. Though 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 supervision 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. and the structure is also supported by large
buttresses which can still be seen on building's exterior corners. There were three vaulted water chambers on the ground floor and a single horizontal water wheel. The
water wheel was attached to a vertical shaft that went up to the second level (the current entrance room) where the grinding stones were located. One of the grinding stones was attached to the shaft, and rotated along with the water wheel. A second stone was placed above the rotating stone, with corn and grain between the stones. It was the first water-powered grist mill in Southern California, While some have called Father Zalvidea's horizontal design a "mechanical marvel, evolved and constructed by a mastermind," others considered the design flawed as it splashed moisture up the shaft, leaving the flour damp. The mill was operational for only seven years, during which time it provided food for the missionaries and Indian neophytes, there were 1,644 Tongva-Gabrieleños in 1816 ==Subsequent uses as a residence and golfing clubhouse==