After seeing another surge of visitors at California’s state parks over the weekend, state officials announced Sunday that they are temporarily closing vehicular access to all 280 state parks in hope of slowing the spread of the coronavirus.

While trails and bathrooms remain open in most state parks, officials said they would continue to monitor crowds, and if visitors can’t maintain safe distances, they would take additional measures, which could include fully closing parks.

“On Saturday, many state parks once again experienced visitation surges that made it impossible for the public to implement appropriate social/physical distancing practices,” read a news release from the California Department of Parks and Recreation. “During this pandemic disease, every person has a role to play in slowing down the spread of COVID-19.”

State parks officials had already temporarily closed campgrounds, museums, visitor centers and many parking lots in the state park system out of safety concerns. The weekend before last brought record crowds to some parks.

Across California’s parks and wilderness areas, local, state and federal land managers have shut many visitor services to keep people from congregating and adhere to state and federal health guidelines. The Centers for Disease Control and Prevention has advised people to avoid crowds and stay at least 6 feet apart. Gov. Gavin Newsom on March 19 ordered residents to shelter in place.

On Sunday, officials in San Francisco sent a text alert to residents, advising: “Get fresh air, but please stay in your neighborhood. If you have to drive to a walk or hike, it’s too far.”

Sunday’s closure of parking lots in state parks follows Thursday’s blanket shutdown of U.S. Forest Service campgrounds in California through April 30. Trailheads and most boat ramps remain open on Forest Service lands.

The federal order, which covers 750 campgrounds in the state, was designed “to provide for public safety,” said Randy Moore, the regional forester for the Pacific Southwest Region of the Forest Service.

National forests span roughly 20 million acres across 19 national forests in California, with thousands of trailheads and hundreds of lakes. Each national forest is expected to publish a detailed list of closures in the coming week.

In the Sierra Nevada, rangers had not planned to open many areas until the end of April, when the trout season is scheduled to open, or in May when the snow melts. While many sites are closed, phones at some Forest Service offices will be tended to for visitor information, what are called “virtual offices,” several rangers said.

At Shasta-Trinity National Forest, which spans more than 1 million acres in the north end of the state, a check Sunday with rangers revealed that the closures add up to 60 campgrounds, 17 group campgrounds, four cabin rentals and 24 day-use and picnic areas.

“The new rules here make sense for most,” said Harold Jones at Sugarloaf Resort at Shasta Lake. “Everybody needs to be smart right now.”

At the same time, boat ramps remained open for giant Shasta and Trinity Lakes, and many other lakes on national forest lands.

The Bureau of Reclamation also has kept boat ramps open at Lake Berryessa near Napa and New Melones Reservoir near Sonora, yet a different manager closed them at Lake Sonoma.

In Lake County, after a crush of visitors, the county Health Department closed Clear Lake to all access, as well as Blues Lakes along Highway 20 and Lake Pillsbury in Mendocino National Forest.

This past week, a person from Woodland did not take the order at Clear Lake seriously and reported that he was out fishing in a boat. A sheriff’s deputy in a boat patrol spotted him and escorted him off the lake and back to his car.

State parks officials did not have the exact numbers of people visiting their parks over the weekend. But Gloria Sandoval, the group’s deputy director of public affairs, said, “Visitation is higher than usual for this time of the year compared to previous years.”

“The visitation surges that we saw last weekend and (Saturday) made it impossible for the public to implement appropriate social/physical distancing practices,” Sandoval said. “The farther apart we stay from each other, the closer we are to ‘Flatten the COVID-19 Curve.’”

Officials say park restrooms and employee offices are being cleaned more frequently.

“State parks will continue to monitor visitation and physical distancing at all state park units,” the department’s news release said, “and if the safety measures implemented thus far are not sufficient to protect public health, additional measures may be taken to fully close parks, including trails, bathrooms and other amenities.”

Rusty Simmons and Tom Stienstra are San Francisco Chronicle staff writers. Email: rsimmons@sfchronicle.com, tstienstra@sfchronicle.com Twitter: @Rusty_SFChron, @StienstraTom