The O'Dwyer Memorial in downtown Yuma is dedicated to a Mexican-American and Native American buisnessman who helped tranform the farming industry in Yuma and the surrounding area. While completing the virtual cache here (GC7B9Z8), the scientist inside me took to note the geology that was incorporated into the memorial. This memorial was created using a giant uncut and unpolished peice of granite. But not just any type of granite. A special type called pink granite. Let's first discuss the geology of granite in general before I go into detail about what makes it so pink.
Granite is an igneous rock that cooled slowly over millions of years within the Earth. It formed when solid rock (most likley another igneous rock) was completly melted. This melted rock then cooled to form granite. Granite can form in a few different ways, but the most common is at convergent plate boundaries where two tectonic plates colide with one another. If two continental plates crash into one another, uplift will occur as the plates run into each other. However, it at least one of the plates is oceanic, subduction will occur where the oceanic plate will be recycled into the interior of the earth. Subcution occurs when one plate (the one that is most dence which is always oceaic) dives beaneath a continental (or another oceanic) plate.
For rocks located near convergent plate boundaries, where the tempurature and pressures are high enough, melting can occur without recycling. This typcally occurs right above the subduction zone in the area between the diving oceanic and floating continental plates. Over millions of years, the liquid rocks coo. Once tectonic forces begin to shift into a new direction, as they do on timescales of millons of years, these burried granite formations can be uplifted. Possibly the most famous example of this is the granites of the Sierra Mountains, which formed by subduction processes.
What makes this rock so pink is that it has an abundance of a certain mineral called Pottasium Feldspar, or simply K-felds, or orthoclase. Orthoclase is a common mineral in granite but it only this abundant when high ammounts of it exist within the liquid magma. Below is a chart of other common minerals that can be found in granites.
Works Cited
https://graniteobjectsgauteng.co.za/2014/09/29/granite-formed/
https://stoneyard.com/product/pink-granite-cobblestone/
https://www.history.com/this-day-in-history/yosemite-national-park-established
https://geologycafe.com/class/chapter3.html
TO LOG A FIND ON THIS CACHE YOU MUST ANSWER ALL THE QUESTIONS BELOW. YOU CAN CONTACT ME THROUGH MY EMAIL OR THE GEOCACHING MESSAGE CENTER TO SEND YOUR ANSWERS. ANY INCORRECT ANSWERS MAY RESULT IN A CLARIFICATION RESPONSE FROM ME.
1. "O'Dwyer Memorial" on the first line of your email AND list all geocaching names of your party so I can match your answers to them. If you all want to learn something, I would prefer each cacher send me individual emails in the spirt of earthcaching.
2. Take a photo of you (or your signature item if you don't want to show your face) with the rock in the background. Please do not show the plaque as that has the answer for the virtual cache here. This photo MUST be uploaded to your "found it" log. Please do not send any photos through the message center as Groundspeak compresses images. Each log MUST have a unique and different photo. No two logs may contain the same photo.
3. Describe the (a) textures, (b) range of colors and (c) relative size of the rock.
4. Using the mineral chart above, what is the most dominate mineral in this rock?
5. Using the mineral chart above, name at least two other minerals that are present in this rock. You cannot use the answer you had in question 4 for this question.
6. Why do you think this rock is exceptionally pink? Explain your answer.