asphalt - natural asphalt from seeps
When petroleum seeps to the surface and the volatiles escape, natural asphalt forms. We have specimens from oil seeps in California. The first production of petroleum was from tunnels dug into the slopes of Sulfur Mountain, Ventura County, California. The oil tunnels produced continuously from 1861 to 1998, and oil still works its way to the surface to form tar/natural asphalt.