A visit to a panel along the San Juan River for color and content
Sand Creek panel in late afternoon on a cloudless day/ Photo: © Donald J. Rommes
Desert varnish is the shiny patina that develops on stable rock surfaces in a dry environment. This thin coating comprises water-borne silicates, iron, and manganese bound to the rock surface by bacteria and microscopic plants. In places, large, continuous portions of a canyon wall may have a coating of desert varnish that has been accumulating for thousands of years. Typically dark gray or black, desert varnish was a favorite surface for petroglyphs because carving into the dark coating revealed the lighter rock below and emphasized the glyphs. Desert varnish continues to accumulate slowly and will eventually re-coat the glyphs. The degree of re-patination is one way of determining the age of the glyphs.
Desert varnish is reflective and, on a cloudless day, can appear cobalt blue or cyan, depending on the sun's angle in the blue sky.
The wall shown here has a sizeable continuous coating of desert varnish. Thousands of petroglyphs were carved into the rock face over thousands of years, but they are heavily re-patinated and not immediately apparent in the intensely reflective surface. I wanted this photograph to be appreciated first for its color, then for its identity as a rock face, and finally, for the many embedded petroglyphs.
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