Figure 4. (A) Magnetic map enhancing shallow magnetic sources of the San Leandro gabbro and vicinity. Patterned area, San Lenadro gabbro; red outlines, gabbro slivers defined by magnetic anomalies. Explanation as in Figure 2. Geology modified from Graymer (2000a). (B) Geophysical boundary of the San Leandro block and other geophysical lineaments defined by maximum horizontal gradients of gravity (blue) and magnetic (red) data. Bold blue and red lines define boundary of the San Leandro block. Geology modified from Graymer (2000a). Jgb (violet), gabbro; sp (blue), serpentinite; Tn (brown), Neroly Sandstone; black lines, faults. Bold black lines, recent trace of the Hayward and Chabot faults (Lienkaemper, 1992; Graymer, 2000a). Eastern edge of San Leandro block correlates with the Chabot fault.