Gable Creek Formation
The Goose Rock Conglomerate (GRC) found within the boundary of the Sheep Rock unit is a portion of the Gable Creek formation (GCF). The GCF encompasses a wide swath of late cretaceous river deposits trending East-Southeast. The conglomerate outcrop in the monument, with its well-rounded river rocks stuck in a sand stone matrix, would have been near the mouth of a large river and looked similar to a modern delta, like the Nile delta in Egypt. Though there haven’t been any dinosaur fossils found in the park from this formation, further down the geologic section there was a plesiosaur excavated from a similar unit of the GCF. The overall Gable Creek Formation portrays trends of high energy fluvial systems (river deposits) to marine alluvial fans (mudstones and siltstones).
Did You Know?
Some of the earliest rhino fossils in the world were found in the John Day beds. We call these the "running rhinos".