A new causeway across Candlestick Cove connected the completed section in South San Francisco with San Francisco and opened on July 11, 1957. Planning began in 1951, when bids were taken for an experimental causeway wide extending south from Candlestick Point; rather than pumping out soft bay mud and back-filling with sand, fill dirt would be dumped directly into the Bay to see if the mud underneath could be displaced instead. This section of the Bay had water up to deep, overlying soft mud deep, which in turn was overlying harder, compacted mud. The compacted mud was deemed sufficiently strong to support the weight of the freeway, but it was hoped that excavation of the soft mud layer could be avoided by dumping fill at a sufficient rate, later calculated to be per day. The experiment was deemed a success, and the remaining of causeway was put out for bid in 1954, awarded in 1955 to Guy F. Atkinson Co. By that time, over of fill had already been placed.