Cataclasites in a fault zone exposed in a bedrock quarry near San Marcial, New Mexico, suggest multiple modes of deformation in interlayered sedimentary and volcanic rocks
— Kevin M. Hobbs

In the southernmost outcrop of pre-Quaternary rock in the Chupadera Mountains, Socorro County, New Mexico, a down-to the- south normal fault is exposed in a bedrock quarry just east of New Mexico State Road 1. Physical characteristics of this fault zone grant insight into timing and methods of faulting in a Rio Grande rift sub-basin that contains few fault outcrops. This quarry exposes silty sandstones of the Spears Group and the Andesite of Willow Springs, which are of similar upper Eocene age. The east wall of the quarry exposes the fault, where both the hanging and foot walls comprise andesite in a ~20 m wide fault zone around a 1.5 m wide fault core. Outcrop geometry suggests that the Spears Group sedimentary rocks are no more than ~10 m below the fault outcrop. Nearly all fractures in the fault zone are filled with cataclasized sedimentary rock showing physical and mineralogical similarities to the sedimentary rocks of the Spears Group. Cataclasites at the study site contain clasts with a smaller average diameter than the nearby Spears Group sediments, and microtextural observations suggest grain-to-grain comminution during faulting likely caused quartz spalling. Other features in the fault zone include zones of oxide clast concentration within cataclasites and post-faulting calcite vein mineralization.