Exploring the extraordinary geology of North America
Regular readers of Deposits will know that we have never regarded geology as something that stops at national borders. The rocks beneath our feet are parts of much larger stories: continents assembled and torn apart, oceans opened and closed, mountains raised and destroyed, ice sheets advanced and retreated, and rivers repeatedly reorganised the landscapes through which they flowed.
Over the coming issues, however, we are going to travel rather further afield than usual. Deposits is beginning an ambitious programme of articles exploring the geology and landscapes of North America. At the heart of this will be a new six-part series on the plate-tectonic history of North America, which starts next Monday (16 November 2026).
Some readers may remember our earlier four-part series examining the plate-tectonic history of Britain. The new series takes the same basic idea, but applies it to an entire continent and over a vastly greater geographical area. Inevitably, that requires rather more space.
We begin deep in the Precambrian with the assembly of Laurentia, the ancient continental core around which much of North America was eventually constructed. From there, we follow the opening and closing of oceans, continental collisions and the building of the Appalachians; the assembly and subsequent breakup of Pangaea and birth of the Atlantic; the long history of subduction beneath western North America; the construction and later transformation of the American West; and finally the complex tectonic world that extends today from Alaska and the Arctic to Mexico.
The intention is not simply to provide a chronology of moving plates. Plate tectonics gives us the framework within which much of the geology encountered elsewhere in North America begins to make sense. Mountain ranges, sedimentary basins, volcanoes, earthquakes and even the routes subsequently taken by rivers have inherited aspects of a geological architecture assembled over hundreds of millions – and in places billions – of years.
But the six-part series is only one part of what we have planned. North America also contains some of the most familiar geological landscapes on Earth: the Grand Canyon, Yellowstone, the Great Lakes, Death Valley and the great mountain ranges of the west. Yet, familiarity can sometimes disguise just how extraordinary these places are.
Why, for example, is there an enormous canyon where the Colorado River crosses the Colorado Plateau? Did glaciers really excavate the basins occupied by the Great Lakes? Why does the Delaware River cut through a mountain ridge, rather than simply flow around it? Why is Yellowstone sitting where it is? And what could possibly have produced the immense dry channels and abandoned waterfalls of the Channeled Scablands?
Those are the sorts of questions we intend to explore in articles that are likely to be much more substantial than our usual ones to cover the subjects adequately. Rather than simply describing famous geological localities, we want to begin with the landscape itself. Look at it carefully. Ask what is unusual about it. Then try to reconstruct what happened.
Sometimes the answer will involve processes operating slowly over tens or hundreds of millions of years. At other times, the landscape records events of extraordinary violence. The Channeled Scablands of Washington State, for example, preserve the effects of immense Ice Age floods. In Alaska, Aniakchak records both the collapse of a great volcano to form a caldera and the later catastrophic drainage of a lake from within it. In Utah, the shorelines of ancient Lake Bonneville record a body of water vastly larger than the lakes occupying the region today.
Other landscapes conceal much older geological stories. At Buffington Pockets in Nevada, erosion reveals evidence of enormous movements of rock associated with thrust faulting. The strange forms of the Granite Dells in Arizona show what weathering can eventually do to solid granite. Elsewhere, lava flows have engulfed forests and left remarkable geological traces of the trees that once stood there.
One particularly ambitious part of the project (starting on Monday, 23 November 2026)) will take us through three of the most celebrated landscapes of the American Southwest: the Grand Canyon, Zion and Bryce Canyon.
These will form a three-part exploration of the Grand Staircase. The connection between them is fundamental. The geological succession exposed around the rim of the Grand Canyon does not represent the end of the story. Travelling northwards towards Zion and ultimately Bryce Canyon takes us, broadly speaking, upwards into progressively younger rocks.
But each landscape poses a different question.
At the Grand Canyon, we will investigate how the Colorado River came to carve such an immense gorge through an elevated plateau. At Zion, enormous cliffs of sandstone take us into a Jurassic world dominated by vast fields of wind-blown dunes. At Bryce Canyon, the emphasis changes again as weathering and erosion have transformed much younger rocks into an extraordinary landscape of amphitheatres, fins and hoodoos.
Taken together, the three allow us to move through a remarkable thickness of geological history while examining very different relationships between rocks, tectonics and landscape.
And there will be plenty more. And, indeed, this is where we would particularly like the help of Deposits readers. North America is far too large, and its geology far too varied, for us to pretend that we have identified all the best stories. Some of the most interesting geological localities are not necessarily the famous national parks or textbook examples. There must be countless unusual landscapes, remarkable exposures and geological puzzles across the United States, Canada, Mexico and the rest of the continent that deserve a wider audience.
If you know of one, please tell us about it.
We would be delighted to receive suggestions for future subjects. Better still, if you know a particular area or aspect of North American geology well, why not consider writing about it yourself? Deposits welcomes submissions, and you certainly do not need to propose one of the famous localities. An unfamiliar place with a good geological story may be exactly what we are looking for.
This new North American material will sit alongside, rather than replace, the British geology that has always been central to Deposits. There is considerable value in looking at the two together. Processes that may be difficult to recognise in one landscape can be spectacularly obvious in another. Once understood on the enormous scale of the American West, for example, a geological process may become much easier to recognise in subtler exposures closer to home.
North America also gives us the opportunity to range across almost every branch of the Earth sciences. Glaciation, volcanism, earthquakes, sedimentation, fossils, continental rifting, mountain building, weathering, river evolution, deserts and catastrophic floods can all be explored through landscapes in which the evidence is often remarkably well exposed.
The intention, therefore, is not to produce a succession of conventional accounts entitled “The geology of…”. Wherever possible, we will begin with a question.
- Why does the landscape look like this?
- What happened here?
- And, perhaps most importantly, how do we know?
That last question lies at the heart of geology. The landscape we see today is only the latest stage in a history stretching back billions of years. The geologist’s task is to use what remains – rocks, fossils, structures and landforms – to reconstruct what came before.
North America provides some wonderful places in which to do exactly that. We are looking forward to exploring them – and we hope that you will join us.
Jon Trevelyan (editor)