# Component Three - Geology/Climate

The two readings for this Component are the two articles most directly related to geology in our textbook, A Natural History of the Sonoran Desert (Arizona-Sonora Desert Museum, 2015). The first, "The Deep History of the Sonoran Desert," is an eloquent rendering of what the biotic communities in the region evolved from. The second, "The Geologic Origin of the Sonoran Desert," is a basic overview of the formation of the basin-and-range landscape.
Our guest lecturer for this Component was one of the College's most accomplished - and the longest serving - among our faculty, Professor of Geology Fred Croxen. Fred actually gave two separate presentations, one on basin-and-range formation, the other on hydrology and water use.

## A. Arizona-Sonoran Desert Museum, '"The Deep History of the Sonoran Desert"'
### Guiding Questions

In "The Deep History of the Sonoran Desert" the author describes the evolution, and eventual assemblage, of the Sonoran Desert biological community. What about this story changes your understanding about the biological community of the Sonoran Desert?
Does this story alter your sense of time regarding the Sonoran Desert?
The author refers to some ecosystems as the "grandmother" of other ecosystems. Is this idea new to you? Do you think if offers insight? or perhaps an analogy too imperfect to be helpful?
Does this story alter your sense of connection between the Sonoran Desert and the neighboring regions?
Do you find any parallels between the formation of the Sonoran Desert biotic community as a whole and the formation of the human societies that are here now?

### Student Discoveries 2021

The analogy of ecosystems as “grandmothers” of other ecosystems is very logical and understandable because everything on the planet has appeared over time and evolved to its state as it is today. Ecosystems do not appear for no reason, ultimately, they are formed when an older ecosystem cannot survive in its state and must adapt to survive.
most people assume that deserts are desolate and that using this land for military purposes won't do harm to the environment. Which from learning in this class, many people would be wrong to assume this which I find interesting. The fact that the desert biomes are no different than any other biome in terms of life yet people only seem to recognize forests as places of life.
The Sonoran Desert is enriched with much environmental and climatic history. The land holds the many stages that the Sonoran Desert has undergone to become the ecosystem we know of today. The biological community has had to adaptto the various changes the Sonoran Desert has gone through, from tropical to glacial ecosystems to the present day desert.
More than changing my sense of time it makes me aware of the many factors that influence the evolution of the Sonoran Desert, the fluctuations in the weather, the volcanic activity and the rise of the mountains, the glacial melting, the spread of the fault of San Andreas, so many intricate factors that have come to create a different view from the Paleocene epoch. It makes me scared that millions of years of adaptation, and change will come to an end due to the hedonic and egotistical sense of our species.
In my mind I had always pictured the desert as just that, an inhospitable land where only species that have adapted to live there can survive. It feels pretty weird to think that this same place was once a densely wooded forest.
The most surprising thing about this story is learning that the development of the modern community of plants and animals took place only 4500 years ago. This shows us that just like any other place in the world, the Sonoran Deserts continues to grow and redefine itself throughout the years.
For instance, again, going for the typical representation of the word desert is hot, dry, waste land, etc. and while reading this chapter it made me realize there was more. Some of the regions (actually most of them) were either cold or wet. It is that simple detail that left me amazed of how little do I know about where I actually live and its origins.
Knowing about the different kinds of plants that grew millions of years ago gives us a sense of how the vegetation and climate were. Thorn scrubs developed to be able to withstand dry areas. Baja California used to be a part of the Mexican mainland until it drifted apart a couple of million years ago. During the Miocene era, volcanic eruptions were able to change the climate in the provinces of North America. I personally think that the author's use of grandma to describe other ecosystems offers an understanding as to how some other ecosystems are the way they are because of other ecosystems. For example, thorns curbs are a transition between tropical deciduous forest and the Sonoran Desert. The grandma is a tropical deciduous forest because it's older and less of now due to the dry climate. The story alters my sense of connection between the Sonoran Desert and other regions because the author mentions how they influenced a change in each other. For example, the expansion of the modern Sonoran Desert in Arizona and California resulted in modern communities and plants. After the human population started increasing the desert became dryer and warmer. New plants started to adapt such as thorn scrubs. Although, many people still debate whether the change in climate was caused naturally or due to pollution we can’t deny that humans brought over toxins, land waste, deforestation, etc.

### Student Discoveries 2020

And also how it took about 8 million years for the Sonoran Desert to form it is considered the youngest biotic community.
Throughout all these years, the Sonoran has expanded and changed many different times due to climate changes. The most recent expansion of the Sonoran Desert was approximately 9,000 years ago. This timeline seems unrealistic. When someone sits down and thinks about how long it's taken a desert to be the way it is right now, it is remarkable. The authors made us open our minds and see the Sonoran Desert in a different way. The headline "Whose Child is it," really captured my attention. After examination of fossils of different animals, researchers concluded that the "mother" of the Sonoran Desert is the Thornscrub and that the "grandmother" is the Tropical Deciduous Forest. After reading the reasoning behind this, it made more sense. It's fascinating to think that the place we live in today once contained animals that we would never see in this area anymore.
I was surprised to discover that the Sonoran Desert is actually one of the youngest biotic communities on the continent! The recent expansion of the Sonoran Desert occurred about 9,000 years ago and then it took 4,500 years later for animals and plants to complete their assembly.
I personally liked the “grandmother” analogy. I found it interesting to think of thornscrub as the mother of our desert, and ancient tropical forests as a grandmother, each passing on valuable traits to their genetically similar but unique children. As I thought of this process, I became kind of disconcerted as I thought of what the next generation might be, and what would be left for a potential great-granddaughter. It was also insightful to know that it has always been changing and has taken thousand of years to develop into the place it is now. The formation of the Sonoran Desert and the formation of human society are parallels. The formation of the desert derives from the evolution of the planet creating new and beneficial biomes for plants, animals, and humans. In contrast with humans, our evolution and technological advances usually cause harm to the environment.
Living in the desert my entire life, I can say I thought other climates and biomes derived from the desert but the Sonoran Desert and the other three are among the youngest biotic communities. With this being said, this story altars my sense of time with the Sonoran Desert and when it essentially evolved. I do not think this story alters my sense of connection between the Sonoran Desert and the neighboring regions because I really did have a sense of connection other than the surface of what a desert is and what it provides.
After the many mass extinctions taking place, the desert has gone through many changes and continues to do so as the earth warms and cools over time. I also never knew that the desert took so long to form to what it is currently.
Being able to read about how the Sonoran desert came to be was fascinating. I never really thought about the amount of time it took for the desert to become what it is today. Especially reading about how the recent expansion of the Sonoran Desert occurred 9,000 years ago. Another interesting thing that I read was the formation of the Baja California Peninsula. Even though this even occurred about 6 million years ago it still had an enormous impact on the environment and the landscape of this area.“Whose Child is it” really captured my attention as well because after researchers examined fossils from different animals they found out that the “mother” of the Sonoran Desert is the Thornscrub and the grandmother is the Tropical Deciduous Forest. After reading about the different environment it’s interesting to see how much the Sonoran Desert has changed and to think that different plants and animals other than the ones we have today used to live in the Sonoran Desert.
I didn't mean to get existential, however, even though our lifespans our short, this generation is negatively impacting the climate around the Sonoran Desert at a faster pace than ever before. This chapter even highlights the fact that, "global climate models indicate that temperatures in the Southwest will likely increase by 5.4 degrees fahrenheit to 10.8 degrees..."(pg 69), which is interesting as climate change has been a recurring topic in our lectures.
Reading this made me really think about how long Earth has been around and how it has evolved and changed in those years. The geological time scale that was shown and explained in the reading was very helpful with describing each period and how they transitioned from one another. It was very interesting reading how the vegetation and ecosystems transition throughout time.
One thing that changed my understanding of the biological community of the Sonoran Desert was the different types of regions that there are with the most being the colder ones. However, throughout my whole life I have been living in the desert which brings me to the point that I have always thought that the desert held different parts in the temperature due to the climate change that has been getting worse and worse by the minute. When it comes to the time that is around the Sonoran Desert it did not alter my own because like many other biomes across the rest of the world it made sense that time there had a different schedule. When hearing that some ecosystems were the ‘’grandmother’’ of other ecosystems it did not surprise me because just like other ecosystems that are around us most if not all had to have started with a beginning biome. In other words, every biome that has been created later on must of had a beginning biome that was the first of the next biome that is created. All in all, after reading the chapter I believe that it strengthened my idea of the connection between the Sonoran Desert and the neighboring regions because I originally already had an idea of the connections but with the reading it helped broaden the view, I had on it. I believe that there is a general connection between the Sonoran Desert and the formation of human societies through the similar reproduction process and ultimately the adaption that both sides have when in an environment

## B. Arizona-Sonoran Desert Museum, "The Geologic Origin of the Sonoran Desert"
### Guiding Questions

In "The Geologic Origin of the Sonoran Desert" the author describes the stages of development that led to the formation of the Basin and Range landscapes. What about this story surprised you?
Has your sense of the landforms of the Sonoran Desert altered?
Some landforms, like bajadas are the work of a much wetter climate. Does this "memory" of changing climates change your sense of what the climate of the Sonoran Desert means?
Some landforms, like dune fields, are the creation of the wandering delta of the Colorado River. Have a look at a satellite view of the Sonoran Desert and take a minute to explore the placement of the dune fields, imagining them now as the wandering delta of the Colorado River. Now, has your view of the role of the river in the story of the Sonoran desert changed any?
What connections do you see between the geologic history of the Sonoran Desert and the settlement patterns of humans in the Sonoran Desert?

### Student Discoveries 2021

If the geologic history of the Sonoran Desert did not occur the way it did, we might not have the settlement patterns we do today. Changing one part of geological history has effects on other aspects such as species survival and settlement patterns.
When speaking about a desert, one tends to immediately picture a dry, flat land. A place that seems incapable of sustaining any form of life. However, in analyzing the landforms of the Sonoran Desert, that image begins to vanish.
from the initial formation of Earth this specific region has gone through many different climates due to many events that led to the change in the currents of wind, the patterns of rain, changes in latitude and separation from the equator, and subduction of plates all of these factors have made the surroundings take a particular and diverge shape similar to one of the species residing in this areas. I can say with all certainty that the Sonoran Desert is more alive than most of the regions on Earth.
When I thought of different regions, I always thought of them as completely different entities. I thought that with the different climates each species would remain in their respective region and only move if a powerful enough force made them. Reading the chapter made me realize that the separate regions are a lot more connected to each other than I thought.
The Geologic Origin of the Sonoran Desert" story gave the reader a better understanding of the geological processes that have shaped the Sonoran Desert. The most interesting aspect of this week's reading was the Sonoran Desert fossil legacy. I always like to think that nature has its own unique way of working and reminding us that it has existed for centuries.
I always knew there were changes in temperature whenever there was a change in season. One day it could be extremely hot and the next extremely cold. Since I have been living in the desert my whole life, I do not feel the change for other people who might not have grew up living in the desert they might notice the change since they are new and have not gotten used to it.
With the development of mountains millions of years ago and different altitudes the Sonoran Desert’s climate began to change and become more diverse. Reading about the land formations gives us an idea of how the land came to form its mountains and vegetation. I never learned to what extend the earth’s crust played a role in changing modern earth. Now the changes in the Sonoran Desert have to do more with human pollution than natural occurrence. A bajada (slope) forms from by a combination of alluvial fans. This is located next to mountains and is made of loose settlement like debris that move down the mountains making cone-shaped lumps. Light rainfall does not have enough force to move the debris down. Heavy rainfalls is able to produce mud, move rocks, and help with vegetation down the mountain canyons. Which is how heavy rains are able to make alluvial fans. The area needs to be wetter. I didn’t know how greatly heavy rain were able to change the way the desert looks. Dunes are created by an accumulation of sand due to wind. Various dunes of the Sonoran Desert come from the sand of the Colorado River Delta. This area has help contribute to the deserts changing environment. From a satellite view we can see the how delta of the Colorado River land looks to be branching out throughout the land bringing various resources to animals and plants. Humans settlement patterns in the Sonoran Desert have depended on the weather and environment. The formation of mountains and lands is very important to humans because with that came the presence of water. Now and days we greatly rely on technology and imports to survive.

### Student Discoveries 2020

Also I found it interesting how much the Colorado River not only give the area around where it passes water but how canals are made to provide the areas farther from the Colorado River that are in need of water.
The story of the formation of the Basin and Range landscapes is quite impressive. After years of the tectonic plates shifting and wrinkling the earth's crust, the Basin and Range landscape is the way it looks today. It's taken years for those mountains and valleys to form and fill with gravel. What impresses me the most is being able to see how much the landform has changed. The plates underneath us are continually moving or shifting. They continue to form new mountains or volcanoes underwater that eventually can become islands. My view on the role of the river in the Sonoran Desert has changed quite a bit. It's interesting to see that the Colorado River eroded parts of the grand canyon. The Colorado River is an essential source for many other regions because they depend on its water.
Another thing that surprised me about the landforms of the Sonoran Desert was that the mountains in Tucson were once a volcano on the western side of the Santa Catalinas. This finding was discovered by scientists from the University of Arizona!
I find that so often I get caught up in the rat race of my daily life that I tend to think of the desert as the creosote bushes outside. However, the section titled The Sonoran Desert Landscape Today really made me pause and appreciate the totality of what I had learned so far. Thinking about it all, with the knowledge of how it formed, from sky islands to rivers and dry washes, mountains and dunes, I was really proud of where we live.
I thought that some formations were just naturally there from the beginning of the Earth’s creation. I didn’t know that movement of the earths crust could cause it to stretch or wrinkle.
My sense of landforms has been changed, before reading this I did not think that certain geological changes had much of an effect on how the land looks. I thought that mountain ranges, deserts, et cetera had all been placed in a specific area since the start of time. I think it is interesting to see the aspect of time and see the perspective of others as the story states, “We tend to think in terms of lifetimes or centuries. What can 10,000 years possibly mean to us let alone 65,000 or 70 million?” (page 71).
I never fully understood how the land formed or came to be. The formation of the Basin and Range Landscapes were very surprising to me. I can finally understand how the earth's landscapes came to be and it's all because of the Basin and Range Landscapes. I can for sure say that my view on the earth's landscapes have changed and I am now educated on the formations of many of earth's amazing features.
Reading about the geological aspect of how the Sonoran Desert came from was quite interesting. All over the world there are earthquakes, hurricanes and so many more natural disasters that occur. This gave rise to so many changes in the landscape we see today even though it took millions of years to get here. Reading about the Basin and Range Landscapes it was very surprising to me. Being able to read and understand how earths landscapes formed changed my perspective on this subject and it also showed me how lucky we are to have all that we have around us.
Another interesting subtopic that caught my attention in this chapter was the mention of volcanism in the area. I've always been fascinated with volcanos since a young age due to their destructive, and creative nature, and learning that the mountains of Tuscon are composed of rhyolite is a great detail that I did not know.
It is amazing to think that these dunes have been there for the past 25,000 years and up until this reading I had no form of explanation for why there were dunes. Based on what I read the sand was blown there from the Colorado River Delta which came from the Grand Canyon. Now I have an explanation for how the dunes were made. One thing that surprised me when reading about the formation of the Basin and Range landscapes was how they were formed as well as the amount time that must have taken to build it itself. In addition, it made me realize how significant the Sonoran Desert is in the role it has for other biomes and landscapes such as the Basin and Range one. When it comes to the Sonoran Desert and the landforms of it, I believe that it did alter my sense of it because of the amount of importance there is to it as well as the way that it was formed. When reading about the changing climates it changed my view of the Sonoran Desert and it meaning because in the beginning I had always thought that it had one season or temperature that was all year long but after reading about the climates changing it opened my eyes to new sense of how the Sonoran Desert is and the true meaning of it. I would say that my view on the role of river in the Sonoran Desert stayed the same because I’ve always thought that the river held an important role for all biomes especially the Sonoran Desert. One connection that I did see between the Sonoran Desert and settlement patterns of humans in it was the adaption that they had to face in order to survive in that type of environment. One other connection would be that both had to adapt to the environment as it was changing over the decade in order to have an adequate life suitable enough to the biome

## C. Fred Croxen, AWC Professor of Geology (Land, 2020)
### Description:

Around 20 million years ago the Sonoran Desert began to form because of the volcanic explosions in the Pinacate region.
About 12 1/2 million years ago the Baja Peninsula began to separate, and it's continuing to form today. Also 6 million years ago the Colorado River began to grow in size. The North American plate has been moving on top of the frogian plate around the Jurassic era. The ranges have acted as dams from the Colorado River. This occurred long before the formation of the Sonoran Desert.
About 2 million years ago, the Northern Hemisphere was going through a Glacier expansion.
Fred Croxen talked about the geology of the Sonoran Desert region, how the Basins and Range were developed, and what even about the Bouse Limestone dilemma.
Around 6 million years ago, the Colorado River up to the Upland area carved itself. Arriving at Yuma 2 million years later.
Croxen talked about the Grand Canyon and how the formation of it was roughly 6 million years ago and in the 1800's the Grand Canyon was being harmed.
Roughly 15.97 million years ago was when the mountains we see, began to form. The Basin Range created where we live and the mountains surrounding us.
Professor Fred Croxen had a very interesting presentation but one thing that the mentioned was the Bouse Formation. In the last 10 years Lower Colorado Geologists named four classes and the Bouse Formation was among them. This class was formed about 5 million years ago and is still controversial among geologists. This class was first identified by Parker, Arizona in the Bouse Wash. The main issue with this claim is that the wash pointed to a marine background and many researchers said that it is impossible. With a marine background the land would of had to rise a good amount so researchers dismissed the idea because of this.
Juniper in was found in Packrat middens near Wellton hills using carbon 14 which suggests that there was once Juniper near this area, showing how the climate and land has changed in the area.
Croxen's view of the way to which land has been used was interesting with one of the most interesting ones being the bouse formation being named due their being a bouse wash.

### Reflection:

Professor Croxen is like a walking encyclopedia for anything that has ever happened in the Sonoran, from ancient geology to BLM wells, he knows it all. Also...possibly the only person alive who could make me feel a sense of rapture at USGS pack rat den data Professor Croxen really gave us a great deal of information to hold onto as we listened to his talk on land. He really knows his way around the desert.
Professor Croxen is very knowledgeable about the Sonoran Desert. He described so many different developments in science regarding the the Sonoran Desert and it was fascinating to learn about these new developments.
The amount of knowledge Professor Fred Croxen has about the Sonoran Desert is truly astonishing. He had files after files of information and he knew them all by heart. He had all the answers to every random question we asked.
Professor Croxen's details about the Sonoran Desert gave me a broadened view on the Sonoran Desert in the way that it functions and the plants and animals that occupy it. The amount of knowledge that he shared with us also gave a expanded view on the impact that human infrastructures have made on the Sonoran Desert which made me realize the amount of damage that is being done and continues to do so I love Professor Croxen's presentations. What stayed in my mind the most about this one was about the fact that geologists can use pack rat middens to find out how old a rock formation is. That absolutely blew my mind, pack rats aren't just some cute little critters, but they're helpful too.

## D. Fred Croxen, AWC Professor of Geology (Water, 2020)
### Description:

The Salton Sea doesn't come from the ocean and has its own history; its man-made. Water is constantly being recycled. Fred Croxen mentions that the water in the river has "probably traveled through other organisms." He also told us that there are many myths about water. One of the myths beings that wells do not connect to underground streams or rivers.
Water is being recycled in the Colorado River. If an individual is drinking tap water, it is very likely that the water they are drinking was once consumed by other organisms.
Fred Croxen showed us a brief process of how ground water is found, and how ground water affects the life around it.
The cause of fissures are due to pumping out groundwater, space begins to collapse.
The water we have in Yuma is from the canals which stem from the Colorado River.
Professor Fred Croxen went into great detail about the different ways to get water in our area. In Yuma, Arizona water is supplied through different canals and is taken to the community. In San Luis and Foothills, Arizona their water is supplied through wells. Since agriculture is very popular in Yuma many of the big farms use aqua firms to get enough water for their fields.

### Reflection:

His presentation on groundwater and the Colorado River gave a true sense of urgency to how dire our situation is.
I genuinely enjoyed his presentation on water and had fun measuring the water in the well at AWC. We need to be careful and mindful of how much water we are pumping out of the ground because the Earth can only replace it at a certain speed. As Croxen told us the places that used to have water collapse and the basin sinks. Learning about the the different water supplies in the area I live in was really incredible. I also learned about ground water that will stay with me and be useful down the line.
I really enjoyed his presentation even though he talked about a topic that is new to me, he did a great job getting our attention. I really loved our little experiment out by the well measuring the depth of the water. /
Fred Coxen had an extensive knowledge on geology and I enjoyed both lectures he gave. A highlight was when we went outside to test the water level of the well! It was a fun experience and learning how to use one of the tools that is very common to geologists was very interesting.
Professor Croxen always manages to relay so much information in an incredibly engaging way. The top two things that blew my mind were that Somerton, AZ water actually comes from wells and the fact that ground water is always moving. I also got to use the machine to test how deep into the well the water runs (I didn't do it correctly but it was still fun!).