The confluence of the Pecos and the Rio Grande is the Chihuahuan Desert's lowest, hottest point. The landscape bears the evidence. Across sun-blasted limestone, stunted plants seem to writhe and twist, waiting out the harsh sentence of soil and sky.

From uplands on the Pecos, a trail lead into a side canyon, then to a shallow cave – and the utterly unexpected.

Images blanket the 25-foot cave wall. Towering human figures with outstretched arms, renderings of deer and centipedes. Abstract or ambiguous forms – a stepped arch, an undulating mass – part-serpent, part-catfish.

The paintings here at White Shaman Shelter, and at related sites across the Lower Pecos, have long fasc...