El Molino Viejo, also known as The Old Mill, is a former grist mill in the San Rafael Hills of present-day San Marino, California, United States, and was built in 1816 by Father José Maria de Zalvidea from the Mission San Gabriel Arcángel (San Gabriel Mission). It is the oldest commercial building in Southern California, and was one of the first ten sites in Los Angeles County to be listed on the National Register of Historic Places, receiving the recognition in 1971. The old mill has also been designated as a California Historical Landmark.Construction and operation as a grist millThough there are varying accounts of the exact date, San Gabriel Mission records indicate it was built in 1816. The mill was built on land owned by the San Gabriel Mission, and was designed by Franciscan Father José Maria de Zalvidea, then in charge of the mission. It was built by Tongvan Mission Indian laborers "under the watchful eye" of Father Zalvidea.The mill was built like a fortress. Its lower walls are nearly five feet thick at the base, and are made of brick and volcanic tuff. Some have written that the thick fortress-like walls were intended to allow the padres to barricade themselves in the event of "a disturbance among their somewhat uncertain converts." The upper walls are made of sun-dried adobe slabs, and the building's surface is covered with a lime mortar made from burnt sea shells. The pine and sycamore beams are tied with leather thongs, and the structure is also supported by large buttresses which can still be seen on building's exterior corners.
