  We present a new database of $>$300 layer-orientations from sedimentary
mounds on Mars. These layer orientations, together with draped landslides, and
draping of rocks over differentially-eroded paleo-domes, indicate that for the
stratigraphically-uppermost $\sim$1 km, the mounds formed by the accretion of
draping strata in a mound-shape. The layer-orientation data further suggest
that layers lower down in the stratigraphy also formed by the accretion of
draping strata in a mound-shape. The data are consistent with
terrain-influenced wind erosion, but inconsistent with tilting by flexure,
differential compaction over basement, or viscoelastic rebound. We use a simple
landscape evolution model to show how the erosion and deposition of mound
strata can be modulated by shifts in obliquity. The model is driven by
multi-Gyr calculations of Mars' chaotic obliquity and a parameterization of
terrain-influenced wind erosion that is derived from mesoscale modeling. Our
results suggest that mound-spanning unconformities with kilometers of relief
emerge as the result of chaotic obliquity shifts. Our results support the
interpretation that Mars' rocks record intermittent liquid-water runoff during
a $>$10$^8$-yr interval of sedimentary rock emplacement.
