Fracturing along the Grand Hogback, Garfield County, Colorado
— C. H. Garrett and J. C. Lorenz

Fractures in steeply dipping strata of the Mesaverde Group along the Grand Hogback, northwestern Colorado, were previously interpreted to be either entirely of pre-uplift origin, or entirely caused by stresses created during folding and uplift. However, based on fracture characteristics measured at 32 locations along the Grand Hogback, we suggest that only the major fracture set formed prior to uplift, and corresponds to subsurface fractures in nearby flat-lying reservoirs. These are the oldest fractures which developed in the Mesaverde Group and lower Wasatch Formation as a set of west-northwest-trending, throughgoing, regional fractures in response to horizontal compression. Secondary sets of crosscutting fractures post-date the westnorthwest fracture set and can be related to local stresses caused by structural deformation and exposure of strata along the Grand Hogback. These crosscutting fractures resulted from several different mechanisms: (1) fractures that formed in response to cross-sectional folding, (2) fractures that formed in response to planar folding and (3) relaxation fractures. Crosscutting fractures are rare in flat-lying strata in the subsurface.