Beta Regio is a region of rifting and volcanism on Venus. The nature of Beta, a major topographic rise and rift zone, is herein characterized using Pioneer Venus, Arecibo, and Venera 15/16 data. High-resolution (1-2 km) Arecibo and Venera radar images reveal details of faulting and volcanism, and Pioneer Venus altimetry illustrates the density and location of faults in relation to topography. Faults are distributed throughout Beta but are concentrated in Devana Chasma, where they are spaced 5-20 km apart. The pattern of faulting and distribution and sequence of volcanic activity in Beta can be used to help understand how the rift has evolved, including the origin of the high topography of Beta and the origin and nature of Devana Chasma. On the basis of geologic mapping relations and map patterns, Beta appears to have formed as a result of doming in response to a mantle anomaly. At the same time, Rhea Mons, a major shield volcano, was formed. Formation of Devana Chasma followed, with extensive faulting in the rift trough. Geometry of the trough and fault patterns suggests that some degree of lithospheric stretching has occurred. Later volcanism produced a second major shield volcano, Theia Mons, which is superimposed on the western bounding fault of the rift zone. Both uplift and extension have been involved in forming Devana Chasma and Beta Regio and may be important in the formation of other equatorial high-land regions with systems of chasmata on Venus, such as Aphrodite Terra. The bifurcation of Devana Chasma in the vicinity of Theia Mons, and the extension of the rift system south to Phoebe Regio and west toward Aphrodite Terra, suggest that their origins may be linked.

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