The project aims to investigate details of the crustal structure along the San Andreas fault zone north of the San Gabriel Mountains in southern California. This area has been proposed as possible deep-drilling site to investigate an active fault zone. The target area is to be investigated within the scope of the U.S.G.S. project LARSE II (Los Angeles Region Seismic Experiment) which aims to investigate the Los Angeles basin by detailed seismic studies along a line from Santa Monica to the San Gabriel Mountains which covers also, less detailed, part of the adjacent Mojave Desert north of the San Andreas fault zone. The special aim of our project is a combined near-incidence and wide-angle seismic reflection survey by a roll-along procedure using 35 mobile three-component stations of GFZ Potsdam, each supplied with 6 vertical GEOPHONEs (210 seismic channels) along a 50 km long line across the San Andreas fault zone in both areas, i.e. 25 km perpendicular to the active fault line. The resulting detailed velocity-depth cross sections will allow the detailed localization of the fault zone and the detailed structure of the surrounding upper crust down to a depth of 10-15 km, i. e. the depth range on which the observed seismicity is concentrated and which is of immediate interest to the presently applied and other future drilling projects aiming to reach 10 km depth or more. The results of our project will immediately contribute to find and to select an optimal position of the final drill sites.