Ares Vallis, the site for landing the Mars Pathfinder, was chosen to fit several engineering qualifications. Being flat and low in elevation meant that it was a safe landing site. Its position also meant that the solar panels would be well supplied with sunlight. The area was also a good site for geologists to explore, since its features and geomorphology are the result of catastrophic floods. Some of the biggest and most interesting questions about Mars involve the role that water has played in its history.
Image from: NASA/JPL