The Marin Conservation League has raised nearly $70,000 to help the county buy a slice of Janis Joplin’s old Larkspur estate.

A fundraising effort by the 1,200-member group is helping the county piece together the $430,290 needed to buy a redwood-studded half acre at the end of Baltimore Canyon that once was owned by Joplin.

Joplin was living in a creekside house on the property when she died in 1970 of a drug overdose in Los Angeles hotel room.

County supervisors are slated to approve the purchase Tuesday morning. Even with the league’s help, most of the money is coming from county and state funds.

“We are pleased. We are happy to help the county stretch its dollars,” said league president Roger Roberts of San Rafael.

The league already has topped its pledge of contributing $50,000, and donations are still coming in, Roberts said.

“I don’t think we’re done raising money. We are still working on it,” he said.

Roberts said the purchase secures public access to the Baltimore Canyon and Blithedale county preserves. It puts in public ownership the trail that hikers have been using for years, even though they had to scoot around a fence to get to it.

The house on the remaining half-acre remains on the market for $1.5 million.

The county purchase includes permission to cross the residential tract so county maintenance crews can reach an old fire road via West Baltimore Avenue.

A steep trail that the county will be building will not be open to mountain bikes.

More than $225,000 for the purchase comes from state funds from Proposition 12 in 2000 and Proposition 40 in 2002.

Supervisor Hal Brown is contributing $75,000 from his share of the board’s “community service” account. Each supervisor gets $110,000 per year to dole out to pet projects.

The Tamalpais Conservation Club is donating $5,000 and the Mill Valley-based California Alpine Club is giving $3,000. The Sierra Club is donating $1,000.

Sharon McNamee, director of the county Parks and Open Space Department, said that opportunities to secure trailheads are rare. Often the chance arises only when property changes hands – and the owner is conservation-minded.

“Property is expensive in Marin,” she said. “We’ve been waiting for 30 years to get a link from that property.”

The county is buying the land from the estate of John E. Lessin, a well-known Larkspur veterinarian who died in 2007.

Lessin, who cared for Joplin’s dog, bought the house after she died.

The house, which still includes interior design features installed by Joplin, is featured on Internet sites paying tribute to the “last home” of the singer. Joplin threw many parties and jam sessions there featuring an array of 1960s rock stars.

Mike Lessin, son of the late veterinarian, said he and his brother used the trail and wanted to preserve access for future generations.

Supervisor Brown said he started pushing for acquisition after receiving a petition signed by neighbors. He credited the conservation league for delivering on its promise to raise money.

“They went out and really raised some dough,” Brown said.