On April 8, 2000, Spadra Landfill, located in the City of Pomona, closed to the general public after serving the eastern San Gabriel Valley since 1957. The site normally took in 2,500 tons per day (tpd) of refuse but in recent months, as closure approached, was limited to 1,500 tpd. In the short term after closure, most of the trash from the surrounding cities went to the Puente Hills Landfill in Whittier with some going to out of county facilities.

The Spadra Landfill began operations on a 128-acre site formerly known as Smith Ranch. It was operated by the Sanitation Districts of Los Angeles County (Districts) under a Joint Powers Agreement with the California State Polytechnic University (Cal Poly Pomona) and the County of Los Angeles. The Districts purchased additional acreage over the years to add to the landfill. In addition to disposal, the Districts implemented various materials recovery programs at the site. These programs recovered 400,000 tons of greenwaste, 475,000 tons of asphalt, 576 tons of metallic discards, 380 tons of tires and 55,000 gallons of oil. The greenwaste and asphalt were beneficially reused at the site.

In 1985, the Districts entered into the Spadra Landfill and Resource Conservation Agreement with Cal Poly Pomona and the County to create LandLab, a 320-acre center for education and research in the sustainable use of resources while providing for recycling, the diversion of waste materials, and the efficient use of refuse capacity. As part of their responsibilities outlined in the 1985 agreement, Cal Poly Pomona prepared a Master Plan which identified the post closure land uses for the site as a combination of education, research, recreation and open spaces.

With the closure of the landfill, the Districts implemented the Closure and Post Closure Plans for the site. The Plans identified a 15-month period, following the receipt of the final load of refuse, that included the placement of a five-foot final cover over the fill, removal of the weigh scales for reuse at other Districts' sites, installation of a landscape and irrigation system over the final side slopes and construction of access roads and drainage facilities. Under the Post Closure Plan, the Districts will also continue to monitor and maintain the environmental controls, which include groundwater and surface water monitoring, and landfill gas control. Cal Poly Pomona will be responsible for the post closure land development, which initially is for perennial pastures.