This being late winter/early spring, I fully expected we would see some mass movement (e.g. landslides, mudflows, rockfalls, slumps, etc.) along the coast or in the Coast Range. Winters are very wet along the coast and associated mountains, and in the Cascades as well, much more so than here in the valley. That water adds weight, provides some lubrication, but more importantly than the latter, increases pore pressure. This has the effect of "floating" much of the weight of the overburden- that is, counteracting the normal force. Friction is the product of a constant, "the coefficient of friction" (constant for a given material, but not across varying materials) times the normal force, which is essentially equivalent to the weight of material sitting on a surface times the cosine of the dip (angle of slope) of that surface. Cutting through the math, increasing the pore pressure of water in a soil and rock profile drastically reduces friction, not by "lubrication," but in a sense by decreasing its effective weight. But not its actual weight... when all that stuff falls in the road, it's still a heckuva lot to clean up.
Photo unmodified. March 9, 2012. FlashEarth location (Fairly confident about this one, but not certain).
A final shot of the organic-rich mud/silt beds between (what I suspect are) turbidite sands along Route 42 in the southern end of Oregon's Coast Range. Fortunately, we had a stop later where the rock was on our side of the road, and we didn't have to worry about traffic to get to it, though its nature was clearly more deltaic than this appears to be.
Crossing the road didn't seem a good idea at this stop, though I would've liked to get a closer look at those dark layers. I presume they're mostly clastic, but with a high proportion of organic material- based on what I've seen elsewhere in the Tyee Formation, plant fragments. There was clearly a contribution of woody material in the delta area, but farther north, what was transported with the turbidity flows seems to largely consist of reeds and grassy fragments. At this outcrop... well, crossing the road didn't seem like a good idea.
I'm not terribly strong with sedimentary facies recognition, but I do know we're back in the Tyee Formation here. The rhythmic nature of the bedding suggests we're still in deeper turbidites, but just under the tree line, right of center, you can see a darker layer that looks as if it's rich in organic material. There are some coal seams in the the deltaic facies of the the Tyee, though by and large they're not of commercial grade- too thin and too dirty. However, as we turn to the left over the next couple of days, we'll see that the organic-rich nature of the layer above is not unique in this outcrop.
I thought I had taken Route 42 across the Coast Range before, but I was mistaken. For the most part, until we got near Roseburg, it was entirely new to me. In consequence, I couldn't anticipate interesting spots to stop, my sense of location, which is generally pretty good, was pretty much shot, and my knowledge of what we were looking at was tentative. All that said, though, the primary thing I was after was a look at the deltaic facies of the Tyee Formation, and we did have a chance to see that, as well as some other neat stuff I hadn't anticipated. We also stumbled across a couple of long-lost spots I probably would've had a heck of a time finding if I'd set out with them in mind as targets. So all in all, it was a very good late morning and afternoon.
Above, I'm sort of half guessing (but pretty confidently) that we're looking at Roseburg Volcanics, which are correlative and equivalent to Siletz River Volcanics. Though they are not connected in surficial exposures, they almost certainly are at depth. This was the first of a number of "impulse, because we can" stops. Generally I wouldn't bother pulling off the road for basalt (which I affectionately refer to as GDB, for, ahem, "gosh-darned basalt") unless I know there's an interesting feature to see. However, it was interesting to see basalt here. I was uncertain where or if we'd traveled off of Klamath bedrock, which is what we were on at Bandon. The above was not metamorphosed at all though, as far as I could tell, so we were back on Coast Range bedrock. Dana had several firsts this day; at this outcrop she found her first slickenside on her own. Anybody who's done geology knows how exciting it is to recognize something independently for the first time, and have it confirmed by someone with more experience. A number of possibly striated surfaces are apparent to me in the above, but I'm not confident enough to call them slicks.
Looking south from Bandon's Kronenberg County Park, I think the headland in the mid-distance is Face Rock Wayside. As I described a bit more than a week ago, the large differences in resistance to weathering and erosion in the Otter Point Formation lead to the formation of the numerous sea stacks that we see here. Another feature of note is the flat-lying elevated marine terrace to the left.