Tuesday, April 11, 2017

From the Road: The Book Cliffs in Western Colorado (Mount Garfield)

Earlier that day (the same day I stopped in Parachute and Rulison, resulting in three posts about the Roan Cliffs), I had pulled over at the convenient viewing pullout on I-70, which is east of Grand Junction and a bit west of Palisade. It's hard to pass by this cliff, part of the Book Cliffs, without taking a picture or two. This time, unlike most other times, I took only one photo!

The Book Cliffs are capped by sandstone and lesser shale of the Upper Cretaceous Mesaverde Group, which overlies shale and minor siltstone and sandstone of the Upper Cretaceous Mancos Shale. The Mesaverde Group (sometimes Formation, see Geolex) usually consists of several recognized sandstone tongues, members, and formations, with intertongues of Mancos Shale in its lower part. In the area of these photos, the mapped sandstone formation—the buff-colored cliff-former above the Mancos—is the Mount Garfield Formation, obviously named for Mount Garfield, the highest point above the cliffs, on the upper left.
I cropped the photo to zoom in, partly because the nearly white layer just below the sandstone cliff caught my eye. While here, we might as well take a peek at the geologic contacts.
Kmg is the Mount Garfield Formation; Km is the Mancos Shale. The contact I’ve drawn in is largely from the Geologic Map of the Clifton Quadrangle, Mesa County, Colorado (Carrara, 2001), with extrapolation from the Geologic Map of the Palisade Quadrangle, Mesa County, Colorado (Carrara, 2000). The contact very roughly approximates the one shown on the Macrostat online geologic map.

Other photos of mine of the Book Cliffs can be seen here (photos from 2006) and here (photos from 2008). Also check out Ron Schott's GigaPan of the cliffs.

No comments: