Stop 14

Exit Building 1 and walk toward the main flagpole, which is surrounded by a garden of drought-tolerant plants. Before crossing the street, look to your left and you will see a tall communications tower over Building 11, which is the nerve center of the USGS Northern California Seismic Network. Microwave radio antennae on this tower receive signals of earthquake shaking from widely scattered seismometers and feed those signals automatically into computers for rapid analysis of an earthquake’s location and preliminary magnitude.

To the right of the flagpole, at the end of the short sidewalk, is a USGS benchmark “WMC 1994” that can be used to set your hand-held Global Positioning System (GPS) receiver (see ESIC for handout). A GPS receiver is a powerful new tool used by surveyors, map makers, and recreational users. Using satellites orbiting at 12,500 miles above the earth, a GPS receiver automatically triangulates positions by calculating a distance from four or more satellites.

Just beyond the benchmark are three granite boulders donated by the U.S. Forest Service. They are from Sonora Pass in the Sierra Nevada. The source of the rocks is magma (molten rock from deep within the earth) that was intruded into the overlying rock about 86 million years ago, during the Cretaceous Period. The largest boulder on the right weighs nine tons, and all three specimens display large phenocrysts (crystals) of orthoclase feldspar as much as four inches long. Such large crystals formed only in the largest masses of granitic rock, where cooling was the slowest. What’s the biggest crystal you can find?

This completes your tour. We hope that you will have time now or someday in the future to return to the ESIC for an extended time of browsing among the maps and publications; return to the library to browse among the 400,000 volumes; or take a closer look at any of the geologic or botanical specimens and pleasant spots along the tour.

We hope you have enjoyed your tour of the USGS and that you will come back often to view our changing hallway and Visitor Center exhibits.

The USGS Western Region Center sponsors a free monthly public lecture, usually held on the last Thursday of each month. These presentations focus on science topics ranging from maps to meteorites to marshland ecology, and are presented by USGS scientists in non-technical terms. The lectures begin at 7 p.m., and on those evenings, the ESIC remains open until the start of the lecture. Dates and topics may bechecked by calling 650-329-5000 or by picking up a flyer in ESIC.

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