PASADENA, Calif. -- The plucky Mars rover Opportunity is driving out of the giant Victoria Crater nearly a year after a dangerous descent to examine exposed bedrock.

NASA said engineers noticed a power surge in Opportunity's left front wheel and decided to pull it out of the crater before it got stuck. Its twin rover, Spirit, lost function in its right front wheel in 2006 after a similar surge, but can still drive on flat terrain.

Opportunity descended into Victoria Crater last September on the way to study rocks along the Cape Verde cliff face, while in the crater researchers used the rover to inspect bright rock layers.

Scientists said they are still en route to Nevada -- a location named for a rock shaped like the state -- but were unable to scale the crater face where they wanted.

Opportunity and Spirit landed on Mars in 2004 and have operated far, far beyond their original 90-day mission. Researches are using Opportunity to study the Martian atmosphere.