What would indicate the direction an anticline is plunging?

• A. Outcrop widening toward the hinge
• B. Closure of beds at the plunging end
• C. Dip direction perpendicular to the fold axis
• D. Uniform bed thickness around the anticline

Answer: (B)

Plunging folds show a downward tilt of the hinge line, so the way to tell where the fold is plunging is to look for where the beds pinch together and end—the closure of the beds at the end where the axis descends. As the hinge line slopes, the limbs wrap toward that end and the outcrop pattern narrows to a tip, indicating the plunge direction.

Widening of outcrop toward the hinge isn’t a reliable cue for plunge, because it reflects the fold’s overall position rather than the direction the hinge is dipping. The dip direction of the beds, while related to folding, isn’t by itself the indicator of plunge. And uniform bed thickness around the anticline doesn’t reveal which way the hinge is plunging. The key tell is the beds closure at the plunging end.