The lower portion of the Upper Shale Member is exposed in outcrop and lateral continuity of sandstone beds ranges from several feet to several hundred feet. The middle to upper portions of the Upper Shale Member are not exposed in outcrop, however, on borehole images the lithology is composed of very fine-grained sandstone and siltstone. Facies Da deposits separate sheet sandstones of Facies A and are incised by Facies B channel-fill sandstones. This facies type consists mainly of undisturbed laminated mudstone with lesser amounts of siltstone, thin bentonite layers and occasional sandstone stringers. These beds are interpreted to be relatively unburrowed suspension deposits.
Sandstones appear to be graded and occasionally ripple-laminated in outcrop and on borehole images.
This facies type is interpreted to represent late stage spill events associated with the filling of underlying channels. Facies Dc separates sandstone beds of Facies C and consists of laminated siltstone and mudstone with thin sandstone stringers. On borehole images this facies type appears to have a high siltstone and very fine-grained sandstone content with lesser amounts of mudstone and shale. The lithologic and sedimentologic differences between fine-grained deposits of Facies D may be good indicators of the lateral continuity of associated sandstones. While Facies Da deposits are background sediments and are not necessarily good indicators of continuity of related sandstones, Facies Db sediments are found only on top of channelized deposits and indicate that underlying sandstones were deposited in a confined environment.