ABSTRACT
The Colorado River originates in northern Colorado and flows through portions of Utah and northern Arizona before entering the Grand Canyon. This chapter describes the relationships of sedimentary rocks of different types. The field of study that deals with such relationships is called stratigraphy. The chapter provides some examples from the Colorado Plateau Region, especially the area near the border between Arizona and Utah, because the region contains much well-exposed rock. It focuses on sedimentary rocks younger than Precambrian age, because many Precambrian rocks are igneous and metamorphic. The sedimentary rocks of the approximately 1-mile-deep Grand Canyon represent 260 million years of Earth history, averaging out to about 0.01 millimeter of rock per year. The field of stratigraphy involves the study of rock layers. Some principles of stratigraphy can be applied to volcanic or metamorphic rocks, but usually when geologists mention stratigraphy they are thinking of sedimentary rocks only.
