(Map site 16.) The Watt fault follows the yellow line at the bottom of the photo. To the left of the fault is the Plio-Pleistocene Saugus Formation and to the right is quartz diorite. The fault moved and juxtaposed the two rock units after deposition of the Saugus Formation. Erosion removed the overlying rocks down to the level of the nearly horizontal yellow line. Alluvial river deposits covered this unconformity surface as described in photos 4 and 12. Most of these alluvial deposits have since been removed by erosion following uplift of the San Gabriel Mountains, leaving only those shown here along the road. Note that the Watt fault cannot have moved since deposition of the alluvial deposits.