It's in the low nineties and well past noon, and Todd Presho is lurching alongside a highway retaining wall in a cherry picker near San Francisco, feverishly molding a vertical section of freshly sprayed "Shotcrete" before it solidifies in the California sun. The veteran mason is grappling with an unusual challenge: to hand-sculpt a rock face that is visually appealing, structurally robust, and physically impossible for renegade climbers to scale. "I take great care in creating overhangs instead of ledges, and I always space the handholds and footholds far apart," says Presho, describing his technique. "But you see climbers driving by and they're just foaming at the mouth, waiting for us to get out of here."
Presho's project is part of an innovative program that began in California in 1995 when a group of aesthetically sensitive highway engineers adopted the radical notion that cement retaining buttresses needn't necessarily look like a Left Coast version of the Berlin Wall. Unfortunately, however, it turns out that lining roadways with artful slabs of faux granite can be a recipe for mishap: Rock hounds tend to see these walls as outdoor extensions of their local gyms. In 1995, a group of climbers got stuck halfway up a sculpted wall north of Los Angeles and had to be plucked to safety by the local fire department.
Enter Presho, an artificial rock sculptor who has designed waterfalls, building complexes, and aquatic tanks for whales in Hong Kong, Singapore, Mexico, Hawaii, South Africa, and the south of France. Presho got involved with unscalable walls in 1991 while constructing an escape-proof open-air gorilla enclosure at the San Diego Zoo. To date, he has crafted nearly 200,000 square feet of unclimbable retaining walls for the California highway department (this month he will complete a stretch along California 128 through Sonoma's wine country). Meanwhile, transportation departments in Utah, Arizona, and Nevada are contemplating similar schemes.
All of which surely comes as good news to motorists who will no longer have to drive through mind-numbing, monolithic freeway corridors. But it seems only a matter of time before the rock-climbing community begins to interpret these structures as irresistible challenges. "The fact that they are supposedly 'unclimbable' makes them much more appealing," muses Alain Robert, the French climber known as Spiderman who recently pulled off the first free ascent of Chicago's 1,450-foot Sears Tower. "The danger of the cars and the noise wouldn't put me off if I liked the line," he adds. "I'd sure like to try and see if it's possible."