| Garden of the Gods Park is open: |
May 1 - Oct 31 5am - 11pm
Nov 1 - Apr 30 5am - 9pm |
Please leave no trace at the site by staying on trails and practicing CITO. Preserve the formation for future generations to enjoy.
One Billion Years of Preparation
About a billion years ago, molten rock cooled and solidified to create Pikes Peak granite. Then 275-310 million years ago a major period of uplifting occurred and the Ancestral Rockies were formed. The Fountain Formation was deposited layer by layer through alluvial fans on the flanks of mountains.
Next the Lyons and Lykins Formations were deposited. During the Triassic time period (180-225 years ago) the Ancestral Rockies were completely eroded away and buried under their own remains.
The Rockies began forming again about 70 million years ago during another uplift. This uplift known as the Laramide Orogeny tilted the sedimentary formations in Garden of the Gods to their current angles. After millions of more years of uplift and erosion, the rock formations of Garden of the Gods came to their present position. Wind, rain and atmospheric conditions continue to shape Garden of the Gods.
Siamese Twins
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70 million years ago, the Siamese Twins would have been trapped in the freshly formed Fountain Formation. Eventually, the softer rocks around the Siamese Twins were weathered away leaving the Twins as one connected rock. More weathering had to occur to create the arch the Siamese Twins form today. Wind carries particles away from the rock. In addition to wind, rainwater dissolves the small amounts of hematite which bonds the sandstone together, and after millions of years the Twins were weathered enough to create the two columns and arch they are today.
The Siamese Twins are an arkose which is a type of sandstone that contains more than 25% feldspar. The Twins are mostly composed of potassium-feldspar (pink) and quartz (white) grains. These grains came from the Pikes Peak Granite which was eroded and deposited as the Fountain Formation. The grains are cemented together by calcite, but the arkose is crumbly and not well cemented.
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Courtesy of United States Geological Survey |
The Siamese Twins are still connected but close examination reveals a crack in the arch in which weathering is slowly accomplishing its work of destruction. In the future, continuous weathering will cause each column to stand independent.
History in a 1/2 mm
The roundness and size of the particles is a result of the speed of the water in which the particle was deposited in. Particles deposited in slow moving water tend to be large and rough while particles deposited in fast moving water are small and smooth.
Logging Requirement:
Use the reading and your on-site observations to help you answer the following questions. Send the answers to me via my geocaching.com profile within a reasonable amount of time of logging your find.
- What mineral gives the Siamese Twins formation its color? What does this say about the original rock that was eroded and deposited as the Fountain Formation?
- What geologic component do you think caused the Twins look so similar?
- What does the slow weathering of the arch say about the amount of precipitation in the park?
- Based on your answer to the previous question, what agent of weathering (water, wind, ice, plants, etc.) primarily shapes the Siamese Twins?
- Measure two different size particles that have been weathered from the rock around the Siamese Twins. Which particle was deposited in faster moving water? Which one was deposited in slower moving water?
Pictures are most welcome!
Information provided by the following sources was used in the listing:
- Geological Survey Bulletin 707 by Albert B. Fall and George O. Smith
- Important Events in Garden of the Gods Geology by City of Colorado Springs
- The Fountain Formation by Dick Gibson
FTF goes to OF-Erad and k9Jayhawk!
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