Rocky X


October 1, 2008

The birth of a quarry and the adoption of a gneiss little rock.

by Bill Langer

Recent Carved in Stone articles have described a variety of geologic aspects in the life of Rocky, a 1.8-billion-year-old grey and pink gneiss (pronounced like the word ‘nice’) that I rescued from a quarry near Morrison, Colo. This article describes the events leading up to the birth of that quarry.

Imagine a pleasant summer day on the plains near Morrison, Colo. Mammoths and camels are grazing on the prairie grass amongst the pine trees. In the nearby Rocky Mountains, glaciers are slowly melting away. It is 16,000 years ago, near the end of the Ice Age. For much of the previous 1.8 million years, nearly all the higher elevations of the Rocky Mountains of Colorado were covered with glaciers that waxed and waned, gouging out cirques and eroding U-shaped valleys. Massive floods of glacial melt-water loaded with sediment washed down mountain rivers onto the adjacent plains.

When the gravel-laden rivers reached the plains, they eroded wide valleys into the soft bedrock. The gravels that had been the implements of erosion eventually filled the bottoms of the valleys. As the geologic clock ticked on, more gravel filled the valleys, some from the mountain glaciers and some from more recent erosion.

Fast forward to the 1700s. On the plains, the confluence of the South Platte and Clear Creek was a favorite gathering place for indigenous tribes, including the Apache, Pawnee, and Comanche. The Arapahoe and Southern Cheyenne replaced these tribes in the 1800s as settlement pushed eastern tribes west. During 1858, the discovery of gold in nearby stream sediments precipitated the Gold Rush. Denver was founded that same year.

Denver grew rapidly, and the sand and gravel underlying the valleys of the South Platte and Clear Creek (streams with their headwaters in the glaciated Rocky Mountains) soon became Denver’s source of aggregates. Home building boomed following World War II. Interstates crossed the city by the mid 1960s. During that same period, record flooding and the need for water storage in the area stimulated aggressive dam-building programs.

This massive construction created an unprecedented demand for aggregate. Ironically, the development that created this demand encroached on these resources, seriously complicating aggregate production. In 1957, the Colorado Sand and Gravel Producers Association (CSGPA) predicted complete depletion of sand and gravel reserves near Denver by 1977.

In 1971, Jim Cooley elaborated on the problem at the 74th National Western Mining Conference and pointed out that the dire predictions of the CSGPA were right on track. Jim also announced that his company was developing a granite quarry near Morrison, Colo., stating that “in this case…stone appears to have an advantage over distant sand and gravel deposits.”

Cooley Gravel Co. operated three sand and gravel plants in the Denver area and complemented the excess sand production from those plants with stone from Morrison to supply the demand for the expanding building market. Two years after it began operating, Cooley Granite became one of the top three producing quarries in Colorado.

In 1996, Cooley Granite was acquired by the U.K. aggregates business CAMAS. That company evolved into Aggregate Industries, which was subsequently acquired by the Swiss-owned Holcim Ltd. in 2005.

And that quarry in Morrison is where I found Rocky.

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