After Frederick Law Olmsted, Sr.'s retirement, Frederick Law Olmsted, Jr. and his half-brother John Charles Olmsted formed the Olmsted Brothers firm. Significant firm projects include the 1906 Lewis & Clarke Exposition in Portland, Oregon and the 1909 Alaska-Yukon-Pacific Exposition in Seattle. Both Olmsted, Jr., and John Charles Olmsted were stalwart advocates for the emerging profession of landscape architecture, and both were founding members of the American Society of Landscape Architects. The pair terminated the firm's involvement in the 1915 San Diego Exposition rather than despoil the natural landscape of Balboa Park with planned structures. The Olmsted Brothers firm designed park systems for several major cities, including Atlanta, Boston, and Seattle. It was by far the largest landscape architecture practice in the United States in the early twentieth century, with a portfolio that included roadways, state capitols, planned communities, libraries, hospitals, and academic campuses.