The Laramie Mountains are part of the central Rocky Mountains in southeastern Wyoming. Archean and Proterozoic rocks form the bulk of the mountain range due to late Cretaceous–early Eocene (Laramide) basement-involved uplift. Hogbacks made of Paleozoic to Mesozoic age rocks flank much of the
The Laramie Mountains of southeastern Wyoming contain Proterozoic and Archean rocks that are now exposed by a late Cretaceous–early Eocene (Laramide) basement-involved uplift. The Precambrian rocks are flanked by hogbacks of Paleozoic to Mesozoic age rocks as seen in the above photo.
Precambrian cored mountain areas. But what sets the Laramie Mountains apart from the adjoining Colorado Front Range and even the western Great Plains is that upper Eocene to Miocene strata are preserved within the Laramie Mountains and on its sides as paleovalley fill. The reasons for this unusual paleovalley fill preservation can probably be tied to the Laramie Mountains being much lower in elevation than the adjoining Colorado Front Range and that they were not glaciated during the Pleistocene.
I went on a field trip a few days ago specifically to look at the Laramie Mountains Tertiary paleovalleys. It was a really good trip. Emmett Evanoff led the trip and because he’s spent so much time working in the area, he had much info and insight on the paleovalleys. What follows are a few photos from the trip:
High Plains escarpment of Tertiary rocks on the eastern flank of the Laramie Mountains near Chugwater Creek. Eocene White River mudstone and siltstone beds are capped by coarse sandstone beds. An overlying gravelly sandstone unit, probably of the upper Oligocene Arikaree Formation lies above the White River beds. The Miocene Ogallala Formation containing stacked conglomerate sheets caps the entire section.
The walls to the Tertiary paleovalleys near Chugwater Creek are hogbacks of overturned rocks ranging in age from Pennsylvanian to Cretaceous.
We found a Daemonelix burrow in Arikareean strata. The burrow is corkscrew shaped and was probably made by the ground beaver Palaeocastor.
Pat’s food truck was a welcome sight during the field trip. As she said – good food and good rocks – what’s better than that?
Large boulders occur at the base of the White River Formation in the Toltec Tertiary paleovalley. The Toltec paleovalley is on the west side of the Laramie Mountains where basal Tertiary strata are exposed at and close to the range margins.
Polished boulders of Precambrian granite are found in the Garrett paleovalley which now lies in the drainage area of the North Laramie River. Wyoming is well known for wind and these boulders certainly attest to that.