Terry Peak EarthCache
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In order to count this Earthcache as a find, you must complete the following tasks and email the answers to me.
1. What is the elevation at the base of the mountain? (This reading will be taken right as you turn onto the road that takes you to the peak)
2. What is the elevation at the top of Terry Peak?
3. Based on your numbers for questions 1 and 2, how high is Terry Peak?
4. Describe the view of the Black Hills area from the top of the observation deck.
5. Describe the appearance of the igneous rock in the area.
This Earthcache is located at the observation deck at the top of Terry Peak near Lead and Deadwood. Terry Peak is one of the tallest peaks in South Dakota. Although it is only 150 feet shorter than Harney Peak, Terry Peak is easily accessible by car. During the winter, Terry Peak is premiere skiing resort in the Black Hills region. Beautiful vistas of the Black Hills can be seen from this area. Enjoy!
The Black Hills are an isolated mountain range spanning from western South Dakota and into Wyoming. Geologists describe the region as a geological anomaly, calling it an “island of trees in a sea of grass.” The Black Hills is home to the tallest peaks in continental North America east of the Rocky Mountains.
The current landscape of the Black Hills is the result of tectonic activity. The time period between 2.6 million and 65 million years ago was marked by worldwide tectonic activity. During this time period, worldwide tectonic activity occurred. In some parts of the world, tectonic plates split apart from one another, while in other areas, including the Black Hills, the plates collided.
On Earth, there are currently eight major plates and many minor plates. Tectonic plates move in relation to each other at one of three types of plate boundaries: convergent or collisional boundaries, divergent boundaries or spreading centers, and transform boundaries. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along plate boundaries.
Transform boundaries occur where plates grind past each other along transform faults. Plates moving along a transform boundary cause earthquakes. The San Andreas Fault in California is a good example of a transform boundary.
Divergent boundaries occur where two plates slide apart from each other. The space created by these two plates moving apart is filled with new crustal material formed from molten magma that forms below. Mid-ocean ridges, such as the Mid-Atlantic Ridge, and active zones of rifting, such as Africa’s Great Rift Valley, are both examples of divergent boundaries.
Convergent boundaries occur where two plates slide toward each other, forming either a subduction zone, if one plate moves underneath the other, or a continental collision, if the two plates contain continental crust. This type of boundary is responsible for the creation of mountains (continental collision) and volcanic activity (subduction zone).
About 70 million years ago, at a convergent boundary in the Hills, two plates collided and caused an uplift (rise) of the landscape and rock in the area. The majority of the rock that can be found in the area was deposited as sediments at the bottom of an ancient sea that covered the area between 1.6 and 2.5 billion years ago. These sediments eventually hardened to form limestone and other sedimentary rock layers.
Terry Peak, which is largely comprised of igneous rock, was formed when underground molten rock, called magma, pushed up through the sedimentary layers of limestone to form the mountain ranges. During the uplifting, the crevasses within the limestone hills (created by deposits at the bottom of the sea) became filled with magma. These flows of magma, known as intrusions, cooled to form igneous rock. Because limestone erodes as a much faster rate than the harder igneous rock, the igneous intrusions were exposed as the inland sea retreated. The continuous erosion of the igneous and sedimentary rock surround Terry Peak continue to shape the landscape of the northern Black Hills. The igneous rock that now caps Terry Peak is about 300 feet thick. The peak that we see to day is likely, according to geologists, the eroded core of a laccolith, a “near volcano.”
NOT A LOGGING REQUIREMENT: Feel free to post pictures of your group at the area or the area itself - I love looking at the pictures.
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