Craig Cotten named to lead Colorado Division of Water Resources Division 3

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From the Valley Courier (Ruth Heide): “Cotten began serving as acting division engineer after Michael Sullivan moved into the deputy state engineer position last fall. A graduate of Monte Vista High School, Cotten earned a civil engineering degree from Colorado State University in 1990 and returned to the Valley to work for the Division of Water Resources. He had previously served a summer internship with the office. ‘I was able to get hired back on after graduating and have been here ever since,’ he said. Cotten initially served as a hydrographer, measuring stream and ditch flows. He then became lead hydrographer and served in that role until becoming assistant division engineer about two and a half years ago.”

Meanwhile the project to map the San Luis Valley’s geology moves on. Here’s a report from Ruth Heide writing for the Valley Courier:

“We are in the Rio Grande Rift,” [U.S. Geological Survey (USGS) Geophysicist Dr. V.J.S. (Tien) Grauch] explained to Rio Grande Roundtable meeting attendees in Alamosa on Tuesday. “This is why there’s a basin here.” Grauch explained that at one time there was a large body of water (Lake Alamosa) in the basin basically lying between the modern-day towns of Monte Vista and La Jara on the west and the sand dunes and the town of Blanca on the east. Grauch explained that if the fill in this basin were removed, it would look like a deep hole. The Baca Graben is the deep part of the hole, and the dunes are located to the side of that hole. At its deepest point, the Baca Graben is 23,000 feet deep, Grauch said. Using various measurement methods including airborne magnetic surveys conducted from low-flying helicopters over the dunes, experts were able to detect a signal and subsequently map out a fault line running parallel to a known fault line called the Range Front Fault near the edge of the Sangre de Cristo Mountains.

The north/south road to the sand dunes on the surface essentially follows this underground anomaly, Grauch explained. The parallel fault extends northward to where Medano Creek comes out of the mountains “and we lose the signal,” Grauch said. What geophysicists were able to determine about this fault, Grauch said, were: it is about 200 feet deep; it is at least the same thickness as it is deep; and it is more magnetic on the east side than on the west side. Grauch said the hypothesis she is leaning toward is that the parallel fault abuts a thick clay layer. “Where that thick clay ends on the east side it’s abruptly ending against a fault,” she said.

As the USGS team looked under the dunes via its aeromagnetic surveys it mapped other fault trends intersecting the dunes area in northeast/southwest patterns. Grauch said some of those faults coincided with drainages either past or present such as Big Spring Creek.

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