Fossil Horses of Anza-Borrego Desert State Park
The Story of Horse Evolution in Southern California
Few fossil groups illustrate evolution as clearly as horses. The fossil record preserved in Anza-Borrego Desert State Park documents millions of years of horse evolution and provides important evidence for changing environments in southern California during the Pliocene and Pleistocene.

Today, wild horses are not native to North America, but horses actually evolved on this continent. Their ancestors first appeared more than 50 million years ago and gradually evolved from small forest-dwelling animals into the large grazing horses familiar today. Anza-Borrego preserves fossils from some of the final stages of that remarkable evolutionary story.

Horses of Ancient Anza-Borrego
Horse fossils are among the most common large mammal remains found in the park. Their teeth, jaws, limb bones, and skull fragments occur in numerous fossil localities throughout the Fish Creek-Vallecito Basin and surrounding regions.
Several species of the genus Equus have been identified from Anza-Borrego deposits. These horses lived during a period when grasslands, river systems, floodplains, and open woodlands occupied parts of what is now desert terrain.

The fossil record indicates that horses were an important component of the park's ancient mammal communities, living alongside camels, mammoths, gomphotheres, ground sloths, antelope, and saber-toothed cats.

Adaptations for Grazing
One of the most important features of horse evolution is the development of high-crowned teeth adapted for grazing. As grasslands expanded across North America, horses evolved teeth capable of withstanding the wear caused by silica-rich grasses and windblown grit.

Horse teeth are among the most frequently collected fossils in Anza-Borrego because their hard enamel preserves exceptionally well. These teeth provide valuable information about:
  • Species identification
  • Diet
  • Evolutionary relationships
  • Geologic age
  • Environmental conditions
Because horse species changed through time, they are often useful for determining the relative age of fossil deposits.

What Horses Tell Us About Ancient Environments
The presence of horses indicates that portions of ancient Anza-Borrego supported open habitats capable of sustaining large grazing mammals. Their fossils suggest a landscape very different from today's arid desert.

Horse fossils help scientists reconstruct:
  • Ancient grasslands and savannas
  • River and floodplain environments
  • Climate change through time
  • Mammalian evolution in western North America
  • The development of modern ecosystems
By studying horse fossils alongside other mammals, paleontologists can better understand how environmental conditions changed during the formation of the Colorado Desert.

Explore a Fossil in 3D
Rotate, zoom, and examine this specimen from the Anza-Borrego Desert State Park collections.
Interactive 3D Model: Equus enormis maxilla
Specimen Information
  • Catalog Number: IVCM15 V32.01
  • Element: Maxilla
  • Formation: Hueso
  • Group: Palm Spring
  • Epoch: Pleistocene
  • Age: Blancan and/or Irvingtonian
  • Locality: Fish Creek / Vallecito Creek
  • Scanned using Agisoft Metashape
  • Specimen © California State Parks. 3D model produced by the Anza-Borrego Desert State Park Paleontology Society.
Why Anza-Borrego Matters
The Anza-Borrego fossil record contains one of the most important late Cenozoic mammal assemblages in North America. Horse fossils are a major component of that record and have contributed significantly to scientific studies of mammalian evolution, biostratigraphy, and paleoecology.

The abundance and diversity of horse remains preserved in the park continue to make Anza-Borrego an important location for understanding the final chapters of horse evolution in North America.

The Fossil Record
  • Pliocene horse (Equidae Dinohippus)
  • Giant zebra (Equus enormis)
  • Scott's horse (Equus scotti)
  • American zebra (Equidae Plesippus)
  • Medium sized horse (Equidae Equus)
  • South American horse (Equidae Hippidion)

Quick Facts
  • Group: Equidae (horse family)
  • Genus commonly found: Equus
  • Age: Pliocene and Pleistocene
  • Common fossils: Teeth, jaws, skull fragments, limb bones
  • Significance: Important indicators of age, climate, and environment
  • Location: Anza-Borrego Desert State Park, California

Learn More
Read Chapter 15, "Horses," in Fossil Treasures of the Anza-Borrego Desert for a detailed discussion of horse evolution and the important fossil horse discoveries from Anza-Borrego Desert State Park.