Santa Rosa Plateau

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Engelmann Oak Woodlands
Grassland in the Santa Rosa Plateau, California.

The Santa Rosa Plateau is an upland plateau and southeastern extension of the Santa Ana Mountains in Riverside County, southern California. It is bounded by the rapidly urbanizing Inland Empire cities of Murrieta to the northeast, and Temecula to the southeast.

The Santa Rosa Plateau Ecological Reserve preserves approximately 8,400 acres (34 km2) of the plateau, and includes the Moreno and Machado Adobes, Riverside County’s oldest standing structures, and other buildings from the 19th century Mexican land grant Rancho Santa Rosa.[1]


The Santa Rosa Plateau is home to several native plant communities and habitats, including purple needlegrass prairie (Nassella pulchra), California oak woodland (Engelmann OaksQuercus engelmannii), montane chaparral, coastal sage scrub, and vernal pools, which are increasingly rare in urbanized Southern California.

The Engelmann oak was once widespread throughout the western U.S. Now the farthest north they are found is Pasadena. The Reserve has the only protected, reproducing Engelmanns in the states.[2]

A vernal pool is a shallow depression in the soil which fills up with water during spring rains. Fairy shrimp and other minute crustaceans hatch during this time and lay eggs. These eggs remain dormant during the dry months until the next rainy season allows them to hatch. (6)

Santa Rosa Plateau Ecological Reserve[edit]

The Santa Rosa Plateau Ecological Reserve was assembled in several stages; two parcels, comprising 3,100 acres (13 km2), were purchased by The Nature Conservancy in 1984. The intervening parcels were purchased in the 1990s by the State of California, the Riverside County Regional Park and Open Space District, and the Metropolitan Water District of Southern California.

Although the parcels remain under the ownership of separate agencies, they are managed cooperatively, with biological resource management, which includes prescribed fire and habitat restoration programs managed by the Nature Conservancy, and visitor management. This includes operation of a visitor center and a 40-mile (60 km) trail system, managed by the Riverside County Regional Park and Open-Space District (RivCo Parks).


The Reserve is known to be home to 27 species of mammal. This includes 12 species of rodents. The mammals include: badger, big brown bat, California myotis, coyote, gray fox, bobcat, mountain lion, mule deer, opossum, black-tail jackrabbit, desert cottontail, raccoon, brush mouse, cactus mouse, California ground squirrel, California mouse, California pocket mouse, California vole, deer mouse, desert woodrat, dusky-footed woodrat, Pacific kangaroo rat, pocket gopher, western harvest mouse, gray shrew, striped skunk, long-tailed weasel. Most mammals are nocturnal and so are seldom seen by visitors. However, ground squirrels are diurnal and are regularly seen. Coyotes are probably the second most common seen, then mule deer.[3]


The reserve is home to the Southwestern pond turtle. They are on the list of Species of Special Concern. They are not allowed to be taken from their habitat. The longest turtles found on the Reserve are approximately five and a half inches. When they are wet, the are dark, making it easy for them to blend in with the mud at the bottom of ponds. They have webbed feet for efficient swimming and claws, which are used for digging nests, tearing meat, and during courtship. They mainly feed on aquatic invertebrates. They spend most of their lives underwater, which is also where they mate. They leave the water on a daily basis to bask, in order to regulate their body temperature.[4] In southern California, pond turtle populations have declined 95-99%. The Reserve is one of only four to six reproductively viable populations of the Southwestern pond turtle in southern California.[5]

Snakes found on the Ecological Reserve include: San Bernardino ring-necked snake, Hammond's two-striped garter snake, coastal rosy boa, Western yellow-bellied racer, California striped racer, San Joaquin coachwhip, red diamond rattlesnake, Southern Pacific rattlesnake, San Diego gopher snake, California kingsnake.[6]

Other reptiles include: San Diego horned lizard, western fence lizard, granite spiny lizard, side-blotched lizard, western skink, western whiptail, San Diego alligator lizard.


Amphibians found on the Ecological Reserve include: coast range newt, garden slender salamander, black-bellied salamander, western spadefoot toad, Pacific treefrog, California red-legged frog, bullfrog.


The oldest rock seen on the Reserve is meta-volcanic rock, laid down 220-190 million years ago. Above that is found meta-sedimentary rock, consisting of slates, argillites and some quartzite and limestone beds. Gabbro, consisting of feldspar, pyroxene and olivine, was laid down 143-101 million years ago. The granite on the Plateau arrived 119-105 million years ago. Arkosic sand and gravel was deposited by flowing water approximately 23-9 million years ago. Olivine basalt is from a lava flow of 9-6 million years ago.[7]

Human History[edit]

The first Native Americans are thought to have inhabited this area for more than 8,000 years. The Native Americans known as Luiseno, due to their connection to the San Luis Rey Mission, are believed to have arrived about 1,500 years ago. It is thought they only used the Plateau during the warm weather months, and to collect acorns in the fall.[8] If you visit the adobes, you will see indentations in boulders used by the Native Americans to grind acorns and other food.

In 1846, Juan Moreno was granted 47,000 acres by the Mexican governor of California, Pio Pico. In 1855, Moreno sold Rancho Santa Rosa to Augustin Machado. After he died, the land passed through several hands before being purchased by John Deer of England, who moved here. After him the land went to his son, Parker Dear. In 1904 Walter Vale purchased the land to raise mainly cattle.[9]

See also[edit]


  1. ^ Lech, Steve (2011). More Than a Place To Pitch a Rent: The Stories Behind Riverside County's Regional Parks. Riverside, CA: Steve Lech. p. 150. ISBN 978-0-9837500-0-0. OCLC 768249467. 
  2. ^ The Nature Conservancy. "Oak Tree Trail: a self-guided tour."
  3. ^ Bramhall, Rick. "Wild Mammals of the Santa Rosa Plateau." Plateau Press, 2003. Smashwords ebook edition, 2015.
  4. ^ Pires, Marcelo. "Everything You've Always Wanted to Know About Turtles."
  5. ^ Pires, Marcelo. "An Overview of the Status of the Southwestern Pond Turtle (Clemmys marmorata pallida) in Southern California."
  6. ^ Unattributed. "Snakes of the Santa Rosa Plateau."
  7. ^ Loera, Dan and Steve Turner. "A Geologic Field Trip Guide for the Santa Rosa Plateau Ecological Reserve."
  8. ^ Gonsalves, Myra. "Temecula Valley History."
  9. ^ Hicks, Rob. Visitor center handout.

External links[edit] * [1]

Coordinates: 33°32′36″N 117°16′10″W / 33.54336°N 117.26952°W / 33.54336; -117.26952