Just over a century ago, three scientists and naturalists took a drive up the then-new Redwood Highway.

Awed by the towering trees the road north of San Francisco was named for and horrified by the logging they witnessed, John C. Merriam, Henry Fairfield Osborn and Madison Grant launched a movement to preserve the trees that were left. Osborn and Grant would become the inaugural donors of the Save the Redwoods League in March 1918.

Half a century after the non-profit conservation organization was established, in October 1968, President Lyndon Johnson signed legislation creating Redwood National Park. Its boundary would encircle three existing state parks — Jedediah Smith, Del Norte Coast and Prairie Creek Redwoods State Parks — themselves acquired through the Save the Redwoods League in the 1920s.

“Redwood National Park is unique in a number of ways. One of those ways is that it’s really closely entwined with the three state parks of the region, Prairie Creek, Del Norte Coast and Jedediah Smith Redwoods State parks,” said Sam Hodder, president and CEO of Save the Redwoods League. “Save the Redwoods League has played a critical role in securing property for both the national park and the three state parks.”

Save the Redwoods League is celebrating its centennial by partnering with California State Parks to offer free day-use admission to more than 40 redwood state parks on the second Saturday of each month in 2018. This includes the day-use picnic area at Jedediah Smith Redwoods State Park, said Candace Tinkler, chief of interpretation at Redwood National and State Parks.

Though most of the hiking trails and attractions at Redwood National and State Parks are free, the park is planning special activities to coincide with the League’s Free Second Saturday, Tinkler said.

“Every second Saturday will have something special going on,” she said. “For example, in July we have the annual Tolowa dance demonstration at Jed and that happens to be on a second Saturday anyway. On one of the second Saturdays there happens to be a very low tide, we’ll have a special tide pool walk.”

Save the Redwoods League will also bring their own naturalists and scientists to Redwood National and State Parks during the summer to lead special nature walks, Tinkler said.

Meanwhile, Redwood National and State Parks is still in the planning stages for activities and events to celebrate the national park’s 50th anniversary, Tinkler said. There will be the park’s annual Rock the Redwoods concert in Arcata on May 19, she said. But the exact dates for other activities have yet to be decided on, Tinkler said.

Tinkler noted while it is Redwood National Park’s 50th anniversary, the joint management concept between it and the three state parks wasn’t established until 1994.

Conservation movements were unheard of when Save the Redwoods League was established, Hodder said. It was established just two years after the National Park System was founded and helped create the California State Park system, he said.

Since it was established 100 years ago, Save the Redwoods League has protected more than 200,000 acres of redwoods and created 66 parks, according to the nonprofit’s website.

“We were lucky to be able to save as much as we were of the old growth redwood forest,” Hodder said. “The challenge was to be able to keep pace with the rate of harvest and to help save these magnificent giants for future generations.”

Another element of the league’s centennial is its continuing collaboration with Redwood National and State Parks to accelerate the development of old growth conditions in some of the younger forests within the parks, Hodder said. This includes the 26,000-acre Mill Creek property that was acquired in 2003 and is now part of Del Norte Coast Redwoods State Parks.

“Most of the old growth redwood forest has already been harvested except close to 5 percent that we worked to protect over the last 100 years,” Hodder said, adding about two-thirds of the entire 120,000-acre parks complex is young recovering redwood forests. “There still remains some scattered old growth from the Oregon border down to Big Sur, but by and large most of it is either gone or protected in parks and protected open space.”

According to a briefing statement on the 50th anniversary of the parks, efforts to restore original landscapes and drainage patterns may not truly bring back old growth conditions until the park’s 500th anniversary.

Since its founders recognized the necessity of saving the redwoods a century ago, scientists have learned how valuable old growth forests are, Hodder said.

“They’ve been growing here for millions of years and we’ve learned in recent years that they sequester more carbon per acre than any other forest in the world,” he said of the redwoods. “And they’re extraordinarily resilient as well at a time when resilient habitats are critical to our ability to be resilient and sustainable in times that are coming. It’s really critical that we have healthy vibrant redwood forests to sustain us.”

For more information about Free Second Saturdays, visit freeredwoods.org. For more information about Save the Redwoods League’s centennial, visit www.savetheredwoods.org.

Reach Jessica Cejnar at jcejnar@triplicate.com .