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An unusually straight valley, sometimes localized along weakened rock in a fault zone. Its alignment can suggest a fault trace, but erosion along bedding or other structural weaknesses can produce similar forms.

Within a shallow fault zone undergoing brittle fracture, repeated sliding crushes and grinds grains. Expect fault gouge, potentially rich in fine clay minerals, and coarser angular fault breccia; a cohesive, cemented crushed rock is a cataclasite. Slickensides or displaced grains can record the sliding direction.

An opening geological joint need not contain any fault rock: it may be an open crack. If fluids circulated, it can contain a mineral vein, for example calcite or quartz, grown from the fracture walls. Thus comminuted fault rock supports shear, while open space or a crack-filling mineral vein supports opening. Mineral filling is conditional on fluid chemistry and timing; its precise composition cannot be inferred from the photograph.

A displaced drainage forms when repeated horizontal fault slip offsets a channel and its upstream and downstream reaches no longer line up. In plan view, draw two initially continuous channel reaches crossing the fault, translate one side parallel to the fault strike, and connect the reaches by a short fault-parallel reach. A linear valley develops where erosion follows damaged rock along a straight fault zone.

In Attachment A, use the oblique, relatively straight valley running southwest–northeast through the lower centre towards the upper right. For an identifiable example, follow the central approximately north–south drainage to its bend near the southern edge of the central basin, about $(u,v)=(0.46,0.67)$, where $u$ is fraction from the left image edge and $v$ fraction from the top. Mark its deflected reach and the adjacent straight valley. The positional precision is at the level of the supplied image; establishing a numerical fault offset would require correlated piercing points and field checks.