Gray Butte marks part of big caldera

Crooked River Caldera, recently 'discovered,' is one of world's largest

Anne Aurand / The Bulletin /

Published Jan 9, 2013 at 04:00AM

Gray Butte, just northeast of Redmond, offers an easy day hike almost any time of year, and each season offers a distinctly different experience. Spring is known for wildflowers. Late summer is incredibly hot. I thought it would be a lovely place for a winter hike.

Besides, my friend Daniele McKay, a geology instructor at Oregon State University-Cascades Campus, said Gray Butte is part of the Crooked River caldera, an interesting region of recently discovered geologic features.

From some points on Gray Butte, which emerges from the caldera's northwestern fringe, McKay said you can see across the entire caldera, which stretches south to Powell Buttes and east past Prineville. We didn't go quite far enough for that view on our recent hike, but a short meander around the hill opened up an expansive skyline that included northern views of the Cascade Mountains, backed by dramatic winter storm clouds.

The day McKay and I ventured out there with our husbands, it was exceptionally cold. We packed savory lunches, hot drinks and multiple layers of winter clothing. We drove past Smith Rock State Park and down a snow-covered, undulating, single-lane road through a cozy canyon nestled among snow-covered junipers and jagged rock formations.

We saw few other cars on the road to the trailhead, but those we did see appeared to be four-wheel drive. At the trailhead, which starts near the skeletal poplars surrounding the old McCoin Orchard, a bitter wind was blasting. The husbands briefly flirted with the idea of waiting for us in the car with the Hydro Flask of hot toddy.

The trailhead is marked with signs, but the trail itself was somewhat obscured by snow. It might have been difficult to find had there not been snowshoe tracks to follow. The trail skirted the side of the butte, occasionally passing rock cairns that suggested we were on track. Had we wanted to, we could have just bushwhacked straight up the exposed sides of the butte to the summit, where towers of some sort are visible and a 360-degree view would be guaranteed.

But, lacking ambition and hydrating frequently with the aforementioned hot toddies, we decided our goal was to keep traversing the slope until we spontaneously decided we had reached our destination. It was the journey, not the destination, that was important that day.

The four of us caught up on all the things old friends talk about as we gained elevation and postholed through ankle-deep snow.

I also asked McKay to tell me what was interesting, geologically, about this landmark, and how it was possible that its origins were only discovered recently.

In phases of eruptions, she said, the Crooked River caldera started with gas-rich magma chambers forming below the surface and fracturing the overlying rock as it expanded into a dome.

Eventually — about 30 million years ago — the pressure blew the overlying rock to smithereens and the area collapsed in on itself. Much of the rock, ash and lava fell back into the caldera. It formed a dense layer of tuff, a rock made of pumice, ash and other fragments.

Some 25 by 17 miles wide, it's one of the 10 largest known explosive calderas in the world, according to a 2009 report.

Volcanic activity continued, albeit at a much mellower pace. Along the fractures that ring the caldera, magma oozed up and formed Gray Butte, Grizzly Mountain and Powell Buttes, McKay said.

So why did it take geologists so long to figure this out? I asked.

Geologists knew this area was volcanic, McKay said. But there is a lot about geology that has not yet been studied, she said.

How the caldera was created only came to light a few years back, starting in 2005 with a geologic mapping study in Prineville. Geologists then were looking at rock formations and other features so hydrologists could identify water resources and potential hazards such as landslides or arsenic. In the mapping process, geologists sampled rocks and answered some questions about Oregon's volcanic history.

We didn't hike far enough around or up the butte to see the expanse of the entire caldera. After about 40 minutes of walking, we stood on a ridgeline on the northwest side of the butte that offered a view of the Cascades from Mount Bachelor to Mount Jefferson. Ahead of us, another ridge poured off of Gray Butte that I suspect was home to the Creson viewpoint, touted on a Forest Service website as having “exceptional views of the Cascades, Ochocos and High Desert.” To the Creson viewpoint and back is a 3.8 round-trip hike from the trailhead by the McCoin Orchard.

But we had started late that frigid day, and we all had evening plans to return for, so we turned around and headed back to the car, fully satisfied with a fun little adventure.

For a longer, car-shuttle hike or mountain bike ride, a group can leave one car at Smith Rock State Park and hike on this trail, pass the viewpoint and continue along Burma Road to a steep trail down to the Crooked River in the state park, according to the Deschutes and Ochoco National Forest and Crooked River Grasslands webpage.

If you go

Getting there: From Redmond, go north on U.S. Highway 97 to Terrebonne, turn right on Smith Rock Way and follow signs toward Smith Rock State Park. Pass the turnoff to the park, drive about three miles and turn left on Lone Pine Road. In another three miles, turn left on Forest Road 5710. Watch for signs to Gray Butte. After about two miles, bear left at the Forest Road 57 junction to the trailhead, which is on the south side of the road. From a distance, the trailhead can be spotted if you look for the old McCoin Orchard across the road, which is marked with tall poplar trees.

Difficulty: Easy to moderate

Cost: Free

Information: www.fs.usda.gov/recarea/centraloregon or 541-416-6500