For thousands of years, petroglyphs have preserved the hopes, dreams and desires of ancient cultures in the rocks and sediments around Yuma County. The images are carved or pecked into the patina of rocks, and were used by Native Americans to tell stories, describe significant events, and mark trails throughout the Southwest.
     In the Yuma area of extreme southwest Arizona, USA - next door to both southern California and northern Mexico - petroglyphs as old as 9,500 years are found, but it is extremely difficult to give exact dates for them. "Unlike in pictographs, where you leave something behind, petroglyphs don't leave anything, they take something away," said Tom Jones, an archaeologist with Yuma Field Office of the U.S.A. Bureau of Land Management, "...it's almost impossible to carbon date."
     Only by examining both the images' motifs and figures, and the ceramics and tools found near a site, can archaeologists piece together the who and when of a petroglyph's origin. Based on the evidence around the Yuma sites, most of the petroglyphs were created during the Patayan and Hohokam period (700 CE to 1450 CE) but some are much older. "There have been archaic people in the (Yuma) region for thousands of years," Jones said. "So it's possible some could date all the way to 7500 BCE"
     The largest collection can be found at the Painted Rocks Petroglyph Site located just outside the town of Gila Bend, where around 800 images are inscribed on basalt boulders. The petroglyphs are extremely fragile, and should never be touched.

Edited from Yuma Sun (10 July 2011)