There are various methods used to determine the age of a petroglyph or pictograph, but it is difficult to do.  Archaeologists look for associated artifacts, i.e.; stone tools or pottery found close to the rock art.  These can provide clues as to what group of people may have produced the images.  

Archaeologists also look for style comparisons.  At a Clay County site the petroglyphs appear to be derivatives of the Southeastern Ceremonial Complex iconography (1250AD to 1350AD). 

We can tentatively assign a time frame for the site based on contrasting and comparing known icons from that cultural period.

Other methods attempt to directly date both petroglyphs and pictographs.  Radiocarbon dating of pictographs is the most well known.  This requires removing an organic pigment sample from the image.   However, if a sample is contaminated from over lying substances, such as smoke or soot the image can't be accurately dated.  Paint Rock is an example of this.  The site had long been used as an overnight stopping point on a pre- and historic trail. Reportedly, there were other pictographs on this rock which have been covered with charcoal and soot.  Research is on going in developing new methods to date rock art.  Some of these involve trying to date the lichen/moss or patina that develops over the carvings.