The 1999 Mw 7.1 Hector Mine earthquake occurred only 20 km from the 1992 Mw 7.3 Landers earthquake fault. The close spacing between the two earthquakes suggests that the Landers earthquake trigger the Hector Mine event. Based on an elastic half-space model, scientists from the USGS, SCEC and CDMG (2000) have found a negative Coulomb stress change at the Hector Mine hypocenter due to Landers. This negative stress change is inconsistent with the hypothesis of static stress triggering. In this paper, I show evidence of stress triggering of the Hector Mine earthquake by Landers, due to a process governed by viscoelastic flow in the lower crust. This visoelastic flow has produced broad-scale postseismic rebound observed by GPS and InSAR measurements. The result of this study is that viscoelastic flow has significantly modified the regional stress field in the Mojave Desert after the Landers earthquake. The evolving stress field, including viscoelastic flow, has gradually moved the Coulomb stress change at the Hector Mine hypocenter to a positive level. The increase in Coulomb stress exceeded 1 bar right before the Hector Mine earthquake, bringing the Hector Mine ruptures to the proximity of catastrophic failure. ¿ 2001 American Geophysical Union