In the latest sign of California’s persistent drought, the Tioga Road, a historic route through Yosemite National Park and the highest-elevation highway in the state, opened Friday to motorists — the earliest in more than two decades.

Most years, so much snow covers the winding, two-lane mountain road that it can’t be cleared and opened until late May or June.

But now, with the Sierra Nevada snowpack at only 18 percent of the historic average for this time of year, the road is opening on the earliest date since 1988, when it opened April 29 during California’s last major drought.

“There is a little bit of snow on the north facing slopes, but not much,” said Kari Cobb, a spokeswoman for the National Park Service. “There’s just not a lot of snow up there.”

Hiking trails are open now. But campgrounds, the visitor center at Tuolumne Meadows and other visitor services along the road won’t be open for another two weeks or so, Cobb said.

Since records were first kept in 1933, the earliest the Tioga Road has ever opened was April 8, 1977, at the height of another severe drought. The road — a key pass across the Sierra — is usually closed to the public in early November, when the first snowstorms arrive.

Another high-elevation road in Yosemite, the road to Glacier Point, opened April 14.

Major waterfalls in Yosemite Valley, including Yosemite Falls, are thundering now, but by the end of June should be reduced to a trickle, Cobb said.

“The Merced River and Tuolumne River never dry up, but smaller creeks and seasonal springs are probably going to dry up, so the animals will have to go further to find water,” Cobb said. “Backpackers also will have to carry more water.”

Fire danger also will be higher this year than most.

Last August, the Rim Fire burned 257,314 acres in the remote northwestern part of Yosemite and the Stanislaus National Forest. That blaze, caused by a hunter’s campfire in the national forest, was the third largest in state history.

One of the marquee drives in America’s national park system, the two-lane Tioga Road bisects Yosemite’s alpine center, passing through subalpine meadows and forests of lodgepole pine and juniper. It runs 46 miles from Crane Flat to Tioga Pass, where it crests at 9,945 feet in the highest highway pass in California.

The route for centuries was a footpath for Miwok Indians, upgraded to a mining road in 1883 during a brief silver boom, and then a private toll road that charged $2 per horse and rider.

In an unusual act of philanthropy, it became public and part of the park in 1915, when Stephen Mather, the first director of the National Park Service, bought it for $15,000 with his own money and donations from the Sierra Club and the Modesto Chamber of Commerce. He sold it to Congress that year for $10, hoping to bring more tourists into the park.

Paul Rogers covers resources and environmental issues. Contact him at 408-920-5045. Follow him at Twitter.com/PaulRogersSJMN