River Rock, Sonoma County's oldest tribal casino, saw a rush of patrons Tuesday, capturing people who couldn't get into the packed new Graton Resort & Casino in Rohnert Park.

And there was a similar effect at another established casino — Hopland Sho-Ka-Wah — a little farther north in Mendocino County, where business was also booming Tuesday.

Traffic was so heavy into River Rock that the Geyserville-area casino also had to turn people away, according to Dry Creek Rancheria Pomo Chairman Harvey Hopkins.

That included "a couple buses" filled with would-be gamblers.

"We were all just surprised. We didn't think that would happen," Hopkins said of the extra customers coming to River Rock, about 30 miles north of the Graton casino, which opened at 10 a.m. Tuesday.

Hopkins estimated that River Rock had 40 percent more customers than it does on a typical Tuesday.

"We were at full capacity. We closed the gate," he said.

Ramon Carrillo, general manager of the Sho-Ka-Wah casino operated by the Hopland Band of Pomo, said business was about three times as brisk as usual for a Tuesday. He said people decided to come after being turned away from the new gaming palace in Rohnert Park.

"We are at weekend capacity right now. We are definitely seeing an upswing," he said, explaining that instead of the usual 70 to 80 slot machines in play, there were closer to 250 machines in use, similar to a Friday, Saturday or Sunday.

Hopkins estimated there were around 1,800 cars that filled the garage and valet parking at the Geyserville casino.

"As far as income goes it's great," Hopkins said. "Normally we don't have the buffet open (on Tuesdays). We opened it for the extra guests."

The Dry Creek Rancheria, which has operated River Rock for 11 years, was bracing for a hit to its bottom line from the opening of the much larger Graton casino positioned closer to the populous Bay Area.

Hopkins has predicted a revenue decrease potentially as high as 30 percent in the first year or so.

On Tuesday, he said he still anticipates losing customers to Graton in the coming year.

"As soon as the novelty wears off we will figure out which of our guests are coming back," he said.

But for now, he said he's happy to see River Rock get any extra guests that Graton can't handle.

"It's great they got their casino finally open," Hopkins said. "I'm happy for them mostly, and quite pleased the overflow ended up in River Rock. It's more than icing on the cake."

Carrillo also still anticipates a 20 to 30 percent loss of Hopland revenue to Graton once things settle down.

"We went through this when River Rock opened," he said of the crush of people who were turned away and ended up going to the older Hopland facility.

"It lasted a week, or week and a half, after the newness rubbed off and people were able to get in (to River Rock)," he said.

You can reach Staff Writer Clark Mason at 521-5214 or clark.mason@pressdemocrat.com.