From 1925 to 1932 Kassler continued his studies while living at various times in New Mexico, Europe, and North Africa. While in France, he apprenticed himself to a well-known fresco painter. After moving to Los Angeles in 1933, he painted the two largest frescoes done under the WPA; The Bison Hunt for the Central Library in Downtown Los Angeles which was destroyed by weather damage and Pastoral California, at Plummer Auditorium in Fullerton, in Orange County. It was whitewashed in 1938, just four years after Kassler completed it, but was restored in 1997 after spending almost 60 years hidden from view. Kassler was also commissioned by the WPA to paint eight fresco lunette murals for the Beverly Hills, California post office funded by the Treasury Section of Fine Arts. The murals depict the history of the Pony Expresss, postal service, and the daily life of the common American family. The post office is now home to the Wallis Annenberg Center for the Performing Arts. After creating murals for the WPA, Kassler taught at Chouinard Art Institute and later worked as a designer in the aerospace industry.