6.4 Mount Diablo Thrust Fault. From this point to the Junction Office, you will be driving in Franciscan melange, where large blocks of typical Franciscan rocks are exposed along the side of the road. Red radiolarian cherts, along with lesser amounts of shale and graywacke are also exposed. For the next 1.6 miles you will be traveling over Upper Cretaceous Great Valley sedimentary rocks made up mostly of shale with some sandstone beds. The topography consists of low rounded hills cut by the Little Pine Creek running parallel to the road.
Beds dip steeply to the southwest.
1.6 Enter park at this point. Continue traveling on Upper Cretaceous rocks. As you turn left and then right crossing a stream gully, you will notice gray-green rocks along the left side of the road cut just before you cross over the gully. The fault plane dips down and to the north. A prominent outcrop of red chert.