DEATH ZONES 4 & 5: As you move up towards the topmost layer of the digsite, the next layers we find are the Isolated Bones Unit and the Mixed Lithology Unit.
Isolated Bones Unit. The thick layer of Death Zone #4, which is immediately above the Semi-Articulation/Isolated Bone Unit, is relatively barren of dinosaur bones and devoid of plant material.
It appears that this was a time of semi-arid conditions, with mostly wind-blown sedimentation or minor water-related events. Dinosaurs were most likely not present in the area during this time or were migrating through to find sources of water and food. The image shows an isolated scapula and coracoid.
Mixed Lithology Unit. The stratigraphy of this next layer up (Death Zone #5) is complex, with multiple alternating cycles of sedimentation occurring in both humid and semi-arid environments. Evidence of fairly rapid deposition included the discovery of a very large, complete, articulated, Stegosaurus pelvic section that is enclosed by a series of multiple, sedimentologically different layers in which the stratigraphic sequence repeats over and over.
Also within this unit, away from the main fluvial systems, there appear to be areas in which dinosaurs were possibly trapped in muddy ponds or bogs – as evidenced by Stegosaurus Sarah - or were dragged and scavenged prior to burial.
Scattered Bone Unit. The topmost layer -- indicated by the blue 'X' -- is not considered a death zone as it has yielded only isolated bones. Possibly a reworked section of the lower Mixed Lithology Unit, this layer may be one where previously deposited sediment was gouged into, transported and redeposited during flooding events. It contains very infrequent, partial or broken dinosaur bone remains - often poorly preserved.
Isolated Bones Unit. The thick layer of Death Zone #4, which is immediately above the Semi-Articulation/Isolated Bone Unit, is relatively barren of dinosaur bones and devoid of plant material.
Mixed Lithology Unit. The stratigraphy of this next layer up (Death Zone #5) is complex, with multiple alternating cycles of sedimentation occurring in both humid and semi-arid environments. Evidence of fairly rapid deposition included the discovery of a very large, complete, articulated, 
Scattered Bone Unit. The topmost layer -- indicated by the blue 'X' -- is not considered a death zone as it has yielded only isolated bones. Possibly a reworked section of the lower Mixed Lithology Unit, this layer may be one where previously deposited sediment was gouged into, transported and redeposited during flooding events. It contains very infrequent, partial or broken dinosaur bone remains - often poorly preserved.
