We present a spatial analysis of free air gravity and topography for M
ars using new, higher resolution gravity data and the latest digital e
levation data, both represented by spherical harmonics up to degree an
d order 50 and, separately, for harmonic degrees 4-19. Interpreting th
e gravity vs gravity-from-topography scatter diagram in terms of isost
atic compensation for small regions, we find that most of Mars older t
han Amazonian is fully compensated at shallow depths (< 50 km). Except
ions to this include the ancient Tempe Terra region and the central po
rtion of the Isidis impact basin (a known mascon). Most Hesperian-age
and Amazonian-age volcanic plains not located near Tharsis and Elysium
volcanoes are also compensated isostatically at shallow depths, but A
mazonian-age plains near the young volcanic constructs, like Olympus M
ons and the Tharsis and Elysium volcanoes themselves, are not. Both Ol
ympus Mons and Alba have isostatic compensation depths > 300 km.