Geology ROCKS!

“Rocks are records of events that took place at the time they formed. They are books. They have a different vocabulary, a different alphabet, but you learn how to read them.”
-John McPhee

A few weeks ago, Kat and I decided that we would take on a new project and learn about the geology of Arizona. We would learn about how the land was formed, the various changes it has gone through over the billions of years since its formation, and then visit various sites in the valley to look for geological evidence in the rocks. As we began planning the first part of our trip, we gained a school partner for our studies. My niece would be joining us for Spring Break, which meant we had an entire week to include her in our field trips! We decided to begin our lesson at Dreamy Draw Park, a beautiful hiking and recreation area located at the base of Piestewa Peak.

The rocks of Dreamy Draw were largely formed during the Precambrian Era, a huge length of time stemming from the beginning of Earth’s formation approximately 4.5 billion years ago and ending approximately 600 million years ago. The oceans and atmosphere were formed during this time, as well as Earth’s magnetic field, the tectonic plates, and the land masses.The bulk of Earth’s geologic time is contained within the Precambrian Era. Long before the first dinosaurs roamed the Earth and the first fish were swimming in the oceans, even before the first trilobites appeared, North America was just beginning to take shape. After many hundreds of millions of years, when the rocks of Dreamy Draw were forming, the only life forms on Earth consisted of bacteria, algae, and primitive microscopic rooted organisms (something like a very primitive sea cucumber). During this time, Arizona was located near Antarctica and Antarctica was near the equator!

A map of the continental organization approximately 650 million years ago. Image Credit: Tucson Citizen

During the late Proterozoic Era, Arizona was covered by a shallow sea, and over the course of hundreds of millions of years, the land changed dramatically! Volcanoes formed and erupted, lava veins burst open, seeping boiling magma into the depths of the ocean. Subduction zones formed as huge swaths of land pulled away and pushed into and under each other. Mountains jutted upward only to be eroded millions of years later, leaving only traces of their former glory in the form of rocks, hills, and the mountains of the Phoenix area.

I followed the studies of two geologists, Dr. Stephen Reynolds and Julia Johnson, as they surveyed the land and identified the formations, mineral veins, and rocks that make up the Phoenix mountain chain. I was fascinated as I read about how Dreamy Draw specifically contains many rocks from both oceanic and continental origins. That would mean that Dreamy Draw was at one time, a place that was transitioning from an oceanic zone to a continental zone!

Arizona geography during the late Proterozoic Era Image Credit: The Arizona Experience Paleogeograhy Timeline

Some of the oceanic rocks included Greenstone (greenish metamorphic rock, formed by pressure and warm liquids, usually in oceanic areas), Ferruginous Quartz (a quartz with red, brown, or yellow veins which are deposited by iron-rich water), and Meta-Mudstone (mud stone that has undergone a metamorphosis, changing the original properties of the rock).

Some of the continental rocks included Gray and Tan Phyllite (metamorphic rocks with reflective mica, usually found at the eroded base of ancient mountain collisions), Schist (a metamorphic rock that usually originated in mudstone/shale and has undergone intense heat and pressure), and Orthoquartzite (one of the purest forms of quartz, yet mixed with sandstone, thus it is a sedimentary rock).

It was fascinating to read about Arizona’s oceanic history. I was incredibly excited to be able to look for the evidence of it and know what we were looking at. I couldn’t wait to take the girls on an adventure as we went back in time through Arizona’s history! I printed them off some checklists of what to look for and grabbed some small hammers and safety goggles for rock collecting. Then we were off!

The girls were thrilled to go on a geology adventure! As we drove there, I explained the story of Arizona’s transformation. The drama of pushing, pulling, exploding, collapsing, and washing over was exciting for the kids and they were really looking forward to seeing the remains of that epic saga. As soon as I brought the car to a stop in the parking lot, they jumped out and began looking for a place to “go mining”. They ran up to a huge chunk of schist and immediately began speculating as to how it was formed.

They saw a white dust covering large areas of rock and tried to picture the volcano that may have deposited it. They collected samples of found coal and wondered about the plants that may have contributed to its formation. I didn’t yet have the answers to all of their questions but I was more than happy to encourage them as they excitedly ran about calling out to each other to check out each new find.

Finally, it was time to take our checklist to the trail! Kat and Amelie giggled as they called out each specimen of Greenstone they had found. This happened quite frequently, as Greenstone can be found all over the place at Dreamy Draw! As soon as they saw the sparkling crystals of Quartz, however, it immediately replaced the Greenstone as they highly sought after favorite. They found Gray Phyllite samples, the reflective mirrors of Mica, and the sparkling, rough textures of Orthoquartzite and various types of sandstone. Periodically, they would stop along the trail and check their samples against the checklist to make sure they could get a positive ID.

Their absolute favorite rock was the Ferruginous Quartz. We talked about how the iron deposited in the quartz reacted with Oxygen to make the Iron Oxide that causes the reddish color running through the crystals. We saw tiny flecks of quartz in the rough sandstone and talked about how the layers would have been added by sedimentation and then compressed over time to form the sandstone we see today. One of the greatest things I heard that day was my niece say, “I love how all of the rocks here tell a story! You can see how the Earth was made and what it used to be like here!”

One of my most pleasurable experiences was found by giving the kids those tiny hammers and letting them explore the rocks on their own. This brought to light yet another characteristic in identifying rocks and minerals. We had talked some time ago about breaking points and scratch tests to test the hardiness of rocks. Sandstone would be more easily scratched compared to something like quartz. The girls rediscovered this on their own, though, as they realized which rocks would break easily, which could be used to mark on the sidewalk, and which could be marked on using the claws of the hammer. This became yet another situation where I could just smile and watch the thrills of their own discoveries while changing the faces of the rocks they were using.

The best part of all for them, however, was something they added on to our lesson themselves! As they were hiking and looking for rocks, they decided to rest near a large quartz vein. Dazzled by the brilliance of the white crystals, they decided to start a trail side collection. They grabbed tiny pieces by the handful and worked together to carefully move the heavier pieces. Before long, they had amassed quite a collection!

They built a large mouse sculpture out of the rocks and left it on the side of the trail to greet passing hikers. Many who passed by were delighted by the sight of these two girls excitedly talking about quartz while building their sculpture. Kat and Amelie came here to learn about the story of the Earth and its many transformations. They ended up leaving behind a piece of their own story for others to find and be delighted by!

This lesson in geology was one of my favorite lessons of the year so far! During my research, I was able to contact the Phoenix Parks and Recreation Department, where I was pointed in the direction of the North Mountain Visitor’s Center. I also contacted the Arizona Geological Survey, who provided me with a fantastic resource of maps pertaining to Arizona’s geology. Kat and I will definitely be utilizing these resources to not only learn more about the history of Arizona but to also learn more about our desert parks and the rangers who attend to them.

In the coming months, Kat and I will be visiting the Phoenix mountains of North Mountain, South Mountain, and Papago Park. Considering the beautiful geology Arizona has to offer, we’ll also take our lessons to Sedona, Tucson, and we’ll eventually culminate our adventures with a trip to The Grand Canyon! I am excited to see where our curiosity takes us, as well as the kinds of stories we’ll get to read in the rocks when we get there.

For now though, it was wonderful to be able to include my niece in our studies. Not only did we all learn a lot about our local parks, but we had a lot of fun along the way. She is just as much of an enthusiastic learner as the rest of us, and I hope I get more chances to include her in our wonderful learning adventures!

Happy Exploring!


  1. The thing that I love the most about being able to teach my daughter is that I get to share my interests right along with her! Geology is something I've long been interested in, yet I never fully explored it. When Kat mentioned that she wanted to go mining, I thought this would be a great opportunity to show her the wonders of the Earth (literally!).

    The coolest part about this particular lesson, was that we got to include my niece as well. Then my daughter had her best friend doing school right along with her! Both girls were bubbling over with enthusiasm and delight as they were running from rock to rock, identifying them and breaking them open to see how strong they were. I am so grateful to be able to witness them explore their interests as we all enjoy learning together. 🙂

  2. What an incredible adventure these girls had!!! I've been to Arizona once and found it absolutely beautiful. They are so lucky to have had you as their guide. It looks like you have many adventures still ahead of you. I wish all kids could have these types of hands-on experiences.

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