Thursday, July 26, 2012

Quartzville Road Log

Two and a half weeks ago, Dana came into town. Sunday, essentially a half-day, we went up Marys Peak; she'd not been to the summit, and while the view was largely obscured by haze, I think she did get the overall sense of awe at being able to see the general area of the subduction zone, forearc ridge, forearc basin, and volcanic arc, all from one spot.

Monday, which I'll elaborate in a moment, we went into the Western Cascades, to the Quartzville mining district, with Callan Bentley's former student Aaron Barth. Tuesday we went over to the coast to the Agate Beach tsunami dock, north to Depoe Bay, then back to the valley by way of Erratic Rock Wayside.

My intent today is to simply lay out mileages for the Quartzville trip. The original article upon which this log is loosely based is here, but should be taken with a shaker of salt; there are some rather egregious errors. A previous post for the Accretionary Wedge on the area is here. I've omitted a number of stops in the original guide, and added a number of others, to create what amounts to my all-time favorite field trip, one that I've led between 40 to 50 times.

A bit of background is in order. Due to a number of factors (heat, rambunctious cat, downstairs baby squalling from about 4 AM on), I got no sleep Sunday night, so when we left Corvallis at 6:30 Monday morning, I was already pretty brain-dead. I spent the day mostly making sure I was making sense to Dana and Aaron, and way too little of it documenting what we were seeing- so those two are the ones who will have a lot of the best photos. I got some, and some samples, but not nearly what I had intended. I knew it would be a long day, but it ended up being even longer than I'd imagined: we got back to Corvallis at about 11 PM, and I was very nearly hallucinating from exhaustion at that point.

But on to the content: following are the mileages to various stops, and very brief descriptions of what we saw at each.

Mile 0.0: Green Peter Dam (Flash Earth location)

Mile 0.2: vesicular basalt, zeolites and amygdules

Miles 0.7. 0.9, 1.0, 2.0: colorful clays, first stages of hydrothermal alteration (drive-by geology)

Mile 7.7: calcite veins emplaced in fault, casts of slickensides

Mile 7.8: slickensided face, with volcanic neck towering above.

Mile 11.2: debris flow deposits overlain by water-sorted sediments and paleosol. Permineralized charcoal. (Intro here)

Mile 13.2: rest stop, restrooms

Mile 14.9: Quarry- rhyolite dike into intermediate(?) volc rock, heavily mineralized with pyrite. Be careful about safety here: do not approach walls- rocks fall off frequently. In addition the rocks are quartz mineralized- very hard and tough- and break with sharp edges. This is an easy spot to gash yourself open, if you're not careful. If you walk up the road and around the corner (~0.1 miles), there is a badly weathered/altered exposure of a bizarre tourmaline-pyrite breccia. Not easy to find good samples, even harder to find collectible examples, but very cool and weird stuff.

Mile 15.1: Boulder Creek Bridge- leave main road, cross to drive up Boulder Creek

Mile 16.7: Hydrothermal Breccia with lots of pyrite crystals
- turn around and head downhill to main road again

Mile 17.2: during floods of 1996, debris flow came down stream across the valley, wiped out Boulder Creek road from Mile 17.3 to 17.5. Road was gone to cliff face.

Mile 18.3: back on main road, turn up stream.

Mile 18.7: confluence of Boulder Creek with Quartzville creek, eponymous boulder probably emplaced by debris flow.

Mile 21.8 Yellowbottom facilities/restrooms- Yellowbottom campground across road.

Mile 22.0: As corridor of Dougfirs turns into alders, pull off on right (there are a number of pull-outs; the one with best/easiest access to creek is the last one) and walk to stream and Yellowbottom Falls- granodiorite and basalt dikes. Granodiorite is 18 Ma, and believed to be driver of hydrothermal system in this area.

Mile 23.2: Canal Creek 4-way intersection- one road turns perpendicularly up Canal Creek, main road continues along Quartzville Creek. Take the road the runs between the two, diagonally up the hill, toward the Quartzville town site.

Mile 24.2: Cinder cone deposits on right- anomalously young, on top of glacial deposits, so 2 Ma or less- despite the fact that Cascade volcanism had mostly been restricted to narrow modern axis by Pliocene.

(town site wasn't marked on this trip; we slowed down briefly, but didn't get mileage. There is an interpretive sign that comes and goes sporadically, recounting the history of the town, but it wasn't there on this trip.)

Mile 26.0: Snow Storm Tunnel- Gated off now, for reasons I don't understand, but used to use as outstanding example of a safe mine to visit and enter.

Mile 28.2: Red Heifer Pass- road continues through pass, but turn to follow logging access road to right left, [apologies to @GeoHols for this thoughtless mistake] or park here, and walk in. (There *is* room to turn around farther in, but it *does* look tight). The road is purposely blocked and closed about 0.1-0.2 miles in. Maybe a quarter mile or less from intersection, watch for a "fin" rising from the hillside uphill from the road- this is a quartz vein, about 8-10 feet thick, that's resisting weathering and erosion more effectively than surrounding rocks. Nice quartz crystals can be found in the talus pile down onto the road. Even better- and some beautifully colored examples, stained with Fe and Mn oxides particularly- can be found on the hillside at the base of the vein, but it's a scramble and a bit hazardous to get up there, so be careful if you choose to try. (We were hot and tired, so we didn't try.) I've also found barite here a couple times, but it's not common. In addition, there are a number of interesting spots walking along the road- in particular some very nice Liesegang rings, maybe 0.1 mile later, on the right (uphill side) of the road.

-turn around, head back downhill toward Quartzville Creek once again.

Mile 33.3: bridge across Dry Gulch. If you're here during dry season- and you are, otherwise you wouldn't have made it to this point- there's no water flowing. With Dana and Aaron, there was a pool on the uphill side, but no flow. (looking at these mile numbers, I think I may have messed something up, but Dry Gulch is between cinder cone and town site, and the only bridge along this stretch of road.) [addendum- I'm not going to change the numbers I recorded, but it just dawned on me, distances from last stop and to next stop would make much better sense if this was actually Mile 32.3.]

-return to 4-way intersection, and turn sharply right to follow Canal Creek upstream. (Again, I'm thinking I may have messed up the mileages somewhere in these last few stops, but...)

Mile 34.5: Lower bridge across Dry Gulch- again, note there is no flow here, but during peak runoff- warm rain on snow during late winter and during spring melt, there clearly is significant flow in this channel.

Turn around and back track a tenth of a mile to the Cheshire Cat outcrop- an abandoned quarry in columnar jointed basalt that looks like a smile without a cat. A grove of alders has sprung up between the road and the columns, but they're high enough now that if you're watching for it, you shouldn't have any trouble finding it- on hill side of the road (left, as you head back toward 4-way intersection), not the Canal Creek side.

*END* (Return to four-way intersection, turn downstream at Quartzville Creek, and drive back out past Green Peter Dam, to Sweet Home.)

Obviously, I've said very little in terms of details, and really, not much even about generalities. I'm simply laying this out now as a frame. Hopefully, Dana, Aaron and I can fill this in more completely in the weeks to come. I've linked Dana's reports thus far in the individual stops.