The Black Hills had become popular in the late 1890s, but Rapid City became a more important destination in the 20th century. Local entrepreneurs promoted the sights, the availability of the automobile for individual transportation, and construction of improved roadways after World War I led to many more tourists to this area, including President Calvin Coolidge and the First Lady in summer 1927. Coolidge announced that he would not seek reelection in 1928 from his summer office in Rapid City. Gutzon Borglum, already a noted sculptor, began work on Mount Rushmore in 1927, and his son, Lincoln Borglum, continued the work after Gutzon's death in 1941. The work was halted due to the US need to invest in buildup for its entry into World War II; the sculpture was declared complete in 1941. Although tourism had sustained the city throughout the Great Depression of the 1930s, gasoline rationing during World War II decimated such travel. But investments in the defense industry and other war-related growth stimulated the placement of new military installations in the area, bringing more businesses and residents.