The teen had been riding with two other Rancho Cotate seniors, driver Ashley Kellogg, 18, of Rohnert Park and Kellogg's boyfriend, Brenton Deveraux, 18, when their small car crashed at about 7:50 p.m. on Llano Road, west of Santa Rosa.
Based on initial observations, investigators believed Kellogg may have been driving too fast for the narrow, bumpy, rural road, said CHP spokesman Officer Jon Sloat. Inexperience may also have contributed to the crash, according to the CHP.
The driver lost control and her 2008 Honda Civic hit a tree and then a utility pole before flipping onto its roof, landing in a field.
Alcohol was not believed to be a factor.
Kellogg was treated for minor injuries. Deveraux remained at Santa Rosa Memorial Hospital on Wednesday in good condition.
The three Rancho Cotate seniors, all good friends, were on the verge of graduating in the school's May 30 ceremony.
"That's going to have an impact on our graduates," Rancho Cotate Principal Bob Steffen said early Wednesday as he prepared for a difficult day on campus. "It's a tragedy."
Officials at the Snyder Lane campus brought in psychologists, chaplains and a therapy dog Wednesday to help the school's 1,600 students cope with the shock.
"We just provided them with the opportunity and a couple places on campus where they were safe and able to deal with their grief in their own way," Steffen said. "Kids were stressing out ... and finding comfort in one another."
One of those areas was the school auto shop.
It was a favorite place for Carlson. She'd been introduced to it by her boyfriend, Mo Hamade, an auto shop student who graduated last year. She also took classes herself and was a teacher's aide in the shop for Rossi. Her younger sister, Ariana Carlson, a freshman, also was an auto shop student.
Hamade, who attended the vigil with members of his family, spoke briefly about Ashley before breaking down. He was one of several people who asked the crowd not to judge the survivors harshly.
"It was an accident," he said. "A horrible accident. No one should be blamed."
Others who knew her said she was a giggly, vivacious girl who was very social and worked hard in school. She was on course to graduate, said assistant Principal Josh Wilson.
"She was always so bubbly, so positive," Cheyenne Williamsen, 18, said. "She would put others before herself."
During the school day, staff set up picnic benches at the shop so the extra students would be comfortable as they hung out together.
"The kids have all been out at the shop. Kids who had graduated last year, two years ago, three ... maybe four. They've been coming today to the school," Rossi said.
Rossi described Carlson as a selfless teen who often stepped up to lend a hand. "She helped everybody with their projects."
The school requires community service hours of its students and she'd fulfilled hers, but that didn't stop her from volunteering.
"She always worked plenty of events for the Penngrove Social Firemen, car shows, crab feeds. She was always willing to work, just with a smile on her face," he said.
"I'm holding a picture in my hand right now of her from yesterday at lunch," said the teacher.
The photo, taken Tuesday at lunchtime, shows Carlson with six other students, a Rohnert Park police officer and Chief Brian Masterson. The police chief had brought pizza to the teens in gratitude for their work painting city signs as part of a community service project.
"She has the biggest, cutest smile you've ever seen," Rossi said of the girl in the photo.
Rossi wasn't sure what her plans were for fall but said she'd expressed interest in becoming a nurse.
"They were all trying to figure it out. She was doing really well," he said, stunned as he recalled seeing her at the prom, having a great time with her friends, just a few nights ago.
"She was dancing, dressed so nice, Mo and her. That was last Saturday night," he said.
On Tuesday, the two girls had driven to Santa Rosa to pick up Deveraux at his Santa Rosa home. With the sun setting, they were headed back to Rohnert Park to take Carlson home when the crash occurred, Sloat said.
Headed south on Llano Road, the car crashed about a quarter-mile south of the Todd Road intersection.
The speed limit along that part of Llano is 45 mph. CHP officers estimated the driver could have been going 55-70 mph.
All three teens had been wearing seat belts. Kellogg and Deveraux were able to get out of the car on their own. Rincon Valley firefighters had to free Carlson's body from the wreckage.
The crash knocked down power lines, which lay across the road and hung too low for the large emergency vehicles to get underneath, adding to the complexity of the crash response, Rincon Valley fire Capt. Ryan Estes said.
The narrow two-lane road was busy with traffic on Wednesday afternoon as CHP investigators completed their investigation.
A memorial near the crash site was beginning to grow. Someone had left a red candle, flowers and a photo of Carlson and her boyfriend below the oak tree the car hit.
The vigil on Wednesday night was held on a cool, partly cloudy evening as the crowd huddled close in silence, country music playing in the background.
A woman who said she was Carlson's aunt also spoke at the vigil. She said a memorial service would be announced soon for the girl who was remembered for her effervescent personality.
"It will be on what would have been her 18th birthday," the woman said.
Staff Writer Elizabeth M. Cosin contributed to this report. You can reach Staff Writer Randi Rossmann at 521-5412 or randi.rossmann@ pressdemocrat.com.
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