Seeps known as the McKittrick Tar Pits occur in the McKittrick Oil Field in western Kern County. Some of the seeps occur in watersheds that drain toward the San Joaquin Valley floor. These seeps were originally mined for asphalt by Native Americans, and in the 1870s larger scale mining was undertaken by means of both open pits and shafts. In 1893, Southern Pacific Railroad constructed a line to Asphalto, two miles from present day McKittrick. Fuel oil for the railroad was highly desired, especially since there are very few coal-bearing formations in California. The field is produced now by conventional oil wells, as well as by steam fracturing.