![]() What an image appears to be on the surface though, may be very different from the meaning it had for the person who pecked the image into the rock. In some instances the image may represent a clan or family. Some images may have been made to ensure fertility or successful hunting, or may have also been used to keep track of the seasons (marking the equinoxes). They probably all have a deep spiritual significance and may be considered prayers by some people.Ĭurrent speculation has led some researchers to believe that some petroglyphs or pictographs may tell a story, mark a trail, or commemorate an event. Some images were possibly made for religious purposes. Some meanings were not meant to be known or understood by the uninitiated. Some meanings were not meant to be known or understood except by the person who made it. What do the petroglyphs mean? What were the Hohokam trying to tell say? We usually do not try and interpret the images or assign specific meanings. Dating such a site as Signal Hill is usually done by dating artifacts associated with the petroglyphs and in this instance there are no well dated artifacts associated with Signal Hill (Figure 4). Direct dating of petroglyphs is difficult. The petroglyphs at Signal Hill were made by the Hohokam, a people who lived in southern and south-central Arizona from about 450 to 1450 A.D. 2įigure 4: Petroglyphs possibly of deer or sheep. Sometimes the relative age of petroglyphs created on the same rock face can be distinguished by the difference in color of the re-varnished petroglyphs. Older rock surfaces tend to be more heavily varnished and darker than younger surfaces.Īs the process continues, petroglyphs are re-varnished. Each time the rock surface is wetted by rain more manganese and clay are added to sustain the slow growing colony. In the process, the manganese becomes firmly attached to the clay and darkens it. The lichen and bacteria anchor themselves to rock surfaces with the clay particles. Micro-colonies of lichens and bacteria inhabit the varnish and oxidize the manganese. The clay minerals as well as the iron and manganese oxides settle as dust from the atmosphere. The varnish consists of thin layers of clay minerals stained by high concentrations of iron and manganese oxides. The dark outer surface of the rock is a mineral patina called desert varnish. Most of the prehistoric petroglyphs at Signal Hill seem to have been produced by pecking.įigure 3: Illustration of the indirect percussion technique. Much like the incision, or scratching technique, abrasion is where a hand-held stone is rubbed against the rock surface to create the image. Petroglyphs created in this way are fine lined, often not very deeply incised and often difficult to see. The third technique uses incision, or scratching, into the surface of the stone with a piece of chipped stone or other material that can render a fine line. Petroglyphs can also be pecked out through indirect percussion, as a second rock is used like a chisel between the hammer stone and the rock surface (Figure 3). They can be created with the use of a hammer stone, usually a fist sized stone held in the hand, usually a fist sized stone held in the hand, which is battered against the boulder or rock surface. Petroglyphs are created by one of four techniques. Both representational and abstract designs can be seen in Hohokam petroglyphs (Figure 2). Petroglyphs are images, geometric, anthropomorphic, zoomorphic, and others that defy categorizing, produced by removing part of a rock’s darker surface patina or desert varnish. These pictographs tend to be small, painted in black or white paint, and are eroded and difficult to see. ![]() There are a few examples of pictographs at SNP but none are accessible to the visitor. There are two principle categories of rock art, petroglyphs, which are carved into the rock surface, and pictographs, which are painted onto the surface. Figure 2: Drawings of petroglyph designs.
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