J. David Rogers, Dan Wang
Abstract The Mission Peak Landslide of March 22–28, 1998 represented a partial reactivation of a much larger prehistoric landslide complex that developed along the slopes of Mission Ridge during the Late Quaternary time. Its crown scarp is structurally controlled by the Mission Peak fault, and its toe is influenced by the Warm Springs Fault. The active slide encompassed an area of 0.346 km 2 (85.5 acres) and involved over 13 million m 3 (17 million yd 3 ) of materials in an astonishing array of kinematic block reactions, which changed constantly during the first 6 days of movement. Most of the changes in surface morphology were influenced by the underlying geologic structure and stratification and the steep topography of the site, which rises from an elevation of 158.5 m to 562 m (520–1,845 ft) in just 1,255 m (4,120 ft). This paper summarizes evaluations of the areal extent of the slope movement and the various kinematic modes observed at the time, which were investigated during the following year through a program of surficial geologic mapping, subsurface exploration, sampling and testing, and analyses of collected data. A triangulated system comprising 43 benchmarks, 11 exploratory borings, 5 grouted slope inclinometers, and a telemetry network monitoring slope creep was established to allow near real-time monitoring from 1998 to 2008.