Last month I fulfilled a long-held dream of visiting Utah. I think I must have been the last Geologist in the world to make the pilgrimage! So, in a slight move away from the usual UK-based content, this month’s blog will recount some of the geo-highlights that I saw across the California and Utah!
Death Valley
En route to Utah, we had a quick diversion to Death Valley. Located in the East of California, Death Valley is an inhospitable place full of history, rocks, and not much else! The temperatures were well into the 30⁰s when we visited, so time spent out in the exposed dessert sun needed to be limited! The Valley is formed in a half graben, bounded to the East by the Black Mountains in the foot wall and to the West by the Panamint Range formed in the hanging wall. The basin between these two mountain ranges is exceedingly dry – often only around an inch of rain falls every year. What water that does fall can quickly forms flash floods in the mountains, cutting canyons and forming the beautiful alluvial fans at the edges of the valleys (see the picture below).
The Valley does not have any outlets for the inflowing water, and as a result the water will pool into the basin centre. Due to the heat, evaporation quickly causes water to evaporate and a large dried-up lake beds of salt are created (seen in white in the picture). Around these salt flats, sand dunes and Badlands complete this truly remarkable landscape. From Dantes View (pictured) you can view the lowest point in the USA below at Badwater (86m below sea level), and the in the far distance, the highest point in the lower 48 states, Mount Whitney at 4,421m!
Flying over the USA, you really get a sense of scale. This county is massive, and the expansive sites like Death Valley make great analogues for imaging what the UK and North Sea looked like at various times in Geological History. When The North Sea and Europe was a large shallow salty sea in the Permian, 250 Million years ago when the Zechstein salts were deposited, could it have looked similar to Death Valley?
Zion
After Death Valley it was onwards to Utah. First stop, Zion National Park. We got so excited that we ended up walking almost every single trail in the two days we were there!
Zion Nation Park is a deep, steep-sided canyon formed by the Virgin River cutting into the uplifted Colorado Platform. The extremely steep sides are made up of the Navajo Sandstone, a hard Aeolian sandstone (deposited in an ancient desert). The underlying softer layers are eroded and undercut by the Virgin River leading to collapse of the overlying rock, and the steep sides seen today. The canyon is particular spectacular at Big Bend where I think my favourite EVER meander has formed around a promontory called Angel’s Landing (see picture). The steep valley sides make walking difficult, with may switchbacks and steep assents. But the effort is definitely worth it!
Bryce Canyon
High on the Colorado Plateau, Bryce Canyon was very cold and snowy when we arrived. But absolutely stunning and forming a very different landscape from that seen at Zion. Formed along the Paunsaugunt Fault, a wide amphitheatre of rock is eroding west into the Colorado Plateau. Unlike at Zion and Death Valley National Parks where water is the dominant erosive force shaping the landscape, at Bryce, ice has shaped the landscape. Water and snow has found its way into small cracks and fractures in the rocks, and due to the high altitude and low temperatures, this water can freeze through the nights. The expansion of this ice breaks the rocks apart. The ice melts during the warmer days and the who cycle starts again. This erosion has formed a curious variety of rock formations: fins, windows and ‘hoodoos’ that are brilliant to explore. Many has specific names based on their shape such as ‘Thor’s Hammer’, ‘Queen Victoria’ and ‘The Cathedral.’ A truly remarkable and surreal place to explore!
Canyonlands and The Arches
Moving Eastwards to the final leg of the trip, we visited the Canyonlands National Park (The Needles) and The Arches. The Arches demonstrates yet another method of erosion: driven by dissolution. Deep below the park, salt movement has caused the hard Entrada Sandstone at surface to deform and crack. The small amount of rainwater that falls over the park seeps down into these cracks and into the base of the sandstone, slowly dissolving the calcite in the rock that holds the sandstone together. With reduced calcite in places along the base of the Entrada Sandstone, the winter ice easily pulls the rock apart forming the arches that are seen today. Erosion is ever continuing and eventually these arches with break and fall, whilst new ones are created! They make spectacular and unusual features in the landscape.
Finally, sadly, we were off to Salt Lake City to fly home. Utah was everything I had hoped for and more! I thoroughly recommend a trip there for geologizing, hiking or camping. The USA is a huge country with large-scale geology and geomorphology. Visiting these sites is very useful for understanding what the subsurface may have looked like at the time of deposition. For example, the uplifted Colorado Platform and Rocky Mountains make a good analogue for the Caledonian Orogeny of Scotland in the Devonian. The sand dune deposits of the Navajo Formation in Zion National Park are great examples of what many of the Permian Rotliegend Gas Fields in the North Sea look like, and salt deposition in Death Valley and Salt Lake City give analogues to the Upper Permian deposition of the Zechstein across the Southern North Sea and Europe. Every day is a learning day, even when you are on your holidays!
Happy Exploring!
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