Detailed geological studies across the highland-lowland boundary in north central Arabia Terra, Mars provide constraints on the age and nature of processes responsible for a complex array of structures and landforms. The area studied is bounded by 27.5¿ and 47.5 ¿N, 330¿ and 335 ¿W. Highland basement was formed in Early Noachian and was extensively resurfaced in Late Noachian. Materials underlying highland plateaus were emplaced in Middle Noachian. Erosion responsible for fretted terrane and fretted channels most likely occurred in Early Hesperian but definitely prior to the middle of the Hesperian and during or after Middle Noachian. There is good evidence for the involvement of liquid water in fretted channel formation. Within the area mapped, the presence of fretted terrane correlates with evidence for extensive development of large grabens. All lowland materials were emplaced after the erosion that formed fretted terrane and channels; the earliest of these materials were emplaced in mid-Hesperian, and the youngest were emplaced in Late Amazonian. Morphological evidence supports debris flow or rock glacier processes for the formation of the youngest materials. Debris flow materials on the floors of fretted channels are much too young to be related to channel formation. The entire region exhibits a northerly tilt of ~0.1¿-0.15¿ that formed after deposition of the oldest lowland materials but before emplacement of Upper Hesperian and younger debris flow/rock glacier materials. The nature and ages of structures and landforms in this region are not consistent with the presence of a Late Noachian to Early Hesperian convergent plate boundary in northern Arabia Terra. ¿ 2000 American Geophysical Union