Old rock gets folded
Down below the surface and between 1000 to 2000 feet below exists a fault in the Precambrian rock layer, which gave origin to the Bellvue Dome. At the earthcache coordinates you will find an information post that pictures how the fault causes the stratified rock to fold over creating the dome. These same rock formations also have been uplifted on the west side of the valley to create the foothills.
Types of folds
Folded structures are important in geology because they are the cause of many mountains formations. Folded structures are warps in rock layers that may occur upwards, downwards and sideways, caused by extreme compressional techtonical forces. Two types of folds are anticlines and synclines.
An anticline is convex up and has its oldest layers of rock at its core. Anticlines consist of a series of up-arched strata with side portions going in opposite directions away from the center of the fold. Erosion shows the different layers of rock become progressively younger away from the center.
On the contrary a syncline is a series of down-arched strata with side portions dipping inwards in opposite directions towards the center of the fold. An eroded surface indicates that the different layers of rock become progressively older away from the center.
Dome or Basin?
In structural geology, a dome is a deformational feature consisting of symmetrically-dipping folds; their general outline on a geologic map is circular or oval. The strata in a dome are up-arched and dipping away from the center throughout 360 degrees; if the top of a dome is eroded off, the result will be a series of concentric strata that grow progressively older from the outside-in, with the oldest rocks exposed at the center.
The dome’s opposite structure is a basin, which is a down-arched series of strata with layers of rock on all sides dipping in towards the center. An eroded surface would show that layers of rock become progressively older away from the center of the structure.
Characteristics of folds
When a fold (syncline or anticline) has both sides showing a mirror image on the strata with respect to the center of the dome, it is a symmetrical fold. An asymmetrical fold is a fold without a mirror image on the strata with respect to the center of the dome. When the center of the fold is tilted to any degree and the strata dip in the same direction on both sides of it, it is an overturned fold. When the center of the fold is horizontally on the ground and not vertically standing up, the fold is called a recumbent fold.
To get credit for this cache you need to visit the earthcaches coordinates. At the information sign you will enjoy a wonderful view of the Cache La Poudre Valley. Using the map on the sign locate the Bellvue Dome on the landscape and answer the following questions:
- How will you describe the type of folded structure the Bellvue Dome is? Why?
- Using the graph on the sign can you tell how many feet above sea level does the fault that created the dome reaches the Fountain Formation?
- Looking at the dome and checking the information sign, can you tell what two different formations constitute the base and body of the Bellvue Dome?
- What is the formation on the top of Bellvue Dome? What materials is it made of?
- Looking at the landscape and using the map on the information sign to locate it, what is the name of the other noticeable folded structure in this area?
At earthcaches pictures are not a requirement to get credit for it, however this caches are amazing and most if not all of them constitute excellent places to take pictures. Feel free to include any photos with your log.