Abstract OBJECTIVES: The Lower Sego provides an opportunity to study well-exposed, high-frequency sequences and their systems tracts. Criteria for identification of sequence boundaries will be presented. Sequences and their boundaries will be contrasted with parasequences and their bounding surfaces. The Upper and Lower Sego contain well-exposed tidal deposits within the lowstand systems tracts of high-frequency sequences. These tidal deposits and their relationship to incised valleys and systems tracts will be examined. The incised valleys interpreted to form during relative falls in sea level will be contrasted with distributary channels related to autocyclic mechanisms. 0.0 Leave the parking lot of the Grand Junction Hilton, Grand Junction, Colorado. Turn left onto Horizon Drive. Pass under the 1-70 bridge. Turn left onto the entrance ramp for 1-70 west. 0.2 Enter 1-70 heading west toward the Colorado-Utah State line. For the next 20 miles the Interstate will parallel the Colorado River flowing along the west side of the Grand Valley. The Interstate is built on the gray Cretaceous Mancos Shale. To the west of the Colorado River are the red cliffs of the Colorado National Monument. The Monument is operated by the National Parks Service. These cliffs are the eastern edge of the Uncompahgre Uplift As you drive north along the Interstate, the steeply dipping eastern limb of the Uncompahgre is clearly visible. This tight monoclinal fold is the result of horizontal compressional tectonics associated with Laramide deformation (Heyman, 1983). The red rocks in the Monument include, from stratigraphically oldest to youngest: the Chinle Formation

Abstract The Lower Sego, Anchor Tongue of the Mancos Shale, and the Upper Sego are well exposed along the Book Cliffs in western Colorado and eastern Utah. For the most part these strata crop out on public lands and access is excellent due to the constantly maintained roads leading to the gas fields along the front of the cliffs. Nine sequences and their component systems tracts can be seen in these strata. Because of the high-quality exposure and access, the Lower and Upper Sego are excellent units to study the geometry and expression of sequence boundaries and the facies contained between these regionally extensive surfaces. This paper discusses the sequence stratigraphy of the Lower and Upper Sego between Prairie Canyon on the Colorado-Utah border and Sulphur Canyon in eastern Utah. The discussion includes criteria for recognizing sequence boundaries in outcrop, the geometry of incised valleys and the nature of their fill, and the facies of the transgressive and highstand systems tracts within the sequence.