[5] Valles Marineris is located along the equator of Mars, on the east side of the Tharsis Bulge, and stretches for nearly a quarter of the planet's circumference.

[6][7] Most researchers agree that this formed as the crust thickened in the Tharsis region to the west, and was subsequently widened by erosion.

It has also been proposed that Valles Marineris is a large channel formed by the erosion of lava flowing from the flank of Pavonis Mons.

Tharsis volcanism involved very low viscosity magma, forming shield volcanoes similar to those of the Hawaiian Island chain, but, because there is minor or no current active plate tectonics on Mars, the hotspot activity led to very long histories of repeated volcanic eruptions at the same spots, creating some of the largest volcanoes in the solar system, including the biggest, Olympus Mons.

[10] Most sizable craters on Mars date to the Late Heavy Bombardment, 4.1 to 3.8 billion years ago (the Noachian period), and are older than the landslide deposits in Valles Marineris.

Many scientists however agree that liquid water flowed on the Martian surface in the past, when atmospheric conditions were different.

Noctis Labyrinthus, on the western edge of the Valles Marineris Rift System, north of the Syria Planum and east of Pavonis Mons, is a jumbled terrain composed of huge blocks which are heavily fractured.

Most of the upper parts of the blocks are composed of younger fractured material thought to be of volcanic origin associated with the Tharsis bulge.

[12] Terrains such as Noctis Labyrinthus are commonly found at the head of outflow channels, like the one explored by the Pathfinder mission and its Sojourner rover.

They are interpreted to be a place of downward block faulting associated with the removal of ground fluid in catastrophic flood sequences.

[8] In 2024, scientists found evidence that the hypothesized lava came from a volcano they dubbed Noctis Mons, which would be the seventh-highest mountain on Mars at 9,028 m (29,619 ft), and that the eastern part of its base was home to multiple glaciers with potential for hosting life, which could make it a highly valuable candidate target for astrobiology missions.

These valleys have a stubby theater-headed leading edge very much like features seen on the Colorado Plateau near the Grand Canyon that appear from groundwater sapping.

Between the two canyons, the surface is composed of younger fractured material - lava flows and faults from crustal extension of the Tharsis Bulge.

The floor of Melas Chasma is about 70% younger massive material that is thought to be volcanic ash whipped up by the wind into eolian features.

There are also portions of older and younger massive floor material of volcaniclastic origin - only separated in age by crater distribution.

Newer data from Mars Global Surveyor suggest that the origin of this layering is either just a succession of landslides, one over another, volcanic in origin, or it may be the bottom of a basin of either liquid or solid water ice suggesting that the peripheral canyons of the Valles Marineris system could have been at one time isolated lakes formed from erosional collapse.

Eastward from here there is about a 0.03 degree slope upward before reaching the outflow channels, which means that if you poured fluid into this part of the canyon, it would form a lake with a depth of 1 km (3,300 ft) before spilling over towards the northern plains.

The eastern Washington scablands are a result of repeated catastrophic flooding due to the build-up of an ice dam at the head of Lake Missoula in the Late Pleistocene.