Geology Overview:
Earth's three main rock types are igneous, sedimentary and metamorphic.
Igneous: Formed when magma cools and hardens. Sometimes the magma cools inside the earth, and other times it erupts onto the surface from volcanoes, at which point it is called lava. When lava cools very quickly, no crystals form and the rock looks glasslike. Point Reyes' igneous rocks are granitic. They cooled beneath the surface of other rocks before erosion revealed them. They are the park's basement rocks, meaning that other rock types overlie them.
Sedimentary: Formed from particles of sand, shells, pebbles, and other fragments of material that together are called sediment. Over time, the sediment accumulates in layers and eventually hardens into rock. Sedimentary rock is fairly soft and may break apart. Point Reyes' granitic rocks began moving before the San Andreas Fault formed and docked off Point Lobos, where several distinct layers of rock formed above it. As a result, Point Reyes has six major sedimentary formations in it. The peninsula then started migrating north along the San Gregorio fault to merge alongside the San Andreas Fault, along which it now travels.
Metamorphic: Formed under the earth's surface from the change that occurs because of intense heat and pressure. The rocks that result from these processes often have ribbonlike layers and may have shiny crystals on their surface.
Logging Requirements:
Simply email or message me with the answers to the questions listed below. You should be able to figure out the answers based on your observations at the coordinates coupled with the text above. Please do not post your answers in your public logs.
1. Looking low and slightly northwest from ground zero out toward Drakes Bay, you'll see a landform commonly found along an ocean shore. What is this landform called? P.S. - Don't overthink this one!
1a. This landform consists of sand and gravelly rock. This rock eroded from exposures along the shore near the lifeboat station and extending to Chimney Rock's eastern point. This gravelly rock (which may be less visible at higher tide) is granitic. Which of Earth's three main rock types make up this landform?
2. Looking farther north into the distance, you'll see a different type of landform. Describe what you see. What makes it stand out?
2a. Based on the materials that are visible in the layers of this landform, which rock type do you believe it is? Explain why.
3. (optional) Please post a photo of the wildlife that you see at this site, or describe it in your logs!
Sources & Notes
Geology at Point Reyes National Seashore and Vicinity California (http://pubs.usgs.gov/of/2005/1127/chapter9.pdf)
Point Reyes Geologic Activity (http://www.nps.gov/pore/learn/nature/geologicactivity.htm)
Types of Rocks (http://www.learner.org/interactives/rockcycle/types.html)
This EarthCache was placed with the permission of Point Reyes National Seashore.