Saturday, May 3, 2014

Geo 730: May 3, Day 489: Stranded on the Hilltop

Coming around from the east to north side of Erratic Rock Wayside, we're looking into yesterday's "boat prow." On the rock farther back, the line of sight is  from just above the plane of foliation and cleavage, so we're looking almost parallel to, but a little bit down on, that plane. In the closer block, we're looking down onto that same plane. As pointed out by Callan Bently in a comment on yesterday's post, this is almost certainly Belt Supergroup argillite. Also, as in yesterday's post, wine grapes are visible on the right in the mid-distance.

Photo unmodified. July 10, 2012. FlashEarth location.

Friday, May 2, 2014

Geo 730: May 2, Day 488: Argillite Prow

Resembling the prow of a grounded boat, these blocks of argillite were probably once all one larger boulder. Through processes both natural (weathering and frost wedging, for example) and human, they've been split into a number of smaller slabs. This is somewhat metamorphosed, I think; it's more indurated than shale by a long shot, but the foliation and cleavage is not as well developed as I would expect in slate.

In the mid-distance on the left, you can see the wine grapes foreshadowed in Wednesday's post.

Photo unmodified. July 10, 2012. FlashEarth location.

Thursday, May 1, 2014

Geo 730: May 1, Day 487: The Accidental Tourist

Though this was not a particularly demanding day, slogging a half mile or more through sand to the Tsunami Dock (See March 28 through April 8 of this series) took its toll, and the moderate climb up the hill- maybe 150 feet of elevation gain- seemed interminable. It was nice to come around the corner and finally spot the goal of that effort. The fence post on the far right is about four feet high, and the wooden post in the middle left maybe two feet; this is a big hunk of rock to travel some 500 miles.

Photo unmodified. July 10, 2012. FlashEarth location.

Wednesday, April 30, 2014

Geo 730: April 30, Day 486: Wine Sign

This is actually the text below the map in yesterday's photo, and it's particularly appropriate, given the view from the top of the hill. It's also a little misleading. In addition, wine grapes are grown locally on laterites developed from basalts in the area (which includes Columbia River Basalt, and I think also Siletz River Volcanics, though I'm not positive about the second), and in soils developed from Eocene sandstones and siltstones, equivalent to the Tyee Formation. Farther south, west of Roseburg, there are a growing number of vinyards growing in soils developed from the Lookingglass Formation (pre-Tyee sediments derived from erosion in the Klamath Mountains). So it's not incorrect, but neither does it paint a very complete picture. As I said in Monday's post, take these sorts of signs with a grain of salt.

Photo unmodified. July 10, 2012. FlashEarth location.

Tuesday, April 29, 2014

Geo 730: April 29, Day 485: Sign of a Map

Another one of the interpretive signs at the beginning of the trail up to Erratic Rock, showing the general layout of the great floods that scoured the Pacific Northwest toward the end of the last glacial maximum. Judging from pages 16 and 17 of "Origin, Extent, and Thickness of Quaternary Geologic Units in the Willamette Valley, Oregon" (USGS Professional Paper 1620, PDF), in the Corvallis area the Missoula silts are about 4-5 meters in thickness, but thicken rapidly northward/downstream along the Willamette main stem. This site is well north of my home, but I suspect that up on the hill, where the erratic rests, the thickness is much less than here on the valley floor.

Photo unmodified. July 10, 2012. FlashEarth location.

Monday, April 28, 2014

Geo 730: April 28, Day 484: Signs, Signs, Everywhere a Sign

After leaving Lincoln City, Dana and I came inland on OR Route 18, and headed to Erratic Rock Wayside. The parking and pathway from Oldsville Road are easy to miss- I've driven by at least once each time I've visited the spot, and this time was no exception. Hopefully, with the FlashEarth location and modern deally-boppers such as GPS, along with landmarks and cues I'll point out over the next few days, others will have an easier time with it.

A note about interpretive signs: take them with a grain of salt. I don't know who is responsible for designing them and writing them up. They aren't necessarily wrong- I see no outright errors in the one above. But neither are they authoritative. It's not at all uncommon to find misinformation and mistakes on them. I'm mightily glad I live in a place that cares enough to more-or-less permanently make this information available to the public, but for those who find it interesting, whether the sign is interpreting a natural or historical site, such information should be taken as jumping-off point, a start, and an impetus to find more thorough- and likely more accurate and complete- sources.


Photo unmodified. July 10, 2012. FlashEarth location.