Field School, Day 7 (7/12/03) - Paint Mines in Calhan, Colorado
We began Day #7 with a morning lecture by Bob Raynolds. He discussed the multi-disciplined Denver Basin project and the fact that it's also important to present-day issues facing the Front Range. A major part of Bob's work is in researching the aquifers of the Denver Basin. The significant aquifers hold ancient water and do not get replenished from surface water. Therefore, they are limited resources and when they are gone, they're gone. Due to accelerated development throughout the Denver Basin, and most notably Highlands Ranch, the water level in the Arapahoe aquifer is falling at a rate of 10 meters/year, or about 1" per day. This could be a serious problem for communities who rely heavily (or solely) on aquifer water like many areas south of Denver. The aquifers aren't like a big underground bucket of water. The water permeates the rock. When wells are drilled into the aquifer, water is easily removed - first from the most porous rock. As water levels continue to fall, it will become harder and more expensive to extract the water. This known fact will translate into higher water bills for the dependent communities. Eventually, it will be too costly to extract water from the aquifers and other sources such as pipelines or trucks may be the cheaper alternative.We traveled to Calhan to the beautiful paint mines. The history of the name comes from the fact that Native Americans once used the colorful soils of the area to make paint for their horses, faces and tools. The land was recently purchased by the county (with funding assistance from others) and will soon be a county park. The colorful soils of the surrounding region have been mined for decades and used in bricks in buildings of downtown Denver and Coors Field.
Geologically, the Calhan Paint Mines are a great place to see the D1/D2 interface of the Denver Basin. It's also an excellent historical record of the paleosol. Generally, finding the paleosol in the Denver Basin is a tough assignment. It's occasionally revealed in construction project like the Castle Rock Outlet Stores. But, it's either paved over or vegetation quickly hides it once again. In contrast, the paleosol at the Calhan Paint Mines has been protected and preserved by the sandstone deposits of an ancient river. The thick white sandstone of the ancient river provides a caprock over the paleosol to limit erosion (see picture above). The important sites at the paint mines also include: a conifer swamp below the paleosol of the same age as the Castle Rock fossil rainforest; and two Eocene plant localities above the paleosol.
We diagrammed the geologic features in two different locations in the paint mines. During this effort, we discussed important features which should always be in a geologic drawing such as: north indicator, height/width estimates of drawn area; stratigraphic composition labels, paleocurrent flow directions, GPS readings if possible, etc. After the first drawing, we all laid our books on the ground for comparison (see left). Kirk Johnson and Bob Raynolds pointed out differences and important features in the field drawings.
It's impossible to describe the geologic beauty of the area in words. Please see the pictures from Day 7 (link below).