that picture was taken, raise your hand and you can tell us that there's no penalty for wrong guesses, wrong answers. Okay, a few key ideas from geology. First thing is, you know, we live in a really unique location on the continent. If you keep starting from where we are, you can go a thousand miles east and you're just on the plains. And you go a thousand miles west, you're in mountains. And right here, the mountains just jump right out of the plains. And of course, every time we go outside, we can see that. And I'm just amazed every single time I go up close to that boundary, like on 36, how sharp it is. You know, just this gradual, quite flat, and then wham! And I'll just jump right out. So we live in a special place. And that line is to come and I'll divide. Well, actually, what is not quite the kind of, that's the front of the mountain. So the coming I'll divide, of course, is right here. And we're actually also the easternmost point on the kind of divide in North America. So that's another curious thing about Lothar County. So this is a, you know, in recent years, this has been an interesting way that people have been portraying geologic time, instead of like a linear sequence or like a layer of a kind of look, which is how geologists often think about it. But this spiral, which kind of shows time going back, back, back, back, back, back, back, conveys the idea of deep time. So it's really impossible for us to grasp intuitively how old the Earth is or how old the universe is. It's just so much greater than our human time scale. But what interesting thing about this presentation is that it kind of illustrates times that are closer to us we know much more about. So like we know a lot about the last 65 million years. That's called the Centzoic in geologic terms, the Centzoic era, after the dinosaurs died out. And we know quite a bit about the period of the dinosaurs, which is the Mesozoic middle life. And this is an older life year. But even all that time is only a little more than 10% of the age of the Earth. It just goes back and back and back and back. We have very little evidence of what was going on way back then. So how do we know the Earth is so old? How do we know that a rock is any particular age? Well, it wasn't until 150 years ago or a little over 100 years ago that we really knew how old the Earth was when this radiometric dating technique was developed. And not to go into too much detail, but the idea is that certain radioactive elements like potassium-40, an isotope of potassium, decay to a daughter element, in this case, argon-40, at a very predictable rate. And so if you take a rock sample and you have the right equipment, you can measure the ratio of the potassium-40 to argon-40 in the rock and the argon can't get out of this trap in the crystal structure. And then you can calculate, well, that must have been, that rock must have crystallized X number of years ago. And it's not, you know, it's within a few percent kind of thing, but it's enough to get a very good idea. And before this technique was developed, I mean, in the 1800s, people started to get the idea that the Earth was much older than we thought by things like clams, shells, and the Himalayas, like the heck, you know? But even then, their best estimates were in hundreds of those years, not in billions of years. So this kind of told us what's really going on. And you may remember about the rock cycle. This is kind of a complicated diagram. But we have igneous rocks which form from melt, molten rock, either underground called magma, above ground called lava. We have sedimentary rocks which form by the weathering and transportation of other rocks, so usually deposited by wind or water. And then abortion rocks, which are formed due to great heat and pressure, and they show, they didn't actually melt, but they usually show wavy or banded patterns that indicate that they came close to melting and minerals re-segregated and re-crystallized. So we'll use those terms a little bit. Okay, so how Colorado formed? GA needs billions of years of using the geologic thing for that giga-anum, billions of years. So 1.8 to 1.4 billion years ago, that's our first time here again. Okay, here's our first question mark. Yes? Longspeak. Longspeak, yes. Which is what Longmon, of course, is named for. And this, okay, here's another one now. Anybody recognize this place? No? No? Emerald lake, you know? Well, it's the Indian Peaks area. Indian Peaks, yeah. Lake Isabelle. Did somebody say that? Yeah. Yeah. I'm not sure about Pleasant Point and what that is, but so I just wanted to show you some pictures of these big mountains. And interestingly enough, when the Louisiana Purchase was made, it's specified to be up to the continental divide. Nobody even knew where that was. And so Major Long came out in 1820 to figure out, like, well, what did we buy? And he, you know, discovered that he bought Boulder County. Which, because the kind of divide is the western boundary of Boulder County. Okay, so these big rocks, these big mountains, the mountain core, are made out of igneous and metalwork rocks. And if we dig these rocks, we keep coming up with the same numbers, which is about 1.7 to 1.8 billion years old. So something big happened. 1.7 to 1.8 billion years ago. And this is called a banded nice. And, you know, we say in geology, never take nice for granted. So the way you can tell nice for granted from granted is you'll see some evidence of banding or foliation we call it. So some, because this rock was metamorphosed at high temperature and pressure. So how did that happen? Here's another rock without the same age, the Boulder County Granite Diary. Did you go up Boulder County, Boulder Canyon? You'll see this rock. In outcrop, it's often kind of brownish, because that's where the weather is due. But if you see a fresh cut, it's black and white. So this is also about the same age. So again, something big happened 1.7 billion years ago. And here's another one. This one's a little younger. I love this rock because of these oriented crystals. So the reason, the way this formed is it cooled at depth. Slowly cooled at depth. And the crystals grew bigger and bigger and bigger. These are belt-scarred crystals. And then it was injected upward to a shallower depth, where it cooled more quickly. So it cooled more quickly. The surrounding matrix here is made up of smaller crystals. So when you see this rock, you can recall that little sequence. This is called the silver boom granite. This is pink in its fresh cut. And I found this example of a strainer plate. So you can also see this up at Paul Ranch. You go up to the High Fire Paul Ranch. So the big mountains, the mountain core is made up of nicest and grass primarily. Metamorphic and igneous rocks. And these are called the basement rocks. 1.8 to 1.4 billion years old. That's very old. Now on the surface here in the plains, the rocks are much younger and all the way out, you know, to the Appalachian Mountains. There's younger sedimentary rocks. But underneath, there's still basement rocks. It's still a very old, I think it's a better word for rocks. It's just that here in the mountains, the mountains have been uplifted. And the sedimentary rocks have been eroded away. And so we see these ancient basement rocks on the surface. So how did these rocks in the state of Colorado form? Well, let's put this in context here. So 1.8 billion years ago, because there's nothing older than that. So there was nothing there before those rocks were formed. Except ocean. So 1.8 billion years ago, where are we going? Here's 2 billion years old. So we're like 40% of the way back to the origin of the Earth. So to understand what happened at that time, we have to do a little quick review about this idea of plate tectonics. And when I was in high school, around 1970, this was like a new idea just becoming accepted. But it totally revolutionized geology because it provided an explanation for lots of things that previously we could only just observe and describe, but now we have an explanation. So according to this explanation of plate tectonics, and we have very good evidence for this, the Earth's surface is divided into a series of rigid plates. Each plate has, may have ocean crust and or continental crust. So here, this is continental crust. Here, an ocean crust here. Continental crust, ocean crust. The actual boundary is a little offshore between continental and ocean. Ocean and crust. The continental crust is made up of lighter rocks, like mices and granites. And the ocean and crust is made up of denser rocks, like the salt, mostly the salt. Now the boundary between the plates can be one of three types. They can be spreading apart, which is called a divergent boundary. And this is like along the Atlantic ridge here. And when they spread apart, lava or magma from down below moves up and oozes out to the surface and forms new crust. So that's what creates the Atlantic ridge and the Pacific East Pacific ridge and other oceanic ridges around the world. Not a kind of a violent process, kind of a quiet process, but where they come together, we get a lot of action. So where the plates converge is where we tend to get things like volcanoes and earthquakes. So for example here, this little bit of Juan de Fuca plate is going underneath Pacific Northwest. That gives rise to the earthquakes up there and also the volcanoes of the Cascades, standing down here in the Andes Mountains, with the Nazca plate going underneath South America. And that creates a lot of geologic action. So geologists have visually gone around the world to try to explain a lot of things we see on the surface in terms of plate tectonics. So about 1.8 million years ago, this is maybe what this part of the world looked like. This was proto-North America and this is where Colorado was going to become Colorado. And there was a plate to the south that was moving north under Wyoming. The rocks in Wyoming are actually older. Some of the rocks in Wyoming are over 2 million years older than Wyoming. So this existed first. And this plate was moving northward and it was creating a series of island arcs like Japan and trenches where sediment was coming off of the continent. So we have all kinds of stuff coming off, sand, mud, limestone. We also have volcanic rocks. We end up in the mountains in certain places. And all this stuff was moving up and crunching up into proto-North America. And it just basically glommed on and made the continent bigger. This is called continental accretion. And over time the continents have gradually gotten bigger and bigger by this process. At the beginning, we're very, very odd in the Earth's history there probably weren't more than continents. We had oceanic crust. But then this process of continental accretion has gradually built up the continents over time. So Colorado was accreted onto North America 4.8 billion years ago. See, you got a mouth full of geology right there in one sentence. Yeah. Go ahead. I'm glad you asked that question because I can explain it with this slide right here. You've got to repeat the question, please. Repeat the question, please. The question is where does that magma come from? Where does the new rock come from? Where does the oceanic crust come from? So this is like a schematic of what happens when oceanic crust is pushed down under a continent. And as I mentioned, this could be today, this could be Japan, right here at the Isle of Dark being formed. Or many other places. This could be the Andes at the coast of South America. And because this oceanic crust is denser, and when it do collide, this gets forced down into the mantle, the hot rock down below. It's not melted, but it's much much hotter. But because this contains water and is a different mineral composition, when this is forced down into the mantle, it melts. And little streams of magma come up and create volcanoes. Plus it creates this trench where it's going down, like the Mariana's trench that you can point in the oceans. That's an example of subduction. And that trench tends to fill up the sediments that are being eroded off the continent. But eventually all this stuff just gets crunched together. And all this stuff, the volcanic rocks, the sedimentary rocks, all get squeezed together like toothpaste and a vise. These two continents are coming together and this stuff gets pushed down and pushed out, and this is where the metamorphism comes from. So all these nicees, these banded nicees, are eroded out as sand, mud, limestone, volcanic rocks. They were pushed in this vise between the continents and turned into the nicees. And also here's the granites. These are the granites forming here. Equal below the surface. And that became Colorado. Does that answer the question? I was going to say, like a hollow spot, but you explained, no, because things are going in to take its place. Did it leave a hollow spot? That's what I didn't realize. I actually asked the same question when I was a jolly student. Doesn't that leave a hollow spot? We mentioned a little bit about this, but here's a nice drawing. So when rocks melt below the surface, we call that an agma, and two things can happen. It could either cool, come up, make a chamber of magma, and then cool below the surface. If it cools slowly like that, then crystals have time to grow larger. And then we get things like granites. There's a whole suite of different names for those rocks depending on the composition. But this is granite, it's good enough. In other words, it's granite diary, the Boulder County granite diary. They all kind of look like this. They're different just in their composition and in their color. But also, it could actually come up to the surface and come out. Then we call it lava, like what's happening in Hawaii right now. I really want to go see that when I'm back too. And then we get very fine-grained rocks because they cool quickly. So this is like the salt, for example. Okay, so summary, continents grow by accretion during collision events. Colorado was created about 1.7 million years ago during continental collision. And a little 300 million years later, there was another event, we don't know really what happened, but possibly another collision or some other tectonic event which created more granites. There was actually another one about 1.1 million years ago. So, you know, things happen. And it's hard to know exactly what that long ago was going on. The pike's peak rocks are about 1.1 million years old. So that was another tectonic event. Okay? Yeah. How strong is moving and sort of deafening and driving? True. All the time, it's still 1.7 million years old. Why are there like intervals like that? Come on. Great question. So why are there certain intervals? Why isn't it just always happening? So this is like the very big picture about plate tectonics, which is fascinating to be. But we have good evidence that there's a recurring pattern where the continents all come together to make one supercontinent. And like the last time, we called that Pangea. And that's like what happens then is it's like you put the lid on the pot. The mantle heat can escape as easily. And so heat builds up over time and then that forces changes the way the mantle is flowing and continents split apart. But then once they split apart, there's potentially less force driving them. And they eventually kind of come back together. There's this repeating cycle, which happens to be about 300 million years. So it's being driven from underneath. Yeah. Coming from the Earth's interior is driving the motion of the continents. Some people compare it to the continents to scum on the surface of a stew. And if that's the continents, what is that they got? So now we're going to take a big jump in time because we have no rocks between 1.4 billion years old and 315 million years old in this area. There are rocks in other areas, of course. And even nearby, like in Grand Canyon, for example, we have rocks that go back like 600 billion years. But right here in Boulder County, the oldest rocks after the basement rocks are about 315 million years old. Why is that? Well, we don't know because there's no record of what happened. But probably there were rocks here and they were eroded away during subsequent mountain building and whatever went on over all those billions of years. So the story is going to jump forward to 315 million years ago. Let's take literally a bird's eye view here of Boulder County. And there's a very interesting pattern that emerges here. All the rocks from the flat irons east are sedimentary rocks. And all the rocks west of that are igneous and metamorphic rocks. Igneous and metamorphic rocks. So how do we explain that? In science, we always look for patterns and then try to explain them. That's a really dramatic pattern. So this figure comes from a really great book called The Geology Boulder County. If you're interested in the geology of Boulder County, I highly recommend it. Unfortunately, I think it's out of print but you can still get it on Amazon Marketplace. And she goes into great detail but for the life person about the geology of Boulder County and also there's 25 field trips. And here you can take around and look at different interesting things. And this, to me, this is a very helpful diagram of understanding the geology of Boulder County. We'll keep coming back to this actually. So here's the basement rocks, the nicest and granites, the ancient pre-Kingrian rocks. And here are the sedimentary rocks on top of the basement rocks. Now normally sedimentary rocks are laid down horizontally, like a layer cake. And that's what we see over here. In fact, if we were to go out this way all the way out to the Mississippi River in the past, those rocks would be, you'd see basically the same rocks for one thing and for another, they'd be pretty much horizontal. Well, we come here to Boulder County and the Rockies. All of a sudden those rocks are tipped up and pushed out like this. And this is because this happened during the formation of the Rocky Mountains. That's really fortunate for us because we can now see all these interesting rocks. And plus these provide a very interesting terrain where we can have parks and we can do mountain biking and hiking and all kinds of good stuff. So we're really going to focus on this area here. Here's the flat irons sticking up. And that's the first thing I'm going to talk about. Now in geology, because rocks are laid down one on top of the other, the oldest rocks are at the bottom. So if you were to drive up, for example, left-hand Canadian or Boulder Canyon or any of the Canadians here, you're basically driving back in time because the younger rocks you would kind of be younger rocks first and then older and older and older and older. The oldest sedimentary rocks the down formation and the lion formation and then you're into the Cambrian rocks. So I encourage you, let's go driving safely, to keep your eyes open as you pass through the rock cuts. And as a starter point, try to see where you get this transition from sedimentary to it gives a better orbit rocks. That transition right here is called the Great Unconformity. I've always been fascinated by that term and by that thing. The Great Unconformity because it's actually quite common throughout the world, almost every place throughout the world, there's a gap between the Cambrian rocks, the really ancient basement rocks and the overlying sedimentary rocks is a gap in time. So Unconformity means they both conform to each other. There's something missing. In this case there's a whole lot missing. There's over a billion years missing. And if you take our geology hike out at Paul Ranch you get to jump across the Great Unconformity. You get to jump across a billion years of time. That's part of the hike. There's no extra charge for that either. All it is is one thing lying on top of the other and there's a huge gap of missing time. There's no rocks that were deposited for over a billion years. So it's not like they're mixed together or anything. It's just there's a boundary. If one sedimentary rock lies on top of the other and it was deposited right after that in time we call that a conformable boundary. But if there's a gap in time then there's an Unconformity. And lots of times the Unconformity shows evidence of weathering and erosion because this was exposed to the elements before the next thing was put on top of it. So what is that stuff? That's a great question. The best place I've seen this exposed is on Flagstaff Mountain the road. Flagstaff Mountain Road. Flagstaff Road. If you drive up there somebody told me it was there and I drove back and forth until I found it. There's a spot where you've got the Mountain Formation which is sandstone ebbles in it, red, very distinctive, and then right on top is Granite. But if you walk over to Granite it's so soft you can pull it out of their hand. It's been completely weathered still in place but the minerals are all weathered to clay and you could actually pull out a chunk of it because it was exposed to the surface for a long time before you set up your rocks where you put it on top of it. Okay. So now let's put this into context here. 315 million years ago the ancient dinosaurs is the Triassic Jurastic Cretaceous. They're called the Mesozoic but 315 million years ago it's just before that. So it's around here just before the age of the dinosaurs and these are the oldest set of entry rocks in Boulder County. Easy one. Flat Irons. Boulder Flat Irons. Okay, anybody know where this is? All Ranch and Lions. All Ranch and Lions. But did you know that this is actually the same rock formation as the Flat Irons? This is the Fountain Formation Nature Fountain, Colorado. Usually geological formations are named for the a locale when they were first described by a geologist. So this was first described in Colorado and let's take a look at that rock. So we have this interesting concept in the set of entry rocks called sorting. Then all the grains are about the same size. And if it's poorly sorted then they differ a lot in size. What would you say? Is it well sorted or poorly sorted? It's poorly sorted. That's actually an important clue because if sands and gravels are transported for a long distance the action of the water sorts them out because water can only carry a certain size. Let's say you have a stream running down like this same ring creek right past Hall Ranch. If the size of the grains is smaller than a certain amount depending on the current it will be washed down and if it's larger it will settle down. So the stream sorts out things. If things are very poorly sorted because this is a stream deposit that means it was not transported very far. It was transported a very short distance. In fact that kind of very poorly sorted sediment which is sand and gravel and also has other interesting features it has chunks of granite in it. Some of the pieces are kind of sharp they haven't been rounded by the action of water. Also there's some soft minerals that have been preserved else far as they don't last very long when they're being beat up by a stream. And so we know this was transported a very short distance and a high gradient. And so a modern environment that does that is an alluvial fan is a picture of an alluvial fan but to have an alluvial fan you have to have mountains. And so based on the fact that there is a fountain formation there which with an alluvial fan which had to come out of a mountain we infer there must have been mountains there at that time. But they weren't the Rockies. The Rockies only formed about 65 million years ago. So there must have been another mountain range before the Rockies and we call that the ancestral Rockies. And so this thought process that we've just gone through this is what geologists do. They're basically form of detectives, right? You look at evidence, you think about well maybe this could have been this, could have been that. How could that have happened? What was the sequence of events? So I've just got to tell you now we know why we believe there was a mountain range before the Rockies called the ancestral Rockies. Here's another interesting piece of evidence from the Fountainfell Lake formation at Hall Ranch. Didn't that suggest anything to you? What do you think that, how do you think that formed? Water, evaporation? Mud? Yes, all correct. These are mud cracks. And what tends to happen with mud cracks in geology is you know just like in your backyard or your driveway, you get a layer of mud, it dries and cracks, but then another layer comes on top of that like let's say a stand-by layer and fills in the cracks and then later after it's all become a rock, like due to pressure and by the fluids migrating through the rock and cement it all together, the, well what the cracks meant to stand out was a bump, like you know, ridges. These are mud cracks. So what does that tell you about was this in the positive low water or above water? Above, yeah, low water or above water? Much, pretty much below? No? It's got to be right at the surface. It couldn't be like out in the ocean or in the bottom of the lake, right? It's got to be a terrestrial or land deposit. So this is what we think that the ancestral rockies look like maybe 310 million years ago. There's the ancestral Rocky Mountains and there's all these Lubio fans flowing out the streams. Here's some early plants that existed at that time. This picture is found in the Denver Museum of Nature and Science. Outside the Hall of the Dinosaurs there's a series of beautiful drawings or paintings like this called Ancient Denvers and I'm going to show you a few of them but they're like imaginings of what the landscape looked like at different times in the past. So here's what the landscape may have looked like and the people that presented through these put together the available evidence and came up with some reasonable guesses. So here's where we think the ancestral rockies existed based on evidence. We see similar deposits over on this side too. Similar to the found formation. So why did that happen? Well, this was about 30 million years ago and this is when the continents were coming together to make Angaea, which means all Earth. And possibly now we're into the range of kind of speculation but possibly the forces that were transmitted through the continent due to this collision resulted in the rise of the ancestral rockies. At least it's about the same time. So here's another drawing about what may be going on there. Here's your basement rocks that are more like basement rocks. Here's your granites intruded into the basement rock into the graces. Ancestral rockies and alluvial fans. A picture of granite pebbles eroded from the ancestral rockies. One interesting thing about the found formation, like if you go out the whole ranch, you can walk through the found formation, found formation, found formation and then at some point you get the silver gloom granite. And it's actually kind of hard to tell maybe that transition. And the reason is is that the fountain is made out of pieces of the silver gloom granite. And they don't look all that different. They're not the same color and so forth. Okay. What is this? See you. See you. It's a beautiful campus. And it's made out of a very famous rock called the lion sandstone. Here's a movement of brother's stone company in lions. This is actually the rock that we keep playing in my backyard to make my zero escape backyard here. Pieces of the lion sandstone. This machine is used to cut flagstones. Flagstone is just the use of it. Right. It's being used as a flag or something to walk on, essentially. Flagstone is... There could be other things, I suppose. Yeah. Flagstones are typically that of sandstone. Yeah. This is a really beautiful sandstone. It's very hard. It's attractive and it's used all over the country and even in Europe, there are cool yards that are paved with the lion sandstone. Yeah. What do you think? Is it well sorted or poorly sorted? It is a very well-sorted rock so it's not like the found formation. It's not a alluvial fan. Another interesting feature you see in the lions is... So here are the actual bedding planes. In other words, this was for example at the time the rock was laid down and the rock was laid down layer after layer like this. And yet there's these lions that go at an angle. The bedding planes. And this is called because it goes across the bed. Here's the beds of the sandstone and this is going across that. And what this is caused by is dunes. So if you think of a dune there's like an angled slope on the dune. Who's been to great sand dunes? Yeah. Really cool spot. So you've got this angled slope that the wind blows over the dunes and it keeps moving this way. So even though the sand is being deposited let's say at this level overall the layers are going like this. Does that make sense? So that's what this is. You can also get this in deltas. Like in lakes or in the ocean where the deltas are slowing down. And so your is an angle and it's being deposited on the leading edge. So this suggests that this is either by wind or maybe it's a delta but it's certainly well sorted. Now here's an interesting question. Any idea what this is and how this could have formed? I heard it. He said no. Rain drops! Yeah, these are rain drop compressions and it's actually a flagstone in my backyard of alliance formation. So these are rain these are rain drop compressions did it form under water? I mean under deep water like a delta? No. This must have been formed above water. Again, this is just a very quick sketch but to put together all the evidence we believe the alliance was formed by dunes. They are dune formations which are typically very well sorted. Like, yeah. These are also well sorted but these are dunes. Okay. So I don't know if we can cut it out back to you. So what about the one where we have black leaves? Oh yes, that's so interesting. It looks like branching, right? Black branching patterns? Yeah, they're very interesting. So those are formed by mineral solutions that are kind of creeping between the plains of the sandstone and as they do the crystals grow at the edge it's not like a snowflake in a sense. They call that a dendritic pattern for like branching dendritic or branching pattern. Yeah, I don't know a picture of that but that's quite striking when you see it. Here's another interesting pattern in the alliance formation. This is actually a bench at CU. What would a desk do? Wind Wind, yeah. Waves. Wind or waves, exactly. These are called ripple marks and they can form either by wind or in shallow waters. So by itself this doesn't tell us whether it's shallow water or dunes but it's a very interesting pattern and I invite you to keep your eyes open when you're looking around where any place in the alliance is outcropping or in your backyard. Do you see ripple marks? Do you see blood cracks? Do you see rain drop impressions? Man tells you what geologists call the depositional environment. In other words, the environment that was deposited in. You start to get clues about what was going on for the other 10 million years ago. So here's the environment of the mountains. Now maybe they've been worn down somewhat or were farther from the steep part and wind is like streams that are carrying sand down from the mountains and wind is blowing it around making sand dunes and that becomes the alliance formation. Here's perhaps a hardest conception from the ancient Denver's pictures. Notice the ripple marks there again from the mountains and the sand dunes like the great sand dunes. So the alliance is very hard that makes it so valuable as a building material and you'll often see a cat rock like this on top of a butte or a mesa. It's been eroded, the softer rocks above have been eroded away and this is kind of protecting the softer rocks below. So you'll often see this cat rock of lions around the tube. We'll do that depending on where you are. In the Grand Canyon there are other rocks that serve this purpose. But anytime you see centenary rocks you'll often see these resistant cat rocks. Now one way to tell how hard or resistant to erosion a centenary rock is is how steep the sides are. If it's very resistant to erosion they can make vertical sides and if it's less resistant so up in the lions this is the Hall Ranch again the fountain is not that resistant. It's chemically a little different than down around Boulder. Down around Boulder it's very resistant to erosion we have these very sharp flat iron stinging out. This is kind of a tough one. It's like a wide-angle lens view of a beloved park in the area. Hyal, yes that is Hyal Valley Ranch. We're on the south end looking north and this is the valley itself. Okay here these are the resistant ridges made by the fountain and lions narration. And then there are less resistant down below and then there's another resistant rock up here, notice this nearly vertical here. So this is another resistant cab rock and because this is east and notice things are tilting this way you can imagine the younger and younger rocks are piling up like this so these rocks are much younger than these rocks. But this general pattern of a ridge here a valley and another ridge you can see that throughout the foothills in Baltimore County. These are called hog backs. This is one of, this is the fountain lions hog back and this one here is the Dakota hog back. So Hyal Valley Ranch is between two hog backs and what do you think is the west here? Igneous amount of work are very good because now we're we've run out of sedimentary rocks down to the basement rocks curiously enough these actually aren't even as hard as the fountain and lions. You think granted it's like super hard or nice but the fountain is really quite I mean the fountain and the lions depending on where you are is quite resistant. Okay, so here's what I was talking about. In terms of the hog back here's the resistant hog back made by the fountain lions which are bolder as the flat irons then in between we have less resistant younger rocks the lakens formation, Morrison formation and then the Dakota hog back and then we have more recent rocks and this we'll get to this more again but this big fault here you can see the rocks have been offset that's from the rising of the Rocky Mountains that's one of the many, many faults that caused the Rocky Mountains to rise up. So I wanted to if you go to Ohio Valley Ranch and you walk around the like a like and loop of course that's all been burned now. Many people have been there since it burned a big number of people looks a lot different but it's still still an interesting place, still a beautiful place but one of the interesting things from a geology standpoint is the lakens formation has these rocks in it called stromatolites, these are fossils and what they are is algal mats the algae mats that build up these little mouths and these have existed for a good part of Earth history in the art this is an actual photo of stromatolites in Australia they live in shallow ocean water and these are this is a picture of the oldest known fossil the oldest known evidence of life of stromatolites 3.4 billion years old so that's 2, you know roughly 2 thirds the age of the Earth and these are stromatolite fossils but don't put that different from the ones at Pile Valley Ranch you typically see these when they break off you see these concentric patterns like this or from the side you see mountains like this so the next time you're out there keep your eye open they're actually all over the place once you kind of get keyed into looking for them and there's also an interpretive sign that will tell you about them so here's maybe what the this part of Colorado looked like 250 million years ago the shallow sea with stromatolites or algal mats growing Morrison Formation it's very interesting rock it's very widespread there's dinosaur fossils are very commonly found in this throughout the West just south, you know Morrison is Colorado just south of us and of course in Morrison Colorado there's the dinosaur ridge with the dinosaur tracks that's Morrison Formation in this part of the world in Boulder County it's a softer rock so it tends to go over the way so the bottom of the valley at high altitude is Morrison and it looks kind of greenish so near the bottom of the stream is you'll see stream cutting through greenish rock, soft greenish rock that's the Morrison Formation and maybe this is what the world looked like so now we're into the age of the dinosaurs and maybe this is what high up valley ranch looked like 150 million years ago okay so now on to the Dakota Dakota is in the Cretaceous period the last part of the age of the dinosaurs a lot of the famous dinosaurs that you're familiar with the Cretaceous they really should have called the movie Cretaceous Park but that didn't sound as good as Jurassic Park so they owned the Jurassic Park but the Cretaceous the whole story of the Cretaceous in this part of the world is the story of the Cretaceous Seaway so the ocean came in the ocean came in flooded the whole central part of the continent during the Cretaceous during the early Cretaceous you can see evidence of the ocean coming in and advancing over the land in the middle Cretaceous we see evidence that there's deep water here and then at the end of Cretaceous we see evidence that the ocean is going out so the whole sedimentary sequence in the Cretaceous is about the western interior Seaway or the Cretaceous Seaway now you may be wondering how does the ocean get up to 5,000 feet above sea level anybody got an idea about that yes we weren't that high yet that's right at this time 100 million years ago or so we were close to sea level so there's another thing that needs to be explained is how did we get from close to sea level to 5,000 14,000 feet above sea level that needs an explanation but at this time it was above sea level but then you can also ask it was above sea level but you can also ask what caused the ocean to advance and then retreat again well what's that the ice age actually, partly I think it's the reverse of the ice age because there was no Antarctic ice sheet at this time there was a world as a warmer place the Antarctic ice sheet if it was to melt now would reach sea level about 200 feet that's a lot in fact here's a fun fact for any of you for fun facts we do this boundary right here there's a there's a large concentration of Democratic voters why is that why is that I mean well it's because that when the Cretaceous Seaway came in it left rock soils there rocks that became soils that are very good for growing cotton and later cotton plantations brought in African Africans who still live there and vote Democratic so I think geology isn't affecting the modern world I think about that another factor that could have been having to do with the coming into the western Seaway western tier seaway is Pangea was breaking up at this time and I mentioned the idea of a lid on a pot well the the theory goes and I'm not sure really how good the evidence is for this but sounds interesting that there was an increase worldwide in mid ocean ridge activity that coincided with the breaking apart of Pangea so mid ocean ridges are because they may have a warmer rock and as the rock cools it shrinks and also they're like these mantle upwelling below or maybe so if there was more of the activity then maybe the whole oceans were displaced by the swelling of the mid ocean ridges that occurred at the time the MG was breaking up so here's the decoder formation decoder formation is like each deposits that formed when the Cretaceous Seaway was coming in so that's the beginning of the Cretaceous Seaway each deposits here's the decoder hogback on Radford mountain you can see those resistant ridges the decoder is very hard there it is the cap rock at Radford mountain and if you go to Radford mountain you can see a lot of sandstone so it's primarily quartz interesting features at Radford mountain like cross bedding this case is probably each deposits and there's some pebbles there's also at Radford mountain you can see these interesting features it's like scratches scratches in the rock what could possibly scratch a rock like that glacier glacier is a good possibility but actually it's not what caused it in this case falting so there are all these faults along the front range here that have to do with the base of rocks being fractured and lifted up in big blocks to create the Rocky Mountains and here the decoder formation which is pretty hard has slipped against itself because they're called slick-insides slick-insides and if you keep your eyes open just walking up the trail at all range they're all over the place there's a lot of things in nature you look where is that where is that and then suddenly you see one and it's like oh they're all over the place and that's how it is but a lot of these things we're talking about today and I think it's kind of fun I was getting kicked out of it so later Cretaceous rocks so the sea has come in and they laid down the decoder formation there's beach deposits pretty well sorted sand deposits very hard making the decoder hard back but now we get shallow water and then deeper water deposits as the ocean gets deeper and deeper first we have the New Brara limestone this is a giant clam from Boulder County near Yoder Ranch we're taking a hike out there in May we're going to go look at those giant clams in the New Brara formation I'll give you the information at the end of the talk and limestones are shallow water offshore but shallow then we have deep water deposits the pure shale deep water and mud deposits that get consolidated and compacted to make shale which is a sedimentary rock that comes from mud and anybody have heard of bentonite? everybody's nodding well this is from the pure shale unfortunately the pure shale underlies the bedrock for a lot of the front range and when it weathers creates this mineral called bentonite that expands five times or more when it gets wet and then it shrinks when it gets dry and if that's next to your basement wall it's bad news so this has caused millions of dollars worth of damage above that this is what we call stratigraphic water so the mold is at the bottom above that we have the fox hill sandstone I'll show you some pictures of that which is beach here's the water going back out again beach deposits of the cretaceous fuel ain't going back out again and then the Laramie formation which is coastal plain deposits which contain coal these are coal cubes here in the Laramie formation and this is what created the coal deposits in Marshall, Lafayette Superior and yeah so again it's all about the cretaceous seaway and what this diagram has meant to show maybe more interest to people the geologists but unlike most formations most times sedimentary rocks are like older, medium, younger but in this case because the ocean was going out at any given time this was deep water this was shallow water this was on land at a later time this was deep water shallow water land so they're kind of an interesting pattern yeah mire is like a swamp where things are decaying and making coal and the mire can mean like a puddle of mud too we do know how long that took a different way of keeping track of all this information here this is what they call a stratigraphic column this shows all of them different rocks so I'm looking to see when the Dakota started that was about I think it's like 150 to 65 million years so it started coming in about 150 million years ago and it went out about 65 million years ago and the mire shale is very very thick compared to the other formations this was like thousands of feet of mud were laid down okay so maybe this was what our area looked like 70 million years ago when the sea wave was covering it and then only a few million years later sea has gone out and we're in a jungle so this is the formation where the coal deposits are made mire shore lagoonal swampy kind of deposits here's a you want to see the voxels formation, the beach where the sea wave was coming out this is at sandstone ranch beautiful exposure of this this was originally we also do field trips out here maybe the city of Longmont does a field trip out here this was originally mined for sandstone before the lions but the lions were so much better in terms of being hard that this was abandoned after this started mining the lions and here's the coal mines in southeastern boulder county here's the city of boulder here we have the coal mining was one of the big industries in this area in fact although there's many places along the front range that have coal this is the richest coal area in the front range and it's applied the majority of the coal to the whole front range for decades okay, rise of the modern ruckies we're going to only say a few things about this but basically there were for reasons that are not well understood I went online earlier this week and just see is there anything recent about this no, we just don't really know the details here, there's some theories so we do know that there were large compressional forces so there's the cost was being pushed together like this what we know that is the angle of these faults when the crust is being pushed together you get the up thrust fault going on top like this called a reverse fault when the crust is being pulled apart the angle would be like this so we know that there was compression on a continental scale and there's many many faults basically the basement rock fractured into big blocks and the regular blocks were pushed upward and also slid sideways for example, Rabbit Mountain is about three miles out from the rest of the Dakota outback so it slid sideways along some of these faults and the point of this slide is that before the modern ruckies this is like 65 million years ago something really big happened 65 million years ago, anybody know what that is asteroid impact asteroid impact yes that's what we put it into the dinosaurs did you know that you did know that you only know that in school that's amazing so when I was in school in fact when I was in college I was just like a radical new idea but now there's plenty of evidence for that so that was the end of Cretaceous the asteroid impact and about the same time the modern ruckies began to rise that may be a few million years before that and before the modern ruckies we had a set of entry layers like a layer cake and then the basement rocks looked just like Kansas and if this hadn't happened we'd be living basically Kansas today so for whatever reason these compressional forces the basement rocks the big blocks now these things are way up in the air and nature hates things sticking up in the air and so it begins I'm rotting them away, I'm rotting them away I'm rotting them away and now the basement rocks are exposed at the surface but the sedimentary rocks down in the plains are still the ones on top so that's the basic pattern we see now what caused that to happen not really sure a theory that's kicked around for decades and I don't know how much evidence there is there's some but at about this time the this is North America this is the a plate that no longer exists that used to be to our west specifically is now there was subduction going on and at first this was descending typically in a steep angle into the mantle and the theory goes that it for some reason shifted to a shallow angle see the problem with the rocky is that mountains almost always form near plate boundaries and we're not near a plate boundary we're way the nearest plate boundary is 900 miles away so that's a problem for plate electronics and so the idea is maybe this plate that was subducted really extends so underneath all the way out to our area that had contributed to the compressional forces that created the rockies but there are some other interesting things almost all rocky mountain ranges have a mountain of root similar to an iceberg why does an iceberg float above the water the above water part because nine tenths of it is below the water and ice is lighter than water and so the nine tenths that's below the water holds the one tenth above the water to make it in balance and mountain ranges are typically the same way like the Himalayas for example there's lighter lower density rock that goes way now and that holds up the rock above it's floating on the mantle just like an iceberg but the rockies don't have a root like that that's a real puzzle, not a weird thing there does appear to be like a dome of hot mantle below this area we can see a lot of evidence of that extra mantle heat for example the Yellowstone Super Wall came out 25 million years ago but that went off so anyway the conclusion is not really sure but one interesting thing that happened about the same time as the mountain building that created the rockies was that a lot of mineral deposits were placed along the rockies and it's called the Karate of Mineral Belt we're at the very northeast end of the Karate of Mineral Belt with the way down to Durango and there's gold, silver, tungsten and other metals that are placed here there formed by hot solutions coming up from great depths that carried these minerals and placed them in cracks in the rock and this was exploiting a weakness in the crust probably the rockies themselves probably did this weakness also and that weakness goes all the way back when Colorado was climbed on to proto-north America 1.8 billion years ago in the beginning of our presentation so that ancient past is still having an effect today okay glacial geology thanks for your patience and attention we're almost done this is some of the most interesting and visible things we see around here yes, the diamond below it is called Chasm Lake and if you're a hiker this is like unbelievably beautiful destination on Bronx Peak and this is called a glacial circ and so during the last Ice Age this was the head of a glacier and glaciers literally eat their way back into the rock face and they create this kind of amphitheater as they eat their way back into the rock because I have a diagram on this let's see what okay so here's how a circ forms here's the glacier and as the ice is a very like a very viscous fluid a froze downhill and as it froze away here it exposes this and frost breaks off pieces so it keeps kind of eating backwards this way and make this like amphitheater of rock called a circ I don't know if I have the word circ written anywhere C-I-R-Q-U-E and then it often over-escavates here and you get later a lake and then there is like a little hump here and then a deposit at the end it just gets down to a certain elevation where it melts it only gets down as far as it melts as fast as it flows that's what it's like a conveyor belt it's carrying down rock and debris but as it gets further down it melts faster and faster and at some point it's just an equilibrium where it's flowing in and melting at the same rate it just dumps all this stuff there over a period of time and that's called a morning in let's look back here so here's the the circ itself with the head law there's the glacial lake which has a funny word tarn t-a-r-n then here's the like little ridge past the tarn with the zone of abrasion and in a minute I'll show you a picture of glacial scratches that I took a picture of right here there's the glacial striations and polishing so again this is one of these things where it's like the first time you see it it's like oh that's glacial striations and then you look around it's like let's all look in place so I encourage you to look you'll see the scratches are pointing down the valley because that's when the ice was flowing and it's also polished the ice itself is not nearly as hard as the rock of course but the ice is carrying rocks along its base it's kind of like sandpaper another picture of the polishing striations oh this is called a sheet back you come in different sizes this is a small thing but you'll have to get these sheet back shaped rocks where the ice has polished the backside here it plucks away the rocks as it flows over another interesting thing is U shaped valleys I went to when I was 15 I kind of moved to New Hampshire I really like New Hampshire in fact I got moved to Colorado because I wanted to get back to Heading Mountains again and there's lots of U shaped valleys in New Hampshire but this is as good as anything you got in New Hampshire this is before the July Trail I just took this last summer it's out past the old mining town of El Doron which is down the hill from the El Doroski area the El Doroski area is like over there somewhere just over the next ridge but if the valley is cut by a stream it tends to be D shaped so if it's U shaped like this you know it was cut by a glacier quick summary 1.8 billion years ago we had a continental collision Colorado was glommed on to proto-north America and that created all the igneous and metamorphic rocks to make up about high geeks between 350 and 100 million years ago we have the ancestral rockies which produced various sediments that we have today like the fountains and the lions and then we have the advance of the rotation of seaway you know the decoder formation is the beach of the seaway coming in and we have deeper and deeper level sedimentary rocks with the pier or shale thousands of feet of that stuff and then water goes out and we have eventually the fox flows of Laramie with the cold deposits and we have the current Rocky mountains maybe 7 million years present there's been a couple periods of uplift but that's a whole lot of story and glacial geology okay here's some upcoming programs for older Clarkson open space older Kennedy Clarkson open space we have a foothills geology hike being led by Roger Myers who's like the the dean of volunteer geologists around here right now he's my mentor and then fossils of flowers like in May 22 which is where we're going to see the giant clams and there's usually several geology hikes each year and you can go to discover.bouldercountyopenspace.org or Google that and that's where you can sign up see what programs are available and sign up okay thank you so much for your attention