We estimated horizontal velocities at 15 locations in the vicinity of Yucca Mountain, Nevada, from Global Positioning System surveys conducted between 1991 and 1996. We used these velocity estimates to infer slip rates on two major Quaternary faults within the eastern California shear zone (ECSZ), the Hunter Mountain and Death Valley faults. The sum of slip rates across the two faults is well determined at 5¿1 mm/yr (1-&sgr;). Between 3 to 5 mm/yr of this motion appears to be accommodated along the Death Valley fault, implying 30--50 m of strain accumulation over the next 10,000 yr. If so, there is potential for 5 to 10 Mw 6.5--7.5 earthquakes during this period, a finding consistent with paleoseismological studies of the fault zone. Yucca Mountain, which lies 50 km east of the ECSZ, is the proposed location for the disposal of high-level nuclear waste in the United States. ¿ 1997 American Geophysical Union