The Work of Wind and Deserts - The Changing Earth: Exploring Geology and Evolution - page 394

Petroglyphs are the most common form of rock art in North
America and are made by pecking, incising, or scratching the
rock surface with a tool harder than the rock itself. In arid
regions, many rock surfaces display a patination, or thin
brown or black coating, known as rock varnish (Figure 15.20).
When this coating is broken by pecking, incising, or
scratching, the underlying lighter clolored natural rock
surface provides an excellent contrast for the petroglyphs.
Petroglyphs are expecially abundant in the Southwest
and Great Basin area, where they occur by the
thosands, having been made by Native
Americans from many cultures during the
past several thousand years. Petroglyhs can
be seen in many of the U.S. national parks
and monuments, such as Petrified Forest
National Park, Arizona, Dinosaur National
Monument, Utah, Canyonlands National
Park, Utah, and Petroglyph National
Monument. New Mexico —to name a few.

3. Examples of both representational and
abstract art are displayed in these
petroglyphs from Arizona.

4. A petroglyph on a basalt
boulder in Rinconada
Canyon, Petroglyph National
Monument, Albuquerque,
New Mexico.

5. Examples
of rock art from
Tassili n'Aijer,
Algeria.

6. Rock art found in a rock shelter open to visitors in
Uluru, Australia. These rock paintings are the work of
Anagu artists, local Aboriginal people, and are created for
religious and ceremonial expression, as well as for
teaching and storytelling. Each abstract symbol can have
many levels of meaning and can help illustrate a story.

7. The paints used in this rock art are made from natural
mineral substances mixed with water and sometimes
with animal fat. Red, yellow, and orange pigments come
from iron-stained clays, whereas the white pigments come
from either ash or the mineral calcite. The black colors
come from charcoal.

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