Operators of the first Sunnyside Memorial Park promised a mausoleum in 1915 and retained the design services of Sidney Lovell who had designed Rose Hill mausoleum in Chicago. Once oil was discovered on Signal Hill in 1921, a "cemetery war" broke out when it was discovered that the land for mausoleum was sold for oil drilling. Families pressured Long Beach to stop the drilling. City manager Windham announced that Sidney Lovell, president of the American Association of Cemeteries, had been looking for "his final and greatest effort in constructing an artistic burial ground." Windham remarked that if Lovell did not use the design for another site, the city could retain him as a consultant. He also added that with a new cemetery, graves could be removed from Sunnyside and reburied "without expense to the families concerned." Southwest Builder and Contractor magazine announced that in 1922, Cecil. E. Bryan and Association was hired by the Pacific Builders Company doing business as the Sunnyside Mausoleum Association to design a "$300,000 concrete Spanish mausoleum structure on a 5-acre site at Cherry Avenue and Downey-Whittier Blvd." It would include "200x102 ft., 1000 crypts, 1000 sarcophagi niches, 25x70 foot pipe organ, chimes tower, rest rooms, offices, art glass windows, marble inter., bronze trim, and ventilating system." The mausoleum grounds were designed by Clarence Jay who invented the noiseless coffin elevator for the mausoleum which opened in 1923. The east wing was added in 1925 and in 1933, close to 6000 more marble crypts were added.

In 1940, a chapel was built next to the crematorium and much of the original designed décor and architecture remains, including the letters SM inscribed in mosaics on the crypt gates. Much of the 1923 architectural design throughout the property remains the same to this day.

In 1960, the 38-acre cemetery, mausoleum and mortuary were bought by Forest Lawn.

In 1974, a portion of the ground were consecrated for entombment of people of the Jewish faith. The area is called Rose of Sharon Memorial gardens.

It took a number of improvements before Forest Lawn would rename the site Forest Lawn Memorial Park Sunnyside. Outside the mausoleum is a massive mosaic re-creation of Raphael's fresco in the Vatican, The Disputation of the Holy Sacrament. Forest Lawn refers to theirs as "Paradise."

Today, it is known as Forest Lawn Memorial Park and Mausoleum - Long Beach.

This complex is designated as a historical landmark.