To get the most out of your time here you'll want to stop at one of the many viewpoints and go for a walk on a portion of the 27 miles of Oregon Coast Trail. Let the local geocachers be your guide. Many of the traditional and multi-caches just north of this area will lead you to spectacular viewpoints.
But that doesn't apply to this Rainbow Rock earthcache. You can see everything you need to see from this paved roadside pullot at the listed coordinates. The hike to the beach below to get a closer look is entirely optional -- but worth it! Note: The terrain rating is closer to 2 or 2.5 if you hike down to the beach from the optional trailhead.
This dramatic coastal mountain range that makes this area of the Oregon coast so memorable has to do with plate tectonics. Some distance off shore the eastern Pacific Ocean's Juan De Fuca plate is subducting under the North American continental plate. The resulting jumbled coastline is the product of two main aspects of this inexorable slow-motion plate collision.
The edge of the lighter continental plate is being lifted up by the as the denser ocean plate dives underneath. During this process surface materials on the top layer of the ocean plate get scraped off and collect on the edge of the continental plate, much like whiskers collect on a razor. Scoured material that was once part of the sea bottom far offshore can eventually become part of the coastal geology.
Rainbow Rock (down and to your right - please don't cross the guardrail) is composed of colorful folded beds of chert, a hard sedimentary rock that is primarily composed of silica. This kind of bedded chert originally formed on the ocean floor far away from land and the eroded material that is constantly washed into the sea by streams and rivers. The sediments that accumulated on such remote areas of seafloor were made up entirely of the microscopic skeletons of tiny animals called radiolara and plants called diatoms, both of which are made of silica. These tiny shells accumulated over time and formed a muddy ooze that eventually recrystallized and hardened into chert.
The cherts that make up Rainbow Rock were formed on the ocean floor many dozens or hundreds of miles offshore, but they eventually made there way here as the Pacific Ocean plate marched toward and dived under the North American Plate.
To get credit for your find, please e-mail me the answers to the following questions using the Send Message link on my profile page.
1) The number of people in your party and the cacher handles of those that aren't Muggles.
2) From your vantage point, approximately how thick are the individual bands on the face of Rainbow Rock?
3) Estimate how many layers you think there are, in total. The key word here is "estimate".
4) Explain why you think the bands of chert are arranged the way you see them.
5) Let me know if you made your observations from the roadside (listed coordinates) or from the beach (optional coordinates).
6) Not a logging requirement: I'd love to see pictures of you and your party, but please don't put Rainbow Rock in the background.
Source: Roadside Geology of Oregon, David D. Alt and Donald W. Hyndman