A Santa Rosa woman was killed Friday afternoon on Highway 116 in Cotati when her car was rear-ended and pushed into the path of an on-coming big-rig truck, the Highway Patrol said.

Maria Juana Flores, 36, was pronounced dead at the scene of the accident. She had been waiting to make a left turn off the two-lane highway, about 100 yards east of the Cotati limits, when her red Honda was struck from behind by a tourist couple from Huntington Beach.

"I have no idea what happened," said the driver of the silver Hyundai that struck Flores' car. "I just saw a flash, a puff of smoke, that's it, all I remember."

The man, who said he and his girlfriend were visiting relatives in Sebastopol, declined to give his name. He was given a sobriety test at the scene — with the crushed remains of Flores' car lying nearby — about 90 minutes after the 2 p.m. crash, and tested negative.

"There was no arrest on scene and the collision is still under investigation. There are no charges pending as of now," said CHP Sgt. Kevin Mensior.

Further information about Flores was not immediately available Friday.

The crash at the intersection of Highway 116 and Madrone Avenue, just west of Highway 101, closed the road for more than four hours as investigators from the CHP and the Sonoma County District Attorney's Office examined the scene.

Flores was westbound on Highway 116 waiting to make a left turn onto Madrone Avenue when she was struck.

One witness, truck driver Brad Anderson, was waiting in his truck at the intersection when the crash happened right in front of him. A few hours later he stood and watched investigators pick through the debris.

He said: "I heard a poof — like a paper bag getting popped — and looked up and saw the red car go into the other lane. Then the truck was there. It went right over it."

The driver of the truck-trailer rig, Jeffrey Robinson, 38, of Sacramento, couldn't avoid Flores' Honda, CHP Officer Jonathan Sloat said. A shaken Robinson was first placed in an ambulance, then taken by patrol car from the scene to the Rohnert Park CHP station. He was unhurt.

Debris damaged a West Sonoma County School District bus that was pulling up to the intersection on Madrone Avenue but no one on the bus were hurt, Sloat said.

"It was so fast, and nothing seemed out of order," said a Sebastopol woman who would give only her first name, Elaine, and was driving behind the Hyundai sedan that hit Flores. "No one was across the line. We were just coming along on a beautiful day."

The Hyundai sat there, a smear of red paint on its crumpled silver hood. Later a gust of wind lifted up a smashed, window-sized panel of red metal that had been knocked loose from Flores' car, and rattled it on the road.