Skip directly to content

Eldridge Moores

Eldridge Moores
Understanding geology settles you into a region.

Eldridge Moores is a Distinguished Professor Emeritus at UC Davis in Geology and has been with UC Davis for 45 years.Moores served as President of the Geological Society of America in1996 and specializes in plate tectonics and geology of the northern Sierra Nevada.




Could you just describe where we are and what you see around you?

We’re sitting here at Cache Creek Nature Preserve, and what I see is, of course, the pond now filling the pit made by gravel mining. As I look over towards the west, I see a brown ridge coming down, which would be the south end of the Rumsey Hills. Then beyond that in the distance is what some call Blue Ridge, which is covered in chaparral and looks dark here. I can give you the geological description of those.

Yes, I would love that. Can you describe the geology of this place?

This place, first of all, is very close to the big tectonic boundary between two major geologic provinces. So, as we look west, we are looking out across the boundary between the Sierra microplate and the Pacific plate–which is another 60 or 70 miles to the west of us. We see the Rumsey Hills to the right; it’s the south end of a ridge of rocks that are a hundred million years in age. The major ridge that we see in the distance – Blue Ridge – is made of sedimentary rocks that were originally deposited in about 3,000 feet of water and have now been folded up and are standing on end. These sediments continue underneath us here, so if you were to go down through the sedimentary rocks and unlithified materials below us, you would go first into some very young gravel and sands and silts that are river deposits. Then you’d go slowly into a series of things; there’s some volcanic rocks [from] flows that have come down from northeast of the Sierras. Below that there are some volcanic tuff deposits that were deposited by explosive eruptions and air fall. Finally, you go into sedimentary rocks of the so called “Great Valley Sequence;” [these] “Great Valley” sediments were laid down in about 3,000 feet of water some 140 to 60 million years ago between the subduction zone along the western margin of North America and the volcanoes of the ancestral Sierra Nevada.

Can you give me a nutshell overview, then, of how the aggregate ends up in the creek?

Yes, the aggregate itself ends up in this part of the creek by uplift and erosion of the rocks in the Coast Ranges. The aggregate is interesting in that it has all kinds of materials in it, and they’re not only from the Great Valley Sequence, but from the rocks further on, which are called the “Franciscan.” These are rocks that are metamorphosed–formed in high pressures and low temperatures in the subduction zone off the coast of North America. This includes here, dominantly, serpentine– or serpentinite as geologists would say. There are also some young volcanic rocks. These then are picked up by the streams and are brought by Cache Creek and deposited here in the normal processes of river activity.

How can we understand the history of this place by understanding its geology?

Geology is just history with a very much longer timescale.  The way I like to explain it is to let a millimeter equal a year. A human lifetime is perhaps a hundred years, a hundred years is a hundred millimeters, and that’s about four and a half inches. All of human history is about ten thousand years, and that is then ten meters, or thirty three feet. Okay? All of hominid history is about four million years, which is four million millimeters, and that’s four kilometers. That means about 2.5 miles, and if you get out here on the road, that’d get you back about down to Highway 16 or maybe a little bit beyond that. If you keep going and get on Interstate 80, and go east, the dinosaurs would wipe out somewhere like Loomis or Auburn. The first dinosaurs would be at about Donner Summit or Truckee. The first animals would be at about Winnemucca. Then, when you get to Salt Lake City you would be back a thousand million years, that’s a thousand kilometers, and that’s less than a quarter of earth’s history.  If you measure it up, you have to go all the way across the continent, even beyond Boston and into Maine in order to get to 4.56 billion years, which is the age of the earth. So, when we geologists look at the landscape and the rocks, we’re thinking of two things. One is, “what do things look like in three dimensions?” and the second is, “what are the ages of these things, and how have these structures formed?”One can say, and this has been written in a famous magazine called The Economist, that geology underlies everything. It determines the landscape, it determines the agriculture, it determines the location of cities, and towns. It basically forms the basis of economics in the presence of metals and other mineral resources. It contributes a lot, I think, to human history and how humans think of themselves, simply because we are a part of this landscape, and understanding how the landscape formed is actually, I think, a very important part of people figuring out what their place on earth is about. I think if you look at any origin myth in any civilization, you’ll find that there’s something there that tries to explain how the earth formed and how the landscape formed.

How can understanding the geology of the Cache Creek Nature Preserve help the community, help the public, help the general citizen?

It’s important to understand how and why this region got here, the nature of the landscape, and also the economic history of this region. Why is this depression here? It’s here because gravel has been mined. And it’s a mining operation, meaning it’s a nonrenewable resource extraction. Why do we have gravel extraction? What do we need gravel for? Well everyone knows you need gravel for concrete. You need gravel for asphalt roads. This is something we continually mine everywhere. The main thing is: it’s a part of the landscape and the understanding of the landscape gives you a sense of where you are on earth.

What do you think people don’t know about geology?

I think the most important thing that people don’t know about geology is how important it is for their lives and how important it is for them to know in order to lead lives as informed citizens in this twenty first century. A growing population is going to be competing for increasingly scarce resources, not only just gravel in here, or for copper, but for rare earth elements that go into electronics, computers, windmill generators, solar cells and so forth. All these things require some knowledge of geology to understand where they come from and why they are important and how we are going to balance these resource sorts of needs of all the people in the world. In addition, we live on the earth. The earth is an active earth, it has things that happen, events that happen on a long-term scale with respect to human life, that happen real rapidly and cause a lot of trouble when they happen. The Japanese earthquake in March of 2011 was one that wasn’t expected and that caused a lot of problems in Japan. Earthquakes in California are another example. Floods are important. As one uses the land more intensively, it will develop the greater risk of floods. So, in this increasingly inhabited world we need to know something about the geology in order to make a minimal impact on the earth itself and the other life that one sees around us.

How does the geology of this place relate to the daily lives of Yolo County residents?

The water that one gets in Yolo County, by and large, is groundwater. The deposits you see around us that have been mined here are areas where you can see the aquifers that we get the water from. In fact, some reports claim that this region of gravel mining is where the main aquifers for Woodland and Davis are recharged. If that’s true, then it does really affect the life of every citizen of Yolo County. Then, looking out at the scenery is something that affects the life of every person in Yolo County. If you understand the geology of that, you will enjoy it a lot more.

What is the significance of the Cache Creek Nature Preserve?

The Cache Creek Nature Preserve preserves not only what many people refer to as nature, which is animals and plants, but also preserves in its own form. It is a place close to a populated area where people can come out and observe not only the animals and plants in this region but also look out across the landscape. There, they can see the hills and think about how they might have formed. You can do it in a region that’s mostly fairly quiet; it’s not really marked by a lot of traffic. So I think it’s a place where you can kind of settle down and consolidate your feelings on life and yourself.

Written by: 
Jonathan Martindill & Eric Kim

To download the audio, right click on the audio link above and scroll to "Save link as . . ." and choose the directory where you want to store the mp3. In Windows, you may have to use Control + S to select the link.