Berchtesgaden, Germany  - A US woman who spent 70 hours trapped on a rock ledge in the Alps lowered an item of underwear into the valley Thursday as an SOS.

A police helicopter then plucked her to safety from the towering mountains above Berchtesgaden, Germany.

The woman, 24, hurt her ankle and shoulder and suffered cuts to the head in a fall Monday while on a mountain walk.

After three days of vainly trying to attract attention, she took off her undershirt and flicked it up to an aerial ropeway crossing the ledge.

It descended 2,000 metres with the ropeway, which carries logs, to a timber yard where a worker immediately realized the item was connected to the missing-person search being discussed in town.

"That bright idea probably saved her life," a police spokesman said. The woman from Colorado was taken to hospital.

"She is more or less uninjured and in fairly good shape, given the circumstances," the spokesman said. (dpa)