I'm sorry if that last post came off a little harsh.
Admittedly I'm more into the physics side of planetary sci and not a rock nut (geologist) myself. Heres the image to which I thought you might be refering.
From http://themis.asu.edu/pr.html
caption:
Ganges Chasma, Mars as seen in infrared color. This false-color infrared image was acquired over the region of Ganges Chasma in Valles Marineris at approximately 13° S, 318° E. The color differences in this image show compositional differences in the rocks exposed in the wall and floor of Ganges (blue and purple) and in the dust and sand on the rim of the canyon (red and orange). The floor of Ganges is covered by rocks and sand of basaltic lava composition that are seen as blue in this false-color infrared image. A remarkable layer that is rich in the mineral olivine can be seen as a band of purple in the walls on both sides of the canyon, and exposed as an eroded layer surrounding a knob on the floor. The mosaic was constructed using THEMIS infrared bands 5, 7, and 8, and covers an area approximately 150 km on each side. This simulated view is toward the north.
So the floor of the canyon IS basaltic (more like olivine) in composition, not chemicaly altered just mechanically degraded. (They're calling it sand.)
The intense purple coded regions of olivine spectra are interesting as they could represent a flood basalt which could be used to relatively date this region. Now that I think about it, it probably already has....
Space/Science » in reply to Jesus man, read a geology book.
After doing some reading myself....