The guns at Sutter’s Fort, mostly used to make a strong impression on the locals, were a varied collection drawn from passing ships and from the Russians at Fort Ross in what is now Sonoma County.
The armament, as early as 1842, consisted of two brass fieldpieces and a dozen or more iron guns of different kinds brought from Hawaii and purchased from different vessels. In a letter to the California Pioneers published in their Bulletin, dated July 12, 1879, Sutter states the he got six larger cannon in 1841 from the captain of an American vessel who brought them from South America expressly for him, one brass fieldpiece only from the Russians and a few others, including 2 brass pieces from other vessels at different dates. John Bidwell, a caretaker for Sutter at Fort Ross in 1842, states that about 40 rusty guns and one or two small brass cannon were obtained from the Russians. However there are rumors that the iron guns were lost when the raft carrying them from Fort Ross to Yerba Buena was overturned at the entrance to the bay and lost. But no written information is available to back up these rumors. So it is likely that Sutter got most of his guns from Fort Ross — Sutter’s Fort, 1841 by Justin M. Ruhge
The Fort was a structure of adobe with walls eighteen feet high, and three feet thick enclosing an area of 500 by 150 feet. At the southeast and northwest corners projecting bastions, or towers, rose above the walls of the rectangle and contained in their upper stories cannon, which commanded the gateways in the center of each side except the western. Loopholes were pierced in the walls at different points. Guns were mounted at the main entrance on the south and elsewhere, and the north side seemed also to be protected by a ravine — Justin M. Ruhge