The historic, ecologically rare oceanfront estate in Aquinnah owned by the family of Caroline B. Kennedy goes up for sale today with an asking price of $65 million.

Property embraces nearly the entire western shorefront of Squibnocket Pond.

Albert O. Fischer 3rd/Gazette file photo

Property embraces nearly the entire western shorefront of Squibnocket Pond.

Albert O. Fischer 3rd/Gazette file photo

Known as Red Gate Farm, the property served as a private retreat for Jacqueline Kennedy Onassis until her death in 1994. It encompasses some 340 acres of stunningly beautiful windswept coastal dunes, wetlands, hillocks and salt-blasted heathlands between Moshup Trail and Squibnocket Pond.

The prospective sale portends the end of more than 40 years of continuous ownership and conservation of a singular Martha’s Vineyard landscape.

The Massachusetts Natural Heritage and Endangered Species Program has described the property as one of the most important tracts of land in the commonwealth. It includes more than a mile of Atlantic-facing beachfront and embraces nearly the entire western shorefront of Squibnocket Pond.

Mrs. Onassis bought the property in 1978 for $1.1 million from the Hornblower family, saving it from potential development and creating a refuge for herself from an exceedingly public life.

She and her daughter fiercely protected the land over the decades. The family plans to retain ownership of a small portion of the property, but will sell the vast majority of it.

Main house was designed by acclaimed American architect Hugh Newell Jacobson. Landscapes were designed by renowned horticulturist Bunny Mellon. Extensive renovations were completed in 2000.

Christie's International Real Estate

Main house was designed by acclaimed American architect Hugh Newell Jacobson. Landscapes were designed by renowned horticulturist Bunny Mellon. Extensive renovations were completed in 2000.

Christie's International Real Estate

In a letter addressed to the Island community and sent exclusively to the Gazette, Caroline Kennedy recalled her mother’s deep love of the land — and for the Vineyard.

“She loved the old stone walls, the blue heron that lived in the pond behind the dunes, the hunting cabin that was the only thing on the property when she acquired it, the clay cliffs, the Wampanoag legends . . .” Ms. Kennedy wrote in part.

“She bicycled to the Gay Head Lighthouse every morning, and checked the tide charts so she could run on the beach at low tide. She spent late afternoons reading on the deck, and loved the literary life of the Island . . . Together we wove the traditions of summer across three generations — setting lobster pots in Menemsha Pond, entering the Fair and never winning, growing a vegetable garden, bringing home the best shell from the beach every day, getting stuck at the airport when the fog rolled in.”

Currently assessed at about $37 million, the property includes a 6,400-square-foot main residence with five bedrooms and three fireplaces, and a two-story guest house with four bedrooms. There also are two garages, a caretaker’s house, a boat house and the original hunting cabin.

The main house was designed in the traditional Cape Cod style by the acclaimed American architect Hugh Newell Jacobson. The landscapes were designed by Bunny Mellon, the renowned horticulturist who designed the White House Rose Garden when Mrs. Onassis was First Lady.

Kennedy family donated 30 acres along Moshup Trail to the Vineyard Conservation Society in 2013.

Ray Ewing

Kennedy family donated 30 acres along Moshup Trail to the Vineyard Conservation Society in 2013.

Ray Ewing

Mrs. Onassis originally eschewed the traditional pool and tennis courts — “She wanted to swim in the ocean and breathe the salt air,” Ms. Kennedy wrote in her letter — although later both were added to the property. Extensive renovations were completed in 2000.

The property is being offered for sale as a whole. The sale is being handled exclusively by Christie’s International Real Estate and its Vineyard affiliate Land Vest. Island agents are Tom LeClair and Gery Conover.

With acres of undisturbed land, the property is home to two federally-listed endangered species and at least a dozen protected species, including the rare arethusa orchid and the northern harrier hawk. Over the years the Kennedy family has welcomed biologists, entymologists and other natural history experts onto the property for observation, study and educational purposes.

The property originally incorporated 31 lots, but in 2005 the family consolidated it into seven lots in a limited subdivision plan that anticipated separate parcels for each of Ms. Kennedy’s three children. The plan was approved by the Martha’s Vineyard Commission a year later.

One of the lots, a 60-acre parcel fronting the Atlantic Ocean, remains permanently unbuildable.

Map shows locus of Red Gate Farm.

Graham Smith

Map shows locus of Red Gate Farm.

Graham Smith

In 2013, Ms. Kennedy and her husband Edwin Schlossberg gifted an additional 30 acres north of Moshup Trail to the Vineyard Conservation Society. The society has been engaged for many years in an initiative to protect and conserve the globally-rare heathlands along remote Moshup Trail, a ribbon of road that curves through the extreme southwestern edge of Aquinnah with its wildlands and sweeping views of the Atlantic Ocean.

Two other lots were placed on the market the same year — one fronting the ocean and another fronting Squibnocket Pond — but were never sold.

In her letter, Ms. Kennedy said she and her husband were grateful to have been able to raise their children in a place that held so much meaning to her mother and her brother, John F. Kennedy Jr. Mr. Kennedy and his wife, Carolyn Bessette Kennedy, were killed on a summer night in 1999 when the plane he was flying crashed en route to the Vineyard.

“Our family will always come back to Martha’s Vineyard . . . but now it’s time for us to discover new ports of call,” she wrote. “We hope that another family will treasure Red Gate Farm as we have — it’s still the most beautiful place on Earth.”