Luncheon – April 16, 2004

Title: Horsts and Grabens of Colorado’s High Plains
Author: Vince Matthews, Colorado Geological Survey, Denver, CO
Publication: The Outcrop, April 2004, p. 5

The prevalent view of Neogene deformation in the Great Plains contends that it is limited to gentle, eastward tilting during uplift of the southern Rocky Mountains. This deformation is commonly characterized as part of nothing more than a broad up-warping of the whole region. Faulting was thought to play only a minor role in the deformation, either within the mountains or the plains. However, experimental and theoretical rock mechanics suggest that deformation such as this should be accomplished by brittle, rather than ductile, deformation in the upper crust.

Documentation of brittle, Neogene and Quaternary deformation in the Colorado Rockies, on discrete faults with displacements of thousands of meters, raised the question of whether the accompanying deformation in the Great Plains was also accomplished by faulting. Several lines of evidence indicate that Neogene and Quaternary faulting are important deformational components in the Great Plains. Geomorphologic and geologic analysis of the High Plains reveals horst and graben structures occurring over large areas. These features have significance for groundwater, earthquake hazards, and hydrocarbon accumulation.