The photograph at left shows two nearly-vertical pegmatite dikes in the roadcut. Another pegmatite intrusion east of highway. Pegmatites are igneous intrusive rocks containing extremely coarse-grained crystals. They commonly form dikes. The reason for large crystal size in pegmatites probably has to do with the presence of water in the magma from which they formed.
Water allows ions in the magma to be extremely mobile and to form crystals quickly.
Thus, even though a pegmatite may cool relatively rapidly, water allows crystals to grow much larger than would be otherwise possible. 5.4 Beecher Rock - east of road. This rock is a sill , a slab-shaped igneous intrusion. The red color is due to oxidation of minerals containing iron. Beecher Rock shows up as a silhouette on the skyline in this image.