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On the western edge of Albuquerque, a long black cliff of lava holds more than 24,000 petroglyphs — one of the largest rock-art sites in North America. The cliff exists because of volcanoes that erupted about 156,000 years ago, and the carvings exist because of a thin dark coating that desert rock grows over time. Geology and culture are the same story here.
The Geologic Resources Inventory report for Petroglyph National Monument. NPS
The monument
| Size | 7,236 acres, managed jointly by the National Park Service and the City of Albuquerque Open Space Division |
| Established | 1990 |
| Petroglyphs | more than 24,000, most along the West Mesa escarpment |
| Volcanoes | the Albuquerque Volcanic Field — 15 vents (12 inside the monument), about 24 square miles of lava |
| West Mesa | about 17 miles (27 km) long |
Most of the carvings were made by the ancestors of today's Pueblo peoples; the oldest may be thousands of years old, and the youngest reach into historic times. They and their landscape hold deep spiritual and cultural meaning for American Indians today and for descendants of the early Spanish settlers. Petroglyph is also one of 33 national park units with at least one volcano.
A city on a rift
Albuquerque sits in the Rio Grande rift, where the continent is slowly pulling apart — a belt of stretching crust from Colorado's San Luis Valley through New Mexico into Chihuahua. It began opening about 36 million years ago in the south and 22 million in the north; around the monument, faulting started about 26 million years ago.
As the crust stretched, the Albuquerque basin dropped and filled with sediment, while its eastern flank rose as the Sandia Mountains — 15 miles east, 10,447 feet high, granite and metamorphic rock capped with limestone. The Rio Grande, two miles east of the monument, later linked the rift's basins into one river and cut terraces into their fill.
The Albuquerque basin in cross section: faults, basin fill, the river's terraces, and the lava of the Albuquerque volcanoes on top. NPS, Geologic Resources Inventory
The Sandia Mountains, rising as much as 5,700 feet above the Rio Grande. NPS / Chanteil Walter
One-time volcanoes
The Albuquerque Volcanic Field is a monogenetic field: each vent erupted once, in a single episode. Stretching thins the crust, letting heat from the mantle melt basalt near the rift's axis. (New Mexico has others — the Raton-Clayton field with Capulin Volcano, the Zuni-Bandera field with El Malpais.)
About 156,000 years ago, a 4-mile fissure, running parallel to the rift's faults, opened on a broad plain called the Llano de Albuquerque. Along it rose five named spatter cones — piles of half-molten lava globs that welded together — plus smaller vents:
| Volcano (north to south) | |
|---|---|
| Butte and Bond | only 50–60 ft tall; Butte's crater is shallow, Bond's filled in |
| Vulcan ("J") | the tallest and most complex: 6,033 ft above sea level, 130 ft above its base, lopsided to the south and east where the wind blew its ash |
| Black | gentler, with two overlapping craters; its loose cinders were quarried for roads and landscaping |
| JA | steep, with thin lava from cracks late in its eruption |
Vulcan, Black and JA are the Three Sisters on Albuquerque's western skyline. The eruptions were gentle — Hawaiian fire fountains, and slightly more explosive Strombolian bursts that built the cones — 0 to 2 on the Volcanic Explosivity Index.
Six eruptive phases: the first thin, runny flows spread far east from the fissure; later ones were thicker, shorter, and ended in cones. NPS / Michael Barthelmes, from Connell (2006)
How a lava flow became a cliff
The land sloped east, so most of the lava flowed east. The two oldest flows travelled farthest, and their thin, ropy (pāhoehoe) sheets make up West Mesa.
Then erosion turned the landscape upside down. Basalt wears away far more slowly than the sand and gravel around it, so as the softer ground was stripped, the old flows were left standing 100–180 feet above the valley: volcanic inverted topography, common in the dry Southwest. The mesa's edge is probably close to where the lava stopped — there are no stray remnants farther east.
The canvas: desert varnish
The petroglyphs are pecked through desert varnish — a thin dark coat of clay minerals with iron and manganese oxides, built up from dust and water rather than from the rock itself. Here it is especially dark and shiny, rich in manganese. Chip through it and the lighter basalt beneath shows: an image that lasts centuries. Two small erosional windows, where the lava has worn through to older sediment, also hold petroglyphs.
Other things to know
- Fossils: only cobbles of petrified wood in the Ceja Formation, washed in from older Triassic rocks. Protected by law.
- Caves: small, broken lava tubes, 8–20 inches across, near the vents; 57% of the monument counts as volcanic pseudokarst.
- Is it active? No — the USGS does not count the Albuquerque field as active or potentially active.
- Earthquakes: a moderate hazard. Eleven old fault segments cross the monument, none moving in the last 20,000 years, but the rift is seismically active: about a 1-in-500 to 1-in-1,000 chance of damaging shaking in a given year.
- Rockfall along West Mesa, and three abandoned cinder quarries (one needing cleanup; another mined a small cone out of existence before 1990). Stay out of them.
Earthquake likelihood around Albuquerque (top) and projected shaking from a magnitude 6.9 quake on the County Dump fault (bottom), up to "severe." USGS
Maps and reports
The NPS Geologic Resources Inventory has mapped the monument, and the New Mexico Bureau of Geology offers a geologic tour.
Sources
Written from "NPS Geodiversity Atlas—Petroglyph National Monument, New Mexico," Geologic Resources Division, National Park Service; a work of the United States government in the public domain. It draws on Connell (2006), the USGS 2014 seismic hazard map and 2018 volcanic threat assessment, and the Geologic Resources Inventory report.
Licens: CC0 1.0 (offentligt eje) · Bearbejdet efter www.nps.gov
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