INTRODUCTION The mountains, plateaus, and deserts of central and eastern Utah present a display of Upper Cretaceous rocks which for completeness of exposure and clarity of stratigraphic record is possibly not excelled in North America. For nearly 200 miles along the Book Cliffs and over 75 miles along the eastern front of the Wasatch Plateau the entire Upper Cretaceous succession is exposed in barren cliffs and desert stretches almost without interruption, and westward into the High Plateaus and the eastern margin of the Great Basin the conditions of exposure are only slightly less favorable. This point is brought into emphatic relief at the very outset of this discussion because it is important to understand that the facts here presented, and especially those of lateral stratigraphic relationship are not subject to the reservation normal for a region in which any considerable part of the rock mass described is in any way obscured. These Upper Cretaceous rocks embody a group of sedimentary facies which, as regards range in environment, orderly development, and relation to regional diastrophism, present a remarkably clear and stimulating picture of regional stratigraphy. The facies range in variety from coarse rubble and associated heterogeneous sediments of the piedmont environment to fine muds of the offshore sea bottom. Between these two extremes a normal sequence of continental and marine environments is clearly represented in both vertical and horizontal succession, in a record eloquent of conditions shifting with the passage of time. Details as well as regional features of stratigraphy reveal