Hiking with GeoTom #8

GeoTom has been out hiking again and has found another location that he wants his human and others to take a look at.

This one was found while riding with his human on the way to one of their favorite hikes. This area is even safe for GeoDogs as long as they are on leash and right beside their human. While there is plenty of room to park, please be careful. You know how fast humans drive.

GeoTom wants you to check out the quick lesson he has prepared for you.

With this Earth cache we will be taking a look at a very old rock formation called a Hogback that is found on the drive to Larimer County Horsetooth Park. In fact, deposition of the sediments that would become the Dakota Formation began during the early Late Cretaceous (Cenomanian). This deposition marked a reversal from millions of years of erosion. We will discuss how it forms and briefly go over the type of rock that is present at this specific Hogback formation. If you still want more information after this lesson check out The EarthCache Academy.

Hogbacks form where sedimentary strata are turned up on end by a large basement uplift. The actual hogback ridge forms where resistant strata are surrounded by erodible rock that leaves the resistant layer relatively isolated as a hogback.

This all sounds complicated! But let's take a step back and see what this means.

Sedimentary rock is one of the three rock groups, it is a rock that was formed when sediment gets deposited from a fluid; water, wind, or ice.

When layer upon layer gets deposited on top of each other the immense weight of the above layers compress the bottom layers and eventually it becomes "sedimentary" rock. What these sediments comprise of will determine what sedimentary rock it will become ie.shale, sandstone...but that is a completely different topic all together. Strata is the the different layers of sedimentary deposits together. When it is a layer of one deposit only - we call it by its name ie. Shale, another sedimentary rock is sandstone, both of these and many others were formed by this proses of sediment compacting together.when referring to more than one layer of different types of sedimentary rock that is together its referred to as sedimentary strata.

Upliftment is the up movement of all types of rock that is caused by tecttonic plate movement and a numerous amount of other factors. It can literally move mountains. Mt. Everest was uplifted from a ancient seabed to where it is today - because of this you can find marine fossils on mount Everest!The earth's surface undergoes upliftment all the time, We do don't realize this as it happens over a very long time period.

When these upliftments happen, the strata lifts at an angle leaving rock exposed to weathering.

Now that we have a basic understanding of sedimentary rock and upliftment we can now look at the hogback that is found at GZ

This hogback is formed by the Dakota Group of sandstone and consists of a well sorted, fine to medium grainer stone which is well cemented. It is the most prominent hogback forming ridge west of Fort Collins This hogback was formed during the Laramide orogeny period, approximately 50 million years (50 my) ago. Even though the hogback itself formed 50mya, the sediment itself is much older - approximately 150my. The steeply dipping rock stratum, is called a "dip slope." Its other side, its escarpment or "frontslope" or "scarp slope", is an erosion face that cuts through the dipping strata. The angle of the dipslope of a hogback ranges between 30 and 40 degrees. The dip and scarp slope of a hogback also have a similar angle of repose,which is the steepest angle of descent or dip relative to the horizontal plane to which a material can be piled without slumping. A hogback will also have steep sloping sides.

A VERY IMPORTANT REMINDER: Larimer County's Horsetooth Park and the City of Fort Collins Natural Areas prohibit the removal of any flora or fauna and rocks and minerals, even though the geologist in all of us wants to pick up some samples! Please respect these restrictions and help preserve this area for others to enjoy. Remember, take nothing but pictures, leave nothing but footprints.
The above information was obtained using:

TO LOG THIS CACHE:

You must answer these questions and e-mail me your answers. Do NOT post answers in your log (even if encrypted) or it will be deleted. Logs without verification will also be deleted. Photos are not required, but are encouraged (without spoilers).

Logging requirements

Send me a note with :

The text "GC5X2XJ Earthcache" on the first line
The number of people in your group.
How many different layers of sedimentary rock can be seen on the hogback at GZ?
At what angle is the dipslope of the Hogback at GZ ?

*Special Thanks go out to KINGOSRIC for his help on this project.

Additional Waypoints

PK5X2XJ - Public Parking
N 40° 31.728 W 105° 08.290
This is free public parking but is only available during daylight hours.