Seven persons were killed in mass shootings at two separate locations in northern California on Monday, the latest incidents of gun violence to rattle the United States, Reuters reported.

The bloodshed came after a gunman killed 11 persons at a Lunar New Year celebration near Los Angeles, California, over the weekend. It also came on the heels of another mass shooting last week in California, where six people, including an infant, were killed in the small town of Goshen.

In Monday’s attack, the gunman killed four persons at a mushroom farm and three at a trucking firm in Half Moon Bay, a coastal community about 30 miles south of San Francisco.

“Tragedy upon tragedy,” California Governor Gavin Newsom wrote on Twitter.

San Mateo County Sheriff Christina Corpus identified the attacker as 67-year-old Chunli Zhao, who worked at one of the businesses in the shooting sites. The motive for the shooting is not yet known.

“The amount of stress that’s been on this community for weeks is really quite high,” San Mateo County Supervisor Ray Mueller said about the shootings.

In just 21 days into the new year, there have been 38 mass shootings in the US, Reuters reported, citing the Gun Violence Archive database.