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Haven’t been out to hike in the redwoods because you don’t want to pay the entry fee?

That excuse runs out this weekend.

Starting this Saturday and every second Saturday of the month for the rest of 2018, the public will be offered free vehicle admission to 40 of California’s redwood state parks — majestic preserves that are home to the world’s tallest trees. It’s part of the 100th anniversary of one of California’s oldest environmental groups, Save the Redwoods League, based in San Francisco.

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Through the year, there will be 16,800 free passes for day-use admission made available, with between about 1,300 and 1,700 given out each month. To obtain a free pass, visitors must go to FreeRedwoodsDays.org.

The passes can be used at popular parks like Big Basin Redwoods, Henry Cowell and Castle Rock in Santa Cruz County, Mount Tamalpais in Marin County and Butano State Park on the San Mateo Coast. The eligible parks range from Julia Pfeiffer Burns State Park in Big Sur to Jedediah Smith Redwoods State Park near Crescent City just south of the Oregon border.

The number of available passes varies by park, and when they run out, interested visitors will have to wait until the Monday after the second Saturday of each month to go online and reserve a free pass for the following month.

“We want to invite everybody in and make it as easy as we can for the people of California to be inspired by these spectacular forests and the parks that we helped preserve,” said Sam Hodder, president of Save the Redwoods League.

The first redwoods in California were protected in 1864 when President Abraham Lincoln set aside 20,000 acres of Yosemite Valley and the Mariposa Grove of giant sequoias as a preserve. For decades after along the coast, loggers with broad saws and teams of oxen cut massive coast redwood trees, some of which dated back to the Roman Empire and towered more than 300 feet high, for fence posts, railroad ties and lumber for homes.

In 1900, San Jose photographer Andrew P. Hill formed the Sempervirens Club, to preserve redwoods in the Santa Cruz Mountains. He and other conservationists convinced state lawmakers to establish Big Basin, which became California’s first state park.

By 1918, the Save the Redwoods League was founded by Stephen Mather, E.C. Bradley, William Kent, Henry Fairfield Osborn and Madison Grant. Since then, the organization has preserved roughly 214,000 acres in 66 parks, including iconic areas such as Avenue of the Giants in Humboldt County.

The league, which now has 19,000 members and a $13 million annual budget, is earmarking about $182,000 to pay state parks for the admissions, which normally cost $10 per car for most state parks. Camping fees are not included in the monthly free admission.

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“Free Second Saturdays at Redwood State Parks events allow people who might not otherwise be able to visit a park to get outdoors in our spectacular redwood state parks,” said Lisa Mangat, California’s state parks director.

The new program follows similar efforts in 2015, 2016 and 2017 in which the league paid for free admission to redwood parks on the Friday after Thanksgiving to encourage people to get outside and experience nature rather than rushing to shopping malls.

“It’s a way to keep a drumbeat going with enthusiasm for the redwoods,” said Hodder. “It’s kind of our own happy birthday present to the public.”