Guasti, formerly known as South Cucamonga and Zucker, is a formerly unincorporated community in the Cucamonga Valley region of the Pomona Valley, in southwestern San Bernardino County, California. It has since been annexed into the city of Ontario. It is located 3.5 miles (5.6 km) east of downtown Ontario and near the Ontario International Airport.
|Elevation||296 m (971 ft)|
|Time zone||UTC-8 (Pacific (PST))|
|• Summer (DST)||UTC-7 (PDT)|
|GNIS feature ID||1660703|
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.
Guasti has a post office with ZIP code 91743. However, the area is now located in the area of ZIP code 91761, presumably after its annexation into Ontario. The first post office in the community opened under the name Zucker in 1887 and closed in 1900.