My favorite place to have lunch in Montana is at the Grinnell Glacier cirque in Glacier National Park. This is the dining room table: You’re looking at a bedding-plane-parallel exposure of Mesoproterozoic stromatolites here. Every few years, I’m lucky enough to hike up there with motivated students and share food atop this unparalleled view into … Read more
There’s something about conglomerates that just draws me in. Here’s a lovely example — you might even say it’s an exemplar — from Sandy Hollow in Montana: That’s the basal conglomerate of the Cretaceous Kootenai Formation, one of the mappable units in this mappable region. Feast your eyes on those well-rounded pebbles!
After reading the post last weekend about the discordant offshoot of the Purcell Sill, Rich Gashnig (post-doc at Georgia Tech) sent me a few photos he shot at Piegan Pass (at the head of a side-canyon adjacent to the one containing Grinnell Glacier). They show the Purcell Sill leaving one stratigraphic horizon and jumping to … Read more
The Neoproterozoic Purcell Sill is a stark, obvious black stripe in the strata of Glacier National Park. Here it is emerging from behind “The Salamander” glacier, above Grinnell Glacier Cirque: Zooming in, you can see the “baked” (bleached) zones above and below this concordant intrusion. But this time, during my visit to this special place, … Read more
Here’s a really cool hand sample my student Xiuming found when were were exploring the waste rock piles at the Golden Sunlight Mine near Whitehall, Montana, the week before last: That’s a vein of pyrite and chalcopyrite, offset along a series of three small fault zones: Pocket faults! Three for the price of one.
The Friday fold is asymmetric, overturned, and chock full of primary sedimentary features. Join us in Glacier National Park’s Mesoproterozoic Belt Supergroup.
I found this interesting looking slab of gray limestone last summer in the Bridger Range of Montana, in one of the talus slopes on the north side of Sacagawea Cirque. The high-contrast pattern reminded me of something, but I couldn’t say quite what. Then I realized: it looks like one of those indigenous pictographs, where … Read more
On a cold winter’s day, Callan harks back to a summer’s afternoon fossilizing in the Rocky Mountains. A few choice images of Mississippian-aged marine invertebrates are shared.
Here’s a scene from last summer’s Regional Field Geology of the Northern Rockies course… students examining and sketching some tight folds in Cretaceous strata of the Western Interior Seaway, crumpled beneath the Dorado Thrust (a more southerly equivalent of the infamous Lewis Thrust to the north)… I’ve featured this site before, in a previous Friday … Read more
Red argillite (Grinnell Formation?) and white quartzite strata from Glacier National Park, Montana. Heavily adorned with lichens… With bedding traced out… Happy Friday to you!
Here’s a photo from Tom Biggs (University of Virginia), taken on the NOVA Rockies field course last summer. It shows a recumbent fold along the Front Range of Glacier National Park, in Montana, just north of Two Medicine Lake. I hope you get some ‘recumbent’ time this weekend… I know I could use some rest. … Read more
As I’ve mentioned previously, I spent some time making GigaPans this summer out west. Here’s Lily and me on the crest of the Bridger Range, enjoying the clear skies and great geology: When this portrait was taken (by our friend Lindsay), I was shooting this GigaPan: link Try exploring it to see if you can … Read more
My NOVA colleague Shelley Jaye brought this gorgeous banded iron formation fold back from the Archean of Montana: Gorgeous to think about what this rock represents: (1) an anoxic atmosphere, a world where iron was able to dissolve in seawater; (2) some addition of oxygen, causing the iron to precipitate out as iron oxide minerals, … Read more
Today, a view to the southwest, from close to the hinge of the main anticline in the Sandy Hollow area, a classic geological field mapping locality in southern Montana: Triassic-aged Dinwoody Formation dominates the main part of the scene. Note how the strike and dip of the positively-weathering strata wrap around. Our Rockies students mapped … Read more
A lovely example of a volcanic breccia (from the Eocene Absaroka Volcanics of southern Montana) is showcased, in two different photographs.
My Rockies field course has wrapped up for another year – the fifth year in a row I’ve run this intermediate-level ‘regional field geology’ course in collaboration with Pete Berquist of Thomas Nelson Community College. We were fortunate to be joined by two other professional geologists this year: Chris Khourey of NOVA and Tom Biggs … Read more
Callan zooms in on the meso-scale structure of the French Thrust fault, exposed in Sun River Canyon, Montana.
Last week, we took a closer look at the xenoliths (MME’s?) in the Boulder Batholith. Here is a look at a fracture, perhaps a small fault, in that same outcrop. There are no marker units by which we could detect offset here, so we can’t say for sure it’s a fault. But definitely weathering has … Read more
The week before last, I showed you the Boulder Batholith, as it crops out southeast of Butte, Montana. Today, I’ll share a few more photos of xenoliths (or perhaps microgranular mafic enclaves?) from that same outcrop: Man, I miss that old Swiss Army knife. The damned security actors at Calgary Airport confiscated it last summer. … Read more
The Boulder Batholith outside of Butte, Montana, is actively weathering, and shedding off grus. In the third installment of the Transitions of the Rock Cycle series, we watch an igneous rock turn to sediment.