I-70 and Glenwood Canyon, Colorado

Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
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The Colorado River along I-70 in Colorado is something of a coming attraction for the Grand Canyon. Like in the Grand Canyon, a crustal upwarp across the river caused the river to incise a canyon. The upwarp is broader and gentler than the Grand Canyon, but the section extends from Precambrian to early Tertiary. In the middle of the uplift, Glenwood Canyon cuts into Precambrian basement and the Precambrian-Paleozoic contact is exposed. Young volcanic rocks on top of the plateau on either side of the canyon imply that downcutting took place in the last couple of million years.

I first drove Glenwood Canyon on New Year's Day, 1982. It was one of the few remaining stretches on the Interstate system that was not a freeway. It was a conventional two-lane road in a narrow canyon. I have no pictures for the simple reason there were no safe places even to pull off the road. I wondered if this route could ever be made into an Interstate highway.

I drove the route again in 1999. Not only was the route a freeway, the engineering can only be described as brilliant. To minimize impact in the narrowest parts of the canyon, one highway deck rests atop a vertical ribbon, and in many places the two decks overlap one another. This highway has won numerous awards, and deservedly so.

Cretaceous and Tertiary rocks east of Grand Junction.

Approaching the Canyon

Above: the Colorado River canyonBelow: Dipping layers on the west flank of the uplift.

Glenwood Canyon

Left: the westbound deck, rather than being incised into the slope, rides on a vertical wall.
Above: The Colorado River
On the left the oncoming lanes are elevated aton a longitudinal spine and overlap the median. In the cliffs in the distance, the massive Precambrian granitic rocks are overlain by Paleozoic sedimentary rocks. The contact is about 3/4 of the way up the cliff.
Here the unconformity is about halfway up the cliffs.
These jointed Paleozoic sedimentary rocks turn up in a fair number of textbooks, though finding a safe place to photograph them is a challenge (note the foreground motion blurring).
Here we see how the highway is mostly elevated and supported on pillars rather than cutting deeply into the canyon walls.

Below: in one place the road tunnels through the cliffs.

The Great Unconformity

Left and below: the Precambrian-Paleozoic contact. In most cases it is marked by a prominent band of trees.
In the stratigraphically deepest part of the canyon, the entire canyon visible from the highway is in Precambrian granitic rocks.

Engineering the Highway

Left and below: a rest stop in he canyon provides access to a walkway along the river and a chance to observe the highway engineering in safety.
Above: the two decks of the highway.

Left: The lower deck is on pillars to minimize impact on the land. The upper deck is supported by a wall and in places extends over the lower deck.

Above: Tourists

Left: Raft tour

Below: Red beds east of the canyon, probably Pennsylvanian or Permian age.

Lighting in the canyon can be challenging. The foreground is in deep shadow but the distant cliffs and elevated highway are sunlit.


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Created 15 January 2005, Last Update 01 July 2012

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