WILLIAMS, Calif. -- The bus that crashed and killed eight people on a Northern California road was operated in a poorly regulated segment of the nation's transportation system with a patchwork of state and federal rules and spotty enforcement.

Safety advocates and bus industry experts said Tuesday tour bus companies that transport gamblers to casinos don't always follow government regulations designed to assure passenger safety.

"Some of these rogue operations literally do pickups in alleys where they are trying to keep out of the sight of federal and state authorities," said Eron Shosteck, spokesman at the American Bus Association, a Washington, D.C.,-based group that represents about 1,000 motorcoach and tour companies in the U.S. and Canada.

The California Highway Patrol is investigating whether the bus involved in Sunday's crash north of Sacramento was inspected annually, as required by law. They also are looking at whether drugs or alcohol were a factor.

The bus driver, 52-year-old Quintin Watts, didn't have a proper license to carry passengers and the vehicle had an invalid license plate, the CHP said. Watts has been arrested on suspicion of driving under the influence.

Patrol officers believe the bus owner was Daniel Cobb, 68, who died in the crash. State public records show Cobb was certified by the Public Utilities Commission to operate a bus service, and he had an insurance policy.

A witness said the bus carrying 42 passengers to Colusa Casino Resort drifted off a rural two-lane road before the driver "overcorrected" and swerved back. It overturned and rolled completely over, ending up on its wheels facing the opposite direction. About 30 people were injured.

All commercial buses that travel within California undergo annual inspections by the highway patrol, but in cases where companies don't have bus terminals, CHP spokesman Scott Johnson said, "we don't go. If there's no terminal they don't respond."

A bus terminal couldn't be located for Cobbs Bus Service, which listed a Modesto church and a residence in Sacramento as its headquarters.

"Any reputable bus company will have a facility with service bays and customer service lounge," Shosteck said.

The Federal Motor Carrier Safety Administration regulates buses that cross state lines, leaving the responsibility of oversight to states for tour buses like Cobbs Bus Service that ferry casino goers and other tourists within California.

Federal rules also require employers provide mandatory drug and alcohol testing for all bus drivers operating vehicles that carry 16 passengers or more, typically through a private contractor.

In California, bus operators also must enroll their drivers in a state program that informs employers whenever a driver receives a ticket, gets in an accident or has his or her license suspended or revoked.

Records show Watts, of Stockton, had been cited for speeding and other violations that resulted in loss of his license for nearly two years. He regained his driving privileges last January.

Watts didn't have the proper license to carry more than 10 passengers, said Mike Marando, a spokesman at the California Department of Motor Vehicles.

Passengers who survived the crash tell social workers that the bus driver appeared to have dozed off and passengers tried to warn him before the vehicle rolled off the road and tumbled into a drainage ditch.

"The bus driver was sleepy and the bus swung to the left and right side. And they were yelling at him on the third swing when it turned over," said Theresa Saechao of Lao Family Community Development of Sacramento.