Dillon Reservoir is a great spot to spend time in the mountains. Hiking, boating, kayaking, fishing, geocaching and more! Why not add some education to the fun? There are some caches on the way to this one as well. This is located in the Dillon Nature Preserve. From the parking coordinates, follow the trail to the Roberts Tunnel Access Road to the end, then follow the shoreline to the cache coordinates. There are other routes, but you may encounter closures, this route is your best bet. Kayak is NOT required, that is just a fun picture from our adventures.

Here is a view from where the EarthCache is located. As you can see, a very beautiful area!

Geological Map of the immediate area (larger view can be found using the link under sources):

Based on the Geological Map, this area has a lot going on! We have periods ranging from Quaternary to Jurassic, encompassing Holocene to Upper Jurassic epochs. With all these periods coming together in such a small area, how did it happen?

Several types of collisions happened in these time periods that may include:
Unconformity, Intrusive Contact and Fault Contacts and Fractures.

An Unconformity is a buried erosional surface separating two rock masses of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger, but the term is used to describe any break in the sedimentary geologic record. The rocks above an unconformity are younger than the rocks beneath (unless the sequence has been overturned). An unconformity represents time during which no sediments were preserved in a region.

An Intrusion is liquid rock that forms under Earth's surface. Their appearance is often caused by erosion. Coarse-grained intrusive igneous rocks that form at depth within the earth are called abyssal while those that form near the surface are called hypabyssal, which will be smooth or fine-grained. Intrusive structures are often classified according to whether or not they are parallel to the bedding planes of the country rock: if the intrusion is parallel the body is concordant, otherwise it is discordant.

A Fault Contact is a planar fracture in a volume of rock, across which there has been significant displacement along the fractures as a result of earth movement. Energy release associated with rapid movement on active faults is the cause of most earthquakes. Since faults do not usually consist of a single, clean fracture, geologists use the term fault zone when referring to the zone of complex deformation associated with the fault plane. These joints can be very large or very small. I encourage you to read more about them if you are interested.

A Fracture is any separation in a geologic formation, such as a joint or a fault that divides the rock into two or more pieces. A fracture will sometimes form a deep fissure or crevice in the rock. Fractures are commonly caused by stress exceeding the rock strength, causing the rock to lose cohesion along its weakest plane. Fractures can provide permeability for fluid movement, such as water or hydrocarbons. Highly fractured rocks can make good aquifers or hydrocarbon reservoirs, since they may possess both significant permeability and fracture porosity.

There are very large cracks in the rocks, running horizontally and vertically, as seen here:

And very small cracks, seen here gradually:

AGING: When more than one set of joints are developed, younger joints terminate against older joints. Many sets of older joints are orderly, while younger joints increase connectivity of the fracture system. Joints may cross-cut one another if pressure across the earlier fracture is high (closing the joint), or if the early fracture has been cemented by mineral deposits. A deep joint may also cut a shallow, pre-existing joint, making it very difficult to determine relative ages of joints

Bonus: Near ground zero, you should try to find this circular formation:

Not required, but what do you think caused this?

QUESTIONS:
E-mail your answers to me, logs that contain answers will be deleted, thank you.
1. At the site, what kind of contacts are you seeing? Why?
2. What are the orientations of the joints? How far apart are they?
Which joints came first? Why are some much larger than others?
3. Are the rocks in this area Concordant or Discordant/Abyssal or Hypabyssal? Why?
4. How wide is the largest fracture within 15 feet? The smallest?
5. OPTIONAL: Post a picture at the location either with the view or the rocks (or both)

SOURCES: Shout out to jp66 for her help creating this cache! Kellogg, Karl S., Bartos, Paul, J., and Williams, Cindy L., 2002, Geologic map of the Frisco quadrangle, Summit County, Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF-2340, U.S. Geological Survey, Denver, Colorado. Wikipedia. Permission via Brad Eckert, Resource Specialist, Summit County Open Space and Trails.
Online Resource: GEOLOGIC MAP OF THE FRISCO QUADRANGLE, SUMMIT COUNTY, COLORADO

CO-FTF honors go to Team Dennis and Mr and Mrs D, in the snow!