Amistad National Recreation Area
New Visitor Center Hours in October: Closed Sunday and Monday; Tues-Thurs 9AM - 4:30PM and Fri-Sat 8AM - 4:30PM.
YOU DO NOT NEED TO VISIT THE VISITOR CENTER TO FIND THIS EARTHCACHE!
Use the description, the image, and MULTIPLE TRAIL WAYSIDES to answer ALL the following questions.
1. What type of rock are the cliffs?
2. In which rock classification do the cliffs belong?
3. How old are the cliffs?
4. How did the cliffs come to exist?
5. The breakdown of rock also contributes to the soil and vegetation, and this area also contains a unique soil geology. What three different soil types are present here?
The trailhead is a gravel-paved path with waysides highlighting unique features along the trail. Either trailhead will get you to the coordinates, but the West Trailhead is closer.
You will be standing atop the beautiful cliffs lining the Pecos River in the Lake Amistad National Recreation Area, where you can see the Pecos River, the Hwy 90 overpass, the Rio Grande, and Mexico. Once this area was a broad marine region known as the Tobosa Basin, and this specific area eventually evolved into the shallower, carbonate reef Val Verde Basin. So, if this was a basin, how did it turn into a canyonland?
Igneous rocks are formed by the cooling of magma, a silicate liquid generated by partial melting of the upper mantle or the lower crust. Different environments of formation, and the cooling rates associated with these, create very different textures and define the two major groupings within igneous rocks: volcanic rocks form when magma rises to the surface and erupts, either as lava or pyroclasticmaterial, and plutonic rocks form when magma cools within the Earth's crust. Some examples of igneous rock are: granite, lava, obsidian, and pumice.
Metamorphism is the alteration of pre-existing rocks in the solid state due to changes in temperature and pressure. Under increasing temperature and / or pressure existing minerals become unstable and break down to form new minerals. Metamorphic rocks are classified according to the conditions under which they recrystallised. Rocks formed by varying degrees of heat and pressure. Some examples of metamorphic rock are: marble, schist, slate, and quartzite.
Sedimentary rocks are the product of the erosion of existing rocks. Eroded material accumulates as sediment, either in the sea or on land, and is then buried, compacted and cemented to produce sedimentary rock. There are two major groupings of sedimentary rocks: the fragments of pre-existing rocks or minerals that make up a sedimentary rock are called clasts. Sedimentary rocks made up of clasts are called clastic (clastic indicates that particles have been broken and transported); and non-clastic sedimentary rocks occur when minerals/mineraloids are precipitated directly from water, or are concentrated by organic matter/life. Components have not been transported prior to deposition. No clasts are present. Some examples of sedimetary rock are: dolomite, limestone, sandstone, and shale.
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