What is the pink rock near Chinook Pass, US 410, Washington State?

Send your roadside geology question to Doctor Rock! Just add a comment at the bottom, or send an email to : tuckerd at geol dot wwu dot edu (sorry, gotta keep the spammers out!). It would be great if you could include a photo or two of the outcrop you are asking about.
This week's question:
 
Hi Dr. Rock,
When I approach Chinook Pass on US 410, heading east, on the east side of Mount Rainier National Park, the road switchbacks up a massive rock face and there is a dramatic band of orange/pink rock that cuts across the exposure. If I remember right it may be a couple hundred feet thick. Can you tell me the story of this layer?
J. McLarty

Dear J.,
You may be referring to an outcrop shown in a geology guide to Mount Rainier (the reference is below). It is located just east of Chinook Pass. Here is a photo taken from the guide book:

According to the author, Pat Pringle, well-known volcanic geologist in Washington State, the pink rock is a part of the gray rocks below. The pink portion has been baked by the slender layer of gray rock at the top of the outcrop, just visible beneath the tall trees. Hang with me here: It is a multi-stage story. The gray and pink rocks are volcaniclastic rocks, meaning they are fragmented, or broken ['clastic'] volcanic rocks. [but the term is shorter and remains 100% descriptive to folks who understand the technical lingo]. Examples of volcaniclastic deposits are ash, pyroclastic flows['hot broken'], and lahars.The term differentiates these rocks from 'solid' volcanic rocks, or lava flows. The volcanic rocks in the photo are part of the Ohanapecosh Formation, found throughout the Mount Rainier area. These rocks are 35 to 28-million years far older than the rocks of the modern cone. They were erupted from many different volcanoes that came and went over that 7 million year interval, and were buried by younger volcanic rocks and glacial and river deposits. During burial, the Ohanapecosh Formation was also intruded in many places by magma associated with these younger rocks. That is what the dark rock at the top of the outcrop is, a horizontal bed chilled magma called a 'sill' that invaded the buried rocks. The sill may have eventually connected with a vent on the surface, but any evidence for that is eroded. In any case, the hot magma baked the relatively porous rocks it intruded for  many feet above and below. Pink rocks like this are usually indicative of the oxidation caused by the baking. The photo below shows another example.

The pink band is about 3 feet thick. It is the baked zone
at the base of a massive lava flow along US 12
west of Morton, WA.

A thin band of pink rock has been baked by the
intrusion of this dike at Owyhee Reservoir in
eastern Oregon.

The guide book is:
 
Roadside Geology of Mount Rainier National Park and Vicinityby Patrick T. Pringle. It was published in 2008 by the Washington State Department of Natural Resources, and is written for  a non-technical, popular audience. There is a great Geology 101-style introduction, and mile by mile descriptions of the geology along roads all through the Mount Rainier area, extending far beyond the boundaries of the national park.
You can access the book online here:
http://www.dnr.wa.gov/ResearchScience/Topics/GeologyPublicationsLibrary/Pages/pub_ic107.aspx
The photo and description is found on page 119, part of road guide 'F'.

Volcanoes in eastern Oregon are a great geologic road trip.

Doc,
I see that volcanoes are your field of interest. I'm a self-professed volcano nut, and I'm already planning next spring's road trip, maybe to the High Lava Plains of eastern Oregon. The name alone is intriguing! I have heard there are some little cinder cones way out there. What do you know about them? Been there? Worth the visit?
Denise Hodgkins,
Port Angeles, WA

Denise,
There are indeed some young-looking cinder cones and lava flows in eastern Oregon. I think you are referring to Jordan and Diamond Craters. I've been to both areas, and they are definitely worth the visit.



Coffee Pot cone in the far distance.

The Jordan Craters are in the southeast corner of the state, off Highway 95 near the town of Jordan Valley. There a number of cinder cones and lava fresh lava flows- they look as if they erupted yesterday (read about cinder cones in my first-ever Doctor Rock post). However, radiocarbon dates indicate that the most recent eruption, at Coffee Pot Crater, was 3200 years ago. Until usable material for radiocarbon carbon dating was found, this cone was widely held to be only 1-200 years old. It is the only cone in the Jordan Craters accessible by road. Here is a map
http://www.blm.gov/or/resources/recreation/googlemap.php?lat=43.14588&lng=-117.4588
use the 'satellite' tab in the upper right to see topography. The lava flows are the dark areas. Coffee Pot erupted 30 square miles of basalt lava.
The area is administered by BLM. The round trip to the single road accessible cinder cone, Coffee Pot Crater, is 52 miles. The roads are not paved. Be wary. It's not a good idea to take a big rig in there. When I was there in the spring, snow had just melted and roads were a quagmire. I barely made it back out of there in my all-wheel-drive Forester. Pay attention to the weather, and only go after the roads have had a chance to dry out. It is remote country- no services, poor cell coverage, no help. Be smart.
There is a great route guide here: http://www.everytrail.com/guide/birch-creek-ranch-jordan-craters
The Global Volcanism Program (a must-visit site for you volcanophiles out there) has sparse information about the Jordan Craters here: http://www.volcano.si.edu/volcano.cfm?vnum=1202-19.
A pamphlet (a bit dated, from 1977) explains some of the detailed geologic features you can see in the Jordan Craters: http://www.oregongeology.com/pubs/og/OBv39n08.pdf

This is Little Red cone in the Diamond Craters.

The other place is the Diamond Craters, 40 miles southeast of Burns and Malheur Lake. The essential info is on this great website for volcanophiles: http://volcano.oregonstate.edu/diamond-craters. There are about a dozen vents in the area, and a signed nature trail takes you to many of the points of interest. The oldest cone is maybe 60,000 years old, but the youngest is a meer 6,000 or so. While you are in the area, consider traveling the Diamond Loop Back Country Byway, a 67-mile unpaved back-country drive. Well worth it!



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