Guasti, formerly known as South Cucamonga and Zucker, is an unincorporated community in the Cucamonga Valley region of thePomona Valley, in southwestern San Bernardino County, California.
The area was a former major wine producing district in the Cucamonga Valley AVA region, with the Italian Vineyard Company based here. By 1917 the Cucamonga-Guasti vineyards spanned over 20,000 acres, and Secondo Guasti was advertising his vineyard as "The Largest in the World." The community changed its name from Zucker to Guasti after Secondo Guasti, founder of the Italian Vineyard Company, which operated in the area. The Guasti post office opened in 1910.