Lily Mountain Exfoliation Dome

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.

The aim of this EarthCache is to measure the change in elevation between your location on the path near the edge of Lily Lake, and the top of Lily Mountain, using only your GPS receiver. Parking is off of Colorado Highway 7 at the Lily Lake Trailhead at N 40 18.390 W 105 32.264. The loop around the lake is a fully accessible graveled trail, and makes for a pleasant hike at any time of year. Afternoon thunderstorms are possible in the summer months so plan accordingly.

Lily Mountain, at 9,786’, is composed of Silver Plume-type granite of the Longs Peak-St. Vrain Batholith. A batholith is an intrusion of igneous rock into the existing parent rock. In the case of the Longs Peak-St. Vrain Batholith, a pluton of magma approximately 30 miles x 35 miles rose through fractures and faults into the existing metamorphic gneiss and schist of the basement rock. The magma cooled slowly, forming large, coarse crystals of granite. This granite, a closely related form to Silver Plume granite, is slightly pink and was formed deep underground approximately 1.4 billion years ago.

Note the smooth, rounded curves near the top of Lily Mountain. Like Lumpy Ridge to the north of Estes Park, this mountain has been shaped by a form of weathering called exfoliation. At one time, the granite of Lily Mountain was deep underground, covered by thousands of feet of rock. Over time, the overlying gneiss and schist weathered and eroded, and the granite was exposed. Erosion of the overlying rock, and the accompanying reduction in pressure when this rock was removed, resulted in the fracturing and peeling of the granite. This peeling occurred parallel to the surface and has been described as resembling the peeling of the layers of an onion. Exfoliation results in a rounded mountaintop which is relatively “clean”, without many trees or other forms of vegetation.

To log this EarthCache, complete the following:

1.) Take the trail around Lily Lake to the site of the given coordinates. When you have reached this location, take an elevational reading with your GPS receiver and find the difference in elevation between your location and the top of Lily Mountain.

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.

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!