Micro gravity data was collected in a crowded street in Tehran where a subway terrain tunnel is to be excavated. The data is corrected for the gravity effects of the surrounding densely built up area with diverse buildings and the Bouguer gravity anomalies are computed. The residual gravity anomalies are prepared by removing a trend surface. Upward continuation is used to remove the gravity effects of shallow synthetic anomalies such as subsurface galleries and canals. Then the up-ward residual gravity anomalies are used to determine the depth of the bedrock (Hezar Darreh formation). A 2D inversion algorithm is applied on the data and the model is constrained based on prior geology information provided from the bore holes.