Please do NOT post your answers in your log.
Cape Sebastian consists primarily of sandstone. This formation is called Cape Sebastian Sandstone and is approximately 80 million years old and 800 to 900 feet thick. The upper portion of the Cape Sebastian Sandstone contains fine- to medium-grain sandstones with coarse sandstone and some conglomerate found in the lower portion. The fossils found in the upper part of the formation indicate it was formed in a marine environment with a significant amount of agitation. The Cape Sebastian Sandstone is a gray sandstone that weathers to light tan.
Cape Sebastian Sandstone is only found in the Gold Beach Terrane and is one of several formations that make up the Gold Beach terrane. Terranes are fault-bounded areas with a distinctive structure and geologic history. The Gold Beach terrane is believed to have once been part of a forearc of a far offshore island chain that was transported, scraped, and plastered on to the North American Plate through plate tectonics and eventually transported from southern California to the southern Oregon coast through strike-slip faulting. The Gold Beach terrane is considered an exotic terrane because it originated somewhere else.
This earthcache requires approximately .7 mile round-trip of hiking. There is no need to leave the trail to answer the below questions. Be aware of your surroundings and stay on trail and away from cliffs. You may also see a few spots of poison oak (3-leafed oily looking plant) along the trail that are easy to avoid. Avoid touching or brushing up against poison oak.
Please send a message with answers to the following questions:
1. At ground zero you will see an excellent cliff exposure of Cape Sebastian Sandstone. Is weathered sandstone present in this exposure?
2. What colors are visible at the Cape Sebastian Sandstone formation at ground zero?
Information for this earthcache was gathered from the following sources:
Roadside Geology of Oregon by Marli B. Miller
n Search of Ancient Oregon by Ellen Morris Bishop
The Ore Bin, State of Oregon, Department of Geology and Mineral Industries, Ernest H. Lund
oregongeology.org
100 Hikes Oregon Coast & Coast Range by William L. Sullivan