Anticlines are A-shaped structures that develop during crustal deformation as the result of compression that accompanies orogenic mountain building.
(images at left - click to enlarge - top, schematic of an anticline; botttom, road cut exposure of anticlinal fold with syncline to right)
Anticlines are of particular interest to oil-exploration geologists because the Earth's largest oilfields occur in large, gentle anticlines in thick sedimentary rock sequences.
Click here for an image that shows an anticline with a hinge that has a flat top and two steep limbs, creating a box-like shape. Folds with this shape are called box folds. Both synclines and anticlines can be box folds.[links: images: formations: anticline; anticline and syncline near Calico Ghost Town, Yermo, California; anticline; Teton anticline; anticline; satellite: anticlines near Paradox, UT, and anticline crossed by transverse stream, and Uncompahgre uplift; plunging anticlines and synclines north of Moab, UT; plunging anticlines and synclines, Dinosaur National Monument, UT]