In 1971, the crewed Apollo 15 mission landed in the southeastern region of Mare Imbrium, between Hadley Rille and the Apennine Mountains. Commander David Scott and Lunar Module Pilot James Irwin spent three days on the surface of the Moon, including 18½ hours outside the spacecraft on lunar extra-vehicular activity. Command Module Pilot Alfred Worden remained in orbit and acquired hundreds of high-resolution photographs of Mare Imbrium (and other regions of the moon) as well as other types of scientific data. The crew on the surface explored the area using the first lunar rover and returned to Earth with of lunar surface material. Samples were collected from Mons Hadley Delta, believed to be a fault block of pre-Imbrian (Nectarian or Pre-Nectarian) lunar crust, including the Genesis Rock. This was also the only Apollo mission to visit a lunar rille, and to observe outcrops of lunar bedrock visible in the rille wall.