Steve Anderton climbed over the chest-high metal railing of the Perrine Bridge and planted his feet onto a tiny wooden platform little bigger than his two hiking boots.

He paused for a few seconds as he looked out at the Snake River 480 feet below and jumped. While extending both arms, he curled up his body to flip backward and release a parachute, which allowed him to steer to the side of the riverbank in a safe landing.

Dare trying a stunt like that at San Francisco's famed Golden Gate Bridge, and authorities will fine you $10,000. In the rural Idaho town of Twin Falls (population 37,000), officials welcome the jumpers and have made it a worldwide mecca of a tiny but growing extreme sport known as BASE jumping.

"There are no rules basically to ban BASE jumping," said Shawn Barigar, a city council member and chairman of the Twin Falls Area Chamber of Commerce. "The general reaction is 'no harm, no foul.' "

"As long as it is not disruptive and isn't causing any problems, more power to them. They are the ones taking the risk upon themselves."

Anderton, 26, traveled with a group of friends from his native Australia, where he works as a carpenter four months a year to fund travels to exotic jump sites around the world. He has logged 420 jumps to date and makes about seven jumps a day when in Twin Falls, each requiring a 15-minute hike back up from the bottom of the river canyon.

"It's a relatively young sport, so a lot of people are scared of it," he said, wearing a black helmet with a video camera on top to record his adventures. "It's become a lot safer. We're not that crazy; we're just normal people."

For many BASE jumpers, the activity is not a sport. It is a way of life that delivers a unique adrenaline rush.

BASE jumping refers to leaps from "building, antennae, span, Earth." Popular locations include cliffs in Europe, especially Norway, as well as buildings from Moscow's Ostankino television tower to the Petronas Towers in Malaysia.

Twin Falls is considered a great place for newcomers and seasoned jumpers trying new tricks because the canyon spreads across 1,500 feet and offers a wide riverbank for landing. An ample span underneath the bridge allows leeway in case conditions steer the jumper backward.

Locals dispute who made the first BASE jump at a location perhaps best known for stuntman Evel Knievel's failed 1974 jump over the Snake River. But since that time in the late 1980s or early 1990s, word of the city's permissive attitude has spread. Some enthusiasts have even moved here.

Tom Aiello, 33, who grew up in California, relocated a year and a half ago after logging more than a 1,000 jumps in numerous locations, some of which he prefers not to discuss. Many BASE jumpers are reluctant to speak publicly of some of their favored sites, sometimes because local authorities may not approve.

He now teaches the sport and says he rejects many would-be students who do not have extensive sky diving experience -- typically 150-200 jumps -- considered requisite to begin BASE jumping. Also needed is a parachute rig costing about $2,500.

Aiello says he also requires students to write letters saying they know the sport is dangerous and could cause death.

No one pretends this is a sport free of danger. An Internet list maintained by Nick De Giovanni chronicles 90 BASE jumping deaths since 1981, the most recent of which came on July 19. Two have died jumping off the Perrine Bridge in Twin Falls.

Aiello said he has broken the same leg twice and suffered a broken back that landed him in the hospital for two months. "It pretty much hurts all the time," he said, adding his enthusiasm for the sport is undiminished.

Overlooking the Snake River on a recent afternoon, Courtney Allen, 26, a Utah engineer who works on jet engines for missiles, wore a long bandage on his forearm and had minor bruises across his legs from a bad landing the day before.

"Normal people think sky divers are crazy, and sky divers think BASE jumpers are crazy," he said.

Allen broke his wrist a few months ago, but even that mishap did not sideline him. "I was BASE jumping with a cast on," he said. "My doctor really didn't recommend it, but this sport is so addictive you just do it."

BASE jumpers Karin Sako and Jeb Corliss push off from the Perrine Bridge on a training jump in Twin Falls, Idaho, where officials have welcomed the sport. Corliss freefalls from the bridge before deploying his parachute. The site attracts jumpers worldwide for its wide canyon and riverbank for landing.Corliss uses the hallway in a local motel to repack his parachute. For many, BASE jumping delivers a unique adrenaline rush. But no one pretends it's a sport free of danger. An Internet list by Nick De Giovanni chronicles 90 BASE jumping deaths since 1981. Two have died jumping off the Perrine Bridge.