The traffic onslaught began at 9:30 a.m. and by noon the freeway backup peaked for about an hour, stretching 24 miles south to Highway 37, he said.

A traffic sign at Novato warned drivers that it would take an hour to reach Rohnert Park, Caltrans spokesman Steve Williams said. That distance is 22 miles.

At midafternoon, Sloat said he had no official traffic count but estimated that it topped the forecast of 10,000 additional vehicles on the freeway and streets leading to the casino on the western flank of Rohnert Park.

"I would say this is the worst-case scenario," Sloat said. But there were only two collisions on the freeway, both unrelated to the casino crush, he said.

As several surface intersections became clogged around the Wilfred Avenue exit from 101, officers were dispatched to direct traffic.

"We didn't get overwhelmed, but the roads did," Sloat said.

The CHP will continue to put four patrol cars, three motorcycles and a sergeant in the area through Sunday in case the novelty of opening day does not abate, he said.

Casino-bound motorists were advised to consider alternate routes by leaving the freeway at Old Redwood Highway in Petaluma or West Sierra Avenue in Cotati and taking Stony Point Road north to Wilfred Avenue, then east to the casino.

At Golf Course Drive and Commerce Boulevard east of the highway, horns blasted through the morning air as drivers blocked the intersection while trying to squeeze through as lights changed.

A contractor making his way from east Rohnert Park to Home Depot near the casino said he waited through three cycles of a traffic light to get through the intersection.

Roe and Jacques Boyer of Penngrove, also bound for Home Depot, figured they saved time by driving north to Santa Rosa Avenue and doubling back on 101 to the Rohnert Park Expressway exit.

Chris Skaggs, a maintenance worker, shook his head in astonishment at the traffic on Golf Course Drive.

"It's crazy," he said. "Sonoma County will never be the same."

"I think it's exciting," said his buddy, Jerry Winkel, adding that the $800 million mega-casino "just gives (us) a broader range of things to do."

"As soon as we get off work, we're going over," Skaggs said. "I gotta see what a billion-dollar building looks like."

Sgt. Jeff Abrams at the CHP said evening commute hours "went surprisingly well," but that northbound Highway 101 became congested again around 8 p.m. Traffic started backing up at the Golf Course Drive offramp to about Rohnert Park Expressway, he said, making it difficult for folks trying to merge onto the freeway.