Folds are among the most spectacular products of crustal deformation. They form in response to external stresses, generally related to the horizontal movement of tectonic plates (similarly to the folds that form in a carpet). Arid environments often allow for an easy recognition of these large scale structure, due to the absence of vegetation. However, folds similar to the one shown below are found in all mountain belts, Western Alps included. Unfortunately, the presence of vegetation and/or the absence of clear markers, such as colour changes or sedimentary layering, make the recognition of such folds from landscape observations more difficult. Techniques from structural geology, a sub-field of geology, can help reconstructing such complex geometries from field observations

Other stunning examples of large folds can be seen on the following sites:

http://www.iblogyou.fr/Photos/maxi/maxi_18106.jpg

http://ic.ucsc.edu/~casey/eart150/Lectures/Folds/Fig10_1.jpg