Study of three trenches excavated across two faults along the eastern edge of Crater Flat indicates that the main fault movement offset unit QTa in trench 1 at least 2.4 m down to the west, and occurred about 1.1 m.y. ago, as indicated by included basalt ash. Later fault movement, detected in trench 3, and probably related to the faulting at trench 1, displaced unit Q2c a combined distance of 0.8 m down to the west along three faults. Fault movement at trench 3 occurred sometime after 260,000 years ago and before about 40,000 years, but the evidence favors an age that is closer to the older date.