I don't know how George Howard does it but he has come up trumps again with another downloadable 10 page article – see http://cosmictusk.com/the-eyes-have-it-clovis-peck-out-ydb-event-in americas-oldest-petroglyphs … It concerns the dating of petroglyphs in the Great Basin area, in Nevada and Oregon for example, and is published online by Elsevior (www.elsevior.com) from the Journal of Archaeological Science 40 (2013). It has a couple of pages of images – which interested parties might want to check out and compare with Anthony Perratt's petroglyphs. A connection is not obvious and the focus of the paper is on dating them. This appears to be around the time of the Younger Dryas event. Bisected chevron designs, cupules, stacked sets of short vertical lines, and even something that resembles a cup and ring mark(a rotating object) and a cross with round globules at each of the four extremities.