When two huge blocks of the earth's crust slide past each other they can do a lot of damage. One of the results of this motion is a process called cataclasis or grain size reduction where the individual mineral grains of the rocks on either side of the fault get ground up.
The following thin sections are taken from samples along a transect perpendicular to the San Gabriel Fault at Locality 8B. They illustrate how the amount of grain size reduction is inversely proportional to the distance from the fault. (ie: the closer you get to the fault itself, the more ground up the grains). Take the quiz to see if you can put them in order!
Click Here to give up and see the images in order as well as zoomed-in views and more information.