The majority of the river flows through quiet agricultural bottom lands, and as a result its meandering course manages to avoid most of the urban areas and cities in the San Joaquin Valley. About west of Modesto, the San Joaquin meets its largest tributary, the Tuolumne. Near Vernalis, it is joined by another major tributary, the Stanislaus River. The river passes between Manteca and Tracy, where a pair of distributaries – the Old River and Middle River – split off from the main stem just above the Sacramento-San Joaquin Delta, a huge inverted river delta formed by sediment deposits of the Sacramento and San Joaquin Rivers.