Avon is an unincorporated community

Unincorporated area

In law, an unincorporated area is a region of land that is not a part of any municipality.To "incorporate" in this context means to form a municipal corporation, a city, town, or village with its own government. An unincorporated community is usually not subject to or taxed by a municipal government...

 in Contra Costa County

Contra Costa County, California

Contra Costa County is a primarily suburban county in the San Francisco Bay Area of the U.S. state of California. As of the 2010 census, it had a population of 1,049,025...

, California

California

California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

. It is located on the Southern Pacific Railroad

Southern Pacific Railroad

The Southern Pacific Transportation Company , earlier Southern Pacific Railroad and Southern Pacific Company, and usually simply called the Southern Pacific or Espee, was an American railroad....

 3.5 miles (5.6 km) east-northeast of Martinez

Martinez, California

Martinez is a city and the county seat of Contra Costa County, California, United States. The population was 35,824 at the 2010 census. The downtown is notable for its large number of preserved old buildings...

, at an elevation of 10 feet (3 m).

A post office operated at Avon from 1912 to 1960. It was originally called Marsh, and in 1913 the name was changed to Associated. The name Marsh was in honor of John Marsh

John Marsh (pioneer)

“Doctor” John Marsh was born in 1799 in South Danvers, Massachusetts and died in Pacheco, California in 1856. He was an early pioneer and settler in California, and although he did not have a medical degree, is often regarded as the first person to practice medicine in California.-Early life:Marsh...

. The name Associated was for the Tidewater Associated Oil Company, owner of the site.