*NOT A NIGHT CACHE*
LOGGING REQUIREMENTS - YOU MUST SUBMIT THE ANSWERS & REQ'D PHOTO PRIOR TO LOGGING A FIND. All finds that do not meet the logging requirements will be deleted. Post a write note if you will be delayed in sending the answers.
You're looking at the exterior of the State Capitol building and the surrounding buildings (which are waypointed).
Objective: To learn more about the geological history and prevalence of stone that is commonly found in Arizona.
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Arizona - The "Five Cs" and the Capitol Design
We learned that Arizona is famous for 5 Cs: copper, cotton, cattle, climate and citrus. On our trip here, we saw evidence of copper, climate and cattle.
The building you see before you was designed specifically to illustrate that Arizona Territory was ready for Statehood (achieved in 1912). The building is made largely from materials indigenous to Arizona, including malapai, granite, and the copper dome. The design is optimized for the desert climate of Arizona, with thick masonry walls that insulate the interior, skylights, and round "bullseye" clerestory windows to let heat out of the legislative chambers. The building is topped with a stark white weather vane similar to the Winged Victory of Samothrace, visible through a skylight from within the rotunda. This is made from zinc which originated in Ohio.
Famed architect James Riely Gordon won a contest to design the structure of the historic Capitol, which cost over $135,000. His vision for the building utilized materials native to the then-territory, such as granite from the mountains near Phoenix, tufa from Prescott and white oak from the forests in northern Arizona, symbolizing the region's wealth of natural resources. To reduce costs, the dome was initially constructed from sheet metal coated in copper-colored paint. It wasn’t until 1975 that companies in the Arizona Mining Association donated enough resources to sheath the dome in copper, finally realizing the Copper State Capitol’s famous centerpiece in line with Gordon’s original vision. The current iteration of the dome, revealed on January 9, 2022, is the third copper version and is made from recycled copper (the exact provenience is unknown).
Arizona - Geology
Arizona's oldest rocks overall are metamorphosed volcanic rocks, including basalt and rhyolite and related sedimentary rocks, that now constitute the bottom of the Grand Canyon and formed beginning 1.8 billion years ago. The Verde district at Jerome, in Yavapai County also preserves rocks from this period. There, ancient submarine hydrothermal vents precipitated sulfides directly onto an ancient seabed, creating massive copper and zinc ore sulfide deposits. For reference, the south rim of the Grand Canyon is about a 3.5 hour drive from Phoenix.
During the Eocene, Oligocene and Miocene, the Mid-Tertiary igmibrite flare-up, a mountain building event tied to the Farallon Plate, erupted huge quantities of volcanic ash. Many small mountain ranges in western Arizona, including the Superstition, Galiuro, Chiricahua and Tumacacori mountains are predominantly made up of ash flow tuff from these eruptions. You can visit the Superstition Mountains - it's only about a 1/2 hour drive from where you're currently at.
The eruptions are believed to have been partly the result of increasing steep slab subduction into the mantle and magmatic activity shifted from the east to the west, bringing with it changes in mineralogy and rock types. Small basins accumulated volcanic debris, conglomerate and lacustrine gypsum, clay and carbonates. Lava flows and granite intrusions built up the Galiuro Mountains and Chiricahua Mountains. Gold and copper veins mineralized in dike swarms, followed by caldera-related batholiths and silver-lead-zinc skarns. Low angle normal and detachment faults deformed sedimentary and volcanic rocks from the final phase of the event. In the last 14 million years, basalt intruded into the basins and evaporites and other sediments accumulated, including salt beneath Phoenix, clay and zeolites in the Bowie area and gypsum in both the San Pedro and Verde valleys.
In summary,
The oldest rocks in Arizona are the Vishnu Basement Rocks exposed in the Upper Granite Gorge, Grand Canyon. The Brahma Schist, part of these basement rocks, are about 1.75 billion years old. Locally the Brahma is interlayered with Rama Schist Xr and Vishnu Schist (Xv). There are some similarly aged rocks in the Prescott area. Brahma Schist consists of amphibolite, hornblende-biotite-plagioclase schist, biotiteplagioclase schist, orthoamphibole-bearing schist and gneiss, and metamorphosed sulfide deposits.
Copper
Arizona is known as the Copper State because it produces two-thirds of US copper annually. Laramide copper porphyry deposits are common around Tucson and include the Twin Buttes, Sierrita-Esperanza, Rosemont, Silver Bell and Mission-Pima mines, as well as the historical Ajo mine to the west. The Ray, Miami, Pinto Valley, Morenci, Safford, Carlota, Superior and Resolution mines are examples of open-pit extraction sites for copper in east-central Arizona.
These deposits typically have a bulls-eye pattern of mineralization ranging from copper and zinc at the center to zinc, lead, silver and gold in the periphery and silver and manganese on the outer edge.
Image: copper
Tuff
Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock containing 25% to 75% ash is described as tuffaceous (for example, tuffaceous sandstone). Tuff composed of sandy volcanic material can be referred to as volcanic sandstone. Tuff is a relatively soft rock, so it has been used for construction since ancient times.
Tuff can be classified as either igneous or sedimentary rock. It is usually studied in the context of igneous petrology, although it is sometimes described using sedimentological terms.
Tuff is often erroneously called tufa in guidebooks and in television programs but tufa is a form of travertine.
The light tan volcanic flows formed deposits near the valley bottom locally known as Tufa (this is what I'm referring to in the previous sentence), or Tuff stone. These are composed of volcanic ash mixed with very small stones or gravels. As they pushed up to the surface and begin rapid cooling they become hard like concrete.
Image: Tuff
Malapai Rock
Malapai is an Americanization of the Spanish word malpaís, which can be translated as bad terrain. The rock is a black gray slate stone with some air bubble configuration. The term malpaís is widely used to refer to badlands characterized by eroded rocks of volcanic origin. An example of this type of rock is basalt. Basalt is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of the Earth.
Image: Malapai rock
Granite
Granite Mountain (Yavapai: ʼWi:kvte:wa) is a 7,628-foot (2,325 m) mountain located in Yavapai County, Arizona that covers roughly 12 square miles (31 km2). It is composed of Paleoproterozoic biotite granodiorite to granite that is known by geologist as the Mint Wash Granodiorite.The Mint Wash Granodiorite consists of medium to coarse-grained, weakly to strongly porphyritic granite with phenocrysts of gray to pink potassium feldspar up to 3 cm (1.2 in) in length and as much as eight percent biotite that is less than 8 mm (0.31 in) in size. This granite grades laterally into a fine grained, equigranular leucogranite with less than two percent biotite that is less than 2 mm (0.079 in) in size.
The Santa Catalina Mountains north and northeast of Tucson contain the Wilderness Granite, which formed as an intrusion 14 miles below the surface. The Colorado Plateau uplifted and began to erode during the Eocene.
Image: Granodiorite
Image: potassium feldspar
Image: alkali feldspar granite
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Responses to submit - if submitting responses for a partner, be sure to include their geocaching name with your response. EACH PERSON, however, must submit their own unique photo demonstrating they were on site (see Q1 below).
I will read and respond to all submissions. If you will be delayed, consider posting a write note until you are ready to send your responses. If there is a concern, I will note that in my response to you.
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1. Required photo for all cachers - take a photo of you/ your GPS / your caching name standing with the Hypabyssal Gabbro stone. See the WP & example photo. Post this with your log.
2. At GZ, look at the Capitol building. Using your observational skills and the lesson, describe and identify each distinctive layer. Hint: look at the foundation & the next 4 floors NOT including the dome - that's a bonus for the 6th level.
3. At WP1, look at the exterior walls of the Senate building. Describe and identify the type of stones. Hint: there are 2 types of stone on the walls. Look at the stone and not the concrete.
4. ASIDE FROM COLOUR, what noticeable (geological) differences do you see here (WP1) compared to the stones at GZ?
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Thanks for visiting and I look forward to reading your responses.
For those that are new to doing Earth caches, please note that to claim a find you do actually have to answer the questions and submit all components. Read the lesson, look at the features and try your best! 