Hawaii's prominent Gill family and an investment partner have bought close to 4,000 acres on Oahu from the James Campbell Co. with an intent to keep the land in agriculture and preservation uses.

The family, including six children and the brother of the late former Lt. Gov. and U.S. Rep. Tom Gill, acquired the property with California native and longtime Hawaii landowner Edmund C. Olson.

The buyers paid $15 million for the vast tract of land, which runs along the eastern slope of the Waianae Range from Makakilo to Kunia and also stretches leeward near the Kahe Power Plant.

A representative of the Gill-Olson joint venture, local labor attorney Tony Gill, said the group doesn't intend to develop the property, about half of which is zoned for agriculture and half for conservation.

"We approach this with a tremendous respect for the history and traditions up there," he said.

Some of the land is leased out for a variety of income-producing uses, including two ranch operations, telecommunications towers and Camp Timberline.

The land also is viewed as having potential for alternative energy production such as a wind farm, though Gill said the new owners are just beginning to evaluate the property and haven't devised any plans.

"Campbell has been up there 150 years (as an owner), and we expect to be there at least as long," he said.

Along with the Gill-Olson purchase, Campbell Co. sold an adjacent piece of land covering about 3,600 acres to the nonprofit Trust for Public Land for $4 million.

The trust secured most of the money for the purchase from the Army, which manages part of the property known as the Honouliuli Preserve, as well as the U.S. Fish and Wildlife Service, the state Legacy Lands Fund and the city Clean Water and Natural Lands Fund.

Both sales closed Sept. 30.

Campbell Co., which marketed the land for sale through commercial real estate brokerage firm CBRichard Ellis, had sought $22.5 million for the combined 6,500 acres, but also preferred to sell the land to conservation-minded buyers.

Theresia McMurdo, a Campbell Co. spokeswoman, said both buyers have environmental and cultural values that are consistent with the property. "That was the main criteria," she said.

Gill said the acquisition is the first venture into major land investing for the family hui, which includes his brothers Eric, Gary, Ivan and Tim, his sister, Andrea, his uncle Lorin, and Lorin's godchildren.

Olson heads Los Angeles-based A-American Storage Management Co., which is one of the country's largest self-storage businesses with several locations in Hawaii.

A part-time Big Island resident, Olson owns about 13,000 acres there and is a partner in OK Farms LLC. He also bought 1,296 acres in Kunia on Oahu from Campbell Co. three years ago for $4 million.