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'.