Sunday, January 29, 2012

Trail Report: Bobs Mountain Crater, Washington

Well, this is another “report” on a planned hike…  This post started as an off-shoot of the Gresham Saddle Trail post.  However, this one is a hike that I have made before.  I blazed out there in 2004 to check out the “partial summit crater” after reading this excerpt on the Cascade Volcano Observatory website.
CVO Website - Boring Lava Field, Portland, Oregon:
…the volcanoes were probably active from at least 2.7 million to less than 500,000 years ago.

Northwest of the town of Boring, 20 eruptive centers are concentrated within around 100 square kilometers (39 square miles). Vents in the east part of this cluster average less than 2.6 kilometers (1.6 miles) in diameter and 333 meters (1,090 feet) in height above their bases. Lava from Highland Butte and Larch Mountain shield volcanoes from gently sloping plains covering many tens of square kilometers. Well logs indicate that in most places except near vents, Boring lava is between 30 and 60 meters (100-200 feet) thick.

Partial summit craters remain only at Bobs Hill, 33 kilometers (20.5 miles) northeast of Portland, and at a low cone enclosing a lake (Battleground Lake) north of Battleground, Washington, 33 kilometers (20.5 miles) north of Portland. Most other volcanoes still have a low cone shape and are mantled with loess above 122 meters (400 feet) elevation. Below this they were scoured by the cataclysmic Bretz floods from Glacial Lake Missoula around 13,000 to 15,000 years ago.

From: Wood and Kienle, 1990, Volcanoes of North America: United States and Canada: Cambridge University Press, 354p., p.170-172

The Trail:

In 2004, this was a short little hike on paper but a nightmare of snags, tangles, and ditches in reality.   The old logging road to the summit was being closed down and “returned to nature” in a rather severe, definite, and forcible fashion.  Beyond shutting it down for trucks, ORVs, and horses, they pretty much shut it down for hikers, as well.

Six year later, I am curious to see what this trail looks like.  I might make the trip again this spring or summer.  However, it is not a very exciting hike and I am not even sure if the crater is actually a crater, or just an artifact of erosion.

Unfortunately, my pictures from the trip are gone.  Another reason to head up there again.
The trail may have improved, though, since it appears that some logging has occurred up there since I’ve made the trip.  The summit road may have been put back into service.  Then again, it may have also been taken out of service again, like the last time…

The most recent Google Earth images suggest that there may be some decent views to the southeast on the way to the top due to the logging activity that were definitely not present in 2004.

Bobs Mountain Logging

The Crater:

There was not much in the way of a view up there, but that may have changed with the logging.  The main reason to go is to explore the “crater,” but even that is not very exciting.  Unless you are a geology/volcano junkie, or something of a local butte completist, there are many other hikes in the area that are much more interesting, spectacular even, than this one.

However, I seem to fall into both categories, so here I am planning on making the trip not just the one time, but twice even.

On the topographical map below, you can vaguely see the indentation that is referred to as a “partial summit crater”. 


When you are up in it, it does not look much different that any small hillside gully on any slope in the Northwest woods.  In fact, this is all that it may be, at least to my untrained eye.

It is a depression and, unlike most gullies, it does have a rim on all sides, but the down slope rim is not very prominent and, if I remember right, a gully does occupy the steeper slope below the crater-like depression.

I am curious if anyone has really studied the geology up there.  One way or the other, a lot of weathering had obscured things, to the point where this is all that it might be…  Just a feature of weathering, not volcanism.

This is not to say that I wouldn’t like it to be a crater, though.  That would be very cool.  The real question I have is why would this cone still have one when most, if not all, of the other Boring volcanoes do not?  Yes, I am somewhat skeptical of Battle Ground Lake, too.  Though less skeptical of that one.

The “crater” is somewhat visible in the image below…

Notice the depression on the left side of the old logging road descending from the summit.  This is the “crater.”  I will admit that, in this image, it looks more like a crater than it does when you are actually standing in the thing!

However, from the angle and elevation of the view below, it becomes less clear.

Bobs Mountain RenderWidget 1292012 24059 AM

Getting There:

In 2004, I believe I was following the Green Trails version of this USGS map from 2000.  There was no trail marked, except for the logging roads shown.  I believe I drove the North Fork Road to the northern power lines, followed the power lines east until turning south towards the mountain.  I cannot remember if I could drive down to the mountain or not.  I think I parked under the power lines and walked, but it was a long time ago.  Here is where having my old pictures would be useful.

WA_Bobs Mountain_240136_2000_24000_geo

Here is the 2011 USGS map.  It may help clear up the route a bit. 


Now, I haven’t been up there since 2004, and at that time the summit road was barely passable on foot.  However, it does look like the southeast flank of the cone has been logged since then, so the road may have been re-opened… 

Because of this, I wouldn’t plan on driving any closer than you can get on the roads shown in Google maps, but the USGS map above should show the possible hiking routes to the summit from wherever the wheels come to a stop.

Bobs Mountain - Google Maps

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1 comment:

A. F. Litt said...

Some feed back on this "trail report":