LOS ANGELES (AP) _ NASA's Spirit Rover began investigating a trench to see if the minerals inside it can provide clues about whether there was once enough water in the area to support life.

The robot spent about two hours digging the 3-inch trench Friday by running a front wheel back and forth over a stretch of ground in a depression. On Saturday, it studied the trench with a microscopic imager and its Mossbauer spectrometer, a German-built instrument that measures the composition and abundance of iron-bearing minerals.

``Some minerals will be made out of one type of iron or another, and the type of mineral will change based on whether or not there was liquid water in the environment,'' mission manager Jim Erickson said Saturday during a teleconference from NASA's Jet Propulsion Laboratory in Pasadena.

Sprit was to further investigate the trench Sunday and Monday, then continue toward a crater scientists have named ``Bonneville,'' about 445 feet away.

On the other side of Mars, Spirit's twin rover, Opportunity, drove the final 33 centimeters Saturday to be in place to examine a rock called ``El Capitan,'' part a rocky outcropping.

Studies of El Capitan with instruments including the rover's rock abrasion tool will occur over several days. NASA was expected to conduct the first test of the device Monday.

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On the Net: http://marsrovers.jpl.nasa.gov