Andrews Tarn EarthCache
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Rocky Mountain National Park is located west of Estes Park and north and east of Grand Lake. This is a fee area of the National Park Service, and costs $30 per vehicle. This fee is covered in the Rocky Mountain National Park Annual Pass, the Rocky Mountain National Park/Arapaho National Recreation Area Annual Pass, and the America the Beautiful Pass. Please see the following website (visit link) for the entire fee schedule. The park is open 24 hours a day, 365 days a year. Road and Trail Conditions and Closures can be found at: (visit link) Recorded information for the condition of Trail Ridge Road can be found by calling (970) 586-1222. Please remember that all geologic features within the borders of Rocky Mountain National Park are protected by law, as are all natural and historic features. Please do not disturb, damage, or remove any rocks, plants, or animals.
Parking is at the Glacier Gorge Trailhead and the hike is up a well-marked trail. The trailhead parking area is often filled in the summer months, and shuttle bus transportation is available at the Bear Lake shuttle bus parking area. Prepare for a strenuous hike. Your one-way journey will be about 5.2 miles with an elevational change of 2,200’. The starting elevation is approximately 9250’, so bring sunscreen for the bright sun and extra water for the dry air. Afternoon thunderstorms are always possible in the summer months so plan accordingly.
The given coordinates will lead you to the eastern end of Andrews Tarn, the lake formed by Andrews Glacier. A tarn is a lake that occupies the erosional basin of a cirque. In the case of Andrews Glacier, the present form of the cirque was carved out during the Pinedale Glaciation, which occurred from about 10,000 to 30,000 years ago. The primary period of Pinedale Glaciation within the Park lasted from about 18,000 to 20,000 years ago.
At the end of the Pinedale Glaciation, a warming trend began during which the remains of the Pleistocene glaciers melted. When Neoglaciation (the “Little Ice Age”) began around 3,800 years ago, these cirques were again occupied, but with much smaller glaciers.
The rock on which you are standing is a recessional moraine formed at the mouth of the cirque. The moraine has formed a dam across the opening of the cirque, which keeps up the level of the tarn. Stream erosion has begun to cut through the moraine on the north side, and you can see the makeup of the moraine by looking at the glacial till within the cut.
To log this EarthCache, complete the following:
1.) Estimate (or measure with your GPS receiver) the east/west length of Andrews Tarn.
2.) Measure with your GPS receiver the length (east/west) and width (north/south) of the moraine which is acting to dam Andrews Tarn.
Please consider posting photos of yourself, or the local geology, when you log this EarthCache. Photos can be an additional rewarding part of your journey, but posting them is not a requirement for logging this EarthCache, and is strictly optional.
The above information was compiled from the following sources:
2004. Rocky Mountain National Park. In Harris, A.G. et al., editors. Geology of National Parks, Sixth Ed. P. 337-356. Dubuque, Iowa: Kendall/Hunt Publishing Company.
Cole, J.C., and Braddock, W.A. 2009. Geologic map of the Estes Park 30’ x 60’ quadrangle, north-central Colorado: U.S. Geological Survey Scientific Investigations Map 3039, 1 sheet, scale 1:100,000, 1 pamphlet, 56 p.
Colorado Geological Survey. 2003. Messages in Stone. Matthews et al., editors. Denver, Colorado.
Hopkins, R.L., and Hopkins, L.B. 2004. Hiking Colorado’s Geology. Seattle, Washington: The Mountaineers. 240 p.
KellererLynn, K. 2004. Rocky Mountain National Park. Geologic Resource Evaluation Report. NPS D307, September 2004. Online at: (visit link)
Rocky Mountain National Park. Online at: (visit link)
Rocky Mountain National Park was most helpful in the background discussion, aid in the choosing of sites, and review of this EarthCache. My thanks to the Park for allowing the placement of this EarthCache!
Additional Hints
(No hints available.)