And the answer is ...

A few days ago, I posted some mystery photos, which Silver Fox of Looking for Detachment identified correctly, in a general kind of way.  And yes, the location is south of Denver, as Ben Nevis pointed out, and a bit west as well.  The complete answer is ... Mt. Hillers -- one of the five Henry Mountains, south of Hanksville, Utah.

“beyond are red and white sands -- inferior rocks tilted almost to the vertical and interspersed with dikes.  Moreover these sandstone hogbacks seem to trend in a curve around the mountain as far as they extend."  Grove Karl Gilbert describing the south side of Mt Hillers, 1875.

South side of Mt. Hillers, from G. K. Gilbert's journal (1875).

Gilbert’s work in 1875 and 1876 was revolutionary.  He concluded that the Henry’s were not volcanic, but rather intrusive igneous features, which he called “laccolites” (today’s laccoliths).  These intrusions pushed up overlying sedimentary strata, forming the nearly vertical hogbacks at the base.

Mt. Hillers, viewed from south.

The Henry Mountains in southern Utah, south of Hanksville.  Waterpocket Fold on left, Lake Powell lower right.  Note sandstone “hogbacks” along south base of Mt. Hillers (click to view).  From ArcGIS online.

Stay tuned for more about the intriguing Henry Mountains, as well as the work of G. K. Gilbert -- perhaps one of the greatest field geologists ever.