JAUNTS : Mechanics and Etiquette of Bicycling : CORBA volunteers educate beginners about gears, tire pressures, brakes and even rattlesnakes.

When you are mountain biking, you never know what hazard awaits you: unforgiving terrain, not to mention flat tires, poison oak, dehydration, rattlesnakes.

Rattlesnakes? You bet. Just ask the dozen novice riders who signed up for an introductory riding class on a recent Saturday at Malibu Creek State Park in the Santa Monica Mountains.

They were gathered around an instructor, learning about gears, brakes and tire pressure when a small rattler wandered nearby.

“That’s a perfect reason not to go off the trail,” said Mark Langton, an instructor for the Mountain Bike Unit of CORBA (Concerned Off-Road Bicyclists Assn.). “There is a real good chance snakes are there.”

Snakebites and the equally dreaded flat tire are among problems CORBA addresses in the class that the voluntary unit started for new riders in April.

The session runs on the first Saturday of the month, from 9 a.m. to about 1 p.m., with the last half serving as riding time. It’s free, but CORBA memberships ($15) are pushed.

On that Saturday the class was all adults, many in their 30s and 40s. Nearly all of them knew how to work the gears, but beyond that, they were babes in the woods.

Rosine Ackerman had taken her mountain bike out on a trail for the first time the previous weekend.

“It looks so easy--they just ride along,” she said. “I never realized how difficult it was until I started down. I scared myself to death.”

During the first half of the class riders ask questions and listen to Langton talk about the basics. A helmet is a must. So are water, a spare inner-tube and a tire pump. A high energy bar isn’t a bad idea too, along with sunscreen and tools.

Langton goes over how to clean trail dirt from the chain and apply lubricant. He touches on tire pressure, applying the brakes evenly (never use the front brake only), and seat height. He demonstrates how to fix a flat.

He talks about riding etiquette and regulations in the Santa Monica Mountains Recreation Area. (Roads have a speed limit of 15 m.p.h., and a trail is considered anything less than 60 inches wide.)

CORBA has worked since 1987 to open up more land to mountain biking by preaching responsible riding and peaceful coexistence with hikers and horseback riders. The group has about 250 members from Ventura and Los Angeles counties.

Ross Blasman, a Newbury Park biker who oversees the Mountain Bike Unit, says the group’s goal is to open up the entire length of the backbone trail--from Santa Monica to Point Mugu--to mountain bikers.

“At this point the majority of the roads (in the recreation area) are open, but the majority of the trails are closed,” Blasman said.

He designed the introductory class, he said, because a lot of new riders don’t know anything about mountain riding and the parks.

During the second half of the session, riders get on their bikes and ride, but it’s not a brutal trek over some horrendous trail. First Langton takes the group out onto a dirt road where he goes over shifting, coasting and braking.

Then he moves on to something more challenging: “bunny hopping.” He puts a big log in the road and demonstrates how to ride over it. One by one the group--some of them a little weak-kneed--try it. Most bounce over awkwardly, but a few land in the dirt.

Finally, the finale: a hill on a short stretch of trail. It’s narrow, rutted, and it might as well be Mt. Everest to the riders. After switching into the lowest gear, one by one, they attempt the grade. Few make it without stopping. Most push their bikes up a good part of it.

Then Langton gives the word to ride back down. It’s a nerve-jarring experience for a beginner, but an exhilarating end to the class--except perhaps for the guy who loses it half way down and crashes. He’s OK, though, thanks in part to his battered helmet.

* WHERE AND WHEN

WHAT: Introductory class on mountain biking, sponsored by the Mountain Bike Unit of CORBA (Concerned Off-Road Bicyclists Assn.).

WHERE: Camp Fire Center at Malibu Creek State Park in the Santa Monica Mountains, off Las Virgenes Road near Agoura.

WHEN: First Saturday of every month, 9 a.m. to about 1 p.m.

COST: Free. ($15 membership in CORBA is optional)

INFO: Call 378-5100 or 818-706-2789.

FYI: CORBA celebrates its sixth birthday on Sunday, Aug. 8, at the Arts Council Cultural Center, 482 Greenmeadow Drive, Thousand Oaks. From 9 a.m. to 11:30 a.m., they’ll direct rides for all levels of riders. Cost is $3 for CORBA members and $5 for non-members. Raffle includes two bikes.