Geological Maps

This is the Division of Mines and Geology geologic map of California. It is excellent for seeing generalized geologic relationships in California. Note the series of granitic rocks that crop out west of the San Andreas Fault. They appear to originate near the southern Sierras. this hypothesis is supported by similar ages and compositions between these plutons and the Sierran batholith. The group of rocks that contains these plutonic rocks west of the San Andreas Fault is known as the Salinian Block. It contains plutonic and metamorphic rocks similar to those found in the Sierras, but very different from the Franciscan Assemblage, which is shown in green colors from San Francisco to north or Cape Mendocino. The Franciscan rocks are characterized by high-pressure, low-temperature metamorphism, whereas the Salinian Block and Sierran terranes are characterized by low-P, high-T metamorphism. The San Andreas Fault juxtaposes these different rock types near our home here in Santa Cruz.

The map on the right shows an enlarged version of the Division of Mines and geology map for the region around the Monterey Bay Area. The red area near the UCSC campus is the Ben Lomond Quartz Diorite, one of many plutons that occur in the Salinian Block. The brownish orange color represents marine sedimentary rocks, of Tertiary age, whereas the yellow color represents Quaternary deposits in vallies and low coastal areas. A bend in the San Andreas Fault can be seen in the mid-portion of the diagram.

The blue-colored map on the left is a geological map of the campus done by the local consulting firm, Weber and Associates. It shows the basic geologic units discussed in this field trip, including marble (mar), schist (sch), quartz diorite (qd), and sedimentary units (Tsm; Tertiary Santa Margarita sandstone). Note that nearly all the contacts (i.e., borders between the various units) are dashed with question marks. this means that the exact location and nature of the contacts is not exposed. Because of the poor exposure, it is difficult to determine whether the contacts are conformable or faulted. Weber and Associates interperate most of the contacts as faults. An important exception is the Santa Margarita sandstone, which lies conformably on top of the Mesozoic metamorphic and plutonic units.

The red and purple map to the right shows the detail around the UCSC campus from a USGS map of Santa Cruz county (must lookup reference). It shows that the UCSC campus is built upon an "inlier" of plutonic and metamorphic rock (various shades of purple) poking up through the Tertiary sedimentary rocks (reds and tans) that occur nearly all around the UCSC campus. The yellow color represents Quaternary marine terrace deposits.

Each line on the map to the left represents a lineation mapped using photographs taken from the air, and geological maps. The lineations include things like straight canyons or series of aligned sinkholes. This north-south orientation is prevalent on campus and is related to joints and fractures in the campus marble. It can be seen in joints at the quarry, in the orientation of canyons and in the orientation of Empire Cave.