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Geodetic VLBI observations made with the Hat Creek $85'$ antenna were important contributions to the NASA Crustal Dynamics Program (CDP). Among other things, the CDP studied motions of the Earth's crustal plates and deformation in the vicinity of the San Andreas Fault in California.
The $85'$ antenna was one of the three fundamental anchor points in California east of the San Andreas fault that were used from 1983 to 1991 to determine the motions at various mobile VLBI sites along the San Andreas and to determine the Pacific plate motions at Vandenberg Air Force Base and Ft. Ord (California) and Kauai (Hawaii). The Hat Creek site itself was found to be moving $10.6 \pm 0.4$ (one $\sigma$) mm/yr to the WNW (PA $305\deg$) with respect to a ``stable" eastern North America. Hat Creek is located near the western edge of the Northern Basin and Range province. Its motion is thought to be a combination of WNW extension across the Basin and Range, and a small component of NW elastic deformation due to the interaction between the North American and Pacific plates. Geodetic VLBI measurements from Hat Creek to the nearby Quincy and the more distant Ely (Nevada) and Platteville (Colorado) mobile sites were the key measurements in defining the extension rate for the Northern Basin and Range as $8 \pm 2$ mm/yr (PA $ \sim 300\deg$). Hat Creek was also the anchor point for measuring a 5 cm northward seismic displacement at the Ft. Ord mobile site due to the Loma Prieta earthquake.
We will show the motion of California and Pacific basin sites for which Hat Creek contributed important data.
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