From http://fti.neep.wisc.edu/neep602/LEC1/trip.html:
On the second EVA, the Lunar Rover took us seven kilometers away from the Challenger to the South Massif, where we sampled boulders at the base of the south wall of the valley and explored an avalanche deposit that had moved out away from the Massif. Our surprise, but not altogether unexpected discovery of the orange soil also occurred during the second EVA. This chemically unusual material from 3.5 billion year old volcanic fire fountains has given new insights into the origin of the moon and the nature of its interior.
The third EVA provided an opportunity to study the large boulders that had rolled and bounced down the north wall of the valley. From them, we hoped to learn more about what happens when large objects from space hit, break, and partially melt planetary crusts. During the detailed examination of one very large boulder, the unexpected discovery of a subtle contact between two types of impact generated debris units, one intrusive into the other, again proved the worth of the trained human eye in exploration.
Questions often arise as to whether robotic exploration of the moon or any other planet would be less expensive than human exploration and provide all the essential scientific return. This question, of course, can never be answered to everyone's satisfaction if only because of sincere disagreements over what constitutes "essential science.". Clearly, robotic systems will and must make increasingly important contributions, however, the spontaneous human observation, integration, and interpretation of the total dynamic situation involved in space activities, and a calculated human response to that situation, will be as irreplaceable in the future as throughout the past.