Diamond Ranch High School is a high school that serves students from Diamond Bar and Phillips Ranch, California, United States, and is operated by the Pomona Unified School District (PUSD) in Pomona, California – part of the Greater Los Angeles MSA. Diamond Ranch's athletic teams compete in the Hacienda League of the CIF Southern Section.

Pomona is a city in eastern Los Angeles County, California, United States. Pomona is located in the Pomona Valley, between the Inland Empire and the San Gabriel Valley. At the 2020 census, the city's population was 151,713. The main campus of California State Polytechnic University, Pomona, also known as Cal Poly Pomona, lies partially within Pomona's city limits, with the rest being located in the neighboring unincorporated community of Ramona.