The fatal crash Sunday of a casino-bound bus in Colusa County has raised concerns about the state's ability to regulate a growing trade of mom-and-pop companies ferrying thousands of gamblers daily to local casinos.

Investigators said Tuesday they are still piecing together basic information about the Sacramento bus company and rookie bus driver behind California's worst intercity bus crash in at least 15 years.

Eight people were killed Sunday evening when a Cobb's Bus Service coach carrying 43 people tumbled into a watery ditch on a thin, straight stretch of rural road south of the Colusa Casino Resort.

The bus does not appear to have been registered as required with state regulators. The incident has CHP officials talking about reassessing their oversight practices.

"We would like to think people aren't lying to us and trying to hide stuff," CHP spokesman Robert Kays said. "We are looking for ways we can catch these rogue buses. We have the same concerns the public has. We want people to be safe on our highways."

Among the dead in Sunday's crash was Daniel Cobb, 68, the company's registered owner.

The CHP has arrested the driver, 52-year-old Quintin J. Watts, on suspicion of driving under the influence. Blood-alcohol tests are pending. Officials said they are looking into reports Watts fell asleep at the wheel. Watts was reported in fair condition Tuesday evening in Woodland Memorial Hospital.

"We had enough probable cause on the DUI, but it could be something else," Kays said. "It's possible he could have fallen asleep."

State officials and private bus industry representatives say the growing number of Indian casinos in California, including several around Sacramento, has sparked a rise in private tour bus traffic.

Cobb's Bus Service is one of nine private companies on the Colusa casino's official list of bus services.

Some companies serve essentially as headhunters for casinos, and are paid a fee for each gambler shuttled to the casinos' doorsteps, a helpful service to casinos in rural areas.

"They want business, so they will pay the bus fare," said George Chang, who manages Ace Tours, a small San Francisco bus service to several casinos in the Sacramento area.

Thunder Valley Casino in Lincoln pays bus companies, including the one that crashed in Colusa, on average $5 for every person bused in, a spokesman said.

Officials with Cache Creek Resort and Hotel in Capay Valley say they do not have a formal arrangement with any bus service.

"It's not something we push real hard for," spokesman Cean Burgerson said.

Most customers drive themselves to casinos at Colusa, Thunder Valley, Jackson Rancheria and Cache Creek, representatives said.

However, based on interviews with those casinos, The Bee estimates bus companies transport more than 2,000 people a day to local casinos.

All West Coachlines in Sacramento, one of the region's largest charter bus companies, can have more than half its 39 buses headed to casinos on busy days, said general manager Ken Sanders.

Since the Sunday crash, Sanders said he has gotten calls from concerned regular customers. He said he welcomes the scrutiny.

"You have to look for upfront answers or the red flag goes up," he said.

All West's 58 drivers undergo criminal background checks, he said. The company does not hire felons, requires an annual physical and performs random drug tests, he said.

"Even if they show a trace, they're gone," he said.

The Colusa crash is the deadliest of three reported casino bus crashes in Northern California in the last year. A 75-year-old pickup driver was killed by a casino bus that hit him from behind in Amador County last December.

A state bus association representative said he is not surprised by Sunday's crash, given the proliferation of companies vying for business in an arena where profit margins are often slim.

"It is like gambling; eventually your number is going to come up," said Mike Waters of the California Bus Association. "Dealing with the human factor, driving a 30,000-pound vehicle, all it takes is a second of distraction. It doesn't take much to go sideways."

Call The Bee's Tony Bizjak, (916) 321-1059. The Bee's Phillip Reese contributed to this report.