Newspaper Rock petroglyphs May 24

Marlene in front of petroglyphs at Newspaper Rock. The petroglyphs have been created over time, some from as early as 700 AD. The black looking coating on the rocks is called desert varnish; created from iron, manganese, clay and sand. The blacker it is, the more manganese is in the mix. The varnish takes thousands of years to make, but the exact process is not yet known. Theory 1: a chemical reaction between rainwater mixing with clay containing iron/manganese then the mixture oxidized by the water causing the mixture to bond to the rock. Theory 2: Bacteria grows on the rock; as they grow they have more concentration of iron/manganese; then the mixture gets oxidized and becomes cemented to the rock. This wall seems protected from the elements with a generous overhang (not shown); that could one reason it has lasted so long in good shape.