Upon the highest mountain tops and in the deepest valleys below are found the scattered remains of past Native American cultures that called the Great Basin their home. Archaeologists for decades have probed deep into rock shelters and wandered along long-vanished shorelines of ancient lakes in search of primordial artifacts.

They have found weapons that brought down megafauna, stone grinding implements to process almost microscopic seeds, and houses built of brush and stone. They have found burials, goods of the deity, woven baskets to haul pine nuts, and hooked wooden sticks to pull animals from burrows. They have also found writing on the walls.

Petroglyphs are symbols of a culture's world view. We may never know the meaning behind the symbols, but when viewed in context with a site's other artifacts, they give us insight into the people who left them. That context is lost when people deface or remove rock art. There are places in southern Nevada where vandals have actually used chain saws to take petroglyphs off rock faces. They may have preserved the images, but they've destroyed what is most valuable and meaningful-their context.

It is against the law for anyone to remove or damage archaeological artifacts on public lands. There are no such restrictions on private property, although occasionally owners will consult with DRI or other archaeologists before they develop their land.

I started noticing wall paintings and engravings shortly after I moved to Nevada in 1958. Rock art became more than a passing interest about 12 years ago, after I found several sites on the Mt. Rose alluvial fan southwest of Reno.

Watching the rural landscape become transplanted with buildings, the thought came to me that the area's rock art would be destroyed before being recorded. Documenting the Mt. Rose engravings implanted in me a burning desire to record these vestiges of Nevada's past before vandals and bulldozers scoured them off the face of the earth. Since then, I've recorded hundreds of rock art sites all over the state. Some petroglyph districts extend for miles, and even after repeated visits, their end is not yet in sight.

There has been a recent explosion in the interest in rock art. Many avocationals are out documenting the ancient images, and professionals are placing the pictures in context.

The first major published work of petroglyphs in the United States was written by Garrick Mallery in 1886 for the Bureau of American Ethnology. He listed only four sites for Nevada. Mallery's work was updated in 1893 and the Nevada section had expanded to four pages.

Years later in 1958, one of California's best known archaeologists, Robert Heizer, and his graduate student, Martin Baumhoff, and others began compiling data on the petroglyphs of eastern California and Nevada. Their volume, Prehistoric Rock Art of Nevada and Eastern California, was published in 1962 and detailed about 90 prehistoric sites in Nevada.

While there have been some outlandish theories about the origins of petroglyphs (including notions they were made by aliens or Vikings), Heizer and his students concluded the meaning of petroglyphs is the manifestation of hunting magic.

Since then, additional insights have been made from my own research and that of others, I believe that Great Basin petroglyphs were made in connection with everyday living.

I think that, in addition to the best times for hunting game, the petroglyph makers knew when the berries were ripe, when the seeds were ready for harvesting, and where the best places were for their homes. I think they looked to the mountain tops and the sky for spiritual and physical well-being. Their art reveals they watched the sun swing a 60-degree arc over the east and west horizon during the year and saw a new moon every month.

I have seen family scenes, birth scenes, lizards, foot and paw prints, images of the sun, and abstract art out of this world (or mind). Researchers in South Africa have found that aborigines making petroglyphs there today do so while in a state of trance.

If Great Basin petroglyphs were made during altered states of mind, this would explain why sometimes, when we think we see a lizard image, we are not sure if it is a lizard or a human figure.

Some eerily human forms sprout horns and have large feet and extended digits. Some animal forms look like bighorn sheep, but may have unusual adornments.

We may never know the meaning behind such symbols. But the more we look, the more we'll be able to see what's behind the writing on the walls.