Synclinory
A synclinory or syncline is a large-scale geological structure in the form of an indentation. The two wings of the structure fall towards each other, as the word implies.
A synclinorium usually consists of a series of individual folds that join together to form a tub-shaped structure.
The counterpart to a synclinorium is an anticlinorium in the form of a curve in which the wings "fall away from each other".