Firewood and coal were the fuels used by early Mill Valley residents to heat their homes and cook their food. In about 1910, town gas became the preferred fuel after the San Rafael Gas and Light Company built an immense gasholder on Third Street in San Rafael. In the 1930s, natural gas replaced town gas. Natural gas is almost 100% methane. Town gas typically contained only 35% methane, the other components being 50% hydrogen, 10% carbon monoxide and 5% ethylene. Town gas, also known as “manufactured gas” or “coal gas”, is usually made by the pyrolysis of bituminous coal. For many years, town gas had been produced in San Rafael for local consumption. The installation of a gasholder in 1930 allowed the plant to supply town gas to customers in the Ross Valley, Sausalito and Mill Valley. A gasholder is a large container in which either town gas or natural gas is stored. The volume of the container changes to accommodate the quantity of stored gas as the cap moves up and down. They are typically about 200 ft. in diameter holding about 2 million cu. ft. of gas. All of the 35 gasholders that existed in California have been demolished.