The San Ramon Valley Branch Line of the Southern Pacific entered service in 1891 with two flag stops in the area that would become the City of Pleasant Hill: Hookston, located today where the Iron Horse Regional Trail crosses Hookston Road, and Sparkle, where the Southern Pacific and Sacramento Northern Railway intersected and today stands the Pleasant Hill BART station.

The area began to be suburbanized in the 1920s following prohibition, as the many local vineyards were removed and the formerly agricultural land was subdivided for housing.

In 1954 the monument was moved to its current site at the intersection of Boyd Road and Contra Costa Boulevard to make way for the construction of State Route 21.

Developed largely in the years following World War II, the area did not have a post office until 1948.

In 1991, the city began planning the redevelopment of the area around the intersection of Monument and Contra Costa boulevards.

The privately owned and operated outdoor shopping center was designed to resemble a typical small Main Street.

Starting in 2003, CinéArts operated the former Century 5 Theatres, screening primarily independent and foreign films.

Due to changes in viewing habits, as many people screened movies at home, business continued to decline.

On its last night of operation, CinéArts screened Stanley Kubrick's classic 2001: A Space Odyssey.

[13] Sywest gained the approval of the Pleasant Hill City Council for its proposal to tear down the theater and redevelop the property as a two-story, 73,000+ square-foot building to house a Dick's Sporting Goods.

On very rare occasions, the temperatures can reach the one hundred degree range during extreme heat waves.

The Gregory Gardens subdivision developed in 1950 required purchasers of new homes to accept a Covenant that restricted ownership to Caucasians (such provisions have since been ruled as unconstitutional).

[28] The Covenant also limited the structures that could be built, animals allowed on premises, and commercial activities.

Notably the city authorized a study in the 1980s of hillside development, which included detailed mapping of biota, geotechnical hazards, sound levels and other environmental constraints.

These studies were used to establish appropriate zoning and development densities for all the principal undeveloped hillside areas within the city.