When continental plates collide. Mountain building is also known as orogeny, and it refers to the process of forming mountains. When two continental plates collide, the crust of the Earth is thickened and folded, causing the land to rise and form mountains. This process can take millions of years, and the resulting mountains can be hundreds of miles long and several miles high. Examples of mountain ranges formed by continental collisions include the Himalayas, the Andes, and the Alps.