The graph shows mining deaths in the United States during much of the 1900s. A bar graph titled Number of Deaths in U S Mining Industry. The x axis shows Decades, from the 1920's to the 1970's. The y axis shows number of deaths, from 0 to 30,000. 1910's, 25,000; 1920's, 22,500; 1930's, 12,500; 1940's, 11,000; 1950's, 4,800; 1960's, 2,500; 1970's, 1,000. What does the graph demonstrate?