Through the relentless action of plate tectonics, erosion, gravity, heat transfer and flexural loading, mountains are built, sustained and destroyed over time. The problem of separating the signal of mountain building from other non-steady sources, e.g., contemporary hydrological loading associated with municipal water extraction, drought, mining, and earthquake cycle effects, is at the forefront of geodetic research. Estimation of the long-term vertical motions from tectonic forcing provides an essential background for understanding contributions to sea level changes that are not attributable to changes in volume of the Earth's oceans. GPS networks provide high precision, stability and point coverage at thousands of locations with geographic spacing near 20 km and strong connection to a global reference frame, while Interferometric Synthetic Aperture Radar (InSAR) provides complementary blanket coverage at resolution near 10 m. Integrating these datasets improves vertical motion maps and our ability to separate the various contributions to elevation change. I will discuss the use of space geodetic measurements to study and monitor active crustal deformation in the western United States, especially in Southern California and the Intermountain West, where the Basin and Range province widens the continent by ∼1 cm each year. A case study in the southern Great Valley illustrates how measurements should be corrected for groundwater loading before being used to estimate long-term crustal deformation properties such as slip rates on faults.

Bill Hammond studies active deformation, earthquakes and geodynamics of the western United States using space-based geodetic techniques. He is an Associate Professor at the University of Nevada, Reno, working in the Nevada Geodetic Laboratory, which is a part of the Nevada Bureau of Mines and Geology in the University's College of Science. His previous employment includes 4 years at the U.S. Geological Survey in Menlo Park, CA. He earned his Bachelor's degree in mathematics at U.C. Berkeley and his Ph.D. in geophysics at the University of Oregon, Eugene. He and his family enjoy the Sierra Nevada scenery while living in Truckee, CA.

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