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This an earthcache with multiple stops. It will show the finder the significance of Boulder Creek to the city of Boulder, Colorado. Second stage at N 40° 00.633 W 105° 18.200. A possible midpoint of interest is N 40° 00.338 W 105° 24.399.
The primary water source for the city of Boulder, Colorado is Boulder Creek. The creek was named well ahead of the city's founding, for all of the large granite boulders that have cascaded into the creek over the eons. It is from Boulder Creek that Boulder City and hence Boulder is believed to have taken its name. Boulder Creek has significant water flow, derived primarily from snow melt and minor springs west of the city. The creek is a tributary of the South Platte River.
The oldest rocks in the Boulder area are Precambrian in age, and have been dated at about 1.7 billion years before present time (BP), as measured from the decay of radioactive elements. The Precambrian rocks consist of granitic and metamorphic rocks. The oldest Precambrian rocks in the Boulder area are metamorphic rocks, which means they were transformed by heat, pressure, and chemical reactions from older rocks into their present form. The Precambrian rocks were most likely originally laid down as sediments, such as sand and mud, in an ancient sea. These rocks were deeply buried beneath younger strata, and the metamorphic transformation occurred deep in the earth. The most common types of Precambrian metamorphic rocks west of Boulder are schist, gneiss, and quartzite and are found in the foothills and mountains west of the Boulder area.
On at least two occasions, mountains were formed from these rocks and they were uplifted by great forces from below. Hot molten magma was injected into the rocks, forming granitic rocks. The rocks have been uplifted and exposed to the surface by tectonic processes and erosion. The predominant Precambrian granitic rock in the Boulder Canyon area is the Boulder Creek granodiorite, and it makes up the walls of Boulder Canyon.
At the beginning of the Paleozoic Era, about 600 million years ago, ocean water gradually flooded across the old eroded surface of the Precambrian rocks. Sands were deposited along beaches, and lime mud was precipitated in the deeper waters of the ocean as it covered Colorado. The sands and lime mud were buried under great thicknesses of younger strata and were transformed into sandstone and limestone.
For most of the next 300 million years, a gentle pattern was repeated over most of Colorado, with intervals of gradual flooding by the sea and deposition of sediments, followed by slight uplifts and erosion. None of the rocks deposited during this time period are found near Boulder; they were either not deposited because the land was slightly above sea level, or they have since been eroded away.
During the early part of the Pennsylvanian Period, about 300 million years ago, two mountain ranges were pushed up in central and western Colorado. These ranges are known as the Ancestral Rockies. This event pushed Precambrian rocks well above the land surface and exposed them to weathering. Erosion cut into these rocks and carried floods of loose debris away to the east and west. This debris was deposited as a mixture of coarse and fine fragments, forming the sandstones and shales that make up the Fountain Formation. The Fountain Formation has a deep red color because of oxidation of iron in the minerals, and contains well-developed layering or bedding. The Formation was originally laid down flat, but was steeply tilted during fairly recent mountain forming. The Flatirons, directly west of Boulder, where Boulder Creek flows, is composed of Fountain Formation.
It is here at the beginning of this earthcache journey that you see these mountainous beginnings.
Boulder is an attraction for tourists and a geological feature close to Boulder is visited by many each year: Boulder Falls, located at N 40° 00.338 W 105° 24.399. This would make a nice rest stop, and interesting on your way between the start and end points.
During the present great interval of geologic time - the Quaternary Period -the Boulder area has seen erosional effects of glaciation. At least four times during the past million years or so, vast sheets of ice have moved southward out of the Arctic to cover much of Canada and the northern United States. There were many active glaciers in the mountains west of Boulder, but none of the glaciers seemed to have extended below the 8000 foot level of elevation, so there are no deposits of glacial debris near Boulder. Geologists recognize at least three distinct periods during which the mountain glaciers grew and gouged their way down the valleys from the continental divide. Floods of meltwater from the ice hastened the erosion. Glacial deposits and erosional features can be seen near the towns of Nederland and Eldora.
This lack of glacial action at the lower altitudes contributes to the fact that the contours of the land nearer Boulder are different than Nederland/Eldora. Near Boulder the land is flatter and mesas are in evidence.
To claim this earthcache, please email:
1) the altitudes of the starting and ending points mentioned above and your reasoning why the difference is important in the health of the Boulder area.
2) name the geological formations you see at each point
3) take and post with your log a picture of your group at each location
Additional Hints
(No hints available.)