April 27, 2003
G 203 Road Log
Start                North Plain's McDonalds Parking Lot
Mile 0              Left the parking lot to head west on Highway 26.  Then we headed north 
9:15am             on Highway 47, towards Vernonia.  We will be exploring some exotic
                        terrains that attached themselves to the North American Plate approximately 40 to 50 mya.  We will hopefully find some dentalia shells, which the Native Americans used as a sign of wealth. 
Mile 17.0        Highway 47  Keasey Formation
9:36am             This is a road cut that show an angular formation of the Keasey
                        Formation.  Keasey formation has been dated to the Eocene or the Oligocene Epochs of the Cenozoic Era, or 36 to 40mya.  The Keasey Formation is presented on an anti-cline, showing alternating thick layers of tuffaceous siltstone and smaller, 8-10 inches, of a basalt sill. 
Keasey Formation                                                                            Basalt Sill
The siltstone layers were showing "dimple" spots that are calcareous concretions.  This is one of the very common characteristics of the Keasey Formation.  They are product of weathering.  A particle of material becomes separated from the other material and is joined with other particles until it just falls out of the formation.
          Calcareous Concretions                                                         Layering of Keasey Formation
While we were at this stop, Sara found a gastropod fossil.  Gastropod means stomach/foot.  It lives in the last little chamber of the shell.  To feed, it turns its stomach inside out and pushes it outside the opening at the end of the shell.  This is the same opening in the shell that its foot extends from.  Therefore, it was thought that it moved by "walking" on its stomach.
Mile 17.4        Highway 47 -  Banks-Vernonia State Park
9:55am             This area is underlain by Cenozoic rocks that are younger than 50 million years. 
                        We are North of Manning and South of Vernonia near the Horseshoe Trestle.  This is in the Eastern Coast Range.  Keasey Formation 35 to 38mya
 This is a top view before the rock was broken up.                                       Side view after rock was broken
These fossils are a bi-valve and a Dentalium pseudonyma.
Gastropod
Fossils found at the Banks-Vernonia State Park.
This is a volcanic ash, marine environment that is very close to an island arc of the Oligocene ocean.  The fossils were settled after the death of the animal.  They were probably deposited in very quiet water.  The fossils were probably washed in by the ocean current. 
This is probably the actual fossil bed for the fossils we found.
It was unfortunate that we were not able to bring the fossils that we found out of the park.  At 10:40am we were notified that we were in an area that has been protected from fossil hunters, by Mike Shannon a State Park Ranger. 
Mile 30.8        Timber Road -  Nehalem River
11:33am           Keasey Formation 38 to 40mya.  Shallow marine environment.
                        Here we found a huge assortment of different marine fossils.  They were found scattered along the edge of the road and in fossil beds in the hillside.  Thyasira fossils were found in a bed.  They were probably living when they were covered up by sediment.  They are clams or bi-valves.  This landscape is made of Arkoses sandstone conglomerate with feldspar and basalt from an Island Arc. 
The Island Arc was attacked to the North America Plate through the subduction of the Farallon plate.  The Farallon plate is now three different plates, the Juan de Fuca, the Cocos, and the Nazca plates.
Timber Road
Dentalium schencki Fossil
Mile 84.2        Ecola Park -  Astoria Formation
12:52pm           The beach is made of mature sand.  The color is a good indicator of maturity.  The
                        sand is most likely made of quartz and feldspar particles.  The  rocks are the sand for tomorrow.  They will become sand with the continuation of weathering.  The cliff face is the winter beach berm.  The area that is exposed is most likely the backshore.  The water is covering the foreshore.  The logs show where a high tide has been.  The sea stacks and sea arch have been formed by an area of land that jetted out into the longshore current, where it interrupted and absorbed the energy. 
The Astoria Formation is a middle to lower Miocene Epoch formation of the Cenozoic Era.
                  Sea Stacks and Sea Arch                                                                         Costal Environment
The majority of fossils that we located on this trip were all marine animals.  The fossils that were found by most were shells. It is pretty easy to tell the difference between a newly deposited shells from the fossils because of the lack of color in fossils.  Most of these animals have descendants that still exist today.
The fossils are replacement fossils.  Replacement fossils are formed through a natural mold being filled with sediment or minerals and then hardening.  The replacement material takes the place of the original
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