Welcome to stop 1 of the Petroglyph Viewing Trail in Piedras Marcadas Canyon. You've hiked 2 tenths of a mile or.32 kilometers.
The landscape of this canyon formed about 200,000 years ago with a series of volcanic fissure eruptions. The first two eruptions yielded extensive amounts of lava which flowed naturally downslope, east towards what is now the Rio Grande Valley. The following eruptions produced thicker lava flows, eventually blocking the volcanic vents and allowing lava to accumulate, creating the volcanic cinder cones. Today, this 17-mile volcanic escarpment is known as Albuquerque's West Mesa.
The volcanic rock produced by the eruptions is a metal-rich, igneous rock known as basalt. Sometimes, basalt has many little holes in it called vesicles. Vesicular basalt is made from gasses escaping the lava before it cools and hardens. Over time, the exposed surface of basalt darkens in color due to precipitation, extreme temperatures, airborne particles, and microorganisms which collectively cause the metals and minerals to oxidize or rust. This thin layer of oxidation is called desert varnish.
Petroglyphs were made by removing this thin layer of desert varnish from basalt -- to learn more about the process of making petroglyphs and of the people who created them, continue hiking.14 miles or.22 kilometers to stop 2.
Source: U.S. Department of the Interior, National Park Service