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Geology of the SMNHC

Go on a virtual geology tour in the east mountains of the Sandias to learn about the ancient past.

Tour Introduction

Join Dr. Spencer Lucas from the New Mexico Museum of Natural History and Science as he highlights geologic features along the trails at the Sandia Mountain Natural History. Gain an understanding of the geology and rocks unearthed here, and what they teach us about our part of the mountain.

Geology Resources

View and download accessible PDF files.

Take the Tour!

Stop 1: Fossil Area

Find fossils of aquatic animals who lived in an ancient shallow sea that covered New Mexico.

Stop 1: Fossil Area

This area has cobbles of Pennsylvanian limestone full of fossils of marine animals – crinoids, brachiopods, bryozoans, corals, and sponges. These cobbles are loose deposits, not bedrock. The bedrock here is Triassic mudstone.

Closeup view of bryozoan fossils with black ovals inside small thin walls.

Close-up of a Bryozoan Fossil.

A screenshot of the fossil hunt guide for identifying and learning about limestone fossils at the SMNHC.

Learn more about animal fossils found by
downloading our Fossil Hunt Guide.

Stop 2: Glorieta-San Andres Contact

Examine evidence of change from sandy dunes to shallow sea.

Stop 2: Glorieta-San Andres Contact

Layers of Glorieta and San Andres rock touching.

The contact between Glorieta Sandstone and overlying limestone of the San Andres Formation is exposed here. This records the change from land (sandstone) to sea (limestone) during the Permian, about 270 Ma.

Artist's representation of a yellow sand dune field next to the ocean with two giant lizard-like reptiles on the sand.

Artist's representation of the seafloor during the Permian with large ammonites swimming in the blue water, and light cream sand with a couple plants on the seafloor.

Stop 3: Oldest Bedrock

Take a look at the oldest bedrock exposed here.

Stop 3: Oldest Bedrock

Reddish brown sandstone and siltstone (some with ripple marks) of the Permian Yeso Group are the oldest bedrock exposed on SMNHC trails.
Ripple marks on Yeso sandstone.

Reddish brown sandstone and siltstone (some with ripple marks) of the Permian Yeso Group are the oldest bedrock exposed on SMNHC trails.

Magnified view of a thin layer of Yeso sandstone grains. Magnified Yeso sandstone grains more zoomed in.

Images of the rock at the microscopic level.

Stop 4: Shark's Tooth

A real shark tooth embedded in a limestone boulder!

Stop 4: Shark's Tooth

Black spot on boulder that is Petalodus shark tooth fossil with penny next to it for scale, which is a little smaller than the fossil.

Shark tooth on limestone boulder. This block of limestone has a large tooth of the shark Petalodus. The block is loose and also contains brown nodules of chert, unlike any of the local Permian limestone bedrock. This is evidence that it is actually Pennsylvanian limestone which moved from a different location.

Artist's representation of a Pennsylvanian era Petalodus shark swimming through the blue sea.

Stop 5: Glorieta Sandstone

Check out sandstone made up of sand from a vast desert.

Stop 5: Glorieta Sandstone

Rock cliffside at Stop 5 on the Geology trail, with exposed Glorieta Sandstone from an ancient desert.

The outcrop of Glorieta Sandstone here is about 10 meters of sandstone exposed along the canyon wall. This sandstone formed around 270 million years ago as part of a vast desert that covered part of the Southwest.

A closeup view under a microscope of a thin slice of Glorieta sandstone.A closeup view under a microscope of a thin slice of Glorieta sandstone.

Glorieta Sandstone at the microscopic level.

Stop 6: Paradise Benches

Decipher the pattern of past ecosystems between desert and ocean.

Stop 6: Paradise Benches

Rocky wall of limestone layer from the San Andres Formation, above and below Glorieta sandstones, showing the history of desert- sea- desert in the ancient past.

Limestones of the San Andres Formation exposed here were formed on muddy seafloors during the Early Permian. Above and below are Glorieta sandstones. The pattern of sandstone-limestone-sandstone-limestone records the march of desert (sandstone) and sea (limestone) back and forth over time on this landscape.

Stop 7: Strike Valley

Encounter rock from a long-ago riverbed.

Stop 7: Strike Valley

Reddish sandstone rock from the Moenkopi Formation.

Thin beds of reddish sandstone are river deposits of a vast Middle Triassic floodplain. These rocks of the Moenkopi Formation are softer than underlying sandstones and limestones and overlying sandstones and conglomerates. Thus, they form a “strike valley” between two ridges (cuestas).

A closeup view under a microscope of a thin slice of Moenkopi sandstone.

Moenkopi sandstone at the microscopic level

Stop 8: Overlook

Get a big picture view of the geology on this side of the mountain.

Stop 8: Overlook

View of mountain with forest and rock layers from the Stop 8 interpretation trail overlook.

The view to the north/northwest shows the basic geological structure of the SMNHC. The center sits near the base of the vast dip slope of the Sandia Mountains, which is underlain by Pennsylvanian limestone that is exposed at the crest of the mountains. The trail apex on the west side of the property is on the cuesta formed by Permian sandstone and limestone. The SMNHC buildings sit in the Triassic strike valley, and this overlook is on the Triassic cuesta along the SMNHC’s eastern boundary.

Stop 9: Triassic Cuesta

The last stop on the tour displays rock from a huge ancient river.

Stop 9: Triassic Cuesta

Grey conglomerate rocks with large rocks of different colors and types set into it. 

Late Triassic sandstone and conglomerate form a ridge here, also known as a cuesta. These 230-million-year-old rocks represent huge, Mississippi-size rivers that flowed from what is now Texas to a seashore near what is now the Utah-Nevada border.

Painting of ancient triassic riverbed ecosystem with giant salamander-like amphibians at the river with tall trees around.

Artist's representation of a giant Triassic salamander-like amphibian.