SOUTHERN CALIFORNIA’S ENVIRONMENT At the Crossroads : Wildlife: <i> VEGETATION, ANIMALS AND HABITATS </i> : SUCCESS STORY : A Corona Sanctuary Thrives

Less than a mile from the whitewashed tracts of new homes that symbolize Riverside County’s economic boom, one of the few river sanctuaries left in Southern California thrives.

Here, near Corona, willow trees grow as thick as straw in a broom, and the dense underbrush provides a haven for scores of waterfowl, including the least Bell’s vireo, a nearly extinct songbird. Vegetation is so wild and undisturbed along the Santa Ana River behind Prado Dam that scenes in a movie about Contra supporter Oliver L. North in the jungles of Vietnam and El Salvador were filmed here.

The area, known as Prado Basin, has so far weathered the impacts of runaway urbanization that has nearly encircled this wilderness island. It remains a refuge for more than 40 different bird species, largely because it is the only stretch of the Santa Ana River flowing through San Bernardino, Riverside and Orange counties that has been untouched by developers or flood control engineers.

“It is the most extensive and, perhaps, most significant lowland riparian habitat left in Southern California south of the Kern River,” explained biologist Kimball Garrett of the Los Angeles County Museum of Natural History. “The Prado Basin is a treasure.”

Spread across 10,000 acres, the area is a catch basin for winter storm runoff from the Santa Ana River and its tributaries. As a result, the U.S. Army Corps of Engineers, which owns much of the basin, built Prado Dam in 1941 to prevent flooding downstream in Orange County.

The abundance of water trapped behind the dam has sustained a lushness in the basin critical to the survival of the least Bell’s vireo. Only about 300 pairs of the gray songbird with the distinctive yellow bars on its wings exist in the United States; about 30 pairs are found in the Prado Basin.

The species migrates each winter to Mexico, then returns to build hanging nests less than three feet above the basin’s waterways.

But the vireo’s future, much like that of the basin itself, is tenuous. Federal officials say Prado Dam can no longer protect hundreds of thousands of downstream residents from a major flood. A $1.1-billion package of flood control improvements along the Santa Ana River would double the height of the 540-foot dam, and hundreds of acres of vireo habitat in the Prado Basin would be destroyed. The 15-year project has already been approved by Congress.

Biologists and local officials are devising a plan to relocate the threatened vireo pairs to higher ground in the basin, but such operations are tricky and often unsuccessful, some warned.

“The species is so fragile there is concern it might not survive such disruption,” Garrett said.

Equally troubling to environmentalists is upstream pollution and its impact on vegetation and waterfowl in the basin. Runoff carrying fertilizers, chemicals and waste is flowing into the river from boom towns in Riverside and San Bernardino counties. How the tainted water is altering the basin concerns Garrett and the others.

With 90% of the riparian habitat in Southern California already destroyed, Garrett said preserving Prado Basin is an environmental priority. Despite the flood control project and threats upstream, Garrett and others hope to maintain at least some of the basin as open space.

“To lose Prado would be a blow,” he said. “Without it, several generations of Southern Californians might never see some species of birds.”