O.C. Benefit Called on Account of Mud : Storm: Runoff causes much damage to Irvine Bowl. Canceled concert was to have aided fire victims. Pageant of the Masters probably won’t be affected.

For the first time in the Irvine Bowl’s 50-year history, weather-caused damage has forced immediate performances to be canceled, although next year’s Pageant of the Masters probably won’t be affected.

The 2,700-seat outdoor bowl had barely survived when flames roared down Laguna Canyon on Oct. 27. But Thursday’s post-fire rainfall proved too much as a powerful river of mud washed down the steep, newly barren hillside and burst into the bowl.

Not only has a benefit concert by singer Graham Nash and comic Elayne Boosler scheduled for Saturday been canceled, but a planned Thanksgiving weekend art show also may have washed away in the mudslide, said Glen Eytchison, pageant director.

The Moulton Theatre, next door to the bowl and the home of the Laguna Playhouse, sustained water damage, but tonight’s performance of “Oliver!” will go on as scheduled, officials said.

Hours after an assistant called Eytchison and uttered the words, “It’s over,” he was trudging through the thick layer of mud in what was once his office beneath the bowl stage.

“I’m totally stunned,” Eytchison said.

Computers floated in the muck; doors had been knocked off their hinges. “Next year’s Pageant of the Masters was about five days away from being completed. Now it’s buried in what looks like three feet of mud,” he said somberly.

Late Thursday morning, the outdoor bowl and stage looked as if a tornado of mud had swirled down the hillside and carved a path through the area, tossing aside an assortment of props, tools and sets in its wake.

“Somehow, a fog machine stored up in our tool shed ended up in the kitchen” beneath the stage, Eytchison said. “Don’t ask me how.”

Eytchison and other pageant officials said it was too early to assess the amount of damage done by the mud, other than to call it substantial.

Tim Wilcox, press spokesman for the 60-year-old summer pageant, said that although there appeared to be damage to the stage supports and backstage area, he did not expect it to affect next year’s staging of the pageant, in which costumed volunteers re-create famous paintings.

Most of the damage was centered in the pageant workshops offstage and the area beneath the stage.

Touched off by only a short, early morning rainstorm about 4 a.m., the wall of mud had apparently burst through a chain link fence and rolled through the wood shop on the north side of the bowl before descending down a ramp toward the stage.

By then, the mud had gathered enough force to ram its way through a solid steel door protecting the orchestra pit below the stage. Then it rolled through two large dressing rooms, several offices, a kitchen, costume shops and a conference room before proceeding out to a courtyard and over the Festival of Arts grounds.

“It’s a major, major, major mess,” said Terry Neptune, owner of the Tivoli Terrace, which is next to the bowl and escaped most of the mud. “It’s hard to believe there could be this kind of damage.”