The Trail Member of the upper Cretaceous Ericson Sandstone, part of the Mesaverde Group, is exposed along hundreds of square kilometers through Wyoming along the flanks of several Laramide structural uplifts. This presents a unique opportunity to study the detailed architecture based on bed-scale heterogeneity and better assess the reservoir potential of these strata in outcrop exposure on a regional-scale, and to then relate these observations to producing fields nearby. The fluvial-dominated Trail Member formed as sediments traveled from the active Sevier thrust belt to the Cretaceous Interior Seaway, forming a basinward progradational clastic wedge along a relatively high gradient. The high energy, tectonically active setting led to preservation of sand-rich, often compositionally immature fluvial strata. Though there is an abundance of sand-rich strata in the Trail Member, production from this interval has been unpredictable in current and past fields such as the Trail Unit of southwestern Wyoming.Twelve detailed stratigraphic columns were described at three sites along the eastern flank of the Rock Springs Uplift to show facies heterogeneity beyond what is often available through wells, 69 hand samples were collected for determination of porosity and permeability, and photogrammetric characterization was performed at the three sites. Average porosity decreases along strike from north to south along with net-to-gross. The vertical changes in fluvial architecture within the Trail Member reflect changes in available accommodation. While thickness of the Trail Member is highly variable, ranging between 79 to 108 meters across the study area, there is an overall trend of thickening to the south. Although the character of the Trail strata changes appreciably along strike direction, this interval is consistently rich in sand, and grain size does not change drastically along the length of observed outcrops. This study demonstrated that spatial variability in the thickness, local accommodation, porosity, and net-to-gross of the Trail Member, as well as temporal variability in the amount and character of reservoir sands and channel stacking patterns play an important role in the unpredictability of this reservoir. This study will enable reservoir modeling and aid in future exploration projects within the Trail Member and other comparable systems with similar fluvial architecture and internal heterogeneity.



College and Department

Physical and Mathematical Sciences; Geological Sciences



Date Submitted


Document Type





Trail Member, Ericson Sandstone, Mesaverde Group, Wyoming, Laramide structural uplifts, Cretaceous Interior Seaway, Rock Springs Uplift, net-to-gross, temporal variability, reservoir modeling, fluvial architecture