My next post about the Geology of the National Parks Through Pictures is from one of the closest National Parks to our house, yet one that we didn't visit because it was so far out of the way from anything.
You can find more Geology of the National Parks Through Pictures as well as my Geological State Symbols Across America series at my website Dinojim.com.
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Although Great Basin is within a few hours of our house, it did take us living here for 11 years before we ventured out towards it since there is absolutely nothing on the way to the park, and really not much in the way of places to stay once you get there. We had a trailer by this time, that we took with us to camp in the first come-first serve campground and we got a fantastic spot. However, we were later kicked out of the campground because snow melt was washing out the road to the campground. So we ended up just outside of the park, in the literal middle of nowhere. But we got what we went to do, which was tour the park and tour the main attraction, the Lehman Caves.
Entrance sign shot showing the South Snake Range mountains, which are mostly encompassed within the park.
Within the main part of the park stands Wheeler Peak at over 13,000 feet tall. There is a road that goes most of the way up to the top, however it was closed when we were there (at the end of May) due to snow coverage on the road and was still too high to remove. However, we were able to hike up the road a bit.
The views up Wheeler Peak Scenic Drive were spectacular, overlooking the surrounding valleys. The mountains and all of the surrounding valleys sit within the "Great Basin" of which park is named after.
Another view of the valleys from Mather Overlook, which is the highest we could drive up the Wheeler Peak Scenic Drive at just over 9,000 feet in elevation. The Great Basin was formed as part of the Basin and Range Province of the United States. At one point in time the western edge of North America was being compressed by the Farallon Plate pushing up against North America, squeezing the continent as the Farallon plate subducted (went beneath) North America.
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| Graphic of the Farallon Plate subducting beneath North America. Image courtesy of the NPS. |
Eventually most of the Farallon Plate was entirely subducted beneath North America, especially along the Californian coast, and the compression was released. This essentially allowed North America to expand outwards, like a squeezed sponge being let go. This expansion thinned the crust, while also producing a series of linear mountain ranges and valleys.
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| Graphic of the Basin And Range expansion producing linear mountains and valleys. Image courtesy of ISU.edu. |
As the expansion progressed, the crust was broken up into a series of smaller blocks. These blocks rotated as the crust stretched out. The rotation of the blocks produced the mountains along the upper corners, with gaps along the lower corners. These gaps eventually were filled with sediment eroded off the mountains, forming the valleys between the mountain ranged.
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| Coverage of the Great Basin. Image courtesy of the NPS. |
With the thinning of the crust, this area also ended up being lower than the surrounding regions. Because of this water is not able to flow out of the Great Basin, hence the terminology of "basin". Unlike water along the eastern portion of the country and along the west coast, water here does not reach the oceans. All precipitation here eventually ends up in end-basins, such as the Great Salt Lake, where its only outflow is through evaporation.
The rocks within the South Snake Range are mostly comprised of sedimentary rocks like sandstones, shales, and limestones that were all deposited during the Cambrian Period, around 550 million years ago. Seen here is the principle limestone of the region, the Pole Canyon Limestone, and the one in which the Lehman Caves was developed within. The Pole Canyon Limestone was deposited within a warm, shallow sea near the equator. This limestone formed from the dead shells of ancient sea creatures that built up over time. These shells, made up of calcium carbonate, naturally dissolve in acids, even if the water is only slightly acidic.
Over time the limestone was slightly metamorphosed (producing small amounts of marble). It was also cracked and fractured from the mountain building events (orogenies). You can also see that the limestone was rotated during these events, as seen in the lower part of the cave map. As the rocks cracked, this allowed ground water to seep into the limestone. The groundwater, which becomes carbonic acid by absorbing carbon dioxide from the soil and air, slowly dissolved away the limestone as it passed through the cracks. Over time, those cracks widened from the dissolution.
Here is the original, natural cave entrance to Lehman Caves. This is up above the current entrance, which was blasted into the caves through the limestone walls.
As the water dissolves the limestone, it also deposits limestone. This is how cave formations are formed. The tiny bit of calcite that is within the dissolved water precipitate out of the water as the water drips off the surface of the rocks. Here stalactites are continuously formed and getting bigger as water runs down them from the overlying limestones. Calcite deposits on the tip of the stalactite, and whatever calcite remains within the water can then get precipitated directly below the stalactite on the ground as a stalagmite. These eventually will meet to form a column, as seen here in the background.
Lehman caves is covered in absolutely gorgeous formations throughout the caves.
Some of the thinner, soda straw, stalactite formations.
Looking up at some of the stalactites directly above the narrow passage.
View of some of the fantastic cave formations.
More soda straw formations. You can see here the tube through which the water is traveling, giving the soda straws their name, from the overlying limestone. As the water reaches the end of the straw, calcite is deposited at the tip, creating new straw layers as the stalactite grows. Eventually these straws will close up and build outwards, producing the more typical stalactite formations.
There is even standing water within the caves here, that very slowly seeps down into the limestone and other rock formations below the cave floor.
Some more columns, stalactites, and stalagmites.
More cave formations. Here showing a few of the "draperies", which are cave formations formed as water flows down the the side of the cave. These are more often known as flowstones.
Some of the more delicate features within the cave. All cave formations form a type of rock known as travertine. Travertine is a product of the flowing water precipitating calcite, and can be formed within caves as seen here, or outside caves where flowing water is precipitating calcite, such as around geothermal features.
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