Utah Rock Puzzle

November 14, 2016


Photographer: Roger Hopkins
Summary Author: Roger HopkinsNovember 2016 Viewer's Choice

This is a view from the southern end of Cedar Mesa near Muley Point in southeastern Utah. At the bottom of the cliff 1,000 ft (300 m) below you can see the Johns Canyon Road following the ancient floodplain of the San Juan River. The present day river is well entrenched another 1,000 ft lower in a series of deep meanders called the Goosenecks. The view continues to the south for 20 mi (32 km) past Davis Mesa to where the monoliths of Monument Valley punctuate the horizon.

In the immediate foreground is a puzzle: How did the light-colored boulder get on top of the huge dark fallen block? If you can help solve this puzzle please follow the Discuss on Facebook link below and post your ideas. I can only guess how this happened.

Here are a few clues that may be of use: Both the boulder and the fallen block are Cedar Mesa Sandstone, part of the Cutler Formation of rock, formed in the early Permian Period (290 million years ago), that forms the upper half of the mesa. The lighter white color may be caused by bleaching of surface rock by rain and or sunlight over the ages. The dark black color is a superficial coating of desert varnish formed of clay, silica, manganese, and iron particles carried by the wind. In this area, most of the desert varnish forms very slowly on the exposed vertical surfaces. There are numerous vertical joints (fractures in the rock) that can explain the flat surfaces of the huge blocks that have broken away from the cliff. Note the brownish red color is caused by oxidation of iron content in the rock.

Views from other angles are available here that show the overall context and may help you solve the puzzle. Photo taken on October 13, 2016.