OTR Field Trip – September 15, 2012

Title: Bike Tour of the Geology of Glenwood Canyon, Garfield and Eagle counties, CO

Leader: Johnathan L. White, Colorado Geological Survey

Description:  Published in the August 2012 Outcrop

Introduction
This fall marks the 20-year anniversary of the official grand opening  of the Glenwood Canyon Interstate 70 Project when both eastbound and westbound lanes were opened. Final completion of rest areas and miscellaneous work was completed in 1994. Included in the project was the construction of a bike/pedestrian path  on the north bank of the Colorado River that parallels the Interstate.

The Colorado River formed Glenwood Canyon by incision into the southern flank of the Laramide White River uplift that rises towards the northwest onto the Flat Tops. While some Neogene incision occurred, much of the downcutting occurred during Quaternary glacial periods such that, at the close of the Pleistocene, the canyon was cut over 3,000 vertical feet below the rim. Thousands of vertical feet of downcutting have developed magnificent exposures of the entire Early to Middle Paleoglenwoodzoic stratigraphic section of Central Colorado along the canyon walls. Sedimentary formations exposed include the Mississippian Leadville Limestone, the Upper Devonian Chaffee Group, the Lower Ordovician Manitou Formation, the Upper Cambrian Dotsero Formation and, most visually pronounced, the nonconformity where the 500-foot thick cliffs of Upper Cambrian Sawatch Quartzite overlie Precambrian metamorphic and granitic basement rock (Fig. 1).

Bike Tour
The bike path is approximately 16 miles long from the Glenwood Spring Hot Spring Pool to the east trailhead at the entrance to the canyon. The rise is gradual, beginning at 5,750 feet at the mouth of the canyon in Glenwood Springs and rising to 6,160 feet to the canyon entrance, about 400 feet in elevation change. The actual tour will be a round-trip ride of 32 miles with a lunch break at the Hanging Lake Rest Area.

The bike tour will include many stops where we will discuss the geologic history of the canyon, the rocks exposed, geologic structure, as well as the geologic complexity of Holocene surficial deposits in the canyon that required extensive geological and geotechnical investigations to design and construct the highway. From the engineering challenges, the need to address sensitive environmental concerns, and the construction effort put into this impressive civil highway project, the Interstate 70 Glenwood Canyon Project won several national and international awards in construction and engineering excellence.

For those participants who do not want to bike the entire round-trip length, there are several options if one wishes to park a second vehicle as a shuttle. Parking is available at the Grizzly Creek Rest Area (5 miles), the Hanging Lake Rest Area (10 miles), the Bair Ranch Rest Area (13 miles), or the east trailhead parking lot at the canyon entrance (16 miles). The east trailhead is accessible by a frontage road from Dotsero at Exit 133 on Interstate 70. The trail to Hanging Lake is another option. This 1.2-mile narrow trail is steep and considered a more difficult trail by the USFS as it rises over 1,000 feet in elevation from the bike path into Dead Horse Canyon.

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