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The Regional Connector Transit Corridor Project is a 3-km (1.86 mile) underground light rail project in downtown Los Angeles, California being constructed by the Los Angeles County Metropolitan Transportation Authority (Metro). The project consists of 5.7-m (18'-10") inside diameter 1,417-m (4,650-ft) long twin bored tunnels, 789-m (2,590-ft) long cut-and-cover tunnels, 247-m (810-ft) open trench structures with approximate depths up to 7.6-m (25-ft), an approximately 17-m (56-ft) wide 14.5-m (48-ft) high 91-m (300-ft) long crossover cavern, cross-passages at three locations between bored tunnels, and three underground stations to be constructed by cut-and-cover. The open cut excavations will encounter artificial fill, alluvium, and weak clayey siltstone or silty claystone of the Fernando Formation. The bored tunnels will be excavated by an Earth Pressure Balance Machine (EPBM) mostly through Fernando Formation, with some mixed ground conditions. The crossover cavern will be excavated entirely within the Fernando Formation. Groundwater, gas, and seismic conditions along the project alignment also required characterization as part of the Preliminary Engineering for the final design and construction of the project that would be part of a design-build contract. For the Preliminary Engineering, a geotechnical investigation including historical information review, soil/rock borings, and laboratory and field tests were conducted, resulting in the production of multiple geotechnical reports and memoranda including a Geotechnical Data Report and Geotechnical Baseline Report. This paper presents the geotechnical aspect of the underground light rail project in an urban area and summarizes the geotechnical investigation program and findings for the project.