Sunday, February 28, 2010

Two Years Ago Today: Things in My Truck

Two years ago today, I was on my way to work one early and frozen morning, having the usual things in my truck: coffee mug with hot coffee in a nearly worn out turquoise "cool cup;" old bottle found somewhere in the field; plastic acid bottle with white lid; bright orange and yellow safety vest with multiple pockets; a "Life is Good" bag filled with miscellany including an extra fleece overshirt; a blue day pack, hidden behind the LIG bag; and brown winter jacket, long and warm for cold days. A roll of duct tape sits around the shift lever. An inverter lies part way under the seat, easy to reach from either side of the truck. Binoculars are in the glove box. A small ice chest carrying my lunch is on the floor below the glove box. Extra shoes and boots, a folding chair, a fire extinguisher, and a first aid kit all live behind the seat. My hand lens is probably dangling from the rear view mirror. There are untold, countless items in the back of the truck, enough things to camp with for a couple days if need be.
When I got home that night, two years ago today, I felt like fiddling around with colors and came up with these two versions of part of the early morning interior view.

Friday, February 26, 2010

Geology on the Road: Slate near Connors Pass, Highway 50

If you drive east of Connors Pass on Highway 50, to the location embedded in the map at the bottom of this post, you will come to this wonderful roadcut exposure of slate, along with many other wonderful roadcut exposures before and after this one (including a few faults, some shattered limestone, and much more slate). Watch for places to pull out while going downhill to the east (there are fewer places to pullout when going uphill to the west), and listen for the heavy truck traffic (and fast cars) when crossing the road. This part of Highway 50 overlaps with U.S. Route 6, an overall busier truck route.
I stopped here to get some garden rocks, but spent a lot of time - at this exposure and at others - checking out the geology. The phyllitic, calcareous slate (to slaty phyllite) is medium to dark gray, usually shiny, and before regional metamorphism it was either a thin-bedded shaly limestone or a limy shale (or both). It was assigned to the Lincoln Peak Formation by Drewes (1967), according to Hose and Blake (1970) - neither map is available online.
For this closer view, the hammer handle is parallel to lineation on the phyllitic slaty surface, and the hammer head is pointing parallel to some weak crenulations, which are stronger above and to the left of the hammer.
I love this shiny rock!
Here, I'm looking edge on at the slaty cleavage and parallel to the crenulations. Folding of the slaty cleavage is weak; there are a few cracks breaking through the slate at some of the crenulations - these may represent a weak or incipient crenulation cleavage. Looking edge on into the crenulations is difficult in the nearby roadcuts up and down the highway because the slate usually dips fairly steeply towards the road. This view requires considerable placing of face next to rock. Little crenulation folds like these can usually be seen only in float pieces.

View Highway 50 in Nevada in a larger map

Wednesday, February 24, 2010

What Dust Hazard?

There's more of a mud and snow hazard this time of year! This sign was seen on a recent roadtrip across central Nevada. Everything brown is yucky, stick-to-boot-type mud.

View Highway 50 in Nevada in a larger map
Zoom in and check out the meanders and cut-off meanders on Slough Creek!

Monday, February 22, 2010

What is Continuity?

I am a geologist, and these are going to be notes that I write in little journal books I carry around. ...a whole lot of them are going to lack any structure at all, but if you know a geologist, you know that that is the way he expresses things. Notes: there is no continuity in a geologist’s life, not in an active, busy one, anyway.”

Rick Bass, Oil Notes

This blog post, a submission for the March Scientiae Carnival, will explore the topic of continuity. Scientiae is facing a problem in continuity — will it continue or not — which is one reason why the topic is so appropriate. Bear with me: I'm a geologist, I may meander a bit.

For the hell of it, I'm currently searching "My Documents" for files that have the word "continuity" in them. I'm doing this for a specific reason: I think I've written about this subject before; but also for a more general reason: to see how often I've used the word. Found: ten files.

"Perhaps the process of individuation is not the same for everyone. Perhaps some people individuate through becoming something different from their parents, more so than I am from mine. Perhaps not, though — maybe I underestimate our differences sometimes and overestimate our similarities other times. Right now, I like the sense of stability and continuity I find by seeing myself in my parents, even though I have spent much of my life — and even much of the past four years — trying to be different." (1995)
"...a life buttressed by the strength and continuity of the granite of the Sierran batholith, which looked down on the valley from the east, forming the backbone of my early life." (2000)
"And maybe there is more continuity in my life than [Rick Bass] is referring to above. Maybe." (2004)
"I think that some of the continuity in a geological career or in a geologist’s life comes through seeing old places again and through watching/seeing/knowing where former colleagues are working.... This knowledge can be obtained by following the movement and careers of other geologists (engineers, techs, miners, et cetera) and by following the evolution and history of certain properties, projects, and mines. One can also follow the status and changes in mining and exploration companies in general. So, I think there is continuity after all, despite what Rick Bass said in that one book of his...." (2007)
"Further work is recommended to test for continuity and thickness of this deep zone, and to see if it shallows to the east or south." (date withheld)

So, is there no continuity in a geologist's life, especially if the geologist is an exploration geologist of some sort? It's true that one rambles and roams from place to place, town to town, prospect to project, company to company — but is there a larger, greater sense of continuity somewhere? Sometimes, I'm really not sure. When I first read the words by Rick Bass, quoted at the beginning of this meander blog post, I felt that despite certain breaks, disruptions — fault lines in my life — that there had been a certain continuity, which I described earlier as the remembering or revisiting of continuous life aspects, for example people. I think I was referring to something larger than that, though, but am not sure I can describe what I really meant.

When I think about continuity, I first have to say that my parents have been a constant in my life: they have provided a backdrop to what I've done with my life through all these many years. And yet I know that they will not always be here sharing my life with me, even if from afar by phone, through visits, and through email. And when I think about that, I feel sad. But as I write that, I also realize that the constancy in this one aspect of my life is larger than it seems: despite an anticipated future in which they are no longer here, they will still, in some way, provide a backdrop or internal place of permanency inside me for what I will do in the future. They will always be part of me; they will always be here. That is one sense of continuity, although that sense is also combined with a similarly large sense of discontinuity.

Geologists of the exploration persuasion (and many geologists of other persuasions) are always looking for (and sometimes finding) continuity between this outcrop here and that one over there, a correlation that will provide an understanding between two spatially distant areas. Once a correlation is found between these two outcrops — no matter how distant they are — a certain geological understanding might come about. For example, one might then realize that these distant outcrops represent the same moment in geologic time. This type of continuity can easily arise when the rock type and rock formation at the two distant outcrops are the same (for example the Ely Limestone of Pennsylvanian age). You might see identical and very specific fossil assemblages in the two outcrops, an indication that the two outcrops are from the same bed or geologic horizon; you might see other geologic indicators hinting at correlation, such as specific types of chert nodules; and you might notice that the particular bed is overlain by another diagnostic bed and underlain by even another diagnostic bed, if you are very lucky. You might then realize that you are seeing the same bed at both exposures, and you will therefore come to realize that you are looking at practically the same time in geologic history in both places. You've just found continuity in time across spatial distance by correlating two outcrops of one specific cherty limestone bed containing a particular key fossil or set of fossils. [This may be a rather meandering way of explaining part of the stratigraphic principle of lateral continuity.]

Another way in which you might, as a geologist, recognize continuity in geologic time across outcrops separated by spatial distance, is to find a correlation in key fossils from a particular geologic time interval, even though the two outcrops in question are of different rock types. Here we have a concept that's slightly more complex, but one might find the same trilobite in a Cambrian shale in this area over here and find the same trilobite in a Cambrian limestone some tens of miles (or more) away.

Another example of this second type of geologic continuity would be what happens with correlation of tephra beds: a resultant volcanic ash layer or bed that is deposited after one particular volcano erupts ash during one single volcanic event. An example would be the eruption of Mt. St. Helens on a particular day in 1980: on May 18th, 1980, Mt. St. Helens ash was spread far and wide across the northwestern U.S., and where it is preserved as a layer, one can identify that particular day in geologic time. Another example would be the eruption of the Mazama Ash from Mt. Mazama (now Crater Lake) on an unknown day about 7000 years ago. That ash was blown even farther and wider across the western U.S., and it was deposited in a recognizable layer and preserved in more than one kind of geologic environment. One can correlate that particular moment in geologic time from clayey lake sediments in southeast Oregon to rocky talus deposits in central Nevada. The geologic formations are different, they are separated by a distance of hundreds of miles, but those different geologic formations — a lake bed in Oregon and a talus slope in Nevada — were forming at exactly the same time. That's demonstrable geologic continuity between dissimilar geologic formations. These particular geologic beds — lake clay and talus — may not survive to become parts of future rock formations, but maybe they will.

Another way that geologists find continuity in the field, is to walk out contacts between particular rock formations from outcrop to outcrop, mapping them on paper and with GPS. Geologists map the correlation between rock formations, fault exposures, and mineralized zones this way: by mapping them in the field, by following them on the ground from outcrop to outcrop. The continuity an exploration geologist looks for will often be a speculative one during this mapping phase, one that will be later proven — or disproven — through drilling. The mineralized area might be continuous for hundreds of feet or even miles; this is a kind of spatial continuity that is required for mining. It's good, also, to find continuity in assay grade and in other economic parameters such as metallurgy. I look for these kinds of continuity while prospecting, I try to predict and project these kinds of continuities when mapping, I sometimes prove these kinds of continuities by drilling.

When I once again think about continuity in my life, I really have to go back to basics. I know that in some ways I am the same (or at least similar) to ways I was in the past. Certain characteristics will, perhaps, be found within me throughout my life. I have an experience of continuous (or mostly continuous) memory from one point in my life to another — a seeming persistence of myself through time — but I also know that I have changed through that time, sometimes profoundly. I wonder then — when I think of my life, my character, myself as containing a certain kind of continuity — am I deceiving myself?

So I go even farther back, back to basic basics. And I think that geology itself is something continuous in my life: it goes back to an early time in my life, if one considers geology to include my early childhood interest in rocks.
I am a geologist. I was a geologist. I will be a geologist. I will always be a geologist.

I have been other things, I have done other things, but there is something basic about being a geologist that will stay with me no matter what I might do in the future. For one thing, I will probably always have rocks in the house. If I clean them out, I just make space for new rocks to come in. It happens every time I remove various rock piles scattered from truck to garden to living room to garage. It doesn't seem to matter what I'm doing with my life at the time — geology, art, travel, school — a new and interesting rock will somehow work its way into my house, often when there isn't really room, and sometimes when I'm not really looking.

I often, however, have a hard time seeing the day-to-day, year-to-year continuity in my life. My outward activities change, my jobs change, the places I go for work change, the people I work with change. Perhaps it's easier to see continuity when one is younger. Perhaps continuity is really an illusion, something I create in my mind in order to feel something solid, something dependable, something constant, something rocklike in myself and in my life.

I am a geologist. The rocks, the earth — they are always the same. See how they don't move (except during those occasional events like earthquakes, volcanic eruptions, and landslides). See how the landforms and topography of even geologically active areas remain solid enough and constant enough that we can use topographic maps made in the 1970's and earlier — at least for most of the basics. But because I am a geologist, I know that all those statements are exactly and precisely incorrect. The rocks and the earth, the landforms and the topography do not stay the same, no matter how much I think they do, no matter how much I wish they would. The topographic maps of the 1970's and before show identity of topography until you come down to the details that are changing day to day and year to year. The stream beds have moved. The talus slopes have creeped. Lava flows have massively changed the topography in Hawaii, and they do so on a daily and yearly basis. Shorelines and barrier islands have moved. Deltas have changed their shapes. Rapids in canyons like the Jarbidge and the Grand have changed: they move, they increase, they diminish. New rapids form. Old ones disappear. Nothing is the same; the only constant is change.

Mountains like the Sierra Nevada, rock solid and made of granite, always give me a feeling of continuity. The Sierra Nevada in particular has provided some sense of structure and constancy in my life since I can remember. I was not born near them, but grew up with them looming above me. I have lived more than 3000 miles away from them, and they have even then been part of my life. They are there; they provide a sense of where I am, a sense of location, even when I can't see them across the many mountains of the Great Basin. When I am in Alaska, there they are, miles and miles to the southeast. When I am on the East Coast, there they are, miles and miles to the west. They are always there. Through my life, they have always been there. It is, thus, easy for me to extrapolate back in time to think that they have always been there — and they have been there for a very, very long time, but not forever. It is also easy for me to extrapolate into the future and find no future in which they don't exist. In my lifetime, they will always be there. In the geologic history of the far future, they will be there as mountains for a very long time. Even after they are no longer mountains, but are plains with an occasional granite knob sticking out through future sediments that have long since buried them, they will be there as a geologic province for a very, very long time (look at the ancient Appalachian Mountains, no longer the same as they were when first a mountain range akin to the Sierra Nevada, yet still, hence these many geologic eras, well-recognizable as a geologic province). Someday, however, every trace of the Sierra Nevada will have been subducted into the mantle by some future, yet-to-form subduction zone. They will not be there forever. They have not been there forever, no matter how much I'd like to think so, no matter how much I wish they were and will be. Even this one rock-hard, granite-solid seeming constant in my life isn't. When I think about continuity, at least today, I find little, maybe none. I find that sad, and yet, there it is.

Continuity: I get up in the morning at about the same time every day, I make the bed and turn on the computer, while the computer is turning itself on I make coffee. I heat my cold cup with hot water, I take the coffee to the room and start up my internet connection. I sign in to Blogger and open up my main blog page, I check the weather on one to three websites using two to ten weather subpages, I turn on or sign in to one or more social network sites and check them, or not. ... No matter what my current state of life is, I find or set up some kind of routine. The routine provides me a sort of comfort, but it doesn't provide any real continuity.

Photos from Wikimedia:

Friday, February 19, 2010

One Year Ago Today: A Stop in Baker, NV

One year ago today, after a rousing snowshoe trip, MOH and I stopped at this establishment in Baker, Nevada (one of very few establishments in Baker, Nevada).
I love the colors of the place, and could probably spend all my time taking pictures.
If you ever stop by, be sure to notice that you can see the Snake Range detachment fault from the front of the building, just under and north of the main sign. The fault can also be seen on the banner of this blog and in a couple other posts. (And the fact that you can see the fault in this photo makes this One Year Ago post also qualify as a Friday Fault Photo post.)
After going inside, you can have a meal in a cheery room...
...or, if you've a mind to, you can have one of a couple fine draft beers. Mmm... makes me thirsty. Bye!

Disclosure: This is not a paid-for restaurant review, just a random blog post.

Monday, February 15, 2010

Links: Rheomorphic Tuffs and Voluminous Silicic Lava Flows

My blogging will be light through this coming week - unless I find some unexpected free time - so I'm going to post some links I found recently about rheomorphic tuffs and voluminous silicic lava flows. My first exposure to these kinds of rocks - ash-flow tuffs or ignimbrites that are so strongly welded that they can be mistaken for rhyolite flows and domes - was in the High Rock country north of Gerlach, NV, and near Soldier Meadow, back during my days of uranium exploration. The rocks in question in that area were peralkaline (or peralkalic) ash-flow tuffs that showed laminated textures more typical of flows. Rheomorphic tuffs (RT - my abbreviation) can apparently be difficult to distinguish from extensive or voluminous silicic lava flows (VSLF - my abbreviation). The rhyolite of Dorsey Creek (Tdc) - which we saw here and here near Jarbidge, NV, and which erupted about 8 million years ago from the Bruneau-Jarbidge eruptive center - is a voluminous rhyolite flow. I'm not sure I'd be able to tell these things apart - RT v. VSLF - without doing some real research and going on a good field trip or two.

Volcanological aspects of peralkaline silicic welded ash-flow tuffs (1974): Bulletin of Volcanology [abs].

Mid-Tertiary silicic alkalic magmatism of Trans-Pecos Texas: Rheomorphic tuffs and extensive silicic lavas (1989): NM Bureau of Geology and Mineral Resources [buy Memoir 46, it looks good!]. NOTE: the silicic magmatism of the region is "commonly peralkaline" and includes "strongly rheomorphic welded tuffs, and unusually widespread silicic lavas." This is a field guide.

In situ formation of welded tuff-like textures in the carapace of a voluminous silicic lava flow, Owyhee County, SW Idaho (1996): Bulletin of Volcanology [abs]. NOTE: this is about the Badlands Rhyolite, a VSLF with textures similar to rheomorphic tuffs.

Field guide to the Rattlesnake Tuff and High lava Plains near Burns, Oregon (1999): Oregon Geology. NOTE: This is the only full article in the batch, and it not only mentions rheomorphic tuffs and peralkaline magmatism, but it is also a field guide.

Distinguishing strongly rheomorphic tuffs from extensive silicic lavas (1992): Bulletin of Volcanology [abs] - wherein Chris Henry and John Wolff state that, "Extensive silicic lavas could be appropriately termed flood rhyolites."

Rhyolitic ignimbrites in the Rogerson Graben, southern Snake River Plain volcanic province: volcanic stratigraphy, eruption history and basin evolution (2008): Bulletin of Volcanology [abs].

Northwestern Nevada: An early caldera-focused system of the Yellowstone hotspot track (2009): 2009 Portland GSA Annual Meeting [abs]. NOTE: About the Soldier Meadow Tuff and the peralkaline rhyolite flows and tuffs of the High Rock Canyon volcanic center.

The Soldier Meadow Tuff of the High Rock Caldera, northwestern Nevada (2009): 2009 Portland GSA Annual Meeting [abs]. I'm sorry I missed this session!

Wednesday, February 10, 2010

Road to Jarbidge: South into Nevada!

And so, I relaxed at the Jarbidge Forks, before turning back to my truck. It was the second day on my journey to Jarbidge, and I was going to make it this time!
But first (from the first day), we'll take a quick look to the north, downstream in the canyon of the Jarbidge River. The geology of the canyon walls is a bit deceptive. The rocks are dark-looking from a distance, so it's easy to imagine they are all basalt. It's not that simple, though. The thin flow on the distant canyon rim in the above picture is composed of a basalt mapped as Tbf, basalt of Big Flat, on this map, a portion of which is shown below. All the rocks you see in the foreground on the right side of the canyon (on the east)—all those chocolate-colored brown rocks—are part of a thick, widespread, high-volume rhyolite mapped as Tdc: the rhyolite of Dorsey Creek, sometimes called the Dorsey Creek Rhyolite. It erupted from the Bruneau-Jarbidge eruptive center.
1 This southeast part of the mapped area just barely shows the Jarbidge Forks area: it's the easternmost canyon junction, located just a little below the center of this map snippet, below a "Tbf" label.
Looking upstream to the southeast (a view from the second day) we see a similar geologic situation in the East Fork of the Jarbidge River. The map shows that the uppermost flow is still the basalt of Big Flat. The basalt is underlain by a section of Tsl—lower undivided sediments—with the rhyolite of Dorsey Creek below that, underlain by another section of Tsl. The photo doesn't really show these units that well, but was taken more as an overview shot.
And finally, at about 12:30 pm on the afternoon of the second day, I left the Jarbdige Forks and forayed south toward Jarbidge. The flow on the canyon rim, if we are still inside the mapped area, may be Tda: the basalt of the Diamond A Desert. Like the basalt of Big Flat, this younger baslat is underlain in this area by the rhyolite of Dorsey Creek. The rhyolite pinches out rapidly to the south and is replaced by a thick section of Tsl, likely the slope former in this photo. I took the photo because of the cirrus clouds, and wasn't really thinking about the rocks at the time. Location of the photo is inexact due to a failure of my GPS-track–saving system.

The basalts are Pliocene or Miocene, the lower undivided sediments are Pliocene or Miocene (and Miocene where below the rhyolite of Dorsey Creek), and the rhyolite of Dorsey Creek is Miocene, dated at 8.1 Ma.
I then left Idaho and entered Nevada. There was, for once, a nice pullout—so I pulled over and took a photo of the Idaho sign, looking back to the north. The road was wider in Nevada. Yay!
While at the pullout, I shot a couple pictures of the hoodoos on the west side of the canyon—unknown formation, unknown rock type.
It was fall...
...beautiful, beautiful fall.
At 1:00 pm on the second day, I arrived in Jarbidge. The sign says: *JARBIDGE* PLEASE SLOW DOWN, THIS IS OUR TOWN.

Some References:
Bonnichsen, Bill, 1982, The Bruneau-Jarbidge Eruptive Center, Southwestern Idaho, in Bill Bonnichsen, and Roy M. Breckenridge, eds, Cenozoic Geology of Idaho: Idaho Geological Survey Bulletin B-26. p. 237-254.

Bonnichsen, Bill, and Breckenridge, R. M., eds., 1982, Cenozoic Geology of Idaho 1982: Idaho Geological Survey Bulletin B-26, 725 pp.

Bonnichsen, Bill and Jenks, M.D., 1990, Geologic map of the Jarbidge River Wilderness Study Area, Owyhee County, Idaho: U.S. Geological Survey, Map MF-2127, scale 1:50000.

Cathey, H. E., and Nash. B. P., 2009, Pyroxene thermometry of rhyolite lavas of the Bruneau–Jarbidge eruptive center, Central Snake River Plain [abs.]: Journal of Volcanology and Geothermal Research, Volume 188, Issues 1-3, p. 173-185.

Friday, February 5, 2010


I thought about following a recent trend of daily rock, outcrop, and mineral posts by making one such post per week, then reality hit me over the head and I backed off. This week, however, I have a nicely polished specimen of unakite to show off, even though the specimen isn't mine: I photographed it in Alaska.

Although currently residing in Alaska, this chunk of unakite is from the Blue Ridge Mountains of Virginia. (It's been around.) Unakite, a gemstone sometimes used as a building stone, is a metamorphosed or altered former granitic rock, with a type locality in the Unaka Range of the Great Smoky Mountains of eastern Tennessee and western North Carolina. Callan Bentley describes the origin of typical Blue Ridge Mountains unakite as being a 1.1 billion year old granitoid that got metamorphosed "during Alleghanian mountain-building, between 300-250 million years ago."
This enlargement shows an epidote veinlet cutting some of the reddish pink potassium feldspar in the upper right corner. That's an antique 10X Triplet hand lens for scale.
Here you can see a tiny quartz veinlet cutting the pistachio-green epidote, the reddish-pink K-spar, and the irregular gray masses of quartz.

I first visited the locality where this unakite was collected way back in my undergrad days while on a field trip led by W.D. Lowry. Later, probably while on an outing to some great camping location in the Blue Ridge Mountains, I visited this site with my entire family. My dad collected this particular piece of unakite—somewhere east of Charlottesville, on an east-west road south of the main east-west road heading west from Charlottesville (now I-64), on the west side of the mountains.

I thought maybe I could find the location in Google Street View, but that search was pointless until I did a little research on unakite localities near Charlottesville. And guess what? I think I found our site: somewhere on Highway 56 about one to two miles east of Vesuvius, VA, near an old unakite quarry, possibly between this roadcut and this roadcut. There's a chance that we were on some back road south of Highway 56, but still somewhere within the general Irish Creek–Big Mary's Creek–Little Mary's Creek unakite collection area of Rockbridge County, VA.

I have my own unakite around somewhere, either on a shelf or in a box at the lake. It's one of my favorite rocks, probably because of it's spectacular color, and also because it's likely one of the first rocks I collected as a budding, first- or second-year geologist. (Or maybe a Virginia trilobite was one of my first collections?)

Ron Schott's unakite pebble.

Andrew Alden's polished unakite.

Thursday, February 4, 2010

Road to Jarbidge: To the Jarbidge Forks

The Jarbidge Mountains—visible in the distance to the south and southwest (left)—are in Nevada; we are still in Idaho, trying to make it to Nevada. Here, we haven't really come to the end of the 3 Creek–Jarbidge Road, we've merely come to the end of the pavement: Pavement Ends.
The sign says: Hill [squiggly] Slow - Next 2 Miles.
And with the north end of the Jarbidge Mountains in the background, the dirt road curves and descends into the canyon of the East Fork of the Jarbidge River. The sign says: Watch For Ice. I didn't see any ice, but it was fall—maybe not the right time of year.
The road down into the canyon is fairly narrow, with a cliff on the right and air on the left. I didn't notice any pullouts, so taking photos of the scenic canyon was tricky.
I stopped briefly in the middle of the road at one point and looked south up the East Fork toward the Jarbidge Mountains.
I then completed the descent, arriving at the bottom of the canyon at the same time I arrived in Murphy's Hot Springs. The place appeared to be inhabited, but I didn't drive in to see if a commercial hot springs is currently in operation. The Idaho Office of Energy Resources lists Desert Hot Springs Resort (aka Murphy's Hot Springs) on their Geothermal Springs of Idaho page; they then link to Hot Spring Heaven (dated April/May 2000), which tells the history of Murphy's Hot Springs and gives an out-of-service number to call for information or reservations. So, another trip will be required determine the status of the springs and small settlement.
Driving northwest along the East Fork of the Jarbidge River, I spotted a couple pullouts occupied by hunters and other campers. The road is narrow enough in places to prevent the passage of two side-by-side vehicles, so I had to watch constantly for traffic coming around corners, traffic that included people on 4-wheeler ATV's. The sign says: Watch For Falling Rock.
These are some of the rocks that warrant watching, in case they start falling. The exposure is most likely part of a formation commonly or at least locally known as the Dorsey Creek Rhyolite or rhyolite of Dorsey Creek. I didn't stop to examine these rocks: I didn't see pullouts in appropriate places. Maybe some other time.
I finally arrived at The Jarbidge Forks, Idaho—at 3:10 in the afternoon on the first day, and 12:15 pm on the second day. This is where I decided to turn around on the first day, not knowing that I could have gotten gas, food, and lodging 23 miles down the road in Jarbidge, Nevada.
The Jarbidge Forks consists of the intersection of the East Fork of the Jarbidge River coming in from the southeast, with the main Jarbidge River coming in from the southwest. Farther downstream to the north, the Jarbidge River joins the Bruneau River before the Bruneau flows into the Snake River near Bruneau and Grand View, Idaho. You Are a Long Way From Anywhere, warns this informative sign.
I stopped here both days, to take in the river and canyon views. This shot of the Jarbidge River is looking downstream to the north.
And this photo of the Jarbidge River looks upstream to the south. There's a boat ramp just out of view for river runners, usually expert kayakers.
This is some of the most isolated country anywhere. If you get into trouble on the river, you're probably the one who will have to get yourself out of it.
Info and nice canyon pictures.

A few Dorsey Creek Rhyolite References:
Bonnichsen, Bill, 1982, The Bruneau-Jarbidge Eruptive Center, Southwestern Idaho, in Bill Bonnichsen, and Roy M. Breckenridge, eds, Cenozoic Geology of Idaho: Idaho Geological Survey Bulletin B-26. p. 237-254.

Bonnichsen, Bill, and Breckenridge, R. M., eds., 1982, Cenozoic Geology of Idaho 1982: Idaho Geological Survey Bulletin B-26, 725 pp.

Bonnichsen, Bill and Jenks, M.D., 1990, Geologic map of the Jarbidge River Wilderness Study Area, Owyhee County, Idaho: U.S. Geological Survey, Map MF-2127, scale 1:50000.

Tuesday, February 2, 2010

Road to Jarbidge: Jarbidge Mountains

About 20 minutes west from Salmon Falls Dam, depending on how fast you drive or how many photo stops you make (~25 km or 15 miles), the Jarbidge Mountains come in sight across the volcanic plain. This view is looking southwest to SSW toward the mountains from the 3 Creek–Jarbidge Road. The view is quite similar to the picture in this Wikipedia link, although they incorrectly state that their view is to the northwest.
A closer shot from the same location reveals that a the southern end of the volcanic plain is tilting to the north, right at the junction of the Basin and Range (Jarbidge Mountains) and the Owyhee Plateau—a volcanic plain elevated above the Snake River Plain (SRP), and an area where the track of the Yellowstone hot spot went through about 8 to 14 million years ago. You can also see at least three glacial cirques from this angle, along with Matterhorn, the highest peak in the range. The Matterhorn, third peak from the left, may not be a proper glacial horn, as I can only identify two cirques that have helped shape it.
Now—after 40 to 45 minutes, 60 km or 37 miles—we've come to the last leg of the Jarbidge Road before it drops into the East Fork of the Jarbidge River. We're looking almost due south at the Jarbidge Mountains, behind the northward tilting volcanic plain that looks as though it's been pushed upward by the mountains. Instead, though, the tilting may be from downwarping related to development of the Snake River Plain, although most references discuss downwarping of the eastern SRP, for example here and here, rather than downwarping of the west-central portion of the SRP.
This is the part that fascinated me. I noticed this gap in the tilted plain as I got closer and closer to the downgrade into the East Fork of the Jarbidge River.
The gap is a canyon, or set of canyons, carved into the plain by the East Fork of the Jarbidge River and one of its tributaries, God's Pocket Creek.
The mountain one sees through the gap is called God's Pocket Peak.

Some Links and References:
Beranek, L.P., Link, P.K., Fanning, C.M., 2006, Miocene to Holocene Landscape Evolution of the Western Snake River Plain Region, Idaho: Using the SHRIMP detrital zircon provenance record to track eastward migration of the Yellowstone Hotspot. Geological Society of America Bulletin, September/October 2006, p. 1027-1050.

Hughes, Scott, SRP-Yellowstone Volcanism: Digital Geology of Idaho, Idaho University.

Link, Paul, Neogene Snake River Plain-Yellowstone Volcanic Province: Digital Geology of Idaho, Idaho University.

USGS, Description: Idaho Volcanoes and Volcanics: USGS/Cascades Volcano Observatory, Vancouver, Washington, webpage dated 01/22/03.

Snake River Plain: Digital Atlas of Idaho, Idaho Museum of Natural History.

Southern Idaho Topographic Development: Digital Atlas of Idaho, Idaho Museum of Natural History.

Related Post:
Road to Jarbidge: Salmon Falls Dam

Monday, February 1, 2010

A Few (Mostly) Late January 2010 Geoblogic Links

Here, in non-chronological order, are a few of the geoblogospheric posts that have caught my eye recently.

A photo of megabreccia on Mars at Arizona Geology. (I love breccias!)

A great aerial view of Lassen Peak at Geotripper, part of his Other California series.

Coal and the fossil record of climate change in the Canadian High Arctic by Anne Jefferson of Highly Allochthonous.

The answer to something I've always wondered: Inkstain FAQ at jfleck at inkstain: What’s With the Easy-Do Parties Lady? at jfleck at inkstain.

A 1000th geblogospheric post: 1K at NOVA Geoblogand read the comments.

Sand posts at Ron Schott's Geology Home Companion: Salt and Pepper, White, Multicolored, Green, and Black—my favorites are the S&P, multicolored, and green (at least today).

And speaking of sand, more on the continuing and neverending story of Sand: The Neverending Story: A virtual book tour by Michael Welland, so far at Clastic Detritus and NOVA Geoblog, soon to be at Andrew Alden's Geology and BLDGBLOG.

And, in case you haven't already seen this, the results of the recent geoblogosphere survey by Lutz Geissler, Robert Huber, and Callan Bentley at

If you are going to the Tucson Gem and Mineral Show in February, contact Lee Allison of Arizona Geology about a Geoblogger get together.

And finally, I loved seeing this mix of art and geology: a review of the Geo Sapiens Geologic Art Exhibit at Clastic Detritus; the full exhibit is at the Two Wall Gallery.