Fold mountains form due to powerful compressional forces bending and crumpling rocks underground. These forces cause the formation of anticlines, where rocks fold upwards, and synclines, where rocks fold downwards. Many young fold mountains are found along plate boundaries where compressional forces from colliding plates cause massive folding of rocks. Examples of fold mountains formed this way include the Himalayas, the Rockies, and the Andes. Folding occurs in stages from symmetrical to asymmetrical folds and eventually to overfolds and overthrusts as the compressional forces increase.