The Old Mill, El Molino Viejo, was completed in 1816 as a gristmill for Mission San Gabriel and originally sat on 160 acres. Today, the historic adobe building sits among almost two acres of garden. The Old Mill garden is lovingly tended by the Diggers Garden Club, member of the Garden Club of America. The Old Mill property belongs to the City of San Marino and is officially marked a California Historical Landmark.

In 1928, acclaimed landscape architect Katherine Bashford was hired to create a garden. In keeping with the simple mission tradition, she designed a rectangular walled garden and replanted trees of fig, citrus, pine, live oak, sycamore and pepper to the Mill’s property. Bashford was one of a handful of early modern landscape designers to use outdoor spaces such as patios to take advantage of the southern California climate. Much of Bashford’s aesthetic is still evident in the garden today with its meandering pathways and shaded patios. With over 50 different species of trees and woody shrubs, the gardens provide a beautiful landscape for many artistic and community events, and contain several specimens of native trees and woody shrubs including California Live Oak, Toyon, Catalina Cherry, Western Red Bud, Ceanothus, and a Hybrid California Mission Grape vine propagated from the San Gabriel Mission. The mission vine dates back to plantings made by Father Junipero Serra.