We quantitatively analyze the area-age distribution of bedrock based on data from the most recent geologic map of the conterminous United States of America <King and Beikman, 1974a, 1974b>, made available in digital form by the United States Geologic Survey. The area-age distribution agrees surprisingly well with older data <Higgs, 1949> but provides much higher temporal resolution. The mean stratigraphic age of all sedimentary bedrock is ~134 Myr; that of Tertiary-Cambrian sediments is ~104 Myr. The analysis also reveals area coverage of some minor lithologies, such as ultramafic rocks that cover ~0.15% of the conterminous United States. Area coverage of 162 lithostratigraphic units is made available as an Excel data sheet.