Helen Lundeberg’s historic Work Progress Administration (WPA) mural “History of Transportation” is now located in the Grevillea Art Park (230 S. Grevillea Avenue 90301) in downtown Inglewood. When the piece was first created and installed in 1940, it was located in Centinela Park along the then very busy commuter street Florence Avenue. As you can see in the pictures below, the 60-panel 240-foot long piece shows the human history of the Centinela Valley (the geographic location of Inglewood), with an emphasis on transportation.
In terms of other WPA work in California: UC Berkeley has created this great California New Deal site. More info about WPA murals is also collected here at www.wpamurals.com. This wpainla blog also has some great local info.
The “History of Transportation” is a petra-chrome mural. This process was developed by Stanton Macdonald-Wright as a way to create WPA murals that could last for many years in the bright Southern California sunlight. This mural has survived, thanks both to the hardy construction method and also the recent million dollar restoration, completed in 2007. Here is a nice Los Angeles Time piece about this mural and its restoration; another great article about the restoration process can be downloaded here at www.incca.org.
The petra-chrome construction technique is variant of terrazzo; the panels were created from a mixture of rock aggregate, pigment, and concrete that is set and polished. As far as I can gather the differences between between petra-chrome and terrazzo involve the type of rock aggregate used and also the way the edges between colors are formed. In petra-chrome there are no metal strips separating colors (as usually seen in modern terrazzo), making the edges look almost like they were cut. Maybe because of this petra-chrome is sometimes compared to stone mosaic techniques like opus sectile.
Variants of the terrazzo technique are super old. Archaeologists use the word to describe a neolithic version that was constructed from burnt lime, clay, and ochre (for coloring). Floors of this type have survived 10,000 years. The Romans used techniques similar to terrazzo such as opus tesselatum and opus vermiculatum, which involved the placement of broken marble and travertine in concrete. The creation of modern terrazzo is credited to Venetian craftsmen in the 17th century who built terrace floors using marble chips and scraps set in clay and and then sealed with goat’s milk. Over time, concrete began to be used instead of clay. The terrazzo technique became popular in the 1920s with the advent of electrical polishing machines (basically large floor polishers). Terrazzo was also ideal for Art Deco designs, with their large flowing curves. (Nowadays a thinner version of terrazzo is also created using epoxy and resin rather than concrete). For more information on this process you can also check out this preservapedia.org page (or also here at arcadianflooring.com and zanetticompany.com).
Below I list some other prominent works in terrazzo in Los Angeles. This list is very partial as the technique was so popular in the 20s and 30s. For example the sidewalks on Broadway in downtown LA are covered with this terrazzo stuff! The Miracle Mile also boasts a lot of terrazzo. Each entry in the list below has two links: the first goes to a picture of the terrazzo that’s there, the second leads to info about the building in question. The photos are gleaned from the Terrazzo Floors flickr pool.