REDWOOD CITY -- A judge Thursday ordered billionaire Vinod Khosla to testify in a courtroom battle over his decision to bar the public from a picturesque San Mateo County beach enjoyed by several generations of Bay Area residents for fishing, surfing and picnics.

Khosla, a venture capitalist known for investing in alternative energy, has fought to keep his ownership of Martins Beach a secret since he bought the 89-acre property in 2008 for $37.5 million, but he will now be thrust into the spotlight. He is scheduled to testify Monday afternoon.

The decision by San Mateo County Superior Court Judge Barbara Mallach came on the opening day of a trial that centers upon the conflict between two fundamental principles: the constitutional rights of a private property owner and the public's right to access the California coast. It is arguably the most important such clash since media mogul David Geffen lost a legal battle a decade ago to keep the public from crossing his property to reach Carbon Beach in Malibu.

The Deeney family, the previous owner of Martins Beach, allowed the public to visit for a fee. But Khosla, who bought the land under the name Martins Beach LLC, discontinued that practice in 2010, permanently locking the gate on a private road off Highway 1 that leads down to the ocean.

The beach, located a few miles south of Half Moon Bay, is framed on either side by cliffs and cannot be accessed from the north or south except by boat. Under California law, the public has the right to access the beach up to the median high tide line.

Eric Buescher, lead attorney for the Surfrider Foundation, argued Khosla knowingly violated California law. Locking the gate and two other acts -- painting over a billboard advertising the beach and hiring security guards -- changed both the public's ability to access the water and the intensity of its use, Buescher said. Those steps constituted development under coastal law and required a permit from the California Coastal Commission, he said, which Khosla never sought.

"That process is important because it protects the public's rights and interests," Buescher said outside court.

Jeffrey Essner, attorney for Martins Beach LLC, countered there is no right of public access to Martins Beach, since the public was invited onto the property for a fee. Withdrawing the invitation, he said, does not amount to development.

"Access is not development," said Essner. "I can't emphasize that point more."

Essner said his client has not constructed any buildings or fences since buying the property, which is home to about 40 rental cabins whose leases will expire in the coming decade. The Deeney family built the gate more than two decades ago, he said, and they often locked it -- during winter months, for instance, or private events.

"The evidence will show," said Essner, "that Martins Beach LLC never engaged in any act of development."

Khosla's ownership of Martins Beach LLC was finally confirmed last year during a separate lawsuit brought by a group called Friends of Martins Beach. San Mateo County Superior Court Judge Gerald Buchwald ruled in that case, which was argued on different grounds, that the question of the public's right to access the beach was moot because the land was in private hands before the United States acquired California following the Mexican-American War. Gary Redenbacher, attorney for Friends of Martins Beach, plans to appeal.

Khosla's attorneys fought to prevent him from testifying in this trial, but Mallach rejected their argument that Khosla's testimony is immaterial. Essner and co-counsel Dori Yob claimed Thursday that property manager Steven Baugher, not Khosla, makes all decisions pertaining to the property, including barring public access.

Contact Aaron Kinney at 650-348-4357 or akinney@bayareanewsgroup.com. Follow him at Twitter.com/kinneytimes.