| Following Martineau, the symbol on the left is probably a locator combining two meanings: the referenced thing is in this direction (the straight line) and it's distant (the left-branching fork). What the locator is referencing is probably indicated by the symbol on the right. I cannot find a direct analog from Martineau; the closest meaning may be "caves." The locator appears to point to the canyon in the background, and the park hosts indicated that they had found additional petroglyphs in that canyon. See LeVan Martineau, The Rocks Begin to Speak, Las Vegas, NV: KC Publications, 1973.