The headquarters building of the 67,000-acre Rancho Petaluma, this is the largest existing adobe structure in California.

Constructed by Salvador Vallejo for his older brother, General Mariano Guadalupe Vallejo, the two-story house is built in the Monterey Colonial style. The building is built on a U-shaped plan to form three sides of a quadrangle measuring 200 by 145 feet in size. A fourth section or wing, never fully completed, was intended to enclose the large central courtyard on the fourth side. The walls of the house were three feet thick and 20 feet high. A broad two-story veranda ran around the interior and exterior of the U-shaped building. Iron grills and solid wooden shutters covered the windows and doors. Living quarters were located on the second floor, and storerooms and Indian workshops on the ground floor.

The foundations are of native field stone. Oxen hauled the handhewn redwood timbers from forests some 50 miles to the north, and Indians manufactured the adobe brick on the spot.

The first thatched roof of the structure was replaced by a shingled roof in the 1840s.

By 1910 the building had fallen into a bad state of repair. In 1951 the house and 5 acres became a California State Historical Monument.

The adobe has been carefully repaired and reconstructed.

Quoted from the NRHP nomination dated 7 February 1967.

Rancho Petaluma Adobe is a National Historic Landmark and is California Landmark 18.