Mantling on Utah’s Hogback Ridge

August 03, 2022

TomMc_EPOD.MantlingHogbackRidgeUtahMcGuire (002)

TomMc_EPOD.LowerCalfCreekFallsMcGuire (4) (002)_a

Photographer: Thomas McGuire   

Summary Author: Thomas McGuire  

For 5 miles (8 km), Utah’s Route 12. between Escalante and Boulder, Utah, follows the narrow 1,000 ft (305 m) high Hogback Ridge of Navajo Sandstone. Spectacular long views on either side of this highway show tan-to-white-to-yellow Navajo 'slickrock'. The ridge is also bounded by deep canyons: One is Calf Creek, with two impressive waterfalls (bottom photo); on the opposite side is Boulder Creek, with narrow slot canyons.

But there’s a clear sign of something missing. Part of the ridge is strewn with giant boulders of basalt. Clearly there were lava flows that covered the Navajo Sandstone along an unknown part of the ridge and probably much more. For most of the 5 miles (8 km), all that’s left are the lava-boulders mantling the sandstone.

Basalt is very resistant to weathering and erosion, so it forms the cap rock of many flat-topped mesas in the Southwest. As the sides of the mesa erode back, basalt boulders fall from the top and cover the slopes along with the underlying rock type that make up the body of the mesa. An observer can be forgiven for thinking the whole mountain is basalt when the bulk of the bedrock is hidden beneath its thin mantle of basalt and boulders, which will completely erode away with (geologic) time. When this happens, there’ll be no record of the lava flows that once covered significant areas around Hogback Ridge.


Hogback Ridge, Utah Coordinates: 37.8144, -111.4091

Related Links:

Cap Rock Fails in Sudden Debris Flow 

Slickrock: A Rock Surface, a Town, A Geologic Unit

Author’s Earth Science Books Web Site

The Under-Rated Value of Earth Science Education