GUNG GO FOR GOO.

"Go!" shouts the starter.

Stop watches click. The jeep leaps forward with a roar, and I'm with it. Moving quickly in the dappled forest twilight, we straddle a bank, splash into a stream, barely make it up the other side between two trees and race hell-for-leather down an open stretch. I'm holding on for life.

A sharp left turn. And there suddenly are two of the biggest ruts I've ever seen in a road. We'll never make it, I think. But we do. The jeep rattles violently and my vertebrae reorganize. Grunting, the jeep climbs the hillock, then begins its descent, slipping and sliding in the thick mud. Trees come flying at me. Then another sharp turn to the left. We pivot, plunge into the stream and come up the other side, engine screaming.

The stop watches click at l :49. The second fastest time of the day. Driver Art Archer nods his approval.

This ride took place one gray Sunday afternoon in a backwoods area five miles west of Redwood City, where a small group of 40 jeeps assembled for a Mud Run.

The event was hosted by the Redwood Jeep Club, and included members of the Sacramento Jeepers and the East Bay Hillhoppers Jeep Club. All are under the auspices of the California Association of Four-Wheel Drive Clubs, comprised of 71 individual clubs.

When you go to a Mud Run, getting there is half the fun..The competition site, deep in the woods, is reached by a circuitous road. The mud is up to your ankles, and the road has enough potholes to qualify for a war torn supply route in Vietnam.

At the site the jeeps line the road in the sylvan twilight. The course is not long, but it's tricky. Full of angles and sharp curves, it tests a driver's skill and a vehicle's endurance.

Ray Cronin, a tall, Gary Coopefish Hayward auto salesman, makes the run in a little under three minutes. Two years ago he rolled 240 feet down a cliff at a fourwheel drive competition in Georgetown. Yet, among fourwheelers, the serious accident is rare. Cronin considers himself lucky. "You only get away clean once," he says.

Another jeep comes barreling across the stream and crosses the finish line. It's driven by a woman. Her name is Vy Archer, a member of the Hillhoppers who has raced in competitions for about five years. Mrs. Archer, a petite mother of four, has a living room full of first place trophies. Her husband, an auto supply dealer, is the driver who gave me my hair-raising ride.

Has she ever had an accident on the course?

"No," she says, then blushes. "Oh well, I did once put a little teeny dent in our right front fender."

"Women drive differently from men," says Lonnie Wiseman, a pert 24 year old. "Women drive more on feeling. The man pushes more."

When Lonnie's husband first bought their jeep, she didn't want to race it. But after her first competition, she found she liked to challenge herself. She feels it helps make her a better driver.

Racing isn't all there is to four-wheeling, however. Most clubs schedule weekend excursions into the snow country the forests or the sand dunes, where fun is measured by the trouble one gets into. Four-wheelers get bored quickly when there's no struggle.

The sport is a popular family pastime -- mother, kids, even the dog goes -- and stresses responsibility. Four-wheelers do their share in keeping remote areas and campsites clean.