While flying home for Thanksgiving, I saw this interesting geological formation out the airplane window. I was able to find it on Google Maps, which labels it as “Cayuse Basin”.
The only information I’ve been able to find about it is this blog post, which says it’s a “breached structural dome”, but it doesn’t explain what that means.
Does anyone here know anything more about it? What is it, how did it form, how old is it?
Basically, the underlying rock was dissolved away and the roof collapsed.
https://en.wikipedia.org/wiki/Dome_(geology)
I really have nothing to add to this. I don’t think bob++ is correct, though.
I would’ve pegged that for a volcanic caldera.
Is that in a volcanic/tectonic active area?
Bob is incomplete.
Basically its a laccolith.
Its listed here in this doc about lacoliths.
laccolith is a dome formed by magma…
so then this cayuse basin is where what bob said happened to the dome… the insides washed away and so it collapsed, leaving only the base/ring of the dome …
a caldera is formed where the rock strata melts and sags into a lot of magma…kind of opposite… the dome is where the magma pushes the rock strata up.
its only a bit north of yellowstone ffs. of course its volcanic in origin.
The basin itself isn’t itself a laccolith, it’s a dome ofsedimentary rock (most likely) formed by the intrusion of a laccolith underneath. This intrusion would have stressed and fractured the overlying rock, making it preferentially erode and leaving a ring. This would make it a breached dome but not a breached structural dome (that’s from intersecting folds). IT’d only be a laccolith if there was an intrusive core but the geological map of Montanajust shows sediments and a single dyke. As to how old the actual erosion of the landform or the intrusion is, I don’t know, but the actual sediments that make up the basin are roughly 325-330 million years old.