In her book, Guide to Native Rock Carvings, Beth Hill examines these questions. She gives a fascinating introduction to the subject of Aboriginal Petroglyphs of the Northwest Coastal Region - BC, Washington, Oregon and Alaska. Beth Hill and her husband Ray have travelled the coast for close to 20 years, recording the known sites, and discovering others. Out of this came Indian Petroglyphs of the Pacific Northwest, with over 1,000 photos and illustrations. A truly comprehensive study.