This Earthcache will allow you to observe some of the details of the sandstone bluff that has been created from the excavation of part of this hill to make way for building construction.

Sandstone is a sedimentary rock composed mainly of sand-size mineral or rock grains. Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any color, but the most common colors are tan, brown, yellow, red, gray and white.

 A predominant additional colorant in the southwestern United States is iron oxide, which imparts reddish tints ranging from pink to dark red (terra cotta). Red sandstones are also found in the Southwest and West of England and Wales, as well as central Europe and Mongolia.

Formation:

Sandstone is formed when grains of sand are compacted and cemented together over thousands or millions of years. The sand grains often are composed of the minerals quartz or feldspar that were worn off other rocks and ground down into pebbles. As new layers are deposited the previous layers are compacted and additional minerals deposited by groundwater act as a cement to bind the grains together. After years and years of pressure and compacting the sandstone becomes a strong dense rock formation. Since the layers are formed from grains of sand slight color variations may be visible as well as differences in color shades, but individual distinct layers are usually not noticeable as each layer blends into the next.

This particular bluff was created by drilling vertically at very close intervals until huge pieces of the rock could be removed from the hill. The vertical groves are an indication of this process. Although the face of the bluff now appears rather smooth, it originally would have been a very rough and jagged surface from huge pieces breaking off in the drilling process. The current semi-smooth face can be attributed to weathering.

Weathering:

Over the years surfaces of bluffs and cliffs similar to this will go through the process of weathering. Weathering describes the breaking down or dissolving of rocks and minerals on the surface of the Earth. by the action of rainwater, extremes of temperature, and biological activity. It does not involve the removal of rock material. Water, ice, acids, salts, plants, animals, and changes in temperature are all agents of weathering.

There are three types of weathering, physical, chemical and biological.

Physical weathering is caused by the effects of changing temperature on rocks, causing the rock to break apart. The process is sometimes assisted by water.
 

There are two main types of physical weathering:

• Freeze-thaw occurs when water continually seeps into cracks, freezes and expands, eventually breaking the rock apart.
• Exfoliation occurs as cracks develop parallel to the land surface a consequence of the reduction in pressure during uplift and erosion.

Chemical weathering is caused by rain water reacting with the mineral grains in rocks to form new minerals (clays) and soluble salts. These reactions occur particularly when the water is slightly acidic. Chemical weathering (especially hydrolysis and oxidation) is the first stage in the production of soils.

There are different types of chemical weathering, the most important are

• Solution - removal of rock in solution by acidic rainwater. In particular, limestone is weathered by rainwater containing dissolved CO2, (this process is sometimes called carbonation).
• Hydrolysis - the breakdown of rock by acidic water to produce clay and soluble salts.
• Oxidation - the breakdown of rock by oxygen and water, often giving iron-rich rocks a rusty-colored weathered surface.

Biological Weathering is caused by living organisms that can contribute to the weathering process in many ways:

Trees or other plants  put down roots through joints or cracks in the rock in order to find moisture. As the tree grows, the roots gradually prize the rock apart.

Many animals bore into rocks for protection either by scraping away the grains or secreting acid to dissolve the rock.

Even the tiniest bacteria, algae and lichens produce chemicals that help break down the rock on which they live, so they can get the nutrients they need.

Logging Requirements

You will need to complete the following requirements to log this Earthcache:

Send a geocaching message or email  with the answers to the questions below. Found It logs without the required information sent within 7 days of logging will be deleted. Do NOT post any answers in your found It log. 

Answer the following questions based on your reading and observations at the posted coordinates. 

1.  Not including the height of the railroad tie retaining wall , Give me an estimate of the height of the Sandstone bluff. ( You can also access it from the top as well and measure going down with a long tape measure.) 

2. Based on your reading what mineral would you attribute the main color in this Sandstone bluff?

3. Explain in your own words the layers you can see in the sandstone. Are they distinct and well defined? Are they compacted very close together? Are there any color variations? 

4.Describe any of the types of weathering you observe at the location. Be sure to inspect the entire length of the bluff. 

5. Are there any color variations due to the weathering? If so, what colors are present and what type of weathering do you image would have caused it. 

6. Include in your log a photo with you and your favorite Geocaching item at the Sandstone bluff. 

 

Thank you for visiting this earthcache. 

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