Some 40 Chileno Valley residents gathered on the Marshall-Petaluma Road Tuesday morning to complain to county Public Works staff about a hump in the road that has contributed to two serious accidents in the past two years.

The most recent crash happened at 2:20 p.m. Saturday, when two teenage girls driving west crashed into a tree after crossing the hump between the county line and the intersection with Chileno Valley Road.

The passenger, Chileno Valley resident Kathy Dolcini, 15, remains in critical condition at Santa Rosa Memorial Hospital with severe head and upper-body injuries.

Driver Melissa Scarborough, 16, of Petaluma, suffered two fractured legs and is recovering at Sutter Medical Center in Santa Rosa.

The Dolcinis, a prominent ranching family that has spread across the Chileno Valley since the 1870s, has been hit hard by the hump in the Marshall-Petaluma Road.

Two years and three days earlier, Kathy Dolcini's older sister Sara and her younger cousin Jonathan Dolcini died when Sara lost control of her Volvo after sailing over the hump at more than 80 miles per hour.

Highway Patrol spokesman Wayne Ziese on Tuesday said it doesn't appear that Melissa Scarborough was driving anywhere near that speed but added that investigators still haven't determined how fast she was driving.

What they do know is that she crossed the center line slightly as she went over the hump, lost control of her Toyota MR2, and smashed into a large tree on the west shoulder.

Since the impact was on the driver's side of the car, and Scarborough's legs were obviously badly injured, the first man to reach the car thought she was in the worst shape, said rancher Sally Gale, also a member of the Dolcini family.

That man was Mark Francisco, a former paramedic who lives on Gale's ranch. "He behaved heroically, according to the neighbors," Gale said.

Rescuers soon realized, however, that Dolcini was the more seriously injured. Both girls, juniors at Petaluma High, were airlifted by helicopter to Santa Rosa.

The Dolcini family and many of their neighbors have intensified their efforts to get the Marin County Public Works Department to do something about what they believe is a menacing hump in the road.

Elaine Dolcini, Kathy Dolcini's aunt, said on Monday that the family made a few phone calls to former Supervisor Gary Giacomini's office two years ago, but nothing was done about the road.

"We will not stop this time. The county will do something, or we will do something," Dolcini said, adding that residents of Chileno Valley are prepared to level the hump themselves.

They may not have to. On Tuesday, Tho Do, assistant transportation engineer for Public Works, went to the crash site to assess the situation. After driving over the rise at various speeds, Do said he'll recommend some kind of leveling job.

First, he said, his department will likely conduct a speed survey to find out how fast people generally drive through that section of Marshall-Petaluma Road and what happens when they drive too fast.

"Something needs to be done," he said. "We'll do something to smooth it out." If his recommendation is accepted, he said, "this will be a very high priority."

Do said a couple of women had asked the county to come out to Chileno Valley to hear their complaints, but he was surprised that Sally Gale and Elaine Dolcini had organized much of the vast Dolcini family and many of their neighbors for a show of solidarity.

"I expected to see two ladies and when I got here," he said. "I saw a big crowd here, and that impressed me," Do added.

What the crowd told Do is that some young drivers take the hump too fast for a thrill; that unfamiliar drivers overreact to a tricky configuration of bumps, turns, and trees; and that the speed limit is largely irrelevant.

Elaine Dolcini said her theory is that people who aren't used to the road see a large tree on the right as they approach the crest and react by edging slightly to the left and perhaps crossing the double-yellow line.

Once they hit the left-center area, she added, drivers encounter an uneven bump, and if they're going too fast, they lose control, overcompensate, and hit a second tree on the right, the tree that both Sara Dolcini and Melissa Scarborough both hit.

"It'll throw you off balance," she said.

Neighbor Todd Horick added that high school-aged drivers often hit the hump at high speeds for fun and said he's tired of responding to accidents there and finding badly injured kids.

Highway Patrol spokesman Wayne Ziese called the section of road "a spot where kids like to experience the thrill of a rollercoaster ride... Inexperienced teens are the problems here, [and] the families are looking for answers."

Supervisor Steve Kinsey agreed, saying rural-area dwellers have a "special obligation to train our children" about what driving on country roads are all about.

At the same time, he said, he'll encourage the Department of Public Works to approach the issue from a community-safety perspective" rather than from an engineering and road-maintenance perspective.