Boulder OverView EarthCache

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geoawareUSA1: Been Disabled for quite some time with no response from cache owner.

geoawareUSA1
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Hidden : 9/9/2008
Difficulty:
2 out of 5
Terrain:
1 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:


This EarthCache is located at a scenic turnout from westbound US-36 between Denver and Boulder, just past Louisville.

The stop is atop a ridge, which gives a brilliant view of the Front Range, Boulder Valley, and the area’s most beloved geological feature – the Flatirons.

Taking a full, 360-degree look around you, you will see that you stand more or less at the intersection of two great geological entities: the Great Plains, and the might Rocky Mountains. What is not so obvious is that you are also standing at the intersection of two generations of geologic strata (geologic what?? ..... rocks.)

WHAT

To the East, the bulk of what you see (or would see, if you could sweep off the dirt, dust, and man-made objects) is either Upper Cretacious Sandstone, or the Denver formation. Below these two is a blanket of the older Pierre Shale, which can be found on the surface closer to the mountains. These three strata (layers of rock) date to the Cretacious Age in geologic time: that is, roughly 70 – 150 million years ago (mya). Let not the numbers fool you – in our time scale, this is very young!

To the West are exposed many layers of older rock: most notably sandstone strata known as the Morrison (~200-250 mya), the Lyons (250-280 mya), and Fountain (280-320 mya) formations, repectively. Each of these may be seen from this EarthCache location (barring rainy or foggy days), and are pointed out on the informational panel at the site. On a clear day, you can see peaks beyond the foothills – these are made up of even older strata: Precambrian (500 or more mya) granitic and metamorphic rocks.

Diagram taken from Boulder, A Sight to Behold


WHY

You might be asking yourself why it is that older rocks should appear above newer ones. Geology should work like a closet floor – you store some stuff in boxes... but after a while you realize that you have layers and layers of boxes, the most recent on top and the old stuff way at the bottom – right? Well, in general, yes. It sort of works that way. But this area is unique in its deviation from the standard rules.

To wrap our heads around the “why”, we must turn the clock waaaay back....

From the beginning of the so-called Paleozoic Era (550-600 mya) to the Pennsylvanian (290-320 mya), most of Colorado lay beneath a shallow sea. The continental plate was at that time drifting northward and rotating into its current orientation, with Colorado in the equatorial region. During the Pennsylvanian, two great mountain ranges were uplifted in central and western Colorado. These are known as the Ancestral Rockies because of their geo-spacial relation to the present-day Rocky Mountains. These ranges, however, with their 10,000+ ft. peaks eroded down to “low hills” within the next 100 million years. The mountains were reduced to fine sands, silts, and mud, which was deposited at the sea floor. This deposition, under the sea’s pressure, became a reddish sandstone and conglomerate known today as the Fountain formation.

During the Triassic (200-250 mya) and Jurassic (150-200 mya) Eras, Colorado’s shores were repeatedly lapped and covered by the periodic advance and receding of the sea. In the early part of the Jurassic, sand dunes “were slowly covered by river-borne sand, then by varicolored shales and sands of the Morrison formation, laid down in streams, marshy areas, and lakes. Dinosaurs flourished in this moister climate, and their fossils and footprints are numerous in rocks of late Jurassic age.”

This pattern repeated itself, with subtle variations, giving us the Dakota formation, the Pierre, and the Niobrara – all of which can be found in the environs of Boulder.


The Fountain formation, along with these younger layers, were “dragged and faulted upward by the rebirth of the Rockies during the Laramide Orogeny, 72-40 million years ago.” The diagram on the info panel illustrates how, just as pulling the rug out from under a stack of boxes will turn things on end (so to speak), so too this faulting and uplifting has reoriented these rock layers.

To claim credit for this EarthCache, study the above description, the diagrams on site, and the view in front of you. Send the answers to the following questions to me via my geocaching profile.

  1. According to the sign found at this site, what formation are the Flatirons part of?
  2. How does the age of this formation compare to the formation of:
    • the ancestral Rocky Mountains
    • the current day Rocky Mountains
  3. Were there ever dinasuars in this area?
  4. Describe in your own words the difference between the Flatirons feature and the other ridges that don't have a feature like the Flatirons. Why do you think the Flatirons might have become such a prominent feature in this particular location?
Additionally, please photograph yourself with your favorite angle of the view (not the info panels!) in the background. Attach this photo to your log. Please also include the number of people in your team and whether this is your first EarthCache find.

References:

Roadside Geology of Colorado, 2nd Ed.. Halka Chronic and Felicie Williams. Mountain Press Publishing Co., 2008.

Boulder, A Sight to Behold; Guidebook. Donald D. Runnells. Estey Printing Co, 1976.


A special thanks to the Colorado Historical Society for maintaining this location and many others, and for granting permission for this EarthCache.

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