 It was the largest privately owned adobe structure built in California and is the largest example of the Monterey Colonial style of architecture in the United States.A section of the former ranch has been preserved by the Petaluma Adobe State Historic Park and it is both a California Historic Landmark and a National Historic Landmark.The Rancho Petaluma Adobe State Historic Park is located on Adobe Road on the east side of the present-day town of Petaluma, California.