After World War II, residential development continued to expand in the watershed of Darby Creek. The automobile replaced railroads as the dominant form of transportation, and it allowed workers to live farther from their places of employment. As a result, the population of Springfield Township more than doubled between 1950 and 1960. The Tinicum Wildlife Preserve was established in 1955 after the Gulf Oil Corporation donated a diked impoundment on the creek to the City of Philadelphia. Local resident Jean Diehl started a grassroots campaign to preserve the marsh in 1969, and "Two Studies of Tinicum Marsh" was published the following year which demonstrated the ecological importance of the marsh. The Folcroft Landfill and the Clearview Landfill operated along the creek between the 1950s and the 1970s before closing in the mid 1970s. The former is on the west bank of the creek and the latter is on the east bank. They supposedly accepted municipal waste, demolition waste, and medical waste. A number of businesses operated at the site of the Clearview Landfill after its closing.