The Mars monolith is a rectangular boulder discovered on the surface of Mars. It is located near the bottom of a cliff, which it likely fell from in the past. The Mars Reconnaissance Orbiter took pictures of it from orbit, roughly 180 miles (300 km) away.
More than this, other interesting objects and anomalies was been discovered on planet Mars.
Here a video of a detailed zoom in an original HiRISE picture where is visible another possible monolith.
Mars Monolith Mistery
Layers in Uzboi Vallis
picture ID: PSP 008338 1525
Credit: NASA/JPL/University of Arizona
27 24 40.06 S – 35 18 30.46 W
hires original files: http://hirise.lpl.arizona.edu/PSP_008338_1525
soundscapes by freesound.org
Another interesting anomaly is the Phobos Monolith.
“The Phobos monolith is a large rock on the surface of Mars’s moon Phobos.
It is a boulder about 85 m (279 ft) across.A monolith is a geological feature consisting of a single massive piece of rock. Monoliths also occur naturally on Earth, but it has been suggested that the Phobos monolith may be a piece of impact ejecta. The monolith is a bright object near Stickney crater, described as a “building sized” boulder, which casts a prominent shadow.
It was discovered by Efrain Palermo, who did extensive surveys of Martian probe imagery, and later confirmed by Lan Fleming, an imaging sub-contractor at NASA Johnson Space Center.”