Oregon Hikers

It's not a volcano, but Canemah Bluff is an interesting geologic -- and historical -- relic as well. I think they were part of the Boring Lava deposit. Have you explored that area?

Wonderful write up!

awildman wrote:It's not a volcano, but Canemah Bluff is an interesting geologic -- and historical -- relic as well. I think they were part of the Boring Lava deposit. Have you explored that area?

"The bluffs are part of a rock bench sandwiched between the Willamette River and the higher plateau to the east. The underlying geology of the bench is Columbia River Basalt. The top of the bluff is composed of more recent Troutdale formation and Boring Lava deposits. During the Missoula Floods, the steep bluffs and bench where the Canemah Bluff natural area is located were exposed, scoured and steepened as floodwaters repeatedly spilled into and out of the Willamette Valley."

Looks like the bluff itself is a bit older than the Boring Lava deposits but definitely a part of it now =D.

AWESOME Job! So what's the origin of the West Hills? I hadn't realized it was related to the Boring Vents.

Charley wrote:AWESOME Job! So what's the origin of the West Hills? I hadn't realized it was related to the Boring Vents.

"The [West] hills (Tualatin Mountains) date from the late Cenozoic era, and range up to over 1000 ft (305 m). Composed mainly of basalt, the mountains were formed by several flows of the Grande Ronde basalt flows that were part of the larger Columbia River basalts."

They're quite a bit older than the Boring Lava deposits =D.

"During late Miocene and early Pliocene epochs, one of the largest flood basalts ever to appear on the Earth's surface engulfed about 163,700 km² (63,000 mile²) of the Pacific Northwest, forming a large igneous province with an estimated volume of 174,300 km³. Eruptions were most vigorous from 17–14 million years ago, when over 99% of the basalt was released. Less extensive eruptions continued from 14–6 million years ago."

"The [Boring Lava flow] zone became active at least 2.7 million years ago, and has been extinct for about 300,000 years."

@HeadIdiot: Thanks for the slotting in the geologic details. I'll just add a couple of things:

@awildman: There is such a formation as the Canemah basalt that is part of the Boring Field. If you look at a geologic map of the Oregon City area, you see a vast area of it southeast of the Bluff. I'm guessing this probably issued from Highland Butte, one of the larger Boring volcanoes (Just as Angel's Rest in the Gorge is a Boring outflow from the area of Larch Mountain). The Bluff itself, and the corresponding cliffs on the West Linn side, is Wanapum Basalt of the Columbia River Basalts (about 13 million years ago as opposed to 2 mya for the Canemah basalts).

Yes, I've done quite a few walks in the Oregon City area, including the Bluff, with family, friends, small children, etc. I do these short excursions when I don't have time to get out for a day-long adventure and I'm maniacally comprehensive, so when I get a window, I strike out for some other unexplored but semi-natural sliver of our urban area.

@Charley: As HeadIdiot's post indicates, the West Hills are primarily Columbia River basalts, but overlain by sediments (Troutdale Formation) and then, as in the West Gorge and throughout the area, came the Boring vents pushing themselves through. The final significant chapter was the windblown volcanic loess that got plastered against the east side of the hills during the Ice Age, making them prone to landslides and quite unbuildable. That's why we're able to have Forest Park! Here's a good layperson's account of the geology of the West Hills: http://www.foresthiker.com/?page_id=2261

My house is a few hundred feet from the water-towered summit of Cornell Mtn., a Boring volcano that happens to be perched on top of the West Hills. The extra bump makes it the highest point, I think, in the West Hills=Tualatin Mtns., or at least highest within the built-up Portland area, at 1280+.

The West Hills is a fault block range, and it's sheer coincidence that this volcano is superimposed on it. The fault block is actively rising today, which makes it a young fault block range. "Mid-Cenozoic" and "older than the Boring volcanoes" refer to the age of the rocks here (Columbia River basalts), not the age of the hills as hills.

Thanks, Bobcat, for doing this exploration project for us! A very worthy project. I want to try Mt. Talbert.

Thanks for the post Bobcat. This is a great rundown of the Boring peaks and included a couple of trails new to me.

Rocky Butte was used as a rock source by the Oregon Railway & Navigation Co ( a precursor to today's Union Pacific) in the 19th century. I've never been able to determine how much of today's cliffs are natural and how much to due to quarrying.

Bobcat,

Thanks for the great detailed report! You have done a wonderful job researching this and your report is one for the archives.
dn

This is great! I live at the base of Kelly Butte and I have been meaning to go explore but it is a little sketchy up there. I will definitely be checking out some of the others on your list!

Don Nelsen wrote:Bobcat,

Thanks for the great detailed report! You have done a wonderful job researching this and your report is one for the archives.
dn

Great write-up and very interesting for us locals who didn't know all of this already. I have some exploring to do =).