The Mars Orbiter Laser Altimeter (Smith et al., 1999), on board Mars Global Surveyor, acquired hundreds of millions of individual measurements of Mars topography from which along-track pro- files and global maps were produced. We have manually selected
30 altimetry profiles (Precision Experiment Data Records PEDRs) homogeneously distributed through the Northern plains and 40 profiles through the oldest regions of the southern plateaus. Note that we restricted our analysis to latitudes equatorward of about
501 in both hemispheres to exclude higher latitude regions, the topography of which is known to be strongly affected by geolo- gically recent climatic processes (Kreslavsky and Head, 2002; Head et al., 2003). The along-track point-to-point distance between successive points on the MOLA PEDR profiles is around
300 m.