The southern Rio Grande rift has taken about 26 to 28 m.y. The shallow features can also be used (collectively) to trace the Rio Grande rift into far west Texas and northern Chihuahua, where the rift appears to end as a distinct thermotectonic system. These features are interpreted to be shallow manifestations of an asthenosphere upwarp, thinned crust containing dike swarms, and an associated thermal regime beneath the rift, an hypothesis consistent with a variety of geophysical data from the southern as well as the northern portions of the rift. Relative to adjacent more stable areas the Rio Grande rift is a tectonically active, thermally anomalous structure distinguished throughout its length by the combination of high heat flow, recently active volcanoes, exceptionally deep basins and late Quaternary faulting.
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