Santa Rosa Plateau
Ecological Reserve

Riverside County

April 19, 1997

At one time slated to be under housing and shopping centers, the 6,925 acre Santa Rosa Plateau
Ecological Reserve represents one of two remaining strongholds for California's Engelmann Oak
(Quercus engelmannii). Once ranging across southeast California, Arizona and Baja California
before the evolution of the modern Mojave and Sonoran deserts, climate change has clearly
narrowed the geographic distribution of this species. Today, however, the most formidable threat
for this oak is urban/residential development. Not long ago, one could find this oak in areas like
Pasadena and Pomona. Most of these populations have succumbed under the pressure of our ever
expanding city. 90% of remaining stands are found in San Diego County. Two substantial
populations occur around Black Mountain (San Diego County) and the Santa Rosa Plateau.
While certainly survivors remain outside these two locations, the vastness of the oak savannah in
southern California has been lost save within these last bastions of Engelmann oak
habitat (Pavlik, et al., 1991)

. The oak savannah and woodland communities here are stellar, causing one to temporarily forget
the urbanization that presses near its boundaries. Another bonus found here are the springtime
vernal pools, another rapidly disappearing ecosystem of California.

Engelmann oak (Quercus engelmannii) and coast live oak (Quercus agrifolia) mingle in this
hillside display. The silvery-blue/green foliage helps to distinguish the Engelmann species. I
delight in the range of hues within this small assembly of oak.

This most extraordinary cache tree ("granary") is in evident use by an acorn woodpecker clan (Melanerpes formicivorus). While generally every carefully hoarded acorn in these community caches are consumed (making up to half of the acorn woodpecker's diet), some acorns evade their ultimate fate by sprouting and taking root in the decaying wood of a dead tree.

An overview of the Plateau

Indian milkweed (Asclepias eriocarpa)

Pavlik, Bruce M., Muick, P.C., Johnson, S.G., and Popper, M. 1991. Oaks of California. Cachuma Press: Los Olivos.


Revised: January 5, 2003

This site ©2003 Ann Dittmer.