The Old Mill, El Molino Viejo, was completed about 1816 as a gristmill for Mission San Gabriel.  Today, the historic adobe building stands as a testament to the legacy of the California missions and the Spanish presence in early California. The original adobe building sits amongst almost two acres of gardens, lovingly tended by the Diggers Garden Club

The Old Mill Foundation’s over-arching purpose is to maintain, preserve and operate The Old Mill and as a part of that mission, the OMF develops and creates many artistic, educational and community programs at The Old Mill.

El Molino Viejo is an architectural landmark, an adobe monument to the legacy of the California missions and the Spanish presence in early California.
Situated on a hillside about two miles northwest of Mission San Gabriel, El Molino Viejo (The Old Mill) today belongs to the City of San Marino and is operated by The Old Mill Foundation. The Old Mill is a state of California Historical Landmark.

El Molino Viejo's original two-story structure measured 53 by 26 feet. The lower walls are five feet thick and are composed of oven-baked brick and volcanic tuff, while the walls of the upper level are built of layers of sun-dried adobe slabs. The rafters, ceiling, and beams are made of local pine and sycamore; the roof is tiled. The whole surface of the building is covered with mortar made from lime derived from burnt seashells, and buttresses supporting three corners supply additional strength. These were needed not only as reinforcement against earthquakes, but also to counteract the vibration of the wheels turning in water. The present entrance room (with its collection of antique paintings and furnishings) served as the Grinding Room of the mill. Here the heavy millstones ground the grain harvested on the mission lands. A set of millstones, discovered by General George Patton during his childhood in this area, has been preserved on the patio.

The upper room on the top level was originally used as the Granary, where the milled grain was stored. Today, the Old Mill Foundation and the California Art Club have partnered to present plein air art exhibitions. The exhibitions change every four months and are available for sale.
On the western side of the building, in the St Francis patio, the structural outlines of the water cistern still remain. This provided the water to operate the large wooden wheels that were sitting flat in the streams of water. The water flowed through the mill eastward through a ditch to Mission Lake. The lake area is now known as San Marino’s Lacy Park. The small room on the west side of the building, next to the cisterns, was formed from part of the old cistern and serves as the Old Mill Foundation’s administrative office. 

Downstairs, where the wooden wheels once turned in the streams of water, there is a small diorama display, featuring an operating model of the mill, and historic photos. 
The Old Mill sits in the middle of a lush Mediterranean walled garden that highlights many of the trees and plants that would have been in the Mission San Gabriel's garden. The centerpiece of the garden is the Pomegranate Patio where many civic, educational, and organizational events are held. This patio is the home of the Magical Music at the Mill summer concert series, which features intimate chamber music under the stars.