Caswel, J.F. Ellis, and H.C. Wiley filed a mining claim for the Towsley Petroleum Mine in December 1876, located in the Santa Susana Mountains east of the Pico Canyon Oilfield near Newhall Pass. 2½ years later, in August 1879, they received a mineral lode patent from the U.S. government, which gave them title to the oilfield.