Bellvue Dome
Locally know as Goat Hill, the geologic structure that dominates
this landscape is a dome. Bellvue Dome, was formed by the bending
of the sedimentary rocks layer underneath due to the same tectonic
forces that uplifted the Rocky Mountains. A combination of the
river's erosive action and the nature of the fold gives the
dome its actual appearance.
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.
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Anticline Fold |
Syncline Fold |
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.