Oil is often stored in anticlines, while groundwater is more often stored in synclines.
Tips
memory
向斜 'concave-down fold' pairs with 背斜 (bèixié, anticline, 'concave-up fold'). Memory hook: 背 = 'back' arches up like a person's back, so 背斜 arches up; 向斜 dips down like a bowl facing up. Anticlines trap oil; synclines trap water.
