The Birkhoff Basin covered most of the northern part of this region with its ejecta at an early time. Yet an even earlier and larger feature, the Coulomb-Sarton Basin, underlies Birkhoff's ejecta.
The ancient floor of Birkhoff (Figure 10.1) records the subsequent history of several nearby craters: Sommerfield, Rowland, Stebbins, and Carnot.
Birkhoff is small for a basin, only about 10% larger in diameter than the conventional boundary between large craters and basins. There is a faint inner ring, 150 km in diameter. If there were outer rings, they have been obliterated by the surrounding large craters.
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