The following is from the book, Indian Wars, by Bill Yenne.
In 1832, a Zacatecan priest named Father Jose Maria Mercado led an ambush of a group of Pomo people that he mistakenly thought were going to attack the mission. The ensuing firefight resulted in the deaths of more than twenty unarmed Pomo. Both the native and Spanish population in the San Francisco Bay area were outraged at this incident, and Father Mercado was relieved of his pastorship and disciplined.
18 years later...
...In May 1850, the U.S. Army was involved in a brief campaign against the Pomo which would be the largest action to involve the Army in the southern three-quarters of the state. After several miners had been killed during the winter near Clear Lake, north of San Francisco Bay, Captain Nathaniel Lyon led a contingent including three companies of the 2nd Infantry Regiment and a company of the 1st Dragoons on a search and destroy mission. In a series of engagements between May 14 and May 19, more than one hundred Pomo were killed. No soldiers were lost in the Pomo campaign, but one trooper was killed in action on July 25 in a skirmish with the Achomawi in the far northern part of the state.