Currently at the NASA website Mars Rover photo gallery, two images, ‘Spirit Front Hazcam 2169‘ have been removed by NASA.

Authentic NASA Mars Rover image shows extraterrestrial structures, spaceship, on Mars?

NASA’s Mars Exploration Rover Spirit recorded this fisheye view with its rear hazard-avoidance camera after completing a drive during the 2,169th Martian day, or sol, of Spirit’s mission on Mars (Feb. 8, 2010). Image credit: NASA/JPL-Caltech

Close-up view:

Ok, that doesn't look like a landing platform. It definitely doesn't look like a montain either... If you click this link bellow, you'll see a screenshot from Nasa's site, showing the actual image in their photo gallery, so this shouldn't be a hoax.