The Goose Rock Conglomerate found within the boundary of the Sheep Rock unit is a portion of the Gable Creek Formation. This formation encompasses a wide swath of late cretaceous river deposits trending east-southeast. The conglomerate outcrop within John Day Fossil Beds, 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. Fossil wood and spores have been found in the formation within the park, but no other fossils to date. However, further down the geologic section there was a plesiosaur, a marine reptile, excavated from a similar unit of the Gable Creek Formation near Mitchell, Oregon. The overall formation portrays trends of high energy fluvial systems (river deposits) to marine alluvial fans (mudstones and siltstones).
Last updated: December 12, 2017