Figure 2. The Yucca Mountain volcanic field, NV, is a small volcanic field active since large-volume, caldera-forming silicic eruptions ceased about 8 Ma. As in larger volcanic fields, Plio-Quaternary volcanism occurs in spatial clusters. Thus the volcanic eruptions leading to the formation of the NE-trending Quaternary Crater Flat alignment (Northern Cone - Little Cones) were preceded by volcanism at nearby Pliocene vents. Magnetic anomalies (A-D) are buried volcanoes in this area, which has high sedimentation rates. Delineating the volcanic history of this region and the relationship between volcanism, faulting and episodes of extension is a key element of geologic hazards investigations for the proposed high-level radioactive waste repository at Yucca Mountain.