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.
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.
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.