Sylvan Lake 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. Describe the size of the lake.
2. Make your way to the dam. Describe what you see and estimate the height of the dam.
3. Why do you think Sylvan Lake was created?
4. Estimate the length and height of the granite ridge that lines Sylvan Lake.
5. Describe the granite boulders in detail, including color, texture, and size.
This Earthcache is located at Sylvan Lake within Custer State Park. A daily or annual park sticker is required to enter the state park and visit the lake. Sylvan Lake is an excellent spot in the hills to have a picnic or go hiking, fishing, swimming, or boating. Paddle boats are available to rent at the lake. Sylvan Lake is also home to many trailheads: trail 9 will lead you to the top of Harney Peak, the highest mountain east of the Rockies. You may also recognize this lake from the 2007 film National Treasure 2: Book of Secrets. Enjoy!
Dubbed by many as the “crown jewel” of Custer State Park, Sylvan Lake is a man made lake that was created in 1881 when a dam was built across Sunday Gulch Creek to create a reservoir of water. At an elevation of 6145 feet, Sylvan Lake is the highest lake in the state with a maximum depth of 30 feet.
Perhaps most impressive at Sylvan Lake are the granite boulders that border the lake on one side. These unique rock formations surrounding the lake were formed by the uplifting of igneous and metamorphic rocks.
Igneous rock is formed when hot magma or lava cools. This type of rock can occur in one of two forms: intrusive or extrusive. Volcanic rocks (rocks that exit volcanoes in a liquid state and cool to solidify at the Earth’s surface) are extrusive rocks. These rocks come out of the Earth--they are extruded from the earth.
Metamorphic rock begins as a different type of rock, but has changed substantially from its original igneous form. When rocks are subjected to high heat, pressure, or hot fluids, metamorphic rocks are formed. Prime conditions for the creation of metamorphic rocks are found deep within the Earth or where tectonic plates meet. The process of metamorphism transforms the igneous rocks into much denser, more compact rocks.
Granite is an intrusive rock; it forms far beneath the earth’s surface. Beneath the surface, magma is slowly pushed up from the core of the earth. It fills any crack or space it can find, sometimes pushing other rocks out of its way on the subsurface. This process can take millions of years to complete. During this time, the rock slowly cools and solidifies into a hard rock. The granite boulders seen at Sylvan Lake were formed with a large sheet of granite intruded the metamorphic and igneous layers.
Looking closely at the granite boulders, one can see the course texture of the rock. This indicates that the granite cooled slowly while still underground. One will also notice the roundness of the boulders. The rounded form of the granite is due to thousands and thousands of years of weathering and erosion, which has smoothed out the rock.
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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