Glacial Till

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 http://www.nps.gov/romo/planyourvisit/feesandreservations.htm 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: http://www.nps.gov/romo/planyourvisit/road_conditions.htm. 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.

Glacial till refers to the unsorted rock and soils that are deposited from glacial ice. In this three-part EarthCache, the first two stops will be introductions to glacial tills which were dropped from glaciers of the Pinedale and Bull Lake ages of glaciation. Based on what you have learned from these two stops, you will need to identify which age of glaciation was responsible for the till at the third stop.

Glaciation in the Front Range of the Rocky Mountains has been broken into roughly three time “ages”: the pre-Bull Lake age of the middle & lower Pleistocene (beginning about 1.2 million years ago), the Bull Lake age of the upper & middle Pleistocene (lasting from about 120,000 - 300,000 years ago), and the Pinedale age of the upper Pleistocene (lasting from about 10,000 – 30,000 years ago).

N 40 19.131 W 105 38.519 Stop 1: Pinedale Glaciation

To begin your tour, you are standing on the crest of the Bierstadt Moraine, a moraine from the Pinedale Glaciation. Note that the crest is rather pronounced and sharp. Till of the Pinedale Glaciation is distinguished from the till of earlier ages by consisting of larger boulders with sharper edges and less weathering. Many individual boulders can be seen on top of the ground, and these boulders may retain some of the polish and striations which were formed during their movement. Soils tend to be thin and less well-developed, and will support fewer species of plants.

N 40 19.454 W 105 38.155 Stop 2: Bull Lake Glaciation

While walking to the second stop, you will have been walking through till of the Bull Lake Glaciation. Note that in comparison with the till of the Pinedale Glaciation, these sediments have undergone much more weathering. The boulders have been broken down more and are lower to the ground. There are fewer large stand-alone boulders. Soils are more developed, and not only are there more species of plants than there were at Stop 1, but the ground cover from vegetation is greater as well.

N 40 19.618 W 105 37.669 Stop 3: Pinedale, or Bull Lake??

Examine the area at Stop 3. Which of the previous two stops does it most closely resemble? Does the till consist of lots of large boulders sitting on top of the ground, or have the boulders been weathered? Without digging in the area, does the soil seem to be well developed, or sparse? What does the ground cover look like? Use all these clues, and others not mentioned above, to identify which age of glaciation you believe was responsible for the till at this location.

To log this EarthCache, send me an email with the answers to the following question:

1.) Which age of glaciation is responsible for the till at Stop 3? Give me the reasons for your decision in your own words.

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.

KellererLynn, K. 2004. Rocky Mountain National Park. Geologic Resource Evaluation Report. NPS D307, September 2004. Online at: http://www.nps.gov/romo/parkmgmt/upload/romo_geo_overview.pdf

Rocky Mountain National Park. Online at: http://www.nps.gov/romo

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!