Five years ago, just as developers were planning to carve up Curry Canyon Ranch in Contra Costa County into pricey ranchettes, an environmental group raised $7.2 million to buy the breathtaking property, bordered on three sides by Mount Diablo State Park.

It seemed like the perfect scenario. Four of the state park’s trails stop at the edge of the rolling, 1,080-acre ranch. State parks officials had encouraged the purchase, and the group, Save Mount Diablo, offered to sell it to the state to expand the park, just as nonprofits had done time and again. But state parks leaders now say they can’t afford to buy the land, even at a reduced price. So it remains closed to the public.

“This property has just been sitting there, not yet part of Mount Diablo State Park,” said Ted Clement, executive director of Save Mount Diablo. “This is a very significant issue. It’s disappointing to not see the full public benefits realized.”

What’s happening at Mount Diablo is happening all over California.

A review of 50 years of state park land purchases by this news organization — 4,088 transactions since 1970 — has found that the state parks department’s once-energetic pace of acquiring new land for wildlife, public recreation and protection from development is at a historic low.

Previous generations preserved some of America’s most scenic places as California state parks, from Lake Tahoe to the Big Sur Coast to redwood forests and Hearst Castle. But that legacy has ended.

In 2017 and 2018, the state parks department did not add a single acre of land, for the first time in at least half a century.

California has not opened a new state park since 2009, when the U.S. Army donated four miles of beaches in Monterey County to become Fort Ord Dunes State Park. That 10-year drought is the longest stretch California has gone without a new state park since the state parks department was established in 1927.

As a result, California’s 280 state parks, beaches and historic sites are getting more crowded. Parking and camping sites are harder to find. Some land is being lost to development. Other properties are being preserved, but by private groups that often can’t afford to offer public access.

“Even as our population has been growing substantially, we haven’t been expanding our state parks system to accommodate that increased visitation,” said Sam Hodder, president of Save the Redwoods League, a San Francisco organization that has helped establish 66 redwood parks since 1918. “We’re not keeping up.”

State parks officials say big deficits a few years ago, and the lack of a parks bond for 12 years, are largely to blame. Taking on new land means increased costs for rangers and maintenance workers, they add.

“I think it’s just responsible state management that folks are going to expect that when we acquire property we are transparent about all the operating costs,” said Lisa Mangat, California’s state parks director. “I don’t foresee that changing.”

Parks advocates, however, note California’s economy and state budget have recovered, and that the current pattern is a historic retreat.

“The rangers feel horrible about it,” said Mike Lynch, president of the California State Park Rangers Association. “No decisions are being made. No support is there. They feel they can’t do the job that the public deserves. We’re at the lowest point in morale I’ve seen in my 40 years as a ranger and a park superintendent.”

Since 2010, state records show, there’s been a 67 percent drop from the previous decade in the amount of land California acquired for state parks, and an 80 percent drop from the 1970s and 1980s.

Of the 37,811 acres that state parks did acquire from 2010 to 2018, most were not for beaches, forests or urban parks. Instead, two-thirds went to a single park for motorcycle riding in the Mojave Desert, called Eastern Kern County Onyx Ranch State Vehicular Recreation Area.

Meanwhile, the public’s love for parks keeps growing: 79.2 million people visited California state parks and beaches in 2016-17, the most recent year for which statistics are available, a jump of 21 percent from 2009-10.

State parks officials are refusing new land — even if donated — from environmental groups that have spent millions purchasing it, unless the groups also provide large amounts of cash to pay for new rangers and maintenance workers.

That has never happened before. Even during the Great Depression of the 1930s, the state purchased land to establish Mount Diablo, Calaveras Big Trees, Pfeiffer Big Sur, Sonoma Coast State, San Clemente Beach and other landmark parks.

“It’s like roads, schools and hospitals,” Hodder said. “Our parks are every bit as critical to our health and well-being. If we aren’t investing, it’s like not expanding and maintaining your home as your family grows. Your quality of life goes down.”

For more than a century, land was preserved in a familiar pattern.

A historic site or scenic landscape was threatened. Conservation groups sounded the alarm, and convinced state lawmakers to buy the property for the public. Or they bought the land, and donated or sold it at no profit to the state.

That’s how California’s current state park system began.

In 1899, San Jose photographer Andrew P. Hill was ordered out of a redwood forest by a landowner who said the 300-foot tall trees were going to become “firewood and railroad ties.”

Angry that future generations might not see misty, primeval forests that had been around since the Roman Empire, Hill formed a group called the Sempervirens Club, after the Latin name for coast redwood, and led an effort to convince state lawmakers to buy 2,500 acres in the Santa Cruz Mountains and establish Big Basin Redwoods State Park.

Today, 1 million people a year visit Big Basin to see the ancient trees Hill saved from buck saws and axes.

But the state’s longstanding tradition of preserving its most scenic places changed 10 years ago.

Following the Great Recession in 2008, then-Gov. Arnold Schwarzenegger faced a $15 billion state budget deficit. To save $70 million, he proposed closing 220 state parks. But he dropped the idea after receiving 135,000 passionate letters, calls and emails in opposition.

Still, Schwarzenegger told his finance department not to take any new state park land if it would need rangers and maintenance workers. And when Jerry Brown was elected governor in 2010 and faced an even larger, $27 billion, state budget deficit, he continued the trend, and also threatened to close parks.

Now the deficit is gone. California boasts a $21 billion state budget surplus. Yet the bare-bones policy remains in place.

“Here we are in a time of great wealth and largess,” said Sara Barth, executive director of the Sempervirens Fund, the successor to Hill’s organization. “We shouldn’t treat our state parks as businesses that have to break even.”

Barth has seen the trend firsthand.

Her organization raised $8 million to buy 33 acres on the Santa Clara-Santa Cruz county line, and to build a parking lot, restrooms, signs and trails for a new entrance at Castle Rock State Park. But state parks officials say they won’t take the property unless the group also provides a cash endowment to pay for maintenance and rangers.

Park advocates say the approach was warranted years ago, but now that Gov. Gavin Newsom has taken office and the budget has improved, they hope more vision and ambition will be forthcoming.

“We need somebody who has a lot of fire in their belly,” said Audrey Rust, former president of the Peninsula Open Space Trust, a Palo Alto nonprofit that has saved 77,000 acres since 1977.

“Someone who can move mountains. Someone who is an action-oriented visionary, not just people who do spreadsheets. People love California’s beaches. People love redwood forests. People love meadows. California isn’t about skyscrapers and Google buildings.”

So far, Newsom has continued many of Brown and Schwarzenegger’s policies.

The state parks land acquisition budget collapsed under Brown — from $61.7 million in 2009 through 2010 to $3.1 million this year — a drop of 95 percent. The budget Newsom proposed in January contains even less: just $1 million statewide.

Mangat, who Brown named as state parks director in 2014, previously worked as a budget manager in the state finance department. She noted that Brown provided $80 million a year in new funding for state parks as part of the 12-cent per gallon gas tax increase he signed in 2017, which will help hire rangers and reduce the parks’ $1.2 billion maintenance backlog.

He also approved $100 million last year for a new California Indian Heritage Center, she noted, planned for West Sacramento.

Part of the drought in land acquisition, she said, was because no state parks bond had been passed for 12 years until voters passed Proposition 68 last year, a $4 billion parks and water bond that contains about $218 million for state parks.

“We are in a moment in time when we are in a rebuild mode,” Mangat said. “We are in a much better place than we were in two, three, four or five years ago. We have reorganized, and put in all kinds of reforms. And now we are looking at acquisitions.”

But across the state, the lost decade has left nonprofit land preservation groups holding thousands of acres they purchased to help expand state parks, and has closed to the public thousands of other acres the state had already purchased.

Marsh Creek Historic State Park — an expanse in Eastern Contra Costa County that is three times the size of Golden Gate Park in San Francisco and includes 70 miles of trails, a historic pioneer house and potential sites for dozens of new campsites — remains closed 12 years after the state bought it.

Save the Redwoods League has 13 properties totaling 2,680 acres statewide that it says are suitable for state parks, including a giant sequoia forest it would like to add to neighboring Calaveras Big Trees State Park in the central Sierras.

State finance officials say they have no apologies for the past decade.

“It was prudent policy,” said H.D. Palmer, a spokesman for the state Department of Finance. “What happened in 2007 and 2008 was by any reasonable yardstick the worst recession since the Great Depression. The state incurred multibillion budget deficits that have taken years to recover from.”

Brown and his former finance director, Ana Matosantos, did not respond to requests for comment.

What’s the solution?

Parks advocates say state lawmakers desperately need to find a permanent, steady source of funding for rangers and maintenance crews, rather than relying on the ups and down of the state’s general fund every year.

Other states guarantee vehicle license fees, lottery proceeds and other funds for parks. Most Bay Area counties have a dedicated sales tax for local parks. But statewide, the parks operations budget, which Newsom proposed at $618 million next year — just 4 percent more than in 2006, when adjusted for inflation — has no guaranteed funding source.

The last big attempt for one came in 2010 with Proposition 21, a ballot measure to increase vehicle license fees $18 to raise $500 million a year for parks. But voters rejected it.

John Laird, who was Natural Resources Secretary in the Brown administration, agreed that a permanent funding source is the answer. He advocated for new parks, he said, but was often shut down by the finance department, whose director is chair of the Public Works Board, an obscure agency that approves all land purchases.

“With the budget being in better shape, it is time to revisit the acquisitions policy,” Laird said. “Land always gets more expensive, opportunities go away and our population always grows. A generation from now there will be 50 million Californians. We should have a park system that can adequately serve them.”

Leigh Poitinger contributed reporting to this article.