Tuesday, June 30, 2020

Geology of the National Parks Through Pictures - Tonto National Monument

My next post about the Geology of the National Parks Through Pictures was from a rather snowy trip to Arizona where my wife ran an Ironman and then we did a tour of some of Arizona's National Parks, that unfortunately got snowed out towards the end of the trip.


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.

Arizona State Geological symbols can also be found HERE.

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Tonto National Monument
After traveling to Tumacácori NHS, we started to head north towards home. Along the way we stopped at a pretty picturesque park called Tonto National Monument that has a couple of cliff dwelling houses within a short hike of the Visitor's Center.


Obligatory entrance sign shot.

The walls of the Visitor's Center were likely built using the local quartzite, which is the same formation which the cliff dwellings are located within and built from. By the looks of it, these Visitor Center bricks appear to be formed from the Lower Member of the Dripping Spring Quartzite, while the caves are located within the Upper Member. The Lower Member is composed of reddish brown sandstone and quartzite, while the Upper Member is composed of black, gray, red, and brown claystone, siltstone, sandstone, and quartzite.

A view of the local geology surrounding the cliff dwellings. The caves are located within the Upper Member of the Dripping Spring Quartzite, while the majority of the hike took place on top of the Gila Conglomerate.

View up the slope along the hike towards the Lower Cliff Dwellings. Looking up you can see the Upper Member of the Dripping Spring Quartzite, while we hiked up the slope of the Gila Conglomerate.

 As we hiked along you can see the chunks of rock within the Gila Conglomerate. The conglomerate often contained large, angular chunks of the Dripping Spring Quartzite. The ages of these two rocks also varied significantly. The much older Dripping Spring Quartzite formed from siltstones, sandstones, and dolomites that were laid down withing a shallow sea approximately 100 million years ago. The Gila Conglomerate, on the other hand, is the second youngest rock in the park and was formed from stream deposits that were slowly cemented over time by lime (caliche) that was left behind from evaporating water between 0.5 and 15 million years ago.

 Walking along the path we slowly come to the cave opening where the cliff dwelling resides. The caves are located within a section of the Upper Member of the Dripping Spring Quartzite that was especially susceptible to spalling (cracking or breaking into smaller pieces). As cracks started forming around sometime between 50,000 and 400,000 years ago, water carried away the pieces, enlargening the cave opening over time.

 The dwellings within the caves were built around 1300 CE (Common Era) by people of the Salado culture. They lived within these structures for around 150 years, while the climate slowly started to dry out, negatively impacting their agriculture. As life became more difficult, the people started to leave, completely abandoning the place around 1450.

 A view of some of the cliff dwellings. Unlike other local cliff dwellings like Chaco Canyon and Mesa Verde which are built within sandstone, the quartzite blocks that broke off within this cave were too hard to shape and carve. So the dwellings were created by stacking quartzite blocks that were then covered with clay plaster.

A view of some of the cliff front facing buildings. The caves faced east, which allowed the cliff dwellings to face the rising sun but then would soon be covered in shade in the hot summer sun, while in the winter the morning sun would warm up the cave after the cool nights. 

 Turning around, here is the view out of the cliff dwellings towards the valley below with Theodore Roosevelt Lake in the distance, a man-made reservoir created from the local Salt River.

References

Sunday, June 28, 2020

Geology of the National Parks Through Pictures - Tumacácori NHP

My next post about the Geology of the National Parks Through Pictures was from a rather snowy trip to Arizona where my wife ran an Ironman and then we did a tour of some of Arizona's National Parks, that unfortunately got snowed out towards the end of the trip.


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.

Arizona State Geological symbols can also be found HERE.

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Tumacácori National Historical Park

Following our trip to Sagauro National Park, we drove south towards the border to visit our next park, a small historical park preserving a local mission. Typically historical parks are limited on their geology, but there is always geology if you look hard enough.

The entrance sign.

 The family all excited to visit another park :-)

 The main church of the mission that remains standing today. The name Tumacácori (pronounced Too muh kä' koh ree) is interesting because it is a Spanish phonetic rendition of the local O'odham name for their local village. The source of the name in O'odham has been lost to time but it is though that it could mean "caliche hills" representing the desert limestone surface deposits in the area.

Built in the early 1800's, the mission is composed of adobe bricks and plaster. Adobe is a composite material of mud and plant material, often straw, and then baked in an oven. The plaster used was produced from the baking of local limestone, discussed more below.  

 The central alter still preserves some of the original paint on the walls 200 years later.

 The outside of the main church.

The remnants of the storeroom building.

The lime kiln: where all the geology happens. At the kiln, limestone was loaded onto a heavy metal grate and then cooked over a fire. The limestone blocks would begin to swell and crack, at which point they would then be hammered into powder. The powder was then mixed with water creating a paste, and then mixed with sand producing the plaster. The plaster was then ready to be used on the local buildings.

The official source of the limestone was never recorded, however it is assumed to have come from the Santa Rita Mountains, some 25 miles away to the north. Doing some research of my own, I would say that a likely rock unit that the limestone came from was the Late to Middle Pennsylvanian (~300 million years old) Horquilla Limestone from the nearby Mt. Hopkins. Other than being one of the few limestone formations in the nearby mountain, it is also estimated at ~1,000 ft in thickness, making it an abundant source of limestone. The Horquilla Limestone is a fine-grained, medium- to light-grey limestone, interbedded with siltstone and conglomerate beds.

Another view of the main church with the remains of some of the other buildings within the mission.

The Tumacácori mission was located within the Sonoran Desert, which gets on average 3 to 15 inches of rain a year, making it one of the driest places in North America. So, one of the most important features within the desert landscape was the source of water. Here is the remains of the acequia, or irrigation ditch. This is where the mission would redirect the water from the neighboring Santa Cruz River. 

References

Saturday, June 27, 2020

Geology of the National Parks Through Pictures - Saguaro National Park

My next post about the Geology of the National Parks Through Pictures was from a rather snowy trip to Arizona where my wife ran an Ironman and then we did a tour of some of Arizona's National Parks, that unfortunately got snowed out towards the end of the trip.


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.

Arizona State Geological symbols can also be found HERE.

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Saguaro National Park

On our latest tour of the deserts of the southwest we started outside of Tuscon at Saguaro National Park. The National Park is divided into two distinct districts. One to the west of Tuscon (the Saguaro West Tuscon Mountain District), which I'll just refer to as the West District, and one to the east (the Tuscon East Rincon Mountain District), which I'll refer to as the East District. We started out in the West District and ended the day in the East District.

Although we started in the West District, the sign for Saguaro in the East District was far better, so I'm placing that as my entrance sign pic.

Here we started taking a hike through parts of the West District. Saguaro National Park is located within the Sonoran Desert, one of the largest deserts in North America. The Sonoran Desert is the second largest hot desert in North America, extending from Arizona into California and Mexico. It is also the hottest desert in Mexico, while the Mojave Desert holds the record for the hottest in the United States.

The soil of this region is formed from the easily eroded sedimentary rocks overlying the surrounding mountains. The desert environment of extreme heat during the day followed by freezing cold at night causes the softer sedimentary rocks to expand and contract, breaking them down over time. Heavy summer rains then move these broken up rocks into alluvial fans adjacent to the mountains and into the plains. The ground surface is then covered by a rock known as caliche, which is a calcium carbonate rock formed from the leaching of the calcium from nearby limestones. The caliche ends up forming a crust on the surface that slows water from entering the soil. Shallow root systems help absorb any available water before it is lost to evaporation or percolation through the rocky soil. Caliche is often misinterpreted as dinosaur bones due to the white, roundish quality of the rocks.

Although Saguaro is a rather large National Park, it has limited access by vehicles, only having one short road loop in each district. There are several short hikes along each loop though. Here we took a hike up Signal Hill, which had some terrific petroglyphs located at the top of the hill.

 The rocks of Signal Hill and the surrounding country are a granodiorite from the Amole Pluton, which is an intermediate rock with a composition between the common igneous rock granite and its quartz poor cousin diorite. Granodiorite is a course grained rock (meaning we can easily see the mineral crystals) that initially formed deep in the earth from a magma body that slowly cooled at the end of the Cretaceous. This area used to be littered with active volcanoes and it is thought that the region looked similar to modern day Yellowstone. Later plate tectonic extension, a process that had formed the Basin and Range region of the American west, caused these deeply buried rocks to be raised to the surface in the Tuscon region.

Although not directly geological, the petroglyphs are influenced by geology. These petroglyphs were created by people of the Hohokam culture between 450 and 1450 CE (in the common era).

 The petroglyphs were formed from engraving within the desert varnish on the surface of the rocks. Desert varnish forms on the surface of exposed rocks, frequently in the desert, from the accumulation of oxidized minerals of iron and manganese. These iron and manganese varnishes produce a darker, blackish rind to the rock. The minerals are accumulated on the surface by bacteria and lichen that live on the rock. The bacteria and lichens are anchored to the rock by clays particles in the atmosphere that precipitate out every time that it rains, taking with it manganese and iron particles. The bacteria and lichens then oxidize the iron and clay turning the varnish black. The more it rains, the more varnish is added to the rock. It is in this rind that the petroglyphs were carved.

Unlike pictographs, which are painted on and can be washed away unless in a protected area, petroglyphs have the potential to be preserved for a long time after. Over time, the varnish layer will eventually cover over the pictographs when left to its natural processes.

Within the desert, the landscape is dominated by rocks and water retaining plants because a desert, by definition, receives on average less than 10 inches of precipitation in an entire year. The Sonoran Desert averages between 3 and 15 inches per year, varying locally due to elevation differences and whether you are close to, or far away from the local mountains.

As we exit the park in the northeastern portion of the West District we come across the Safford Dacite seen here. This deposit is a gray to light-brown lava flow from the early Oligocene (with different flows aging ~40 to 26 million years ago).

Following our exit from the West District, we proceeded to the East District on the opposite side of Tucson.
 We entered the park towards sunset, so most of our photos were centered on the setting sun.

 Although located fairly closely to the West District, the East District contains rocks that are much, much older. What we are looking at here are Precambrian granodiorite and quartz monzonite rocks from the Wrong Mountain Quartz Monzonite that are ~1.5 billion years old. Monzonites are igneous rocks with a lot of feldspar and relatively little quartz, however this rock has enough quartz to be termed a "quartz monzonite" (greater than 5%). With a large abundance of feldspar, that makes the monzonite relatively softer than other igneous rocks like granite and easier to erode over time.

 Within the igneous Wrong Mountain Quartz Monzonite are banded metamorphic rocks known at the Catalina Gneiss. This beautiful outcrop also has an age of ~1.5 billion years old and represents some higher amounts of metamorphism, altering the original monzonite, granodiorite, and other local igneous rocks.

 Another view of the Catalina Gneiss.

And we leave you with this view of the sun setting to the west.

References

Tuesday, June 23, 2020

Geologic State Symbols Across America - Florida

The next state up for the Geological State Symbols Across America is:

Florida


You can find any of the other states geological symbols on my website here: Dinojim.com (being updated as I go along).

                                                                             Year Established
State Stone: Agatized Coral                                          1976
State Gem: Moonstone                                                 1970

I also have some Geology of the National Parks Through Pictures that I have done for Florida previously. These include:

DeSoto National Memorial
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