Gov. Gavin Newsom on Thursday proclaimed a state of emergency in several California counties, including some in Southern California, in the wake of a series of strong storms that have brought heavy rain and snowfall to the state.

The proclamation, which in part enables local governments to access and make use of state resources more easily, notes that storms beginning Dec. 10 have led to flooding, mudslides, road closures, among other problems that have taxed local emergency response teams.

“I want to thank all our emergency responders for working diligently through trying weather conditions to keep our communities safe,” Newsom said in a statement.

Twenty counties, including Orange County, Los Angeles County, and San Bernardino County were listed under the state of emergency.

He also urged Californians to avoid traveling in the mountains.

“I strongly encourage all Californians to avoid making the situation worse and refrain from traveling on mountain roads until conditions improve,” Newsom said.

Nevada Gov. Steve Sisolak has declared a state of emergency as roads around Lake Tahoe, which straddles California and Nevada, have been intermittently closed or jammed with anxious motorists.

For his part, Newsom has called on cabinet members to coordinate with investor-owned utilities to restore power in that area and others around the state.

Since Christmas Eve, Caltrans has deployed 1,350 field staff working in 24-hour rotating shifts to keep roads open and assist impacted communities statewide, according to the governor’s statement.

Caltrans has also redirected all available crews, assisted with 600 snow plows and cleared hundreds of downed trees.

In addition, the California Highway Patrol has stepped in to assist stranded motorists, direct heavy traffic loads and provide food and water for those in need.