According to the Bureau of Land Management’s Las Cruces District, some of the boulders scattered across the slopes of the Doña Ana Mountains contain unusual trace fossils known as “megafauna rubs.”
Source: BLM – Las Cruces District (via Facebook)
Photos: Courtesy
Cover Photo Caption: A face of a large boulder shows polished areas where extinct animals once rubbed against over many generations. (Photo: Courtesy BLM – Las Cruces District)
The Doña Ana Mountains may be best known for their volcanic origins, but visitors exploring the rugged landscape can also find traces of an entirely different chapter of New Mexico’s natural history—one written by Ice Age giants.
According to the Bureau of Land Management’s Las Cruces District, some of the boulders scattered across the slopes of the Doña Ana Mountains contain unusual trace fossils known as “megafauna rubs.”
Unlike bones or teeth, trace fossils preserve evidence of an animal’s behavior rather than its physical remains. In this case, the fossils may have been created thousands of years ago when large Ice Age mammals repeatedly rubbed against boulders in the area.
A polished portion of a boulder with scale bar. (Photo: Courtesy BLM – Las Cruces District)
Scientists believe animals such as Columbian mammoths, American mastodons, giant ground sloths and camel-like megafauna once roamed southern New Mexico during the last Ice Age. As these animals scratched an itch, shed fur or marked territory, their repeated contact gradually polished rough rock surfaces smooth.
Over countless generations, those interactions left behind a subtle but lasting record of animal behavior that can still be seen and felt today.
The Doña Ana Mountains themselves were formed by volcanic activity millions of years before these animals appeared, creating a landscape where geology and paleontology intersect in surprising ways.
Trace fossils such as megafauna rubs provide researchers with valuable clues about how extinct animals lived and interacted with their environment. While skeletal fossils reveal what an animal looked like, trace fossils help scientists understand what animals did.
A field of large boulders in the Doña Ana Mountains in Organ Mountains-Desert Peaks National Monument. (Photo: Courtesy BLM – Las Cruces District)
The Bureau of Land Management reminds visitors that fossils on public lands are irreplaceable scientific resources. Damaging or removing fossils is prohibited, and visitors are encouraged to follow Leave No Trace principles while exploring public lands.
Long before roads crossed the Mesilla Valley and long before people called southern New Mexico home, mammoths, mastodons and giant sloths may have paused in the shadow of the Doña Ana Mountains—leaving behind polished stones that remain as silent witnesses to a vanished world.
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