We use Global Positioning System (GPS) data from 1993--2000 to determine horizontal velocities of 65 stations in eastern California and western Nevada between 35¿ and 37 ¿N. We relate the geodetic velocities to fault slip rates using a block model that enforces path integral constraints over geologic and geodetic time scales and that includes the effects of elastic strain accumulation on faults locked to a depth of 15 km. The velocity of the Sierra Nevada block with respect to Nevada is 11.1¿0.3 mm/yr, with slip partitioned across the Death Valley, (2.8¿0.5 mm/yr), Panamint Valley (2.5¿0.8 mm/yr), and Airport Lake/Owens Valley (5.3¿0.7/4.6¿0.5 mm/yr) faults. The western Mojave block rotates at 2.1¿0.8¿/My clockwise, with 3.7¿0.7 mm/yr of left lateral motion across the western Garlock Fault. We infer 11¿2 mm/yr of right lateral motion across the Mojave region of the Eastern California Shear Zone. ¿ 2001 American Geophysical Union