California pioneers after 1848 discovered an increasing number of oil seeps—oil seeping to the surface, especially in Humboldt, Colusa, Santa Clara, and San Mateo counties, and in the asphaltum seeps and bituminous residues in Mendocino, Marin, Contra Costa, Santa Clara, and Santa Cruz counties. In Southern California, large seeps in Ventura, Santa Barbara, Kern, and Los Angeles counties received the most attention. Interest in oil and gas seeps was stirred in the 1850s and 1860s, becoming widespread after the 1859 commercial uses of oil were demonstrated in Pennsylvania. Kerosene quickly replaced whale oil for lighting, and lubricating oils became an essential product in the Machine Age. Other uses later in the 19th century included providing paving material for many roads and providing power for many steam locomotives and steam-powered shipping—replacing coal.