San Leandro area (cross section between Hayward and Oakland)
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San Leandro area (cross section between Hayward and Oakland). The cross section cuts through the East Bay Hills (on the right) and the East Bay alluvial plain next to San Francisco Bay south of Oakland (on the left). By comparison to the Mission Peak area, the Hayward Fault in the San Leandro area has a nearly vertical profile. East of the Hayward Fault, a structural basin preserves a thick accumulation of Great Valley Sequence. West of the fault, the San Leandro Gabbro (Jgb) is a large intrusive igneous body that has unique physical properties compared to the Franciscan rocks (mostly volcanic and sedimentary rocks) or the Great Valley Sequence (sedimentary rocks). Gabbro has physical properties more like granitic rocks—being both harder and more brittle than sedimentary rocks. Geologists suggest that that where the Hayward Fault is in contact with the gabbro, it may be more prone to producing higher magnitude earthquakes than in surrounding areas.
For more information about geologic names and words in the legend, see glossary definitions (including Coast Range Ophiolite, Franciscan Formation, Great Valley Sequence, geologic time scale,gabbro, serpentinite, alluvium, and more).
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