The Mangala Valles system of channels heads at one of the graben that comprise Memnonia Fossae, extends northward nearly 1000 km across Noachian and Hesperian highlands, and terminates at basins contiguous with Amazonis Planitia. The Mangala Valles system has previously been interpreted to have formed through one or more catastrophic aqueous floods on the basis of similarities between the characteristics of its channel landforrns and those of terrestrial systems, including the Channeled Scabland of Washington. Although aqueous mechanisms for formation of Mangala Valles are broadly congruous with known characteristics of the channel system, an alternative volcanic hypothesis for formation of the system appears to be worthy of consideration on the basis of (1) its consistency with the volcanotectonic nature of the system and (2) commonalities between the basic nature of the system and that of large volcanic channels of the inner solar system. Estimates based on thermal considerations suggest that formation of Mangala Valles could conceivably have taken place through eruption of a lava volume of ∼2 × 105 km3, or roughly the total volume of the terrestrial Columbia River Basalt Group. The volcanic hypothesis for forrnation of Mangala Valles, and a hybrid hypothesis involving formation of Mangala Valles through aqueous processes followed by or in concert with substantial modification of the system by volcanic erosion and deposition, appears viable and worthy of future consideration.