Opportunity is exploring 'Marathon Valley' on the rim of Endeavour crater. The rover is up on north-facing slopes for improved solar array energy production.

The rover is conducting an in-situ (contact) science campaign on the surface target 'Joseph Collin' (informally named for members of the Lewis and Clark expedition).

The target appears as a curious, unconsolidated pile of coarse, dark grains. On Sol 4263 (Jan. 20, 2016), Opportunity began two sols of investigation using the robotic arm instruments. On each sol, extensive Microscopic Imager (MI) mosaics were collected.

Each was followed with a unique placement of the Alpha Particle X-ray Spectrometer (APXS) for elemental identification. Over the next 3 days (sols), the rover attitude was updated and a series of Panoramic Camera (Pancam) and Navigation Camera (Navcam) panoramas were collected.

On Sol 4268 (Jan. 25, 2016), the final work on this in-situ target was completed with the raising of the robotic arm off the target and the collection of some documentary imagery. The rover is now set to drive away from this site towards new targets up-slope from the current location.

As of Sol 4268 (Jan. 25, 2016), the solar array energy production was 469 watt-hours with an atmospheric opacity (Tau) of 0.478 and a solar array dust factor of 0.691.

Total odometry is 26.50 miles (42.65 kilometers), more than a marathon.