Weaver's Needle is a 1,000-foot-high (300 m) column of rock that forms a distinctive peak visible for many miles around. Located in the Superstition Mountains east of Phoenix, Arizona, Weaver's Needle was created when a thick layer of tuff (fused volcanic ash) was heavily eroded, creating the spire as an erosional remnant with a summit elevation of 4,555 feet (1,388 m). It is set in a desert landscape of cactus and mesquite bush, with large Saguaro cacti particularly prominent. The peak was named after mountain man Pauline Weaver (1797-1867). Weaver's Needle has played a significant role in the stories of the Lost Dutchman's Gold Mine. The Needle's shadow reportedly indicates the location of a rich vein of gold, and many treasure hunters have searched for it. The hunt for gold around Weavers Needle has been pursued by hundreds (possibly thousands) of people.

Pauline Weaver was an American mountain man, trapper, military scout, prospector, and explorer who was active in the early Southwestern United States. He was born in 1797 in White County, Tennessee and died in 1867 at Camp Verde, Arizona. A number of geographic features in Arizona are named after him.

There is compelling evidence for a microbial origin for desert varnish. According to the classic paper by Ronald I. Dorn and Theodore M. Oberlander (Science Volume 213, 1981), desert varnish is formed by colonies of microscopic bacteria living on the rock surface for thousands of years. The bacteria absorb trace amounts of manganese and iron from the atmosphere and precipitate it as a black layer of manganese oxide or reddish iron oxide on the rock surfaces. This thin layer also includes cemented clay particles that help to shield the bacteria against desiccation, extreme heat and intense solar radiation. It has been estimated that up to 10,000 years are required for a complete varnish coating to form on boulders in extreme arid desert regions. The bacteria thrive on smooth rock surfaces on sun-baked boulders in the Colorado Desert of southern California.

In my many visits to the west side of the Superstitions, I thought the blackened rock surface (patina) was caused by desert varnish, a bacterial origin. I revised my previous desert varnish observations with rock-inhabiting fungus (RIF). Under 500x magnification it has the characteristic 2-celled spores produced in an ascus typical of the fungal division Ascomycota (see following link). I also observed RIF along the Hieroglyphic Trail on the east side of the Superstitions. There may be true desert varnish on exposed rock surfaces in the Superstitions. Reddish desert varnish is common on sun-baked boulders in Anza-Borrego Desert State Park and Joshua Tree National Park. Reddish desert varnish is iron oxide while black desert varnish is manganese oxide. Other sources of black surfaces on rocks are crustose lichens and cyanobacteria. They can be distinguished by examination under magnification with a good hand lens, or preferably under a dissecting or compound microscope.

Varnish-coated rocks I have observed in the southwest desert region appeared smoother and better suited for petroglyphs. Extrusive volcanic rocks in the Superstitions coated with RIF have a rough surface and are more difficult to etch.

The trail climbs a gradual rocky slope and then enters the lower end of a boulder-filled canyon, ending at a rocky section with steep volcanic walls where pools persist for much of the year. The massive boulders are coated with black rock-inhabiting fungus (RIF) and lichens. A number of the massive boulders have remarkable petroglyphs carved into the rock surface. This was an important site for the ancient Hohokam Indians who inhabited this desert region over a thousand years ago.